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Hypervelocity stellar meteors

Main resource: Radiation astronomy/Hypervelocity stars

The Hubble Space Telescope image shows four high-velocity, runaway stars plowing through their local interstellar medium. Credit: NASA - Hubble's Advanced Camera for Surveys.{{free media}}

Def. a star moving faster than 65 km/s to 100 km/s relative to the average motion of the stars in the Sun's neighbourhood is called a high-velocity star.

Def. a high-velocity star moving through space with an abnormally high velocity relative to the surrounding interstellar medium is called a runaway star.

Def. a star whose elliptical orbit takes it well outside the plane of its galaxy at steep angles is called a halo star.

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Colors

Main resources: Radiation astronomy/Colors, Color astronomy, and Colors

This gamma-ray spectrum contains the typical isotopes of the uranium-radium decay line. Credit: Wusel007.{{free media}}

The peak at 40 keV is not from the mineral. From the color of the rock shown the yellowish mineral is likely to be autunite.

Autunite occurs as an oxidizing product of uranium minerals in granite pegmatites and hydrothermal deposits.

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Minerals

Main resource: Radiation astronomy/Minerals

This is an image of the mineral pitchblende, or uraninite. Credit: Geomartin.

These crystals are uraninite from Trebilcock Pit, Topsham, Maine. Credit: Robert Lavinsky.

Uraninite is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely [uranium dioxide] UO₂, but also contains [uranium trioxide] UO₃ and oxides of lead, thorium, and rare earth elements. It is most commonly known as pitchblende (from pitch, because of its black color. All uraninite minerals contain a small amount of radium as a radioactive decay product of uranium. Uraninite also always contains small amounts of the lead isotopes ²⁰⁶Pb and ²⁰⁷Pb, the end products of the decay series of the uranium isotopes ²³⁸U and ²³⁵U respectively. The extremely rare element technetium can be found in uraninite in very small quantities (about 0.2 ng/kg), produced by the spontaneous fission of uranium-238.

The image at left shows well-formed crystals of uraninite. The image at right shows botryoidal uraninite. Because of the uranium decay products, both sources are gamma-ray emitters.

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Continua

Main resources: Radiation astronomy/Continua and Continuum astronomy

The 15" refractor at Comanche Springs Astronomy Campus had its finder scope (a Stellarvue 80/9D achromat) equipped with a Baader Herschel Solar Wedge and a Solar Continuum Filter for today's transit of Venus. Credit: Jeff Barton from Richardson, TX, USA.{{free media}}

Lyc photon or Ly continuum photon or Lyman continuum photon are a kind of photon emitted from stars. Hydrogen is ionized by absorption of Lyc photons. Lyc photons are in the ultraviolet portion of the electromagnetic spectrum of the hydrogen atom and immediately next to the limit of the Lyman series of the spectrum with wavelengths that are shorter than 91.1267 nanometres and with energy above 13.6 eV.

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Meteors

Main resources: Radiation astronomy/Meteors and Meteor astronomy

This meteor image of October 17, 2012, is prior to the meteorite fall on the same day. Credit: Paola-Castillo; and Petrus M. Jenniskens, SETI Institute/NASA ARC.

A meteor is the visible path of a meteoroid that has entered the Earth's atmosphere.

Although there are many definitions of a meteor ranging from any atmospheric phenomenon to a fast-moving streak of light in the night sky caused by the entry of extraterrestrial matter into the earth's atmosphere: A shooting star or falling star, for radiation astronomy, an alternative definition is used.

Here's a theoretical definition of a meteor from a radiation point of view:

Def. any natural object radiating through a portion or all of the Earth's or another natural object's atmosphere is called a meteor.

A hypervelocity star "snow-plowing" through the interstellar medium of a galaxy is a meteor and the subject of meteor astronomy.

Meteor astronomy (radiated meteors) is radiation astronomy of large matter objects moving rapidly relative to apparently fixed objects.

A meteor may be as small as an electron. Astronomical objects that are atoms, nuclei, or subatomic particles are part of cosmic-ray astronomy.

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Cosmic rays

Main resources: Radiation astronomy/Cosmic rays and Cosmic-ray astronomy

File:NeutronMonitor.GIF

Cosmic Ray Intensity (blue) and Sunspot Number (green) is shown from 1951 to 2006 Credit: University of New Hampshire.{{fairuse}}

The graph on the right shows an inverse correlation between sunspot numbers (solar activity) and neutron production from galactic cosmic rays.

There is "a correlation between the arrival directions of cosmic rays with energy above 6 x 10¹⁹ electron volts and the positions of active galactic nuclei (AGN) lying within ~75 megaparsecs."

The Oh-My-God particle was observed on the evening of 15 October 1991 over Dugway Proving Ground, Utah. Its observation was a shock to astrophysicists, who estimated its energy to be approximately 3×10²⁰
 eV(50 joules)—in other words, a subatomic particle with kinetic energy equal to that of a baseball (142 g or 5 oz) traveling at 100 km/h (60 mph).

It was most probably a proton with a speed very close to the speed of light, so close, in fact, [(1 − 5×10⁻²⁴
) × c], that in a year-long race between light and the cosmic ray, the ray would fall behind only 46 nanometers (5×10⁻²⁴
light-years), or 0.15 femtoseconds (1.5×10⁻¹⁶
 s).

References

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Neutrals

Main resources: Radiation astronomy/Neutrals and Neutrals astronomy

File:Article-2025275-0D6687D100000578-167 634x704.jpg

The Necklace Nebula glows brightly in this Nasa Hubble Space Telescope image. Credit: NASA.

"A giant cosmic necklace glows brightly in this Nasa Hubble Space Telescope image."

"The object, aptly named the Necklace Nebula, is a recently discovered planetary nebula, the glowing remains of an ordinary, sun-like star."

"The nebula consists of a bright ring, measuring 12trillion miles wide, dotted with dense, bright knots of gas that resemble diamonds in a necklace."

"Newly discovered: The Necklace Nebula glows brightly in this composite image taken by the Hubble Space Telescope last month. The glow of hydrogen, oxygen, and nitrogen are shown by the colours blue, green and red respectively".

"It is located 15,000 light-years away in the constellation Sagitta."

"A pair of stars orbiting close together produced the nebula, also called PN G054.2-03.4."

"About 10,000 years ago, one of the ageing stars ballooned to the point where it engulfed its companion star. The smaller star continued orbiting inside its larger companion, increasing the giant’s rotation rate. The bloated companion star spun so fast that a large part of its gaseous envelope expanded into space. Due to centrifugal force, most of the gas escaped along the star’s equator, producing a ring. The embedded bright knots are dense gas clumps in the ring. The pair is so close, only a few million miles apart, that they appear as one bright dot in the centre. The stars are furiously whirling around each other, completing an orbit in a little more than a day."

Referencse

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Subatomics

Main resources: Radiation astronomy/Subatomics and Subatomic astronomy

File:Helios 2 acr.gif

A mechanism is suggested for anomalous cosmic rays (ACRs) of the acceleration of pick-up ions at the solar wind termination shock. Credit: Eric R. Christian.{{fairuse}}

An "analysis of the energy-loss distributions in the GRS HEM during the impulsive phase of this event indicates that γ-rays from the decay of π⁰ mesons were detected [...] The production of pions, which is accompanied (on average) by neutrons, has an energy threshold of ~290 MeV for p-p and ~180 MeV for p-α interactions, giving, therefore, a lower limit to the maximum energy of the particles accelerated at the Sun."

References

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Neutrons

Main resources: Radiation astronomy/Neutrons and Neutron astronomy

The image shows the hydrogen concentrations on the Moon detected by the Lunar Prospector. Credit: NASA.

Around EeV (10¹⁸ eV) energies, there may be associated ultra high energy neutrons "observed in anisotropic clustering ... because of the relativistic neutrons boosted lifetime." “[A]t E_n = 10²⁰ eV, [these neutrons] are flying a Mpc, with their directional arrival (or late decayed proton arrival) ... more on-line toward the source.” From “neutron (and anti-neutron) life-lengths (while being marginal or meaningless at tens of Mpcs)", the growth of their half-lives with energy may naturally explain an associated, showering neutrino halo.

Fairly large fluxes of neutrons have been observed during solar flares such as that of November 12, 1960, with a flux of 30-70 neutrons per cm^-2 s^-1.

At right is the result of an all Moon survey by the Lunar Prospector using an onboard neutron spectrometer (NS). Cosmic rays impacting the lunar surface generate neutrons which in turn lose much of their energy in collisions with hydrogen atoms trapped within the Moon's surface. Some of these thermal neutrons collide with the helium atoms within the NS to yield an energy signature which is detected and counted. The NS aboard the Lunar Prospector has a surface resolution of 150 km.

References

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Protons

Main resources: Radiation astronomy/Protons and Proton astronomy

This graph displays the flux of high energy protons measured by GOES 11 over four days from November 2, 2003, to November 5, 2003. Credit: NOAA.

"Proton astronomy should be possible; it may also provide indirect information on inter-galactic magnetic fields."

Proton astronomy per se often consists of directly or indirectly detecting the protons and deconvoluting a spatial, temporal, and spectral distribution.

“[A]t the high end of the proton energy spectrum (above ≈ 10¹⁸ eV) [the Larmor radius] deflection becomes small enough that proton astronomy becomes possible.”

"The third largest solar proton event in the past thirty years took place during July 14-16, 2000, and had a significant impact on the earth's atmosphere."

References

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Mesons

Main resources: Radiation astronomy/Mesons and Meson astronomy

J/Ψ production is graphed. Credit: Fermilab.

A meson is a composite subatomic particle bound together by the strong interaction.

Because mesons are composed of sub-particles, they have a physical size, with a radius roughly one femtometre, which is about 2/3 the size of a proton or neutron. All mesons are unstable, with the longest-lived lasting for only a few hundredths of a microsecond. Charged mesons decay (sometimes through intermediate particles) to form electrons and neutrinos. Uncharged mesons may decay to photons.

Mesons are not produced by radioactive decay, but appear in nature only as short-lived products of very high-energy interactions in matter. In cosmic ray interactions, for example, such particles are ordinary protons and neutrons. Mesons are also frequently produced artificially in high-energy particle accelerators that collide protons, anti-protons, or other particles.

In nature, the importance of lighter mesons is that they are the associated quantum-field particles that transmit the nuclear force, in the same way that photons are the particles that transmit the electromagnetic force.

Each type of meson has a corresponding antiparticle (antimeson) in which quarks are replaced by their corresponding antiquarks and vice-versa.

Mesons are subject to both the weak and strong interactions. Mesons with net electric charge also participate in the electromagnetic interaction.

While no meson is stable, those of lower mass are nonetheless more stable than the most massive mesons, and are easier to observe and study in particle accelerators or in cosmic ray experiments. They are also typically less massive than baryons, meaning that they are more easily produced in experiments, and thus exhibit certain higher energy phenomena more readily than baryons composed of the same quarks would.

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Beta particles

Main resources: Radiation astronomy/Beta particles and Beta-particle astronomy

The simulation attempts to answer how thunderstorms launch particle beams into space. Credit: NASA/Goddard Space Flight Center.

A number of subatomic reactions can be detected in astronomy that yield beta particles. The detection of beta particles or the reactions that include them in an astronomical situation is beta-particles astronomy.

Beta particles are high-energy, high-speed electrons or positrons.

Beta particles may be the key to fusion. "If the exterior of the capsule is maintained at a uniform temperature of about 19.5 K, the natural beta decay energy of the tritium will accomplish this through a process known as "beta layering." The very low energy beta particles from tritium decay deposit their energy very close to the location of the original tritium atoms."

"Beta-particles leaving the upper surface of the lunar sample could trigger the upper beta detector, while the lower beta-detector was triggered by beta particles from the lower surface of the sample."

Notation: let the symbol β⁻ designate an unbound electron in motion.

Notation: let β⁺ designate an unbound positron in motion.

Notation: let TGF stand for a Terrestrial Gamma-ray Flash.

References

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Electrons

Main resources: Radiation astronomy/Electrons and Electron astronomy

Aurorae are mostly caused by energetic electrons precipitating into the atmosphere. Credit: Samuel Blanc[1].

Although electron astronomy is usually not recognized as a formal branch of astronomy, the measurement of electron fluxes help to understand a variety of natural phenomena.

Particles such as electrons are used as tracers of cosmic magnetic fields. "From a plasma-physics point of view, the particles represent the correct way to identify magnetic field lines." "The suprathermal electrons in the solar wind and in solar particle events have excellent properties for this application: they move rapidly, they remain tightly bound to their field lines, and they may arrive "scatter-free" even at low energies, and from deep in the solar atmosphere (Lin 1985)." These electrons "provide remote-sensing observations of distant targets in the heliosphere - the Sun, the Moon, Jupiter, and various heliospheric structures." ""[E]lectron astronomy" has an interesting future".

A delta ray is characterized by very fast electrons produced in quantity by alpha particles or other fast energetic charged particles knocking orbiting electrons out of atoms. Collectively, these electrons are defined as delta radiation when they have sufficient energy to ionize further atoms through subsequent interactions on their own.

"The conventional procedure of delta-ray counting to measure charge (Powell, Fowler, and Perkins 1959), which was limited to resolution σ_z = 1-2 because of uncertainties of the criterion of delta-ray ranges, has been significantly improved by the application of delta-ray range distribution measurements for ¹⁶O and ³²S data of 200 GeV per nucleon (Takahashi 1988; Parnell et al. 1989)." Here, the delta-ray tracks in emulsion chambers have been used for "[d]irect measurements of cosmic-ray nuclei above 1 TeV/nucleon ... in a series of balloon-borne experiments".

References

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Positrons

Main resources: Radiation astronomy/Positrons and Positron astronomy

Observation of positrons from a terrestrial gamma ray flash is performed by the Fermi gamma ray telescope. Credit: NASA Goddard Space Flight Center.

"Positron astronomy is 30 years old but remains in its infancy."

"[P]ositron astronomy results ... have been obtained using the INTEGRAL spectrometer SPI". The positrons are not directly observed by the INTEGRAL space telescope, but "the 511 keV positron annihilation emission is".

During solar flares “[s]everal radioactive nuclei that emit positrons are also produced; [which] slow down and annihilate in flight with the emission of two 511 keV photons or form positronium with the emission of either a three gamma continuum (each photon < 511 keV) or two 511 keV photons."

References

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Muons

Main resources: Radiation astronomy/Muons and Muon astronomy

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This is an image obtained from muon radiography of Japan's Asama volcano. Credit: H T M Tanaka.

"TeV muons from γ ray primaries ... are rare because they are only produced by higher energy γ rays whose flux is suppressed by the decreasing flux at the source and by absorption on interstellar light."

Muon decay produces three particles, an electron plus two neutrinos of different types.

References

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Neutrinos

Main resources: Radiation astronomy/Neutrinos and Neutrino astronomy

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This "neutrino image" of the Sun is by using the Super-Kamiokande to detect the neutrinos from nuclear fusion in the solar interior. Credit: R. Svoboda and K. Gordan (LSU).

The field of neutrino astronomy is still very much in its infancy – the only confirmed extraterrestrial sources so far are the Sun and supernova SN1987A. Neutrino astronomy observes astronomical objects with neutrino detectors in special observatories.

Because neutrinos are only weakly interacting with other particles of matter, neutrino detectors must be very large in order to detect a significant number of neutrinos. Neutrino detectors are often built underground to isolate the detector from cosmic rays and other background radiation.

The Super-Kamiokande, or "Super-K" is a large-scale experiment constructed in an unused mine in Japan to detect and study neutrinos. The image at right required 500 days worth of data to produce the "neutrino image" of the Sun. The image is centered on the Sun's position. This image covers a 90° x 90° octant of the sky (in right ascension and declination). The higher the brightness of the color, the larger is the neutrino flux.

References

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Gamma rays

Main resources: Radiation astronomy/Gamma rays and Gamma-ray astronomy

The Moon is seen by the Compton Gamma Ray Observatory, in gamma rays of greater than 20 MeV. Credit: D. J. Thompson, D. L. Bertsch (NASA/GSFC), D. J. Morris (UNH), R. Mukherjee (NASA/GSFC/USRA).

Most astronomical gamma-rays are thought to be produced not from radioactive decay, however, but from the same type of accelerations of electrons, and electron-photon interactions, that produce X-rays in astronomy (but occurring at a higher energy in the production of gamma-rays).

For gamma-ray astronomy, the Vela satellites were the first devices ever to detect cosmic gamma ray bursts.

Gamma-ray bursts (GRBs) are flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies. They are the most luminous electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several minutes, although a typical burst lasts 20–40 seconds. The initial burst is usually followed by a longer-lived "afterglow" emitted at longer wavelengths (X-ray, ultraviolet, optical, infrared, microwave and radio).

References

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X-rays

Main resources: Radiation astronomy/X-rays, X-ray astronomy, and X-rays

This image captures the core of Messier 31 (M31) in X-rays using the Chandra X-ray Observatory. Credit: S. Murray, M. Garcia, et al., Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA.

X-rays are electromagnetic radiation from a portion of the wavelength spectrum of about 5 to 8 nanometers (nm)s down to approximately 5 to 8 picometers (pm)s (ranging over three orders of magnitude).

An astronomical X-ray source may have one or more positional locations, plus associated error circles or boxes, from which incoming X-radiation (X-rays) has been detected.

Generally, a coronal cloud, a cloud composed of plasma, is usually associated with a star or other celestial or astronomical body, extending sometimes millions of kilometers into space, or thousands of light-years, depending on the associated body. The high temperature of the coronal cloud gives it unusual spectral features. These features have been traced to highly ionized atoms of elements such as iron which indicate a plasma's temperature in excess of 10⁶ K (MK) and associated emission of X-rays.

The importance of X-ray astronomy is exemplified in the use of an X-ray imager such as the one on GOES 14 for the early detection of solar flares, coronal mass ejections (CME)s and other X-ray generating phenomena that impact the Earth.

References

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Ultraviolets

Main resources: Radiation astronomy/Ultraviolets and Ultraviolet astronomy

A GALEX image of the spiral galaxy Messier 81 in ultraviolet light. Credit: NASA/JPL-Caltech/J. Huchra (Harvard-Smithsonian CfA).

Ultraviolet astronomy is generally used to refer to observations of electromagnetic radiation at ultraviolet]] wavelengths between approximately 10 and 320 nanometres.

There are many important spectral lines in these wavelengths. Among the most important are the Lyman lines, which are emitted or absorbed when an electron jumps to or from the innermost electron shell in a hydrogen atom. The first three (known as alpha, beta and gamma) have wavelengths of 121.52, 102.53 and 97.22 nm respectively.

Since the Earth's atmosphere strongly absorbs ultraviolet light, especially the shorter wavelengths, ultraviolet astronomy is mostly conducted by satellites. Longer wavelengths can be detected from baloons launched into the stratosphere.

Like the English astronomer William Fox, "In the summer of 1980, reflecting his age, Walter Scott Houston finally underwent surgery to remove a cataract from his right eye. Now to just about anyone else, a cataract would spell the end of a sky gazing career. But not Houston. With his lens removed and a plastic UV-transparent replacement implanted, Scotty reported that a whole new world of star gazing was opened up. The flood of ultraviolet light onto his retina allowed him to see faint blue stars previously invisible by at least one magnitude above the visual limit (to normally sighted observers)."

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Opticals

Main resources: Radiation astronomy/Opticals and Optical astronomy

Actuators are part of the active optics of the Gran Telescopio Canarias. Credit: Vesta.

Optical astronomy includes those portions of ultraviolet, visual, and infrared astronomy that benefit from the use of quartz crystal or silica glass telescope components.

Observations at these wavelengths generally use optical components (mirrors, lenses and solid state digital detectors).

In popular culture optical astronomy encompasses a wide variety of observations via telescopes that are sensitive in the range of visible light. Scientists would call this visible-light astronomy. It includes imaging, where a picture of some sort is made of the object; photometry, where the amount of light coming from an object is measured, spectroscopy, where the distribution of that light with respect to its wavelength is measured, and polarimetry where the polarisation state of that light is measured.

Def. astronomy using infrared, visible and/or ultraviolet wavelengths is called optical astronomy.

Def. an optical system in telescopes that reduces atmospheric distortion by dynamically measuring and correcting wavefront aberrations in real time, often by using a deformable mirror is called adaptive optics.

"Already it has allowed ground-based telescopes to produce images with sharpness rivalling those from the Hubble Space Telescope. The technique is expected to revolutionize the future of ground-based optical astronomy."

The color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. To measure the index, one observes the magnitude of an object successively through two different filters, such as U and B, or B and V, where U is sensitive to ultraviolet rays, B is sensitive to blue light, and V is sensitive to visible (green-yellow) light (see also: UBV system). The set of passbands or filters is called a photometric system. The difference in magnitudes found with these filters is called the U-B or B–V color index, respectively. The smaller the color index, the more blue (or hotter) the object is. Conversely, the larger the color index, the more red (or cooler) the object is. This is a consequence of the logarithmic magnitude scale, in which brighter objects have smaller (more negative) magnitudes than dimmer ones. For comparison, the yellowish Sun has a B–V index of 0.656 ± 0.005, while the bluish Rigel has B–V –0.03 (its B magnitude is 0.09 and its V magnitude is 0.12, B–V = –0.03). The passbands most optical astronomers use are the UBVRI filters, where the U, B, and V filters are as mentioned above, the R filter passes red light, and the I filter passes infrared light. These filters were specified as particular combinations of glass filters and photomultiplier tubes.

An optical telescope gathers and focuses light mainly from the visible part of the electromagnetic spectrum (although some work in the infrared and ultraviolet).

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Visuals

Main resources: Radiation astronomy/Visuals and Visual astronomy

This image shows the 26-inch Warner & Swasey refracting telescope at the United States Naval Observatory. Credit: Waldon Fawcett.

What is “the “old-fashioned” spirit of real-time visual astronomy”? “I think everyone can conjure up a mental image of astronomers at every level and place in history, gazing through the eyepieces of their telescopes at sights far away - true visual astronomy.”

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Violets

Main resources: Radiation astronomy/Violets and Violet astronomy

This image of Venus is taken through a violet filter by the Galileo spacecraft on February 14, 1990. Credit: NASA/JPL-Caltech.

"The aluminium abundance was derived from the resonance line at 394.4nm, and Al is underabundant by ∼ −0.7 dex with respect to iron." "These abundances are the LTE values; no NLTE corrections, as prescribed by Baum ̈uller and Gehren (1997) and Baumüller et al. (1998), have been applied. The prescribed NLTE corrections for T_eff = 6500K, log g = 4.0, [Fe/H] = –3.0 are –0.11 ... for ... Al .... If we assume these values to apply for our lower-gravity star [CS 29497-030], then Al follows iron". The elemental abundance ratios for CS 29497-030 of aluminum are [Al/H] = -3.37, [Al/Fe] = -0.67.

A discovery in violet astronomy is that "carbon stars are enormously fainter in the violet region than expected from appropriate blackbody spectra."

Violet photographs of the planet Venus taken in 1927 “recorded two nebulous bright streaks, or bands, running ... approximately at right angles to the terminator” that may be from the upper atmosphere.

"The “Purple Haze” is a diffuse blueish/purple glow within a few arcseconds of the central star in HST images of the Homunculus (Morse et al. 1998; Smith et al. 2000, 2004). This emission is seen in excess of violet starlight scattered by dust, and the strength of the excess increases into the far UV (Smith et al. 2004; hereafter Paper I)."

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Blues

Main resources: Radiation astronomy/Blues and Blue astronomy

This picture from the Voyager 2 sequence shows two of the four cloud features which have been tracked by the Voyager cameras during the past two months. Credit: NASA.

Blue astronomy is focused on the wavelength range 450-475 nm.

Stars are often referred to by their predominant color. For example, blue stragglers are found among the galactic halo globular clusters. Blue main sequence stars that are metal poor ([Fe/H] ≤ -1.0) are most likely very different in origin from blue stragglers.

"[G]round-based UV [and blue astronomy] is a powerful facility for [the] study of [the] chemical evolution of [the] early Galaxy." UV and B astronomy use radiation over the wavelength range 355.0-500.0 nm.

“To date, all of the reported hypervelocity stars (HVSs), which are believed to be ejected from the Galactic center, are blue and therefore almost certainly young.”

A trace amount of methane is also present. Prominent absorption bands of methane occur at wavelengths above 600 nm, in the red and infrared portion of the spectrum. As with Uranus, this absorption of red light by the atmospheric methane is part of what gives Neptune its blue hue, although Neptune's vivid azure differs from Uranus's milder cyan. Since Neptune's atmospheric methane content is similar to that of Uranus, some unknown atmospheric constituent is thought to contribute to Neptune's colour.

References

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Cyans

Main resources: Radiation astronomy/Cyans and Cyan astronomy

Recent changes in Comet Lulin's greenish coma and tails are shown in these two panels taken on January 31st (top) and February 4th (bottom) 2009. In both views the comet has an apparent antitail to the left of the coma of dust. Credit: Joseph Brimacombe, Cairns, Australia.

Perhaps the most prominent cyan planetary source is Uranus, which has only been visited by the space probe Voyager 2. More recent images come from the Hubble Space Telescope in orbit around Earth.

Methane possesses prominent absorption bands in the visible and near-infrared (IR) making Uranus aquamarine or cyan in color.

“During the Halley Monitoring Program at La Silla from Feb.17 to Apr.17,1986 ... In the light of the neutral CN-radical a continuous formation and expansion of [cyan] gas-shells could be observed.” “The gas-expansion velocity decreases with increasing heliocentric distance from 1 km/s in early March to 0.8 km/s in April.”

Shown at right, "Lulin's green color comes from the gases that make up its Jupiter-sized atmosphere. Jets spewing from the comet's nucleus contain cyanogen (CN: a poisonous gas found in many comets) and diatomic carbon (C₂). Both substances glow green when illuminated by sunlight"

The electric blue glow of electricity results from the spectral emission of the excited ionized atoms (or excited molecules) of air (mostly oxygen and nitrogen) falling back to unexcited states, which happens to produce an abundance of electric blue light. This is the reason electrical sparks in air, including lightning, appear electric blue. It is a coincidence that the color of Cherenkov radiation and light emitted by ionized air are a very similar blue despite their very different methods of production.

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Greens

Main resources: Radiation astronomy/Greens and Green astronomy

File:LASCO C1 coronagraph of solar corona.png

A picture of the solar corona taken with the LASCO C1 coronagraph. The image is color coded for the doppler shift of the FeXIV 530.8 nm line. Credit: NASA and NRL.

Green objects or emission lines in the green portion of the visible spectrum are the subject of green astronomy.

In the image at right the iron (Fe XIV) green line is followed by doppler imaging to show associated relative coronal plasma velocity towards (-7 km/s side) and away from (+7 km/s side) the large angle spectrometric coronagraph LASCO satellite camera.

"Carroll and McCormack (1972) in Dublin reported complex spectra in the blue and green wavelength regions of both FeH and FeD".

For elongated dust particles in cometary comas an investigation is performed at 535.0 nm (green) and 627.4 nm (red) peak transmission wavelengths of the Rosetta spacecraft's OSIRIS Wide Angle Camera broadband green and red filters, respectively. "In the green, the polarization of the pure silicate composition qualitatively appears a better fit to the shape of the observed polarization curves". "[B]ut they are characterized by a high albedo." The silicates used to model the cometary coma dust are olivene (Mg-rich is green) and the pyroxene, enstatite.

In December 2006, seven papers were published in the scientific journal, Science, discussing initial details of the sample analysis. Among the findings are: a wide range of organic compounds, including two that contain biologically usable nitrogen; indigenous aliphatic hydrocarbons with longer chain lengths than those observed in the diffuse interstellar medium; abundant amorphous silicates in addition to crystalline silicates such as olivine and pyroxene, proving consistency with the mixing of solar system and interstellar matter, previously deduced spectroscopically from ground observations; hydrous silicates and carbonate minerals were found to be absent, suggesting a lack of aqueous processing of the cometary dust; limited pure carbon (CHON) was also found in the samples returned; methylamine and ethylamine was found in the aerogel but was not associated with specific particles.

References

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Yellows

Main resources: Radiation astronomy/Yellows and Yellow astronomy

This is a true-color image of Io taken by the Galileo probe. Credit: NASA.

Yellow astronomy is astronomy applied to the various extraterrestrial yellow sources of radiation, especially at night. It is also conducted above the Earth's atmosphere and at locations away from the Earth as a part of explorational (or exploratory) yellow astronomy.

There are yellow objects and emission lines in the yellow portion of the visible spectrum from 570 to 590 nm in wavelength.

Io is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of 3,642 kilometres (2,263 mi), the fourth-largest moon in the Solar System. With over 400 active volcanoes, Io is the most geologically active object in the Solar System. Most of Io's surface is characterized by extensive plains coated with sulfur and sulfur dioxide frost. Io's volcanism is responsible for many of the satellite's unique features. Its volcanic plumes and lava flows produce large surface changes and paint the surface in various shades of yellow, red, white, black, and green, largely due to allotropes and compounds of sulfur.

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Oranges

Main resources: Radiation astronomy/Oranges and Orange astronomy

Cloud bands are clearly visible on Jupiter. Credit: NASA/JPL/USGS.

"[O]range [is] the color of Jupiter".

The orange and brown coloration in the clouds of Jupiter are caused by upwelling compounds that change color when they are exposed to ultraviolet light from the Sun. The exact makeup remains uncertain, but the substances are believed to be phosphorus, sulfur or possibly hydrocarbons. These colorful compounds, known as chromophores, mix with the warmer, lower deck of clouds. The zones are formed when rising convection cells form crystallizing ammonia that masks out these lower clouds from view.

The orange system [in orange astronomy] is a number of emission lines very close together forming a band in the orange portion of the visible spectrum. These lines are usually associated with particular molecular species, including ScO, YO, and TiO.

The orange band from molecular CaCl is "observed in the spectra of many carbon stars."

The Fe VII emission line at 608.7 nm, "frequently observed in the spectra of astrophysical plasmas", has been detected in planetary nebulae, Seyfert galaxies, and quasars.

References

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Reds

Main resources: Radiation astronomy/Reds and Red astronomy

AZ Cancri is a red dwarf. Credit: SDSS Data Release 6.

With respect to the color 'red', there are studies of the redness of objects such as the red dwarf AZ Cancri shown in the visual image at right. Cool stars of spectral class M appear red; they are (depending on their size) referred to as "red giants" or "red dwarfs".

"Ideally all intrinsic colours should be found from unreddened stars. This is possible for dwarf and giant stars later than about A0 (Johnson, 1964) ... However, it cannot be used for stars of other spectral classes since they are all relatively infrequent in space, and generally reddened."

A very important wavelength in this region is the Balmer alpha line, 656.28 nm. It is emitted or absorbed by hydrogen atoms when electrons move between the second and third electron shells. Other Balmer lines, known as beta, gamma and delta, have wavelengths of 486.13, 434.05 and 410.17 nm respectively;[2] these are also in the visual range but are less important than the alpha line.

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Infrareds

Main resources: Radiation astronomy/Infrareds and Infrared astronomy

This is a three-color far-infrared image of M51, the Whirlpool Galaxy. Credit: ESA and the PACS Consortium.{{free media}}

The wavelength of infrared light ranges from 0.75 to 300 micrometers. Infrared falls in between visible radiation, which ranges from 380 to 750 nanometers, and terahertz radiation submillimeter waves.

Infrared and optical astronomy are often practiced using the same telescopes, as the same mirrors or lenses are usually effective over a wavelength range that includes both visible and infrared light.

Far-infrared astronomy deals with objects visible in far-infrared radiation extending from 30 micron (µm) towards submillimeter wavelengths around 450 µm.

Huge, cold clouds of gas and dust in [the Milky Way] our own galaxy, as well as in nearby galaxies, glow in far-infrared light. This is due to thermal radiation of interstellar dust contained in molecular clouds.

Visually dark infrared sources can be radiative cosmic dust, hydrogen gas such as an H II region (e.g. the Orion Nebula), an H I region of hydrogen, a molecular cloud, or a coronal cloud.

There are about 1,892,100 infrared (IR) objects in the SIMBAD database. Some of these like IRAS 20542+3631 are only IR objects. 1RXS J205444.6+361116 is an IR and an X-ray object only. These objects are visibly dark infrared sources. As is 2MASS J21074764+3802561, which is an IR and UV object only.

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Submillimeters

Main resources: Radiation astronomy/Submillimeters and Submillimeter astronomy

The ALMA observations — shown here in red, pink and yellow — were tuned to detect carbon monoxide molecules. Credit: ALMA (ESO/NAOJ/NRAO). Visible light image: the NASA/ESA Hubble Space Telescope.

Submillimetre astronomy or submillimeter astronomy is the branch of observational astronomy that is conducted at submillimetre wavelengths of the electromagnetic spectrum. Astronomers place the submillimetre waveband between the far-infrared and microwave wavebands, typically taken to be between a few hundred micrometres and a millimetre." and "Using submillimetre observations, astronomers examine molecular clouds and dark cloud cores with a goal of clarifying the process of star formation from earliest collapse to stellar birth.

These wavelengths are sometimes called Terahertz radiation, since they have frequencies of the order of 1 THz.

"The Antennae Galaxies (also known as NGC 4038 and 4039) are a pair of distorted colliding spiral galaxies about 70 million light-years away, in the constellation of Corvus (The Crow). This view combines ALMA observations, made in two different wavelength ranges during the observatory’s early testing phase, with visible-light observations from the NASA/ESA Hubble Space Telescope."

"The Hubble image is the sharpest view of this object ever taken and serves as the ultimate benchmark in terms of resolution. ALMA observes at much longer wavelengths which makes it much harder to obtain comparably sharp images. However, when the full ALMA array is completed its vision will be up to ten times sharper than Hubble."

References

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Microwaves

Main resources: Radiation astronomy/Microwaves and Microwave astronomy

File:Milky-way-microwaves-planck.jpg

A view of the Milky Way galaxy in microwaves is captured by the European Space Agency's Planck satellite. Credit: ESA/NASA/JPL-Caltech.

Astronomy specifically focused at the microwave portion of the electromagnetic spectrum is microwave astronomy.

Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz (0.3 GHz) and 300 GHz. This broad definition includes both UHF and Extremely high frequency (EHF) (millimeter waves), and various sources use different boundaries. In all cases, microwave includes the entire super high frequency (SHF) band (3 to 30 GHz, or 10 to 1 cm) at minimum, with RF engineering often putting the lower boundary at 1 GHz (30 cm), and the upper around 100 GHz (3 mm).

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Radars

Main resources: Radiation astronomy/Radars and Radar astronomy

File:2012 LZ1.jpg

This image is of asteroid 2012 LZ1 by the Arecibo Observatory in Puerto Rico using the Arecibo Planetary Radar. Credit: Arecibo Observatory.

Radar astronomy is used to detect and study astronomical objects that reflect radio rays.

"The advantages of radar in planetary astronomy result from (1) the observer's control of all the attributes of the coherent signal used to illuminate the target, especially the wave form's time/frequency modulation and polarization; (2) the ability of radar to resolve objects spatially via measurements of the distribution of echo power in time delay and Doppler frequency; (3) the pronounced degree to which delay-Doppler measurements constrain orbits and spin vectors; and (4) centimeter-to-meter wavelengths, which easily penetrate optically opaque planetary clouds and cometary comae, permit investigation of near-surface macrostructure and bulk density, and are sensitive to high concentrations of metal or, in certain situations, ice."

References

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Radios

Main resources: Radiation astronomy/Radios and Radio astronomy

This image has the radio image of Greg Taylor, NRAO, overlain on the X-ray image from Chandra. The radio source Hydra A originates in a galaxy near the center of the cluster. Optical observations show a few hundred galaxies in the cluster. Credit: NASA/CXC/SAO; Radio: NRAO.

Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies from 300 Gigahertz (GHz) to as low as 3 kilohertz (kHz), and corresponding wavelengths from 1 millimeter to 100 kilometers.

Several satellites have served as observatories for radio waves and specifically for microwaves. The Radio Astronomy Explorer (RAE) 1 is launched into orbit on July 4, 1968, around Earth, while the Explorer 49 (RAE 2) was launched on June 10, 1973, around the Moon.

The COBE was launched into Earth orbit on November 18, 1989. The WMAP was launched on June 30, 2001, into orbit at the Lissajous orbit Lagrange 2 location. Both satellites have aboard detectors designed to perform microwave astronomy, as these are limited to only the microwave band.

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Gravitationals

Main resources: Radiation astronomy/Gravitationals and Gravitational astronomy

The images show LIGO and Livingston, Louisiana, measurement of gravitational waves. Credit: B. P. Abbott et al. (LIGO Scientific Collaboration and Virgo Collaboration).{{free media}}

This photo shows the Livingston LIGO detector. Credit: Caltech/MIT/LIGO Laboratory.{{free media}}

This gravitational wave spectrum includes sources and detectors. Credit: NASA Goddard Space Flight Center.{{free media}}

Gravitational radiation appears to be cylindrical waves of radiation produced by relativistic, undulatory gravitational fields in Euclidean space.

Interaction	Mediator	Relative Magnitude	Behavior	Range
Strong interaction	gluon	1038	1	10−15 m
Electromagnetic interaction	photon	1036	1/r2	universal
Weak interaction	W and Z bosons	1025	1/r5 to 1/r7	10−16 m
Gravitational interaction	photon or graviton ?	10	1/r2	universal

As the gravitational interaction is 10^-36 that of the electromagnetic interaction to produce gravitational radiation requires a massive oscillator.

At right are the results from the first gravitational radiation detection. The images show the radiation signals received by the Laser Interferometer Gravitational Observatory (LIGO) instruments at Hanford, Washington (left) and Livingston, Louisiana (right) and comparisons of these signals to the signals expected due to a black hole merger event.

The wavelength of the gravitational waves is given by for example: 3 x 10⁸ m‧s^-1/400 Hz = 750,000 m, which is way longer than radio waves but expected for such a weak oscillator. 35 Hz corresponds to 8,600,000 m.

LIGO operates two detectors located 3000 km (1800 miles) apart: One in eastern Washington near Hanford, and the other near Livingston, Louisiana. The photo on the left shows the Livingston detector.

"According to general relativity, a pair of black holes orbiting around each other lose energy through the emission of gravitational waves, causing them to gradually approach each other over billions of years, and then much more quickly in the final minutes. During the final fraction of a second, the two black holes collide at nearly half the speed of light and form a single, more massive black hole, converting a portion of the combined black holes' mass to energy, according to Einstein's formula E=mc². This energy is emitted as a final strong burst of gravitational waves. These are the gravitational waves that LIGO observed."

"LIGO’s twin interferometers bounce laser beams between mirrors at the opposite ends of 4-kilometre-long vacuum pipes that are set perpendicularly to each other. A gravitational wave passing through will alter the length of one of the arms, causing the laser beams to shift slightly out of sync."

Later detection confirmed the fusion of two massive stellar-sized objects, a binary neutron star merger.

"According to Einstein's field equations, photon matter subject to quadruple oscillations is a source of gravitational waves."

"In this work, we present a solution to the first stage of a new two-stage global treatment of the vacuum binary black hole problem [1, 2]. The approach, based upon characteristic evolution, has been carried out in the regime of Schwarzschild perturbations where advanced and retarded solutions of the linearized problem can be rigorously identified [3]. Computational experiments are necessary to study the applicability of the approach to the nonlinear regime. From a time-reversed viewpoint, this first stage is equivalent to the determination of the outgoing radiation emitted from the fission of a white hole in the absence of ingoing radiation. This provides the physically correct “retarded” waveform for a white hole fission, were such events to occur in the universe. Although there is no standard astrophysical mechanism for producing white holes from a nonsingular matter distribution, white holes of primordial or quantum gravitational origin cannot be ruled out."

"This fission problem has a simpler formulation as a characteristic initial value problem than the black hole merger problem. The boundary of the (conformally compactified) exterior spacetime contains two null hypersurfaces where boundary conditions must be satisfied: past null infinity I−, where the incoming radiation must vanish, and the white hole event horizon H−, which must describe a white hole, which is initially in equilibrium with no ingoing radiation and then distorts and ultimately fissions into two white holes with the emission of outgoing gravitational waves."

An almost identical signal could originate from a comparable much more massive neutron star fission.

"This is an exciting time to study gravitation, astrophysics and cosmology. Through challenging cosmic microwave background (CMB) and supernovae observations cosmology has been turned on its head. Gravitational radiation astronomy should be the next contributor to this revolution in astrophysics and cosmology."

References

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Superluminals

Main resources: Radiation astronomy/Superluminals and Superluminal astronomy

File:M87 jet Hubble.gif

The two images are a top panel of Hubble Space Telescope image showing the M87 jet streaming out from the galaxy's nucleus (bright round region at far left) and a bottom panel which contains a sequence of Hubble images showing motion of something at six times the speed of light. Credit: John Biretta/NASA/ESA/Space Telecsope Science Institute.

Superluminal refers to the propagation of information or matter faster than the speed of light. Under the special theory of relativity, a particle (that has [mass in special relativity] rest mass) with subluminal velocity needs infinite energy to accelerate to the speed of light, although special relativity does not forbid the existence of particles that travel faster than light at all times (tachyons).

On the other hand, what some physicists refer to as "apparent" or "effective" FTL depends on the hypothesis that unusually distorted regions of spacetime might permit matter to reach distant locations in less time than light could in normal or undistorted spacetime. Although according to current theories matter is still required to travel subluminally with respect to the locally distorted spacetime region, apparent FTL is not excluded by general relativity.

Tachyonic γ rays have not been observed directly as of 2007. "The tachyonic spectral densities generated by ultra-relativistic electrons in uniform motion are fitted to the high-energy spectra of Galactic supernova remnants, such as RX J0852.0−4622 and the pulsar wind nebulae in G0.9+0.1 and MSH 15-52. ... Tachyonic cascade spectra are quite capable of generating the spectral curvature seen ... Estimates on the electron/proton populations generating the tachyon flux are obtained from the spectral fits"

"Tachyonic radiation implies superluminal signal transfer [1-7], the energy quanta propagating faster than light in vacuum, in contrast to rotating superluminal light sources emitting vacuum Cherenkov radiation [8, 9]." "The existence of superluminal energy transfer has not been established so far, and one may ask why. There is the possibility that superluminal quanta just do not exist, the vacuum speed of light being the definitive upper bound. There is another explanation, the interaction of superluminal radiation with matter is very small, the quotient of tachyonic and electric fine-structure constants being q²/e² ≈ 1.4 x 10^-11 [5], and therefore superluminal quanta are hard to detect."

“Observed variations concerning the brightness distributions in four extragalactic radio sources were so rapid that the apparent transverse velocity of expansion is greater than the velocity of light.”

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Galaxy clusters

Main resources: Radiation astronomy/Galaxy clusters and Galaxy cluster astronomy

The universe within 1 billion light-years (307 Mpc) of Earth is shown to contain the local superclusters, galaxy filaments and voids. Credit: Richard Powell.

"Galaxies and clusters of galaxies are not uniformly distributed in the Universe, instead they collect into vast clusters and sheets and walls of galaxies interspersed with large voids in which very few galaxies seem to exist. The map above shows many of these superclusters including the Virgo supercluster - the minor supercluster of which our galaxy is just a minor member. The entire map is approximately 7 percent of the diameter of the entire visible Universe."

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Galaxies

Main resources: Radiation astronomy/Galaxies and Galaxy astronomy

The pseudo-colour image is of the large-scale radio structure of the FRII radio galaxy 3C98. Lobes, jet and hotspot are labelled. Credit: .

Another pseudo-colour image is of the large-scale radio structure of the FRI radio galaxy 3C31. Jets and plumes are labelled. Credit: .

"Over the past 30 years, radioastronomy has revealed a rich variety of molecular species in the interstellar medium of our galaxy and even others."

These regions are non-luminous, save for emission of the 21-cm (1,420 MHz) region spectral line. ... Mapping H I emissions with a radio telescope is a technique used for determining the structure of spiral galaxies.

"In 1974, radio sources were divided into two classes Fanaroff and Riley Class I (FRI), and Class II (FRII).

The distinction was originally made based on the morphology of the large-scale radio emission (the type was determined by the distance between the brightest points in the radio emission): FRI sources were brightest towards the centre, while FRII sources were brightest at the edges.

There is a reasonably sharp divide in luminosity between the two classes: FRIs were low-luminosity, FRIIs were high luminosity.

The morphology turns out to reflect the method of energy transport in the radio source. FRI objects typically have bright jets in the centre, while FRIIs have faint jets but bright hotspots at the ends of the lobes. FRIIs appear to be able to transport energy efficiently to the ends of the lobes, while FRI beams are inefficient in the sense that they radiate a significant amount of their energy away as they travel.

The FRI/FRII division depends on host-galaxy environment in the sense that the FRI/FRII transition appears at higher luminosities in more massive galaxies. FRI jets are known to be decelerating in the regions in which their radio emission is brightest,

The hotspots that are usually seen in FRII sources are interpreted as being the visible manifestations of shocks formed when the fast, and therefore supersonic, jet (the speed of sound cannot exceed c/√3) abruptly terminates at the end of the source, and their spectral energy distributions are consistent with this picture.

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High-velocity galaxies

Main resources: Radiation astronomy/High-velocity galaxies and High-velocity galaxy astronomy

The irregular galaxy NGC 1427A is passing through the Fornax cluster at nearly 600 kilometers per second (400 miles per second). Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA).

"The irregular galaxy NGC 1427A is a spectacular example of the resulting stellar rumble. Under the gravitational grasp of a large gang of galaxies, called the Fornax cluster, the small bluish galaxy is plunging headlong into the group at 600 kilometers per second or nearly 400 miles per second."

"Galaxy clusters, like the Fornax cluster, contain hundreds or even thousands of individual galaxies. Within the Fornax cluster, there is a considerable amount of gas lying between the galaxies. When the gas within NGC 1427A collides with the Fornax gas, it is compressed to the point that it starts to collapse under its own gravity. This leads to formation of the myriad of new stars seen across NGC 1427A, which give the galaxy an overall arrowhead shape that appears to point in the direction of the galaxy's high-velocity motion."

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Active galactic nuclei

Main resources: Radiation astronomy/Active galactic nuclei and Active galactic nuclei astronomy

File:3c111 lo.jpg

The image contains a series of radio images at successive epochs using the VLBA of the jet in the broad-line radio galaxy 3C 111. Credit: M. Kadler, E. Ros, M. Perucho, Y. Y. Kovalev, D. C. Homan, I. Agudo, K. I. Kellermann, M. F. Aller, H. D. Aller, M. L. Lister, and J. A. Zensus.

For active galactic nuclei (AGNs) "bright jet features typically exhibit apparent superluminal speeds and accelerated motions."

AGN "jets with the fastest superluminal speeds all tend to have high Doppler boosted radio luminosities. [...] there is a correlation between intrinsic jet speed and intrinsic (de-beamed) luminosity".

"VLBA images of the jet in the broad-line radio galaxy 3C 111. The picture shows the variable parsec-scale structure of the jet in this active galactic nucleus. The features observed correspond to ejected plasma regions traveling at relativistic speeds. Those appear to be larger than the speed of light due to projection effects. The sixteen images are spaced by their relative time intervals. The images show that a major radio flux-density outburst in 1996 was followed by a particularly bright plasma ejection associated with a superluminal jet component. This major event was followed by trailing features in its evolution. A similar event is seen after mid 2001. The jet dynamics in this source is revealed: a plasma injection into the jet beam leads to the formation of multiple shocks that travel at different speeds downstream (ranging from 3c to 6c) and interact with each other and with the ambient medium. This is in agreement with numerical relativistic magnetohydrodynamic structural and emission simulations of jets."

"Images were taken at 15 GHz with the full Very Long Baseline Array as part of the 2cm Survey/MOJAVE collaboration. The observing runs usually last 8 hr and the total observing time on source is approximately 50 minutes. The typical dynamic range in the images is of 1000:1 (the lowest shown flux density is typically of 1-2 mJy/beam). The images are convolved with a common restoring beam of 0.5x1.0 milliarcseconds (P.A. of 0 deg). The image alignment is (arbitrary) to the brightness peak. The superluminal speeds of the features in the jet were determined from a detailed analysis of multiple Gaussian model fits to the observed visibilities."

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Nebulas

Main resources: Radiation astronomy/Nebulas and Nebula astronomy

This image shows an example of a bipolar planetary nebula known as PN Hb 12 in Cassiopeia. Credit: NASA, ESA, and A. Zijlstra (The University of Manchester).

"Hubble astronomers have found an unexpected surprise while surveying more than 100 planetary nebulae in the central bulge of our Milky Way galaxy. Those nebulae that are butterfly-shaped or hourglass-shaped tend to be mysteriously aligned such that their rotation axis is perpendicular to the plane of our galaxy."

"Astronomers have used the NASA/ESA Hubble Space Telescope and ESO's New Technology Telescope to explore more than 100 planetary nebulae in the central bulge of our galaxy. They have found that butterfly-shaped members of this cosmic family tend to be mysteriously aligned — a surprising result given their different histories and varied properties."

"Planetary nebulae are the expanding gaseous shrouds encircling dying stars. A subset of this population has bipolar outflows that align to the star's rotation axis. Such nebulae formed in different places and have different characteristics and so it is a puzzle why they should always point on the same sky direction, like bowling pins set up in an alley."

"All these nebulae formed in different places and have different characteristics. Neither the individual nebulae, nor the stars that formed them, interact with other planetary nebulae. However, a new study by astronomers from the University of Manchester, UK, now shows surprising similarities between some of these nebulae: many of them line up in the sky in the same way. The "long axis" of a bipolar planetary nebula slices though the wings of the butterfly, whilst the "short axis" slices through the body."

"The astronomers looked at 130 planetary nebulae in the Milky Way's central bulge. They identified three different types, and peered closely at their characteristics and appearance. The shapes of the planetary nebula images were classified into three types, following conventions: elliptical, either with or without an aligned internal structure, and bipolar."

"This really is a surprising find and, if it holds true, a very important one, [...] Many of these ghostly butterflies appear to have their long axes aligned along the plane of our galaxy. By using images from both Hubble and the NTT we could get a really good view of these objects, so we could study them in great detail."

"While two of these populations were completely randomly aligned in the sky, as expected, we found that the third — the bipolar nebulae — showed a surprising preference for a particular alignment, [...] While any alignment at all is a surprise, to have it in the crowded central region of the galaxy is even more unexpected."

"Planetary nebulae are thought to be sculpted by the rotation of the star system from which they form. This is dependent on the properties of this system — for example, whether it is a binary [A binary system consists of two stars rotating around their common centre of gravity.], or has a number of planets orbiting it, both of which may greatly influence the form of the blown bubble. The shapes of bipolar nebulae are some of the most extreme, and are thought to be caused by jets blowing mass outwards from the star system perpendicular to its orbit."

"The alignment we're seeing for these bipolar nebulae indicates something bizarre about star systems within the central bulge, [...] For them to line up in the way we see, the star systems that formed these nebulae would have to be rotating perpendicular to the interstellar clouds from which they formed, which is very strange."

"While the properties of their progenitor stars do shape these nebulae, this new finding hints at another more mysterious factor. Along with these complex stellar characteristics are those of our Milky Way; the whole central bulge rotates around the galactic centre. This bulge may have a greater influence than previously thought over our entire galaxy — via its magnetic fields. The astronomers suggest that the orderly behaviour of the planetary nebulae could have been caused by the presence of strong magnetic fields as the bulge formed."

"Researchers suggest that there is something bizarre about star systems within the central hub of our galaxy. They would all have to be rotating perpendicular to the interstellar clouds from which they formed. At present, the best guess is that the alignment is caused by strong magnetic fields that were present when the galactic bulge formed billions of years ago."

"As such nebulae closer to home do not line up in the same orderly way, these fields would have to have been many times stronger than they are in our present-day neighbourhood. Very little is known about the origin and characteristics of the magnetic fields that were present in our galaxy when it was young, so it is unclear how they have changed over time."

"We can learn a lot from studying these objects, [...] If they really behave in this unexpected way, it has consequences for not just the past of individual stars, but for the past of our whole galaxy."

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Stars

Main resources: Radiation astronomy/Stars and Stellar radiation astronomy

This graphic shows motion of the neutron star RX J0822-4300 from the Puppis A supernova event. Credit: NASA.

It is a type of stellar remnant [(a compact star)] that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons

Neutron stars are theorized as the radiation source for anomalous X-ray pulsars (AXPs), binary pulsars, high-mass X-ray binaries, intermediate-mass X-ray binaries, low-mass X-ray binaries (LMXB), pulsars, and soft gamma-ray repeaters (SGRs).

"The [image on the right] shows two observations of [the] neutron star [RX J0822-4300] obtained with the Chandra X-ray Observatory over the span of five years, between December 1999 [on the left] and April 2005 [on the right]. By combining how far it has moved across the sky with its distance from Earth [at about 7,000 light years], astronomers determined the cosmic cannonball is moving at over 3 million miles per hour, one of the fastest moving stars ever observed. At this rate, RX J0822-4300 [at (J2000) RA 08h 23m 08.16s Dec -42° 41' 41.40" in Puppis] is destined to escape from the Milky Way after millions of years, even though it has only traveled about 20 light years so far."

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Planets

Main resources: Radiation astronomy/Planets and Planetary astronomy

The near-infrared image shows the GJ 758 solar system. Credit: Max Planck Institute for Astronomy.

File:Astrometric analysis GJ 758 C?.jpg

This astrometric analysis consists of motions of point-sources near GJ 758 across five epochs (E1–E5), measured relative to GJ 758’s position. Credit: M. Janson et al., National Astronomical Observatory of Japan.

When the overwhelming radiation from the star GJ 758 is reduced and the star itself eclipsed by a disk, secondary radiation sources appear in the background. These are labeled B and C?.

Subsequent observations with the Subaru Telescope revealed C? to be a background star rather than an object in orbit around GJ 758.

"The source tentatively referred to as “GJ 758 C” [follows] the background star track".

"GJ 758 B exhibits common proper motion with its parent star as well as systematic orbital motion towards the northwest, whereas all other point-sources follow the expected trajectory for background stars (solid arrows). The object referred to as “GJ 758 C” [...] is unambiguously identified as a background star (motion highlighted by dashed blue arrows). The grey plus signs are 1σ error bars. The circle marked as “PSF” shows the size of the resolution element in H-band on [High Contrast Instrument for the Subaru Next Generation Adaptive Optics] HiCIAO."

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Standard candles

Main resources: Radiation astronomy/Standard candles and Standard-candle astronomy

This is a Hubble Space Telescope Image of NGC 4414. Credit: Hubble Heritage Team (AURA/STScI/NASA).

This is an image of Messier 31, the Andromeda galaxy from 1899. Credit: Isaac Roberts.

"In 1995, the majestic spiral galaxy NGC 4414 was imaged by the Hubble Space Telescope as part of the HST Key Project on the Extragalactic Distance Scale. [The galaxy was] observed ... on 13 different occasions over the course of two months."

"Images were obtained with Hubble's Wide Field Planetary Camera 2 (WFPC2) through three different color filters."

"Based on [...] careful brightness measurements of variable stars in NGC 4414, [...] an accurate determination of the distance to the galaxy [was made]."

"The resulting distance to NGC 4414, 19.1 megaparsecs or about 60 million light-years, along with similarly determined distances to other nearby galaxies, contributes to astronomers' overall knowledge of the rate of expansion of the universe. The Hubble constant (H0) is the ratio of how fast galaxies are moving away from us to their distance from us. This astronomical value is used to determine distances, sizes, and the intrinsic luminosities for many objects in our universe, and the age of the universe itself."

"Due to the large size of the galaxy compared to the WFPC2 detectors, only half of the galaxy observed was visible in the datasets collected by the Key Project astronomers in 1995. In 1999, the Hubble Heritage Team revisited NGC 4414 and completed its portrait by observing the other half with the same filters as were used in 1995. The end result is a stunning full-color look at the entire dusty spiral galaxy. The new Hubble picture shows that the central regions of this galaxy, as is typical of most spirals, contain primarily older, yellow and red stars. The outer spiral arms are considerably bluer due to ongoing formation of young, blue stars, the brightest of which can be seen individually at the high resolution provided by the Hubble camera. The arms are also very rich in clouds of interstellar dust, seen as dark patches and streaks silhouetted against the starlight."

Standard-candles astronomy is the astronomical effort to find, study and develop standard-candle candidates for use as standard candles.

Standard candles are stars in visual astronomy that may be used to calculate distances because their characteristics are, or appear to be, distance independent.

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Plasmas

Main resources: Radiation astronomy/Plasmas and Plasma astronomy

Arcs rise above an active region on the surface of the Sun in this series of images taken by the STEREO (Behind) spacecraft. Credit: Images courtesy of the NASA STEREO Science Center.

A magnetic cloud is a transient event observed in the solar wind. It was defined in 1981 by Burlaga et al. 1981 as a region of enhanced magnetic field strength, smooth rotation of the magnetic field vector and low proton temperature . Magnetic clouds are a possible manifestation of a Coronal Mass Ejection (CME). The association between CMEs and magnetic clouds was made by Burlaga et al. in 1982 when a magnetic cloud was observed by Helios-1 two days after being observed by SMM. However, because observations near Earth are usually done by a single spacecraft, many CMEs are not seen as being associated with magnetic clouds. The typical structure observed for a fast CME by a satellite such as ACE is a fast-mode shock wave followed by a dense (and hot) sheath of plasma (the downstream region of the shock) and a magnetic cloud.

Other signatures of magnetic clouds are now used in addition to the one described above: among other, bidirectional superthermal electrons, unusual charge state or abundance of iron, helium, carbon and/or oxygen. The typical time for a magnetic cloud to move past a satellite at the L1 point is 1 day corresponding to a radius of 0.15 AU with a typical speed of 450 km s⁻¹ and magnetic field strength of 20 nT

Def. a "massive burst of solar wind, other light isotope plasma, and magnetic fields rising above the solar corona or being released into space" is called a coronal mass ejection (CME).

An explosive limb flare occurred above 30,000 km in the corona of the Sun. "So the aftermath of the flare explosion, usually visible in disk pictures as extensive Hα brightening, but hidden from us in this case, was seen by the ionosphere as an intense flux of ionizing radiation from the coronal cloud created by the explosion." "The November 20, 1960, event is very similar to that of February 10, 1956, which was observed at Sacramento Peak. A bright ball appears above the surface, grows in size and Hα brightness, and explodes upward and outward." "The great breadth and intensity of the Hα emission from the suspended ball at 2013 U.T. testify to the large amount of energy stored there, as no corresponding macroscopic motion was observed until the explosion at 2023 U.T." "[T]he great energy of the preflare cloud was released into the corona by the explosion of 2023 U.T., and Hα radiation disappeared by 2035 U.T."

"On 16 June 1972, the Naval Research Laboratory's coronagraph aboard OSO-7 tracked a huge coronal cloud moving outward from the Sun."

A coronal mass ejection (CME) is an ejected plasma consisting primarily of electrons and protons (in addition to small quantities of heavier elements such as helium, oxygen, and iron), plus the entraining coronal closed magnetic field regions. Evolution of these closed magnetic structures in response to various photospheric motions over different time scales (convection, differential rotation, meridional circulation) somehow leads to the CME. Small-scale energetic signatures such as plasma heating (observed as compact soft X-ray brightening) may be indicative of impending CMEs.

The soft X-ray sigmoid (an S-shaped intensity of soft X-rays) is an observational manifestation of the connection between coronal structure and CME production.

"Relating the sigmoids at X-ray (and other) wavelengths to magnetic structures and current systems in the solar atmosphere is the key to understanding their relationship to CMEs."

References

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Scattered disks

Main resources: Radiation astronomy/Scattered disks and Scattered-disk astronomy

The diagram shows scattered disc objects out to 100 AU. Credit: Eurocommuter.

Scattered Disk Objects (up to 100 AU): Kuiper Belt objects are shown in grey, resonant objects within the Scattered Disk are shown in green.

The position of an object represents

• its orbit’s semi-major axis a in AU and the orbital period in years (horizontal axis)
• its orbit’s inclination i in degrees (vertical axis).

The size of the circle illustrates the object’s size relative to others. For a few large objects, the diameter drawn represents the best current estimates. For all others, the circles represent the absolute magnitude of the object.

The eccentricity of the orbit is shown indirectly by a segment extending from the left (perihelion) to the aphelion to the right. In other words, the segment illustrates the variations of the object's distance from the Sun. Objects with nearly circular orbits will show short segments while highly elliptical orbits will be represented by long segments.

Main resonances with Neptune are marked with vertical bars; 1:1 marks the position of Neptune’s orbit (and its Trojan asteroids), 2:3 marks the orbit of Pluto (and plutinos) etc.

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Oort clouds

Main resources: Radiation astronomy/Oort clouds and Oort cloud astronomy

This graphic shows the distance from the Oort cloud to the rest of the Solar System and two of the nearest stars measured in astronomical units (AU). The scale is logarithmic, with each specified distance ten times further out than the previous one.

An artist's rendering is of the Oort cloud and the Kuiper belt (inset). Sizes of individual objects have been exaggerated for visibility.

The Oort cloud or the Öpik–Oort cloud is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun. This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun. The outer limit of the Oort cloud defines the cosmographical boundary of the Solar System and the region of the Sun's gravitational dominance.

Most of the comets lay at the distant reaches of our system in a hypothesized Oort cloud. At the very edge of the solar system, these comets orbit in very large loops around the distant reaches of our solar system. The passing of nearby stars, or other objects can alter their orbit, sending them speeding towards the inner reaches of our solar system. These comets typically retain very large orbits such that they will not return (once seen in the inner solar system) for many thousands of years.

Cosmic "ray protons at energies up to 10 GeV [may be] able to build-up large amount of organic refractory material at depth of several meters in a comet during [its] long life in the Oort cloud (~4.6 x 10⁷ yr). Ion bombardment might also lead to the formation of a substantial stable crust (Johnson et al., 1987)."

Sedna was discovered from an image dated 2003-11-14 at coordinates 03 15 10.09 +05 38 16.5. The 3 overexposed stars are apparent magnitude 13. The "bright star" near Sedna is apmag 14.9 and about the same magnitude as Pluto. (Wikisky image of this region) The picture shows an area of the sky equal to the area covered by a pinhead held at arm's length. Sedna is too faint to be seen by all but the most powerful amateur telescopes.

References

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Clouds

Main resources: Radiation astronomy/Clouds and Cloud astronomy

File:HI shell surrounding magnetar.jpg

The image shows an HI shell surrounding the magnetar 1E 1048.1-5937. Credit: B. M. Gaensler, N. M. McClure-Griffiths, S. Oey, M. Haverkorn, J. Dickey, and A. Green.

"The Southern Galactic Plane Survey (SGPS; see the 2002 Annual Report), which combines 21-cm HI observations from Parkes and the Compact Array, is now complete. The SGPS provides a wonderful resource for understanding populations such as magnetars in the context of their environment. Examination of SGPS data around the position of the well-known magnetar 1E 1048.1­5937 reveals a striking cavity in HI, designated as GSH 288.3-0.5-28, that is almost centred on the position of the neutron star. The SGPS data imply that GSH 288.3-0.5-28 is at a distance of approximately 2.7 kpc, and is expanding at a velocity of approximately 7.5 kilometres per second into gas of density ~17 atoms cm^-3."

"Shells like GSH 288.3-0.5-28 are common, and represent wind-blown bubbles powered by massive stars expanding into the interstellar medium. The size and expansion speed of GSH 288.3-0.5-28 then imply that the bubble is several million years old, and has been blown by a wind of mechanical luminosity ~4 x 10³⁴ ergs per second, corresponding to a single star of initial mass 30 to 40 solar masses."

"Usually in such cases, the central star is obvious, in the form of a bright O star, supergiant or WR star at the shell's centre. However, even though this field lies in the rich Carina OB1 region, there are no known stars of the appropriate position, distance or luminosity to argue for an association with GSH 288.3-0.5-28. This raises the intriguing possibility that GSH 288.3-0.5-28 was blown by the massive star whose collapse formed 1E 1048.1-5937. The central location of the magnetar within the HI shell suggests that the supernova occurred quite recently. The corresponding blast waves would impact the walls of the HI shell approximately 3000 years after core collapse, producing significant X-ray and radio emission. The lack of such emission requires the neutron star to be very young, consistent with the small ages expected for active magnetars. A common distance of around three kpc is suggested by the properties of both objects."

References

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Portal:Radiation astronomy/Resource/48

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Portal:Radiation astronomy/Resource/49

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Portal:Radiation astronomy/Resource/50

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