User:Marshallsumter/Radiation astronomy/Blacks: Difference between revisions

Black is the color of coal, ebony, and of outer space. It is the darkest color, the result of the absence of or complete absorption of light. It is the opposite of white and often represents darkness in contrast with light.^[1][2][3]

"Opposite to white: colourless from the absence or complete absorption of light. Also, so near this as to have no distinguishable colour, very dark."^[1]

Black is "[t]he darkest color".^[2]

"Se dit de la couleur la plus foncée, due à l'absence ou à l'absorption totale des rayons lumineux."^[3]("said of the very darkest color, due to the absence or complete absorption of all rays of light.")

Grey or gray is an intermediate color between black and white, a neutral or achromatic color, meaning literally a color "without color." ^[4] It is the color of a cloud-covered sky, of wood ash and of lead.^[5]

The first image at right shows some red pebbles among gray pebbles, which are all the same rock type.

The first image at left shows the various shades of grey.

The second image at left of gray clay shows the cracking from water loss.

Def. the fraction of incident light or radiation reflected by a surface or body, commonly expressed as percentage is called albedo.

Albedo, or reflection coefficient, derived from Latin albedo "whiteness" (or reflected sunlight), in turn from albus "white", is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it. Being a dimensionless fraction, it may also be expressed as a percentage, and is measured on a scale from zero for no reflecting power of a perfectly black surface, to 1 for perfect reflection of a white surface.

Albedo depends on the frequency of the radiation. When quoted unqualified, it usually refers to some appropriate average across the spectrum of visible light. In general, the albedo depends on the directional distribution of incoming radiation. Exceptions are Lambertian surfaces, which scatter radiation in all directions according to a cosine function, so their albedo does not depend on the incident distribution. In practice, a bidirectional reflectance distribution function (BRDF) may be required to characterize the scattering properties of a surface accurately, although the albedo is a very useful first approximation.

Albedos of typical materials in visible light range from up to 0.9 for fresh snow, to about 0.04 for charcoal, one of the darkest substances. Deeply shadowed cavities can achieve an effective albedo approaching the zero of a black body. When seen from a distance, the ocean surface has a low albedo, as do most forests, whereas desert areas have some of the highest albedos among landforms. Most land areas are in an albedo range of 0.1 to 0.4.^[6] The average albedo of the Earth is about 0.3.^[7] This is far higher than for the ocean primarily because of the contribution of clouds.

Two common albedos that are used in astronomy are the (V-band) geometric albedo (measuring brightness when illumination comes from directly behind the observer) and the Bond albedo (measuring total proportion of electromagnetic energy reflected). Their values can differ significantly.

Albedo ${\displaystyle {\alpha }}$ may be given by:

${\displaystyle {\alpha }=(1-D){\bar {\alpha }}(\theta _{i})+D{\bar {\bar {\alpha }}}.}$

Directional-hemispherical reflectance is sometimes referred to as black-sky albedo and bi-hemispherical reflectance as white-sky albedo. These terms are important because they allow the albedo to be calculated for any given illumination conditions from a knowledge of the intrinsic properties of the surface.^[8]

In detailed studies, the directional reflectance properties of astronomical bodies are often expressed in terms of the five Hapke parameters which semi-empirically describe the variation of albedo with phase angle, including a characterization of the opposition effect of regolith surfaces.

The correlation between astronomical (geometric) albedo, absolute magnitude and diameter is:^[9]

${\displaystyle A=\left({\frac {1329\times 10^{-H/5}}{D}}\right)^{2},}$

where ${\displaystyle A}$ is the astronomical albedo, ${\displaystyle D}$ is the diameter in kilometers, and ${\displaystyle H}$ is the absolute magnitude.

Def. any "silicate mineral having a crystal structure of parallel sheets of silicate tetrahedra"^[10] is called a phyllosilicate.

Biotite mica is a common phyllosilicate with the formula K(Mg,Fe)
₃(AlSi
₃O
₁₀)(OH)
₂ - potassium magnesium iron hydroxy-aluminosilicate. It has a nonmetallic luster, a hardness of about 2 to 3, forms hexagonal crystals, and has one perfect cleavage. Biotite mica can be peeled into ultrathin sheets, which is a consequence of its cleavage. Thin cleavage sheets are noticeably flexible (elastic). Thicker pieces of biotite are black-colored. Thin sheets are brownish-black to dark brown to brown.

• 
  Flaky biotite sheets are shown. Credit: James St. John.{{free media}}
• 
  Thick biotite sample features many sheets. Credit: Eurico Zimbres FGEL/UERJ.{{free media}}
• 
  Biotite crystal exhibit pseudohexagonal shape. Credit: Toma1974.{{free media}}

Numerous black prismatic terminated crystals of aegirine are shown in the image on the right with analcite and smaller colorless prismatic terminated crystals of natrolite, which are from 3 mm to 10 mm in length. Aegirine is a pyroxene.

Formula: (Ca
_xMg
_yFe
_z)(Mg
_y1Fe
_z1)Si
₂O
₆, where 0.4 ≤ x ≤ 0.9, x+y+z=1 and y1+z1=1.^[11]

IMA Formula: (Ca,Mg,Fe)
₂Si
₂O
₆.^[11]

Crystal System: Monoclinic, Clinopyroxene Subgroup > Pyroxene Group.^[11]

Common Impurities: Ti,Cr,Na,Mn,K.^[11]

Geological Setting: Major rock forming mineral in mafic igneous rocks, ultramafic rocks, and some high-grade metamorphic rocks.^[11]

Augite is an essential mineral in mafic igneous rocks; for example, gabbro and basalt and common in ultramafic rocks, occurs in relatively high-temperature metamorphic rocks such as mafic granulite and metamorphosed iron formations, commonly occurs in association with orthoclase, sanidine, labradorite, olivine, leucite, amphiboles and other pyroxenes.^[12]

Baryte, barite or barytes is a barium sulfate mineral (BaSO
₄).^[13] Baryte is generally white or colorless, and is the main source of the element barium. The baryte group consists of baryte, celestine (strontium sulfate), anglesite (lead sulfate),^[14] and anhydrite (calcium sulfate). Baryte and celestine form a solid solution (Ba,Sr)SO
₄.^[15]

Cassiterite is a tin oxide mineral, SnO
₂^[16] that is generally opaque, but it is translucent in thin crystals.

Color: Black, brownish black, reddish brown, brown, red, yellow, gray, white; rarely colorless, Crystal habit: Pyramidic, prismatic, radially fibrous botryoidal crusts and concretionary masses; coarse to fine granular, massive, Mohs scale hardness: 6–7, Specific gravity: 6.98–7.1.^[16]

Common Impurities: Fe,Ta,Nb,Zn,W,Mn,Sc,Ge,In,Ga; Recorded ages: Mesoarchean to Jurassic : 2974 ± 59 Ma to 156 ± 4 Ma - based on 13 recorded ages.^[16]

Columbite, also called niobite, niobite-tantalite and columbate [(Fe,Mn)Nb
₂O
₆], is a black mineral group that is an ore of niobium. It has a submetallic luster and a high density and is a niobate of iron and manganese. This mineral group was first found in Haddam, Connecticut, in the United States. It forms a series with the tantalum-dominant analogue ferrotantalite and one with the manganese-dominant analogue manganocolumbite. The iron-rich member of the columbite group is ferrocolumbite. Some tin and tungsten may be present in the mineral. Yttrocolumbite is the yttrium-rich columbite with the formula (Y,U,Fe)(Nb,Ta)O
₄. It is a radioactive mineral found in Mozambique.

Columbite has the same composition and crystal symmetry (orthorhombic) as tantalite. In fact, the two are often grouped together as a semi-singular mineral series called columbite-tantalite or coltan in many mineral guides. However, tantalite has a much greater specific gravity than columbite, more than 8.0 compared to columbite's 5.2.^[17]

Columbite is also very similar to tapiolite. Those minerals have same chemical composition but different crystal symmetry: orthorhombic for columbite and tetragonal for tapiolite.^[18] The largest documented single crystal of columbite consisted of plates 6 millimetres (0.24 in) thick measuring 76 by 61 centimetres (30 in × 24 in).^[19]

Columbite contains varying amounts of thorium and uranium, which makes it radioactive to various degrees.^[20]

Cronstedtite is a complex iron silicate mineral belonging to the serpentine group of minerals with chemical formula is Fe²⁺
₂Fe³⁺
(Si,Fe³⁺
)
₂O
₅(OH)
₄.^[21]

Colour:Black, dark brown-black, green-black, Lustre: Waxy, Sub-Metallic, Hardness: 3½, Specific Gravity: 3.34 - 3.35, Crystal System: Trigonal, Member of the Serpentine Subgroup > Kaolinite-Serpentine Group.^[21]

Cronstedtite is a major constituent of CM chondrites, a carbonaceous chondrite group exhibiting varying degrees of aqueous alteration. Cronstedtite abundance decreases with increasing alteration.^[22]

Davemaoite is a high-pressure calcium silicate perovskite (CaSiO
₃) mineral with a distinctive cubic crystal structure.

"Davemaoite is a vehicle for radioactive isotopes that help to heat the planet’s mantle."^[23]

"Davemaoite is mostly calcium silicate (CaSiO
₃), but it can scavenge radioactive isotopes of uranium, thorium and potassium. These isotopes generate a lot of heat in the lower portion of Earth’s mantle — the layer that lies between the planet’s crust and core. That makes davemaoite an important player in managing how heat moves through the deep Earth and, in turn, how heat cycles between the mantle and crust to drive processes such as plate tectonics."^[23]

"The greenish, octahedral-shaped diamond was dug up decades ago in Botswana at the Orapa mine, the world’s largest opencast diamond mine. In 1987, a mineral dealer sold the diamond to George Rossman, a mineralogist at the California Institute of Technology in Pasadena. Tschauner, Rossman and their colleagues began studying it several years ago as part of an investigation into minerals trapped in deep-Earth diamonds."^[23]

The "diamond [was irradiated] with X-rays at the Advanced Photon Source [at Argonne National Laboratory], Lemont, Illinois, which revealed that the inclusions were rich in a calcium mineral,"^[23] using a technique known as X-ray diffraction with the X-ray Synchrotron light source.^[24][25][26]

"It’s the strength of the diamond that keeps the inclusions at high pressure."^[27]

"The version in the diamond has a perovskite crystal structure that only forms at the temperatures and pressures found between 660 and 900 kilometres deep."^[27]

"Davemaoite is one of three main minerals in Earth’s lower mantle making up around 5–7% of the material there."^[27]

"The one found at Orapa is rich in potassium — so one way to find more davemaoite might be to look for deep diamonds in potassium-rich areas."^[28]

Hematite is the mineral form of iron(III) oxide (Fe₂O₃), one of several iron oxides. Hematite is colored black to steel or silver-gray, brown to reddish brown, or red. Huge deposits of hematite are found in banded iron formations.

Samsonite is a silver manganese antimony sulfosalt mineral with formula Ag
₄MnSb
₂S
₆.^[29] It crystallizes in the monoclinic crystal system^[29] with a typical slender radiating prismatic habit.^[30] It is metallic black^[29] to steel black^[30] with no cleavage and a brittle to conchoidal fracture.^[30] In thin fragments it appears reddish brown in transmitted light and also leaves a red streak.^[30] It is soft, Mohs hardness of 2.5,^[29] and has a specific gravity of 5.51.^[30]

Common impurities in Samsonite are Cu and Fe, Class (H-M): 2/m - Prismatic, Space Group:P2₁/m, Cell Parameters: a = 10.3861(6) Å, b = 8.1108(7) Å, c = 6.663(7) Å, β = 92.639(12)°, Ratio: a:b:c = 1.281 : 1 : 0.821, Z: 2.^[29]

Samsonite - Empirical Formula: Ag
₄Mn³⁺
Sb
₂S
₆, Axial Ratios: a:b:c = 1.2782:1:0.8211, Cell Dimensions: a = 10.29, b = 8.05, c = 6.61, Z = 2; beta = 92.79°, V = 546.89, Density (Calc)= 5.60.^[31][32]

Samsonite: Density (measured) = 5.51, Fracture: Conchoidal, Tenacity: Brittle, Association: Pyrargyrite, galena, dyscrasite, tetrahedrite, pyrolusite, quartz, calcite, apophyllite (St. Andreasberg, Germany).^[30]

Stephanite is a silver antimony sulfosalt mineral with formula: Ag
₅SbS
₄.^[33]

Stephanite occurs as a late-stage mineral with other ores of silver in hydrothermal veins.^[34] Associated minerals include proustite, acanthite, native silver, tetrahedrite, galena, sphalerite and pyrite.^[35].

Colour: Lead gray or black, Lustre: Metallic, Hardness: 2 - 2½, Specific Gravity: 6.26, Crystal System: Orthorhombic.^[33]

In the on the right, the black acicular crystals are the mineral tazieffite Pb
₂₀Cd
₂(As,Bi)
₂₂S
₅₀Cl
₁₀ (named after the famous French volcanologist Haroun Tazieff). The substrate is composed of aluminum fluoride, tinted pink by thallium iodide. Image size is 700 microns along the long side. Colours are derived from microphoto of the same scene.

Thorianite is a rare thorium oxide mineral, ThO₂.^[36] It has a high percentage of thorium; it also contains the oxides of uranium, lanthanum, cerium, praseodymium and neodymium. The mineral is slightly less radioactive than pitchblende, but is harder to shield due to its high energy gamma rays. It is common in the alluvial gem-gravels of Sri Lanka, where it occurs mostly as water worn, small, heavy, black, cubic crystals.

Uraninite is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO₂, but also contains 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 unraninite. Because of the uranium decay products, both sources are gamma-ray emitters.

Def. a "substance that resembles a mineral but does not exhibit crystallinity"^[37] is called a mineraloid.

Def. a naturally occurring black glass is called an obsidian.

Def. a "flammable liquid ranging in color from clear to very dark brown and black, consisting mainly of hydrocarbons, occurring naturally in deposits under the Earth's surface"^[38] is called petroleum.

Black and white images are not ordinarily starkly contrasted black and white but combine black and white in a continuum producing a range of shades of gray.

In physics, a continuous spectrum usually means a set of values for some physical quantity (such as energy or wavelength) that is best described as an interval of real numbers. It is opposed to discrete spectrum, a set of values that is discrete in the mathematical sense, where there is a positive gap between each value and the next one.

At left is a continuous spectrum from a deuterium lamp. The tall sharp peaks are discrete emissions and the continuous part is the smoothly varying part between the peaks. The smaller peaks and valleys may be due to measurement errors rather than discrete spectral lines.

"[W]ith Scorpius X-1 ... the visible continuum is roughly what would be expected from a hot plasma fitting the observed X-ray flux.^[39] The plasma could be a coronal cloud of a central object or a transient plasma, where the energy source is unknown, but could be related to the idea of a close binary.^[39]

A spectrum (plural spectra or spectrums^[40]) is a condition that is not limited to a specific set of values but can vary infinitely within a continuum.

In the continuum of colors of visible light [green] is located between yellow and blue.

Continuum light is linearly polarized at different locations across the face of the Sun (limb polarization) though taken as a whole, this polarization cancels.

In optics, a supercontinuum is formed when a collection of nonlinear processes act together upon a pump beam in order to cause severe spectral broadening of the original pump beam. The result is a smooth spectral continuum.

The figure at right shows a typical supercontinuum spectrum about an emission-line source. The blue line shows the spectrum of the source launched into a photonic crystal fiber while the red line shows the resulting supercontinuum spectrum generated after propagating through the fiber.

The inverse Raman effect^[41] in optics ... which deals with the properties and behavior of light) is a form of Raman scattering.

If a material is simultaneously irradiated by intense monochromatic light of frequency ν_L (typically a laser beam) and light of a continuum of higher frequencies, among the possibilities for light scattering are scattering:

• from the monochromatic beam at ν_L to the continuum at ν_L+ν_M (anti-Stokes Raman scattering)
• from the continuum at ν_L+ν_M to the monochromatic beam at ν_L (Stokes Raman scattering)

where ν_M is a Raman frequency of the material.

The strength of these two scatterings depends (among other things) on the energy levels of the material, their occupancy, and the intensity of the continuum. In some circumstances Stokes scattering can exceed anti-Stokes scattering; in these cases the continuum (on leaving the material) is observed to have an absorption line (a dip in intensity) at ν_L+ν_M. This phenomenon is referred to as the inverse Raman effect; the application of the phenomenon is referred to as inverse Raman spectroscopy, and a record of the continuum is referred to as an inverse Raman spectrum.

Both absorption from a continuum of higher frequencies and absorption from a continuum of lower frequencies [can occur]. Absorption from a continuum of lower frequencies will not be observed if the Raman frequency of the material is vibrational in origin and if the material is in thermal equilibrium.

Reverberation mapping is an astrophysical technique for measuring the structure of the broad emission-line region (BLR) around a supermassive black hole at the center of an active galaxy and estimating the hole's mass. It is considered a "primary" mass estimation technique, i.e., the mass is measured directly from the motion that its gravitational force induces in the nearby gas.^[42]

The black hole mass is measured from the formula

${\displaystyle GM_{\bullet }=fR_{\mathrm {BLR} }(\Delta V)^{2}.}$

In this formula, ΔV is the rms velocity of gas moving near the black hole in the broad emission-line region, measured from the Doppler broadening of the gaseous emission lines; R_BLR is the radius of the broad-line region; G is the constant of gravitation; and f is a poorly-known "form factor" that depends on the shape of the BLR.

The biggest difficulty with applying this formula is the measurement of R_BLR. One standard technique^[43] is based on the fact that the emission-line fluxes vary strongly in response to changes in the continuum, i.e., the light from the accretion disk near the black hole ("reverberation"). Furthermore, the emission-line response is found to be delayed with respect to changes in the continuum. Assuming that the delay is due to light travel times, the size of the broad emission-line region can be measured.

Only a small handful of AGN (less than 40) have been accurately "mapped" in this way. An alternative approach is to use an empirical correlation between R_BLR and he continuum luminosity.^[42]

Another uncertainty is the value of f. In principle, the response of the BLR to variations in the continuum could be used to map out the three-dimensional structure of the BLR. In practice, the amount and quality of data required to carry out such a deconvolution is prohibitive. Until about 2004, f was estimated ab initio based on simple models for the structure of the BLR. More recently, the value of f has been determined so as to bring the M-sigma relation for active galaxies into the best possible agreement with the M-sigma relation for quiescent galaxies.^[42] When f is determined in this way, reverberation mapping becomes a "secondary", rather than "primary," mass estimation technique.

"Fermi's Large Area Telescope (LAT) scans the entire sky every three hours, continually deepening its portrait of the sky in gamma rays, the most energetic form of light. While the energy of visible light falls between about 2 and 3 electron volts, the LAT detects gamma rays with energies ranging from 20 million to more than 300 billion electron volts (GeV)."^[44]

"At higher energies, gamma rays are rare. Above 10 GeV, even Fermi's LAT detects only one gamma ray every four months from some sources."^[44]

"Any object producing gamma rays at these energies is undergoing extraordinary astrophysical processes. More than half of the 496 sources [the Fermi hard-source list] in the new census are active galaxies, where matter falling into a supermassive black hole powers jets that spray out particles at nearly the speed of light."^[44]

"One example is the well-known radio galaxy NGC 1275 [above left], which is a bright, isolated source below 10 GeV. At higher energies it fades appreciably and another nearby source begins to appear. Above 100 GeV, NGC 1275 becomes undetectable by Fermi, while the new source, the radio galaxy IC 310, shines brightly."^[44]

"The catalog serves as an important roadmap for ground-based facilities called Atmospheric Cherenkov Telescopes, which have amassed about 130 gamma-ray sources with energies above 100 GeV. They include the Major Atmospheric Gamma Imaging Cherenkov telescope (MAGIC) on La Palma in the Canary Islands, the Very Energetic Radiation Imaging Telescope Array System (VERITAS) in Arizona, and the High Energy Stereoscopic System (H.E.S.S.) in Namibia."^[44]

Ultra-soft x-rays are also known as grenz-rays (GRs).^[45]

"For AM Her's or intermediate polars, there is also a very soft black-body like component, often detected in ultra-soft X-rays. Often only the soft component is detected."^[46]

"Most people have heard of auroras - more commonly known as the Northern and Southern Lights - but, except on rare occasions, such as the recent widespread apparition on 17 March, they are not usually visible outside the polar regions. Less familiar are phenomena known as black auroras, dark patches which often subdivide the glowing curtains of red and green light."^[47]

"Whereas bright auroras are created by electrons plunging downward into the ionosphere, neighbouring black auroras are caused by electrons escaping from the ionosphere - like a kind of anti-aurora. However, until now, scientists have been struggling to explain the relationship between the two auroral types."^[47]

"We found strong evidence of a two-way interaction between the ionosphere and the magnetosphere."^[48]

"Auroral arcs are created by electric currents. The beam of electrons shooting down towards Earth along magnetic field lines is actually an electric current aligned with Earth's magnetic field. It is called an upward, field-aligned current because the negatively charged electrons are moving downward."^[48]

"On the other hand, when a downward magnetospheric current meets the ionosphere, electrons are driven upwards and 'sucked' from the ionosphere, creating a black aurora. However, when the electron density in the ionosphere drops markedly the black aurora becomes less intense."^[48]

"This evacuation of the ionosphere is essential in shaping the black auroras. The process is much more important on Earth's nightside than on the dayside because sunlight creates new electrons which fill the 'hole'."^[48]

The "two-way electrodynamic coupling between the magnetosphere and ionosphere [...] is made possible by a horizontal drift of ions in the ionosphere, known as the Pedersen current, which closes the current system."^[48]

"According to convention, negatively charged electrons flow downward, from the magnetosphere to the ionosphere, in an upward field-aligned current. Electrons flow upward, from the ionosphere to the magnetosphere, in a downward field-aligned current."^[47]

The two images on the left are apparently two successive images of the same aurora showing changes with time and black auroras.

Planck's equation describes the amount of spectral radiance at a certain wavelength radiated by a black body in thermal equilibrium.

In terms of wavelength (λ), Planck's equation is written as

${\displaystyle B_{\lambda }(T)={\frac {2hc^{2}}{\lambda ^{5}}}{\frac {1}{e^{\frac {hc}{\lambda k_{\mathrm {B} }T}}-1}}}$

where B is the spectral radiance, T is the absolute temperature of the black body, k_B is the Boltzmann constant, h is the Planck constant, and c is the speed of light.

This form of the equation contains several constants that are usually not subject to variation with wavelength. These are h, c, and k_B. They may be represented by simple coefficients: c1 = 2h c² and c2 = h c/k_B.

By setting the first partial derivative of Planck's equation in wavelength form equal to zero, iterative calculations may be used to find pairs of (λ,T) that to some significant digits represent the peak wavelength for a given temperature and vice versa.

${\displaystyle {\frac {\partial B}{\partial \lambda }}={\frac {c1}{\lambda ^{6}}}{\frac {1}{e^{\frac {c2}{\lambda T}}-1}}[{\frac {c2}{\lambda T}}{\frac {1}{e^{\frac {c2}{\lambda T}}-1}}e^{\frac {c2}{\lambda T}}-5]=0.}$

Or,

${\displaystyle {\frac {c2}{\lambda T}}{\frac {1}{e^{\frac {c2}{\lambda T}}-1}}e^{\frac {c2}{\lambda T}}-5=0.}$

${\displaystyle {\frac {c2}{\lambda T}}{\frac {1}{e^{\frac {c2}{\lambda T}}-1}}e^{\frac {c2}{\lambda T}}=5.}$

Use c2 = 1.438833 cm K.

Planck's equation is not an exact fit to a star's spectral radiance.

Black-body radiation is the type of electromagnetic radiation within or surrounding a body in thermodynamic equilibrium with its environment, or emitted by a black body (an opaque and non-reflective body) held at constant, uniform temperature. The radiation has a specific spectrum and intensity that depends only on the temperature of the body.^{[49][50][51][52]}

Gravitational radiation appears to be cylindrical waves of radiation produced by relativistic, undulatory gravitational fields in Euclidean space.^[53]

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."^[54]

"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."^[55]

Later detection confirmed the fusion of two massive stellar-sized objects, a binary neutron star merger.^[56]

"According to Einstein's field equations, photon matter subject to quadruple oscillations is a source of gravitational waves."^[57]

"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."^[58]

"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."^[58]

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."^[59]

"Lake ice occurs primarily in the Northern Hemisphere [of Earth], where most of the ice is seasonal: it forms in the autumn, thickens during the winter and melts in the spring."^[60]

In Swedish kärnis means "blue ice", whereas the English term is "black ice". Lots of "blue ice" occurs on lakes with clear water over a sandy bottom. At right is an image of black ice (kärnis) on Lake Vättern.

On the left is an image of black ice over a river in Holland.

Centered in the image on the right is a black ice growler from a recently calved iceberg closing in on the shore at the old heliport in Upernavik, Greenland. Such black ice growlers originate from glacial rifts, or crevasses, filled with melting water, which freezes into transparent ice without air bubbles.

On the left is an image of the surface texture on a black ice growler. There are bowl-like depressions in the surface created by the melting process of sea water.

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{{Principles of radiation astronomy}}