88-588: Einstein Observatory ( HEAO-2 ) was the first fully imaging X-ray telescope put into space and the second of NASA 's three High Energy Astrophysical Observatories. Named HEAO B before launch, the observatory's name was changed to honor Albert Einstein upon its successfully attaining orbit. The High Energy Astronomy Observatory (HEAO) program originated in the late 1960's within the Astronomy Missions Board at NASA, which recommended
176-511: A quasar and an observer. In this case, the galaxy cluster will lens the quasar. Strong lensing is the observed distortion of background galaxies into arcs when their light passes through such a gravitational lens. It has been observed around many distant clusters including Abell 1689 . By measuring the distortion geometry, the mass of the intervening cluster can be obtained. In the weak regime, lensing does not distort background galaxies into arcs, causing minute distortions instead. By examining
264-544: A few bands can be observed from the Earth's surface. These bands are visible – near-infrared and a portion of the radio-wave part of the spectrum. For this reason there are no X-ray or far-infrared ground-based telescopes as these have to be observed from orbit. Even if a wavelength is observable from the ground, it might still be advantageous to place a telescope on a satellite due to issues such as clouds, astronomical seeing and light pollution . The disadvantages of launching
352-607: A few decades of the first refracting telescope. In the 20th century, many new types of telescopes were invented, including radio telescopes in the 1930s and infrared telescopes in the 1960s. The word telescope was coined in 1611 by the Greek mathematician Giovanni Demisiani for one of Galileo Galilei 's instruments presented at a banquet at the Accademia dei Lincei . In the Starry Messenger , Galileo had used
440-504: A focal point. Optical telescopes are used for astronomy and in many non-astronomical instruments, including: theodolites (including transits ), spotting scopes , monoculars , binoculars , camera lenses , and spyglasses . There are three main optical types: A Fresnel imager is a proposed ultra-lightweight design for a space telescope that uses a Fresnel lens to focus light. Beyond these basic optical types there are many sub-types of varying optical design classified by
528-544: A great majority of them – may be dark bodies. In 1906, Poincaré used the French term [ matière obscure ] ("dark matter") in discussing Kelvin's work. He found that the amount of dark matter would need to be less than that of visible matter, incorrectly, it turns out. The second to suggest the existence of dark matter using stellar velocities was Dutch astronomer Jacobus Kapteyn in 1922. A publication from 1930 by Swedish astronomer Knut Lundmark points to him being
616-478: A mass-to-light ratio of 50; in 1940, Oort discovered and wrote about the large non-visible halo of NGC 3115 . Early radio astronomy observations, performed by Seth Shostak , later SETI Institute Senior Astronomer, showed a half-dozen galaxies spun too fast in their outer regions, pointing to the existence of dark matter as a means of creating the gravitational pull needed to keep the stars in their orbits. The hypothesis of dark matter largely took root in
704-682: A significant fraction of dark matter was ruled out by measurements of positron and electron fluxes outside the Sun's heliosphere by the Voyager ;1 spacecraft. Tiny black holes are theorized to emit Hawking radiation . However the detected fluxes were too low and did not have the expected energy spectrum, suggesting that tiny primordial black holes are not widespread enough to account for dark matter. Nonetheless, research and theories proposing dense dark matter accounts for dark matter continue as of 2018, including approaches to dark matter cooling, and
792-491: A similar inference. Zwicky applied the virial theorem to the Coma Cluster and obtained evidence of unseen mass he called dunkle Materie ('dark matter'). Zwicky estimated its mass based on the motions of galaxies near its edge and compared that to an estimate based on its brightness and number of galaxies. He estimated the cluster had about 400 times more mass than was visually observable. The gravity effect of
880-475: A single receiver and records a single time-varying signal characteristic of the observed region; this signal may be sampled at various frequencies. In some newer radio telescope designs, a single dish contains an array of several receivers; this is known as a focal-plane array . By collecting and correlating signals simultaneously received by several dishes, high-resolution images can be computed. Such multi-dish arrays are known as astronomical interferometers and
968-438: A small portion of their total radiation in the x-ray spectrum, primarily from their corona , while neutron stars emit a very large portion of their total radiation in the x-ray spectrum. Einstein data also indicated that coronal x-ray emissions in main sequence stars are stronger than was expected at the time. The Uhuru satellite discovered x-ray emissions from a hot, thin gas pervading distant clusters of galaxies . Einstein
SECTION 10
#17327760231821056-424: A smaller fraction, using greater values for luminous mass. Nonetheless, Zwicky did correctly conclude from his calculation that most of the gravitational matter present was dark. However unlike modern theories, Zwicky considered "dark matter" to be non-luminous ordinary matter. Further indications of mass-to-light ratio anomalies came from measurements of galaxy rotation curves . In 1939, H.W. Babcock reported
1144-625: A space telescope include cost, size, maintainability and upgradability. Some examples of space telescopes from NASA are the Hubble Space Telescope that detects visible light, ultraviolet, and near-infrared wavelengths, the Spitzer Space Telescope that detects infrared radiation, and the Kepler Space Telescope that discovered thousands of exoplanets. The latest telescope that was launched was
1232-572: A thousand supernovae detected no gravitational lensing events, when about eight would be expected if intermediate-mass primordial black holes above a certain mass range accounted for over 60% of dark matter. However, that study assumed a monochromatic distribution to represent the LIGO/Virgo mass range, which is inapplicable to the broadly platykurtic mass distribution suggested by subsequent James Webb Space Telescope observations. The possibility that atom-sized primordial black holes account for
1320-452: Is a hypothetical form of matter that does not interact with light or other electromagnetic radiation . Dark matter is implied by gravitational effects which cannot be explained by general relativity unless more matter is present than can be observed. Such effects occur in the context of formation and evolution of galaxies , gravitational lensing , the observable universe 's current structure, mass position in galactic collisions ,
1408-412: Is called an observatory . Radio telescopes are directional radio antennas that typically employ a large dish to collect radio waves. The dishes are sometimes constructed of a conductive wire mesh whose openings are smaller than the wavelength being observed. Unlike an optical telescope, which produces a magnified image of the patch of sky being observed, a traditional radio telescope dish contains
1496-482: Is classified as "cold", "warm", or "hot" according to velocity (more precisely, its free streaming length). Recent models have favored a cold dark matter scenario, in which structures emerge by the gradual accumulation of particles. Although the astrophysics community generally accepts the existence of dark matter, a minority of astrophysicists, intrigued by specific observations that are not well explained by ordinary dark matter, argue for various modifications of
1584-427: Is not known to interact with ordinary baryonic matter and radiation except through gravity, making it difficult to detect in the laboratory. The most prevalent explanation is that dark matter is some as-yet-undiscovered subatomic particle , such as either weakly interacting massive particles (WIMPs) or axions . The other main possibility is that dark matter is composed of primordial black holes . Dark matter
1672-528: Is now also being applied to optical telescopes using optical interferometers (arrays of optical telescopes) and aperture masking interferometry at single reflecting telescopes. Radio telescopes are also used to collect microwave radiation , which has the advantage of being able to pass through the atmosphere and interstellar gas and dust clouds. Some radio telescopes such as the Allen Telescope Array are used by programs such as SETI and
1760-536: Is of particular note because the location of the center of mass as measured by gravitational lensing is different from the location of the center of mass of visible matter. This is difficult for modified gravity theories, which generally predict lensing around visible matter, to explain. Standard dark matter theory however has no issue: the hot, visible gas in each cluster would be cooled and slowed down by electromagnetic interactions, while dark matter (which does not interact electromagnetically) would not. This leads to
1848-482: Is possible to make very tiny antenna). The near-infrared can be collected much like visible light; however, in the far-infrared and submillimetre range, telescopes can operate more like a radio telescope. For example, the James Clerk Maxwell Telescope observes from wavelengths from 3 μm (0.003 mm) to 2000 μm (2 mm), but uses a parabolic aluminum antenna. On the other hand,
SECTION 20
#17327760231821936-474: Is revealed only via its gravitational effects, or weak lensing . In addition, if the particles of which it is composed are supersymmetric, they can undergo annihilation interactions with themselves, possibly resulting in observable by-products such as gamma rays and neutrinos (indirect detection). In 2015, the idea that dense dark matter was composed of primordial black holes made a comeback following results of gravitational wave measurements which detected
2024-399: Is the gravitational lens . Gravitational lensing occurs when massive objects between a source of light and the observer act as a lens to bend light from this source. Lensing does not depend on the properties of the mass; it only requires there to be a mass. The more massive an object, the more lensing is observed. An example is a cluster of galaxies lying between a more distant source such as
2112-406: Is underway on several 30–40m designs. The 20th century also saw the development of telescopes that worked in a wide range of wavelengths from radio to gamma-rays . The first purpose-built radio telescope went into operation in 1937. Since then, a large variety of complex astronomical instruments have been developed. Since the atmosphere is opaque for most of the electromagnetic spectrum, only
2200-581: Is unknown but word of it spread through Europe. Galileo heard about it and, in 1609, built his own version, and made his telescopic observations of celestial objects. The idea that the objective , or light-gathering element, could be a mirror instead of a lens was being investigated soon after the invention of the refracting telescope. The potential advantages of using parabolic mirrors —reduction of spherical aberration and no chromatic aberration —led to many proposed designs and several attempts to build reflecting telescopes . In 1668, Isaac Newton built
2288-434: Is unknown, but there are many hypotheses about what dark matter could consist of, as set out in the table below. Dark matter can refer to any substance which interacts predominantly via gravity with visible matter (e.g., stars and planets). Hence in principle it need not be composed of a new type of fundamental particle but could, at least in part, be made up of standard baryonic matter , such as protons or neutrons. Most of
2376-559: Is well fitted by the lambda-CDM model , but difficult to reproduce with any competing model such as modified Newtonian dynamics (MOND). Structure formation refers to the period after the Big Bang when density perturbations collapsed to form stars, galaxies, and clusters. Prior to structure formation, the Friedmann solutions to general relativity describe a homogeneous universe. Later, small anisotropies gradually grew and condensed
2464-580: The 2dF Galaxy Redshift Survey . Results are in agreement with the lambda-CDM model . In astronomical spectroscopy , the Lyman-alpha forest is the sum of the absorption lines arising from the Lyman-alpha transition of neutral hydrogen in the spectra of distant galaxies and quasars . Lyman-alpha forest observations can also constrain cosmological models. These constraints agree with those obtained from WMAP data. The identity of dark matter
2552-645: The Arecibo Observatory to search for extraterrestrial life. An optical telescope gathers and focuses light mainly from the visible part of the electromagnetic spectrum. Optical telescopes increase the apparent angular size of distant objects as well as their apparent brightness . For the image to be observed, photographed, studied, and sent to a computer, telescopes work by employing one or more curved optical elements, usually made from glass lenses and/or mirrors , to gather light and other electromagnetic radiation to bring that light or radiation to
2640-822: The Earth's atmosphere is opaque to this part of the electromagnetic spectrum. An example of this type of telescope is the Fermi Gamma-ray Space Telescope which was launched in June 2008. The detection of very high energy gamma rays, with shorter wavelength and higher frequency than regular gamma rays, requires further specialization. Such detections can be made either with the Imaging Atmospheric Cherenkov Telescopes (IACTs) or with Water Cherenkov Detectors (WCDs). Examples of IACTs are H.E.S.S. and VERITAS with
2728-579: The Latin term perspicillum . The root of the word is from the Ancient Greek τῆλε, romanized tele 'far' and σκοπεῖν, skopein 'to look or see'; τηλεσκόπος, teleskopos 'far-seeing'. The earliest existing record of a telescope was a 1608 patent submitted to the government in the Netherlands by Middelburg spectacle maker Hans Lipperhey for a refracting telescope . The actual inventor
Einstein Observatory - Misplaced Pages Continue
2816-572: The Spitzer Space Telescope , observing from about 3 μm (0.003 mm) to 180 μm (0.18 mm) uses a mirror (reflecting optics). Also using reflecting optics, the Hubble Space Telescope with Wide Field Camera 3 can observe in the frequency range from about 0.2 μm (0.0002 mm) to 1.7 μm (0.0017 mm) (from ultra-violet to infrared light). With photons of the shorter wavelengths, with
2904-403: The electromagnetic spectrum , and in some cases other types of detectors. The first known practical telescopes were refracting telescopes with glass lenses and were invented in the Netherlands at the beginning of the 17th century. They were used for both terrestrial applications and astronomy . The reflecting telescope , which uses mirrors to collect and focus light, was invented within
2992-512: The 0.15 to 4.5 keV energy range. Four instruments were installed in the satellite, mounted on a carousel arrangement that could be rotated into the focal plane of the telescope: Additionally, the Monitor Proportional Counter (MPC) was a non-focal plane, coaxially-mounted proportional counter that monitored the x-ray flux of the source being observed by the active focal plane instrument. Two filters could be used with
3080-547: The 1970s. Several different observations were synthesized to argue that galaxies should be surrounded by halos of unseen matter. In two papers that appeared in 1974, this conclusion was drawn in tandem by independent groups: in Princeton, New Jersey, U.S.A., by Jeremiah Ostriker , Jim Peebles , and Amos Yahil, and in Tartu, Estonia, by Jaan Einasto , Enn Saar, and Ants Kaasik. One of the observations that served as evidence for
3168-422: The 21 cm line of atomic hydrogen in nearby galaxies. The radial distribution of interstellar atomic hydrogen ( H ) often extends to much greater galactic distances than can be observed as collective starlight, expanding the sampled distances for rotation curves – and thus of the total mass distribution – to a new dynamical regime. Early mapping of Andromeda with the 300 foot telescope at Green Bank and
3256-434: The 250 foot dish at Jodrell Bank already showed the H rotation curve did not trace the decline expected from Keplerian orbits. As more sensitive receivers became available, Roberts & Whitehurst (1975) were able to trace the rotational velocity of Andromeda to 30 kpc, much beyond the optical measurements. Illustrating the advantage of tracing the gas disk at large radii; that paper's Figure 16 combines
3344-632: The CMB observations with BAO measurements from galaxy redshift surveys provides a precise estimate of the Hubble constant and the average matter density in the Universe. The results support the Lambda-CDM model. Large galaxy redshift surveys may be used to make a three-dimensional map of the galaxy distribution. These maps are slightly distorted because distances are estimated from observed redshifts ;
3432-466: The CMB. The CMB is very close to a perfect blackbody but contains very small temperature anisotropies of a few parts in 100,000. A sky map of anisotropies can be decomposed into an angular power spectrum, which is observed to contain a series of acoustic peaks at near-equal spacing but different heights. The locations of these peaks depend on cosmological parameters. Matching theory to data, therefore, constrains cosmological parameters. The CMB anisotropy
3520-627: The James Webb Space Telescope on December 25, 2021, in Kourou, French Guiana. The Webb telescope detects infrared light. The name "telescope" covers a wide range of instruments. Most detect electromagnetic radiation , but there are major differences in how astronomers must go about collecting light (electromagnetic radiation) in different frequency bands. As wavelengths become longer, it becomes easier to use antenna technology to interact with electromagnetic radiation (although it
3608-474: The Solar System. This is not observed. Instead, the galaxy rotation curve remains flat or even increases as distance from the center increases. If Kepler's laws are correct, then the obvious way to resolve this discrepancy is to conclude the mass distribution in spiral galaxies is not similar to that of the Solar System. In particular, there is a lot of non-luminous matter (dark matter) in the outskirts of
Einstein Observatory - Misplaced Pages Continue
3696-403: The apparent shear deformation of the adjacent background galaxies, the mean distribution of dark matter can be characterized. The measured mass-to-light ratios correspond to dark matter densities predicted by other large-scale structure measurements. Although both dark matter and ordinary matter are matter, they do not behave in the same way. In particular, in the early universe, ordinary matter
3784-421: The centenary of the scientist's birth. Einstein ceased operations on April 26 1981, when the exhaustion of the satellite's thruster fuel supply rendered the telescope inoperable. The satellite reentered Earth's atmosphere and burned up on March 25, 1982. Einstein carried a single large grazing-incidence focusing X-ray telescope that provided unprecedented levels of sensitivity. It had instruments sensitive in
3872-429: The dark matter separating from the visible gas, producing the separate lensing peak as observed. Type Ia supernovae can be used as standard candles to measure extragalactic distances, which can in turn be used to measure how fast the universe has expanded in the past. Data indicates the universe is expanding at an accelerating rate, the cause of which is usually ascribed to dark energy . Since observations indicate
3960-403: The dark matter. However, multiple lines of evidence suggest the majority of dark matter is not baryonic: There are two main candidates for non-baryonic dark matter: new hypothetical particles and primordial black holes . Unlike baryonic matter, nonbaryonic particles do not contribute to the formation of the elements in the early universe ( Big Bang nucleosynthesis ) and so its presence
4048-420: The density of the visible baryonic matter (normal matter) of the universe on large scales. These are predicted to arise in the Lambda-CDM model due to acoustic oscillations in the photon–baryon fluid of the early universe and can be observed in the cosmic microwave background angular power spectrum. BAOs set up a preferred length scale for baryons. As the dark matter and baryons clumped together after recombination,
4136-436: The diameter of the observable Universe via cosmic expansion , the scale, a , has doubled. The energy of the cosmic microwave background radiation has been halved (because the wavelength of each photon has doubled); the energy of ultra-relativistic particles, such as early-era standard-model neutrinos, is similarly halved. The cosmological constant, as an intrinsic property of space, has a constant energy density regardless of
4224-516: The effect is much weaker in the galaxy distribution in the nearby universe, but is detectable as a subtle (≈1 percent) preference for pairs of galaxies to be separated by 147 Mpc, compared to those separated by 130–160 Mpc. This feature was predicted theoretically in the 1990s and then discovered in 2005, in two large galaxy redshift surveys, the Sloan Digital Sky Survey and the 2dF Galaxy Redshift Survey . Combining
4312-408: The existence of galactic halos of dark matter was the shape of galaxy rotation curves . These observations were done in optical and radio astronomy. In optical astronomy, Vera Rubin and Kent Ford worked with a new spectrograph to measure the velocity curve of edge-on spiral galaxies with greater accuracy. At the same time, radio astronomers were making use of new radio telescopes to map
4400-460: The first practical reflecting telescope, of a design which now bears his name, the Newtonian reflector . The invention of the achromatic lens in 1733 partially corrected color aberrations present in the simple lens and enabled the construction of shorter, more functional refracting telescopes. Reflecting telescopes, though not limited by the color problems seen in refractors, were hampered by
4488-505: The first to realise that the universe must contain much more mass than can be observed. Dutch radio astronomy pioneer Jan Oort also hypothesized the existence of dark matter in 1932. Oort was studying stellar motions in the galactic neighborhood and found the mass in the galactic plane must be greater than what was observed, but this measurement was later determined to be incorrect. In 1933, Swiss astrophysicist Fritz Zwicky studied galaxy clusters while working at Cal Tech and made
SECTION 50
#17327760231824576-473: The galactic center. The luminous mass density of a spiral galaxy decreases as one goes from the center to the outskirts. If luminous mass were all the matter, then we can model the galaxy as a point mass in the centre and test masses orbiting around it, similar to the Solar System . From Kepler's Third Law , it is expected that the rotation velocities will decrease with distance from the center, similar to
4664-429: The galaxies and clusters currently seen. Dark matter provides a solution to this problem because it is unaffected by radiation. Therefore, its density perturbations can grow first. The resulting gravitational potential acts as an attractive potential well for ordinary matter collapsing later, speeding up the structure formation process. The Bullet Cluster is the result of a recent collision of two galaxy clusters. It
4752-499: The galaxy. Stars in bound systems must obey the virial theorem . The theorem, together with the measured velocity distribution, can be used to measure the mass distribution in a bound system, such as elliptical galaxies or globular clusters. With some exceptions, velocity dispersion estimates of elliptical galaxies do not match the predicted velocity dispersion from the observed mass distribution, even assuming complicated distributions of stellar orbits. As with galaxy rotation curves,
4840-682: The higher frequencies, glancing-incident optics, rather than fully reflecting optics are used. Telescopes such as TRACE and SOHO use special mirrors to reflect extreme ultraviolet , producing higher resolution and brighter images than are otherwise possible. A larger aperture does not just mean that more light is collected, it also enables a finer angular resolution. Telescopes may also be classified by location: ground telescope, space telescope , or flying telescope . They may also be classified by whether they are operated by professional astronomers or amateur astronomers . A vehicle or permanent campus containing one or more telescopes or other instruments
4928-400: The homogeneous universe into stars, galaxies and larger structures. Ordinary matter is affected by radiation, which is the dominant element of the universe at very early times. As a result, its density perturbations are washed out and unable to condense into structure. If there were only ordinary matter in the universe, there would not have been enough time for density perturbations to grow into
5016-414: The imaging detectors: Riccardo Giacconi was the principal investigator for all of the experiments on board Einstein. Einstein discovered approximately five thousand sources of x-ray emission during its operation and was the first x-ray experiment able to resolve an image of the observed sources. Surveys by early x-ray astronomy experiments showed a uniform diffuse background of x-ray radiation across
5104-433: The late 1970s the existence of dark matter halos around galaxies was widely recognized as real, and became a major unsolved problem in astronomy. A stream of observations in the 1980–1990s supported the presence of dark matter. Persic, Salucci & Stel (1996) is notable for the investigation of 967 spirals. The evidence for dark matter also included gravitational lensing of background objects by galaxy clusters ,
5192-505: The launch of a series of satellite observatories dedicated to high-energy astronomy. In 1970, NASA requested proposals for experiments to fly on these observatories, and a team organized by Riccardo Giacconi , Herbert Gursky , George W. Clark , Elihu Boldt, and Robert Novick responded in October 1970 with a proposal for an x-ray telescope. NASA approved four missions in the HEAO program, with
5280-469: The merger of intermediate-mass black holes. Black holes with about 30 solar masses are not predicted to form by either stellar collapse (typically less than 15 solar masses) or by the merger of black holes in galactic centers (millions or billions of solar masses). It was proposed that the intermediate-mass black holes causing the detected merger formed in the hot dense early phase of the universe due to denser regions collapsing. A later survey of about
5368-445: The motion of galaxies within galaxy clusters , and cosmic microwave background anisotropies . In the standard lambda-CDM model of cosmology , the mass–energy content of the universe is 5% ordinary matter, 26.8% dark matter, and 68.2% a form of energy known as dark energy . Thus, dark matter constitutes 85% of the total mass, while dark energy and dark matter constitute 95% of the total mass–energy content. Dark matter
SECTION 60
#17327760231825456-571: The next-generation gamma-ray telescope, the Cherenkov Telescope Array ( CTA ), currently under construction. HAWC and LHAASO are examples of gamma-ray detectors based on the Water Cherenkov Detectors. A discovery in 2012 may allow focusing gamma-ray telescopes. At photon energies greater than 700 keV, the index of refraction starts to increase again. Dark matter In astronomy , dark matter
5544-408: The obvious way to resolve the discrepancy is to postulate the existence of non-luminous matter. Galaxy clusters are particularly important for dark matter studies since their masses can be estimated in three independent ways: Generally, these three methods are in reasonable agreement that dark matter outweighs visible matter by approximately 5 to 1. One of the consequences of general relativity
5632-464: The optical data (the cluster of points at radii of less than 15 kpc with a single point further out) with the H data between 20 and 30 kpc, exhibiting the flatness of the outer galaxy rotation curve; the solid curve peaking at the center is the optical surface density, while the other curve shows the cumulative mass, still rising linearly at the outermost measurement. In parallel, the use of interferometric arrays for extragalactic H spectroscopy
5720-513: The ordinary matter familiar to astronomers, including planets, brown dwarfs, red dwarfs, visible stars, white dwarfs, neutron stars, and black holes, fall into this category. A black hole would ingest both baryonic and non-baryonic matter that comes close enough to its event horizon; afterwards, the distinction between the two is lost. These massive objects that are hard to detect are collectively known as MACHOs . Some scientists initially hoped that baryonic MACHOs could account for and explain all
5808-585: The potential number of stars around the Sun in the appendices of a book based on a series of lectures given in 1884 in Baltimore. He inferred their density using the observed velocity dispersion of the stars near the Sun, assuming that the Sun was 20–100 million years old. He posed what would happen if there were a thousand million stars within 1 kiloparsec of the Sun (at which distance their parallax would be 1 milli-arcsecond ). Kelvin concluded Many of our supposed thousand million stars – perhaps
5896-451: The radio spectrum. Telescope A telescope is a device used to observe distant objects by their emission, absorption , or reflection of electromagnetic radiation . Originally, it was an optical instrument using lenses , curved mirrors , or a combination of both to observe distant objects – an optical telescope . Nowadays, the word "telescope" is defined as a wide range of instruments capable of detecting different regions of
5984-624: The rays just a few degrees . The mirrors are usually a section of a rotated parabola and a hyperbola , or ellipse . In 1952, Hans Wolter outlined 3 ways a telescope could be built using only this kind of mirror. Examples of space observatories using this type of telescope are the Einstein Observatory , ROSAT , and the Chandra X-ray Observatory . In 2012 the NuSTAR X-ray Telescope
6072-461: The redshift contains a contribution from the galaxy's so-called peculiar velocity in addition to the dominant Hubble expansion term. On average, superclusters are expanding more slowly than the cosmic mean due to their gravity, while voids are expanding faster than average. In a redshift map, galaxies in front of a supercluster have excess radial velocities towards it and have redshifts slightly higher than their distance would imply, while galaxies behind
6160-531: The rotation curve for the Andromeda nebula (now called the Andromeda Galaxy ), which suggested the mass-to-luminosity ratio increases radially. He attributed it to either light absorption within the galaxy or modified dynamics in the outer portions of the spiral, rather than to unseen matter. Following Babcock's 1939 report of unexpectedly rapid rotation in the outskirts of the Andromeda Galaxy and
6248-694: The sky. The uniformity of this background radiation indicated that it originated outside of the Milky Way Galaxy , with the most popular hypotheses being a hot gas spread uniformly throughout space, or numerous distant point sources of x-rays (such as quasars ) that appear to blend together due to their great distance. Observations with Einstein showed that a large portion of this x-ray background originated from distant point sources, and observations with later x-ray experiments have confirmed and refined this conclusion. Observations with Einstein showed that all stars emit x-rays. Main sequence stars emit only
6336-465: The standard laws of general relativity. These include modified Newtonian dynamics , tensor–vector–scalar gravity , or entropic gravity . So far none of the proposed modified gravity theories can describe every piece of observational evidence at the same time, suggesting that even if gravity has to be modified, some form of dark matter will still be required. The hypothesis of dark matter has an elaborate history. Wm. Thomson, Lord Kelvin, discussed
6424-454: The supercluster have redshifts slightly low for their distance. This effect causes superclusters to appear squashed in the radial direction, and likewise voids are stretched. Their angular positions are unaffected. This effect is not detectable for any one structure since the true shape is not known, but can be measured by averaging over many structures. It was predicted quantitatively by Nick Kaiser in 1987, and first decisively measured in 2001 by
6512-511: The task they perform such as astrographs , comet seekers and solar telescopes . Most ultraviolet light is absorbed by the Earth's atmosphere, so observations at these wavelengths must be performed from the upper atmosphere or from space. X-rays are much harder to collect and focus than electromagnetic radiation of longer wavelengths. X-ray telescopes can use X-ray optics , such as Wolter telescopes composed of ring-shaped 'glancing' mirrors made of heavy metals that are able to reflect
6600-519: The technique is called aperture synthesis . The 'virtual' apertures of these arrays are similar in size to the distance between the telescopes. As of 2005, the record array size is many times the diameter of the Earth – using space-based very-long-baseline interferometry (VLBI) telescopes such as the Japanese HALCA (Highly Advanced Laboratory for Communications and Astronomy) VSOP (VLBI Space Observatory Program) satellite. Aperture synthesis
6688-470: The temperature distribution of hot gas in galaxies and clusters, and the pattern of anisotropies in the cosmic microwave background . According to the current consensus among cosmologists, dark matter is composed primarily of some type of not-yet-characterized subatomic particle . The search for this particle, by a variety of means, is one of the major efforts in particle physics . In standard cosmological calculations, "matter" means any constituent of
6776-523: The universe is almost flat, it is expected the total energy density of everything in the universe should sum to 1 ( Ω tot ≈ 1 ). The measured dark energy density is Ω Λ ≈ 0.690 ; the observed ordinary (baryonic) matter energy density is Ω b ≈ 0.0482 and the energy density of radiation is negligible. This leaves a missing Ω dm ≈ 0.258 which nonetheless behaves like matter (see technical definition section above) – dark matter. Baryon acoustic oscillations (BAO) are fluctuations in
6864-439: The universe whose energy density scales with the inverse cube of the scale factor , i.e., ρ ∝ a . This is in contrast to "radiation" , which scales as the inverse fourth power of the scale factor ρ ∝ a , and a cosmological constant , which does not change with respect to a ( ρ ∝ a ). The different scaling factors for matter and radiation are a consequence of radiation redshift . For example, after doubling
6952-539: The use of fast tarnishing speculum metal mirrors employed during the 18th and early 19th century—a problem alleviated by the introduction of silver coated glass mirrors in 1857, and aluminized mirrors in 1932. The maximum physical size limit for refracting telescopes is about 1 meter (39 inches), dictating that the vast majority of large optical researching telescopes built since the turn of the 20th century have been reflectors. The largest reflecting telescopes currently have objectives larger than 10 meters (33 feet), and work
7040-404: The visible galaxies was far too small for such fast orbits, thus mass must be hidden from view. Based on these conclusions, Zwicky inferred some unseen matter provided the mass and associated gravitational attraction to hold the cluster together. Zwicky's estimates were off by more than an order of magnitude, mainly due to an obsolete value of the Hubble constant ; the same calculation today shows
7128-399: The volume under consideration. In principle, "dark matter" means all components of the universe which are not visible but still obey ρ ∝ a . In practice, the term "dark matter" is often used to mean only the non-baryonic component of dark matter, i.e., excluding " missing baryons ". Context will usually indicate which meaning is intended. The arms of spiral galaxies rotate around
7216-518: The x-ray telescope planned to be the third mission. One of the three missions of the HEAO program was cancelled in February 1973, due to budgetary pressures within NASA that briefly resulted in the cancellation of the entire program, and the x-ray observatory was moved up to become the second mission of the program, receiving the designation HEAO B (later HEAO-2), and scheduled to launch in 1978. HEAO-2
7304-526: Was able to observe this gas in greater detail. Einstein data indicated that the containment of this gas within these clusters by gravity could not be explained by the visible matter within those clusters, which provided further evidence for studies of dark matter . Observations by Einstein also helped to determine the frequency of irregularly-shaped clusters compared to round, uniform clusters. Einstein detected jets of x-rays emanating from Centaurus A and M87 that were aligned with previously-observed jets in
7392-585: Was being developed. Rogstad & Shostak (1972) published H rotation curves of five spirals mapped with the Owens Valley interferometer; the rotation curves of all five were very flat, suggesting very large values of mass-to-light ratio in the outer parts of their extended H disks. In 1978, Albert Bosma showed further evidence of flat rotation curves using data from the Westerbork Synthesis Radio Telescope . By
7480-470: Was constructed by TRW Inc. and shipped to Marshall Space Flight Center in Huntsville, AL for testing in 1977. HEAO-2 was launched on November 13, 1978, from Cape Canaveral, Florida , on an Atlas-Centaur SLV-3D booster rocket into a near-circular orbit at an altitude of approximately 470 km and orbital inclination of 23.5 degrees. The satellite was renamed Einstein upon achieving orbit, in honor of
7568-556: Was first discovered by COBE in 1992, though this had too coarse resolution to detect the acoustic peaks. After the discovery of the first acoustic peak by the balloon-borne BOOMERanG experiment in 2000, the power spectrum was precisely observed by WMAP in 2003–2012, and even more precisely by the Planck spacecraft in 2013–2015. The results support the Lambda-CDM model. The observed CMB angular power spectrum provides powerful evidence in support of dark matter, as its precise structure
7656-423: Was ionized and interacted strongly with radiation via Thomson scattering . Dark matter does not interact directly with radiation, but it does affect the cosmic microwave background (CMB) by its gravitational potential (mainly on large scales) and by its effects on the density and velocity of ordinary matter. Ordinary and dark matter perturbations, therefore, evolve differently with time and leave different imprints on
7744-447: Was launched which uses Wolter telescope design optics at the end of a long deployable mast to enable photon energies of 79 keV. Higher energy X-ray and gamma ray telescopes refrain from focusing completely and use coded aperture masks: the patterns of the shadow the mask creates can be reconstructed to form an image. X-ray and Gamma-ray telescopes are usually installed on high-flying balloons or Earth-orbiting satellites since
#181818