Messier 87

Messier 87 (also known as Virgo A or NGC 4486, generally abbreviated to M87) is a supergiant elliptical galaxy in the constellation Virgo. One of the most massive galaxies in the local Universe,[a] it has a large population of globular clusters—about 12,000 compared with the 150–200 orbiting the Milky Way—and a jet of energetic plasma that originates at the core and extends at least 1,500 parsecs (4,900 light-years), traveling at relativistic speed. It is one of the brightest radio sources in the sky and a popular target for both amateur and professional astronomers.

The French astronomer Charles Messier discovered M87 in 1781, and cataloged it as a nebulous feature while searching for objects that would otherwise confuse comet hunters. M87 is about 16.4 million parsecs (53 million light-years) from Earth and is the second-brightest galaxy within the northern Virgo Cluster, having many satellite galaxies. Unlike a disk-shaped spiral galaxy, M87 has no distinctive dust lanes. Instead, it has an almost featureless, ellipsoidal shape typical of most giant elliptical galaxies, diminishing in luminosity with distance from the center. Forming around one-sixth of its mass, M87's stars have a nearly spherically symmetric distribution. Their population density decreases with increasing distance from the core. It has an active supermassive black hole at its core, which forms the primary component of an active galactic nucleus. The black hole was imaged using data collected in 2017 by the Event Horizon Telescope, with a final, processed image released on 10 April 2019.

The galaxy is a strong source of multiwavelength radiation, particularly radio waves. Its galactic envelope extends to a radius of about 150 kiloparsecs (490 thousand light-years), where it is truncated—possibly by an encounter with another galaxy. Its interstellar medium consists of diffuse gas enriched by elements emitted from evolved stars.

Messier 87
Messier 87 Hubble WikiSky
The galactic core of Messier 87 as seen by the Hubble Space Telescope with its blue plasma jet clearly visible (composite image of observations in visible and infrared light)
Observation data (J2000 epoch)
Right ascension 12h 30m 49.42338s[1]
Declination+12° 23′ 28.0439″[1]
Helio radial velocity1284[2]
Distance53.5 ± 1.63 Mly (16.40 ± 0.50 Mpc)[3]
Apparent magnitude (V)7.19[4]
TypeE+0-1 pec, NLRG Sy[5]
Apparent size (V)7.2 × 6.8 moa[6]
Other designations
Virgo A, Virgo X-1, NGC 4486, UGC 7654, PGC 41361, VCC 1316, Arp 152, 3C 274,[5] 3U 1228+12.[7]

Observation history

In 1781, the French astronomer Charles Messier published a catalogue of 103 objects that had a nebulous appearance as part of a list intended to identify objects that might otherwise be confused with comets. In subsequent use, each catalogue entry was prefixed with an "M". Thus, M87 was the eighty-seventh object listed in Messier's catalogue.[11] During the 1880s, the object was included as NGC 4486, in the New General Catalogue of nebulae and star clusters assembled by the Danish-Irish astronomer John Dreyer, which he based primarily on the observations of the English astronomer John Herschel.[12]

In 1918, the American astronomer Heber Curtis of Lick Observatory noted M87's lack of a spiral structure and observed a "curious straight ray ... apparently connected with the nucleus by a thin line of matter." The ray appeared brightest near the galactic center.[13] The following year, a supernova within M87 reached a peak photographic magnitude of 21.5, although this event was not reported until photographic plates were examined by the Russian astronomer Innokentii A. Balanowski in 1922.[14][15]

Identification as a galaxy

In Hubble's galaxy classification scheme, M87 is an E0 galaxy

In 1922, the American astronomer Edwin Hubble categorized M87 as one of the brighter globular nebulae, as it lacked any spiral structure, but like spiral nebulae, appeared to belong to the family of non-galactic nebulae.[16] In 1926 he produced a new categorization, distinguishing extragalactic from galactic nebulae, the former being independent star systems. M87 was classified as a type of elliptical extragalactic nebula with no apparent elongation (class E0).[17]

In 1931, Hubble described M87 as a member of the Virgo Cluster, and gave a provisional estimate of 1.8 million parsecs (5.9 million light-years) from Earth. It was then the only known elliptical nebula for which individual stars could be resolved, although it was pointed out that globular clusters would be indistinguishable from individual stars at such distances.[18] In his 1936 The Realm of the Nebulae, Hubble examines the terminology of the day; some astronomers labeled extragalactic nebulae as external galaxies on the basis that they were stellar systems at far distances from our own galaxy, while others preferred the conventional term extragalactic nebulae, as galaxy then was synonym for the Milky Way.[19] M87 continued to be labelled as an extragalactic nebula at least until 1954.[20][21]

Hubble follows spiral flow of black-hole-powered jet
Spiral flow of the black-hole-powered jet, imaged with the Hubble Space Telescope[22]

Modern research

In 1947, a prominent radio source, Virgo A, was identified overlapping the location of M87.[23] The source was confirmed to be M87 by 1953, and the linear relativistic jet emerging from the core of the galaxy was suggested as the cause. This jet extended from the core at a position angle of 260° to an angular distance of 20 with an angular width of 2″.[20] In 1969–70, a strong component of the radio emission was found to closely align with the optical source of the jet.[7]

In 1966, the United States Naval Research Laboratory's Aerobee 150 rocket identified Virgo X-1, the first X-ray source in Virgo.[24][25] The Aerobee rocket launched from White Sands Missile Range on 7 July 1967, yielded further evidence that the source of Virgo X-1 was the radio galaxy M87.[26] Subsequent X-ray observations by the HEAO 1 and Einstein Observatory showed a complex source that included the active galactic nucleus of M87.[27] However, there is little central concentration of the X-ray emission.[7]

M87 has been an important testing ground for techniques that measure the masses of central supermassive black holes in galaxies. In 1978, stellar-dynamical modeling of the mass distribution in M87 gave evidence for a central mass of five billion solar masses.[28] After the installation of the COSTAR corrective-optics module in the Hubble Space Telescope in 1993, the Hubble Faint Object Spectrograph (FOS) was used to measure the rotation velocity of the ionized gas disk at the center of M87, as an "early release observation" designed to test the scientific performance of the post-repair Hubble instruments. The FOS data indicated a central black hole mass of 2.4 billion solar masses, with 30% uncertainty.[29]

M87 was the subject of observation by the Event Horizon Telescope (EHT) in 2017. The 10 April 2019 issue of Astrophysical Journal Letters (vol. 875, No. 1) was dedicated to the EHT results, publishing five open-access papers.[30] The event horizon of the black hole at the center of M87 was directly imaged by the EHT.[31] The image was revealed in a press conference on 10 April 2019, the first image of a black hole's event horizon.[32]


Virgo constellation map
Area in constellation Virgo around M87

M87 is near the high declination border of the Virgo constellation, next to the constellation of Coma Berenices. It lies along the line between the stars Epsilon Virginis and Denebola.[b] The galaxy can be observed using a small telescope with a 6 cm (2.4 in) aperture, extending across an angular area of 7.2 × 6.8 arcminutes at a surface brightness of 12.9, with a very bright, 45-arcsecond core.[6] Viewing the jet is a challenge without the aid of photography.[33] Before 1991, the Russian-American astronomer Otto Struve was the only person known to have seen the jet visually, using the 254 cm (100 in) Hooker telescope.[34] In more recent years it has been observed in larger amateur telescopes under excellent conditions.[35]


In the modified Hubble sequence galaxy morphological classification scheme of the French astronomer Gérard de Vaucouleurs, M87 is categorized as an E0p galaxy. "E0" designates an elliptical galaxy that displays no flattening—that is, it appears spherical.[36] A "p" suffix indicates a peculiar galaxy that does not fit cleanly into the classification scheme; in this case, the peculiarity is the presence of the jet emerging from the core.[36][37] In the Yerkes (Morgan) scheme, M87 is classified as a type-cD galaxy.[38][39] A D galaxy has an elliptical-like nucleus surrounded by an extensive, dustless, diffuse envelope. A D type supergiant is called a cD galaxy.[40][41]

The distance to M87 has been estimated using several independent techniques. These include measurement of the luminosity of planetary nebulae, comparison with nearby galaxies whose distance is estimated using standard candles such as cepheid variables, the linear size distribution of globular clusters,[c] and the tip of the red-giant branch method using individually resolved red giant stars.[d] These measurements are consistent with each other, and their weighted average yields a distance estimate of 16.4 ± 0.5 megaparsecs (53.5 ± 1.63 million light-years).[3]

Enclosed mass
×1012 M
32 2.4[42]
44 3.0[43]
47 5.7[44]
50 6.0[45]

M87 is one of the most massive galaxies in the local Universe. Its diameter is estimated at 240 thousand light-years, which is slightly larger than that of the Milky Way.[44] As an elliptical galaxy, the galaxy is a spheroid rather than a disc, accounting for the substantially larger mass of M87. Within a radius of 32 kiloparsecs (100 thousand light-years), the mass is (2.4 ± 0.6) × 1012 times the mass of the Sun,[42] which is double the mass of the Milky Way galaxy.[46] As with other galaxies, only a fraction of this mass is in the form of stars: M87 has an estimated mass to luminosity ratio of 6.3 ± 0.8; that is, only about one part in six of the galaxy's mass is in the form of stars that radiate energy.[47] This ratio varies from 5 to 30, approximately in proportion to r1.7 in the region of 9–40 kiloparsecs (29–130 thousand light-years) from the core.[43]. The total mass of M87 may be 200 times that of the Milky Way.[48]

Galactic Chromodynamics
Stellar velocity map of the central region of M87, showing the motion of stars relative to Earth. Blue patches represent motion towards the Earth and red ones away from the Earth, while yellow and green are in between the two extremes. The map indicates random motion of the stars.[49][50]

Gas is infalling into the galaxy at the rate of two to three solar masses per year, most of which may be accreted onto the core region.[51] The extended stellar envelope of this galaxy reaches a radius of about 150 kiloparsecs (490 thousand light-years),[52] compared with about 100 kiloparsecs (330 thousand light-years) for the Milky Way.[53] Beyond that distance the outer edge of the galaxy has been truncated by some means; possibly by an earlier encounter with another galaxy.[52][54] There is evidence of linear streams of stars to the northwest of the galaxy, which may have been created by tidal stripping of orbiting galaxies or by small satellite galaxies falling in toward M87.[55] Moreover, a filament of hot, ionized gas in the northeastern outer part of the galaxy may be the remnant of a small, gas-rich galaxy that was disrupted by M87 and could be feeding its active nucleus.[56] M87 is estimated to have at least 50 satellite galaxies, including NGC 4486B and NGC 4478.[57][58]

The spectrum of the nuclear region of M87 shows the emission lines of various ions, including hydrogen (HI, HII), helium (HeI), oxygen (OI, OII, OIII), nitrogen (NI), magnesium (MgII) and sulfur (SII). The line intensities for weakly ionized atoms (such as neutral atomic oxygen, OI) are stronger than those of strongly ionized atoms (such as doubly ionized oxygen, OIII). A galactic nucleus with such spectral properties is termed a LINER, for "low-ionization nuclear emission-line region".[59][60] The mechanism and source of weak-line-dominated ionization in LINERs and M87 are under debate. Possible causes include shock-induced excitation in the outer parts of the disk[59][60] or photoionization in the inner region powered by the jet.[61]

Elliptical galaxies such as M87 are believed to form as the result of one or more mergers of smaller galaxies.[62] They generally contain relatively little cold interstellar gas (in comparison with spiral galaxies) and they are populated mostly by old stars, with little or no ongoing star formation. M87's elliptical shape is maintained by the random orbital motions of its constituent stars, in contrast to the more orderly rotational motions found in a spiral galaxy such as the Milky Way.[63] Using the Very Large Telescope to study the motions of about 300 planetary nebulae, astronomers have determined that M87 absorbed a medium-sized star-forming spiral galaxy over the last billion years. This has resulted in the addition of some younger, bluer stars to M87. The distinctive spectral properties of the planetary nebulae allowed astronomers to discover a chevron-like structure in M87's halo which was produced by the incomplete phase-space mixing of a disrupted galaxy.[64][65]


Supermassive black hole

Black hole - Messier 87 crop max res
The Event Horizon Telescope image of the core of M87 using 1.3 mm radio waves. The central dark spot is the shadow of the black hole and is larger than the black hole’s event horizon.

The core contains a supermassive black hole, designated M87*,[30][66] whose mass is billions of times that of the Sun; estimates have ranged from (3.5 ± 0.8) × 109 M[67] to (6.6 ± 0.4) × 109 M,[67] with a measurement of 7.22+0.34
M in 2016.[68] In April 2019, the Event Horizon Telescope released measurements of the black hole's mass as (6.5 ± 0.2stat ± 0.7sys ) × 109 M.[69] This is one of the highest known masses for such an object. A rotating disk of ionized gas surrounds the black hole, and is roughly perpendicular to the relativistic jet. The disk rotates at velocities of up to roughly 1,000 km/s,[70] and spans a maximum diameter of 0.12 parsecs (25,000 AU; 0.39 ly; 3,700×109 km).[71] By comparison, Pluto averages 39 astronomical units (0.00019 pc; 5.8×109 km) from the sun. Gas accretes onto the black hole at an estimated rate of one solar mass every ten years (about 90 Earth masses per day).[72] The Schwarzschild radius of the black hole is 5.9×10−4 parsecs (1.9×10−3 light-years), which is around 120 times the Earth–Sun distance.[73]

A 2010 paper suggested that the black hole may be displaced from the galactic center by about seven parsecs (23 light-years).[74] The displacement was claimed to be in the opposite direction of the jet, indicating acceleration of the black hole by the jet. Another suggestion was that the change in location occurred during the merger of two supermassive black holes.[74][75] However, a 2011 study did not find any statistically significant displacement,[76] and a 2018 study of high-resolution images of M87 concluded that the apparent spatial offset was caused by temporal variations in the jet's brightness rather than a physical displacement of the black hole from the galaxy's center.[77]

This black hole is the first and, to date, the only to be imaged. An image taken by the Event Horizon Telescope in 2017 was published on 10 April 2019.[32][78][79] The image shows the shadow of the black hole, surrounded by an asymmetric emission ring with a diameter of 3.36×10−3 parsecs (0.0110 light-years). The shadow radius is 2.6 times that of the black hole's Schwarzschild radius.[80]

Interstellar medium

The space between the stars in M87 is filled with a diffuse interstellar medium of gas that has been chemically enriched by the elements ejected from stars as they passed beyond their main sequence lifetime. Carbon and nitrogen are continuously supplied by stars of intermediate mass as they pass through the asymptotic giant branch.[81][82] The heavier elements from oxygen to iron are produced largely by supernova explosions within the galaxy. Of the heavy elements, about 60% were produced by core-collapse supernovae, while the remainder came from type Ia supernovae.[81] The distribution of oxygen is roughly uniform throughout, at about half of the solar value (i.e., oxygen abundance in the Sun), while iron distribution peaks near the center where it approaches the solar iron value.[82][83] Since oxygen is produced mainly by core-collapse supernovae, which occur during the early stages of galaxies and mostly in outer star-forming regions,[81][82][83] the distribution of these elements suggests an early enrichment of the interstellar medium from core-collapse supernovae and a continuous contribution from Type Ia supernovae throughout the history of M87.[81] The contribution of elements from these sources was much lower than in the Milky Way.[81]

Selected elemental abundances in the M87 core[81]
Element Abundance
(solar values)
C 0.63 ± 0.16
N 1.64 ± 0.24
O 0.58 ± 0.03
Ne 1.41 ± 0.12
Mg 0.67 ± 0.05
Fe 0.95 ± 0.03

Examination of M87 at far infrared wavelengths shows an excess emission at wavelengths longer than 25 μm. Normally, this may be an indication of thermal emission by warm dust.[84] In the case of M87, the emission can be fully explained by synchrotron radiation from the jet; within the galaxy, silicate grains are expected to survive for no more than 46 million years because of the X-ray emission from the core.[85] This dust may be destroyed by the hostile environment or expelled from the galaxy.[86] The combined mass of dust in M87 is no more than 70,000 times the mass of the Sun.[85] By comparison, the Milky Way's dust equals about a hundred million (108) solar masses.[87]

Although M87 is an elliptical galaxy and therefore lacks the dust lanes of a spiral galaxy, optical filaments have been observed in it, which arise from gas falling towards the core. Emission probably comes from shock-induced excitation as the falling gas streams encounter X-rays from the core region.[88] These filaments have an estimated mass of about 10,000 solar masses.[51][88] Surrounding the galaxy is an extended corona with hot, low-density gas.[89]

Globular clusters

M87 has an abnormally large population of globular clusters. A 2006 survey out to an angular distance of 25 from the core estimates that there are 12,000 ± 800 globular clusters in orbit around M87,[90] compared with 150–200 in and around the Milky Way. The clusters are similar in size distribution to those of the Milky Way, most having an effective radius of 1 to 6 parsecs. The size of the M87 clusters gradually increases with distance from the galactic center.[91] Within a four-kiloparsec (13,000-light-year) radius of the core, the cluster metallicity—the abundance of elements other than hydrogen and helium—is about half the abundance in the Sun. Outside this radius, metallicity steadily declines as the cluster distance from the core increases.[89] Clusters with low metallicity are somewhat larger than metal-rich clusters.[91] In 2014, HVGC-1, the first hypervelocity globular cluster, was discovered escaping from M87 at 2,300 km/s. The escape of the cluster with such a high velocity was speculated to have been the result of a close encounter with, and subsequent gravitational kick from, a supermassive black hole binary.[92]

Almost a hundred ultra-compact dwarfs have been identified in M87. They resemble globular clusters but have a diameter of ten parsecs (33 light-years) or more, much larger than the three-parsec (9.8-light-year) maximum of globular clusters. It is unclear whether they are dwarf galaxies captured by M87 or a new class of massive globular cluster.[93]


M87 jet
This Hubble Space Telescope photograph shows the jet of matter ejected from M87 at nearly the speed of light, as it stretches 1.5 kpc (5 kly) from the galactic core
M87 Super-Volcano
In this X-ray (Chandra) and radio (VLA) composite image, hot matter (blue in X-ray) from the Virgo cluster falls toward the core of M87 and cools, where it is met by the relativistic jet (orange in radio), producing shock waves in the galaxy's interstellar medium

The relativistic jet of matter emerging from the core extends at least 1.5 kiloparsecs (5,000 light-years) from the nucleus and consists of matter ejected from a supermassive black hole. The jet is highly collimated, appearing constrained to an angle of 60° within 0.8 parsecs (2.6 light-years) of the core, to about 16° at two parsecs (6.5 light-years), and to 6–7° at twelve parsecs (39 light-years).[94] Its base has the diameter of 5.5 ± 0.4 Schwarzschild radii, and is probably powered by a prograde accretion disk around a spinning supermassive black hole.[94] The German-American astronomer Walter Baade found that light from the jet was plane polarized, which suggests that the energy is generated by the acceleration of electrons moving at relativistic velocities in a magnetic field. The total energy of these electrons is estimated at 5.1 × 1056 ergs[95] (5.1 × 1049 joules or 3.2 × 1068 eV). This is roughly 1013 times the energy produced by the Milky Way in one second, which is estimated at 5 × 1036 joules.[96] The jet is surrounded by a lower-velocity non-relativistic component. There is evidence of a counter jet, but it remains unseen from the Earth due to relativistic beaming.[97][98] The jet is precessing, causing the outflow to form a helical pattern out to 1.6 parsecs (5.2 light-years).[71] Lobes of expelled matter extend out to 80 kiloparsecs (260 thousand light-years).[99]

In pictures taken by the Hubble Space Telescope in 1999, the motion of M87's jet was measured at four to six times the speed of light. This phenomenon, called superluminal motion, is an illusion caused by the relativistic velocity of the jet. The time interval between any two light pulses emitted by the jet is, as registered by the observer, less than the actual interval due to the relativistic speed of the jet moving in the direction of the observer. This results in perceived faster-than-light speeds. Detection of such motion is used to support the theory that quasars, BL Lacertae objects and radio galaxies may all be the same phenomenon, known as active galaxies, viewed from different perspectives.[100][101] It is proposed that M87 is a BL Lacertae object (with a low-luminosity nucleus compared with the brightness of its host galaxy) seen from a relatively large angle. Flux variations, characteristic of the BL Lacertae objects, have been observed in M87.[102][103]

Close-Up Look at a Jet Near a Black Hole
Radio wavelength image of M87 showing strong radio emission from the core

Observations indicate that the rate at which material is ejected from the supermassive black hole is variable. These variations produce pressure waves in the hot gas surrounding M87. The Chandra X-ray Observatory has detected loops and rings in the gas. Their distribution suggests that minor eruptions occur every few million years. One of the rings, caused by a major eruption, is a shock wave 26 kiloparsecs (85 thousand light-years) in diameter around the black hole. Other features observed include narrow X-ray-emitting filaments up to 31 kiloparsecs (100 thousand light-years) long, and a large cavity in the hot gas caused by a major eruption 70 million years ago. The regular eruptions prevent a huge reservoir of gas from cooling and forming stars, implying that M87's evolution may have been seriously affected, preventing it from becoming a large spiral galaxy. These observations also indicate that the variable eruptions produce sound waves of about 56 to 59 octaves below middle C in the medium.[104]

M87 is a very strong source of gamma rays, the most energetic rays of the electromagnetic spectrum. Gamma rays emitted by M87 have been observed since the late 1990s. In 2006, using the High Energy Stereoscopic System Cherenkov telescopes, scientists measured the variations of the gamma ray flux coming from M87, and found that the flux changes over a matter of days. This short period indicates that the most likely source of the gamma rays is a supermassive black hole.[105] In general, the smaller the diameter of the emission source, the faster the variation in flux, and vice versa.[105][106]

A knot of matter in the jet (designated HST-1), about 65 parsecs (210 light-years) from the core, has been tracked by the Hubble Space Telescope and the Chandra X-ray Observatory. By 2006, the X-ray intensity of this knot had increased by a factor of 50 over a four-year period,[107] while the X-ray emission has since been decaying in a variable manner.[108]

The interaction of relativistic jets of plasma emanating from the core with the surrounding medium gives rise to radio lobes in active galaxies. The lobes occur in pairs and are often symmetrical.[109] The two radio lobes of M87 together span about 80 kiloparsecs; the inner parts, extending up to two kiloparsecs, emit strongly at radio wavelengths. Two flows of material emerge from this region, one aligned with the jet itself and the other in the opposite direction. The flows are asymmetrical and deformed, implying that they encounter a dense intracluster medium. At greater distances, both flows diffuse into two lobes. The lobes are surrounded by a fainter halo of radio-emitting gas.[110][111]


Photograph of the Virgo Cluster (European Southern Observatory 2009). M87 is visible in the lower left, the upper half of the image is taken up by Markarian's Chain. The dark spots mark the locations of bright foreground stars that were removed from the image. Messier 87 is a member of the Virgo Cluster, and can be seen to lower left of this cluster image.

M87 is near the center of the Virgo Cluster,[39] a closely compacted structure of about 2,000 galaxies.[112] It forms the core of the larger Virgo Supercluster, of which the Local Group (including the Milky Way) is an outlying member.[52] It is organized into at least three distinct subsystems associated with the three large galaxies—M87, M49 and M86—with the subgroup centered around M87 (Virgo A) and M49 (Virgo B).[113] There is a preponderance of elliptical and S0 galaxies around M87, with a chain of elliptical galaxies aligned with the jet.[114] In terms of mass, M87 is a dominant member of the cluster, and hence appears to be moving very little relative to the cluster as a whole.[52] It is defined as the cluster center. The cluster has a sparse gaseous atmosphere that emits X-rays that decrease in temperature toward the middle, where M87 is located.[84] The combined mass of the cluster is estimated to be (0.15–1.5) × 1015 solar masses.[112]

Measurements of the motion of intracluster planetary nebulae between M87 and M86 suggest that the two galaxies are moving toward each other and that this may be their first encounter. M87 may have interacted with M84 in the past, as evidenced by the truncation of M87's outer halo by tidal interactions. The truncated halo may also have been caused by contraction due to an unseen mass falling into M87 from the rest of the cluster, which may be the hypothesized dark matter. A third possibility is that the halo's formation was truncated by early feedback from the active galactic nucleus at the core of M87.[52]


  1. ^ "Local Universe" is not a strictly defined term, but it is often taken as that part of the universe out to distances between about 50 million to a billion light-years.[8][9][10]
  2. ^ Epsilon Virginis is at celestial coordinates α=13h 02m, δ=+10° 57′; Denebola is at α=11h 49m, δ=+14° 34′. The midpoint of the pair is at α=12h 16m, δ=12° 45′. Compare to the coordinates of Messier 87: α=12h 31m, δ=+12° 23′.
  3. ^ This yields a distance of 16.4 ± 2.3 megaparsecs (53.5 ± 7.50 million light-years).[3]
  4. ^ This yields a distance of 16.7 ± 0.9 megaparsecs (54.5 ± 2.94 million light-years).[3]


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Cite error: A list-defined reference named "nickname" is not used in the content (see the help page).

External links

Coordinates: Sky map 12h 30m 49.4s, +12° 23′ 28″

1781 in France

Events from the year 1781 in France

3C 66B

3C 66B is an elliptical Fanaroff and Riley class 1 radio galaxy located in the constellation Andromeda. With an estimated redshift of 0.021258, the galaxy is about 300 million light-years away.The orbital motion of 3C 66B showed supposed evidence for a supermassive black hole binary (SMBHB) with a period of 1.05 ± 0.03 years,

but this claim was later proven wrong (at 95% certainty).Messier 87 (M87), about 55 million light years away, is the largest giant elliptical galaxy near the Earth, and also contains an active galactic nucleus. The smooth jet of 3C 66B rivals that of M87.3C 66B is an outlying member of Abell 347 which is part of the Perseus-Pisces Supercluster.

Black hole

A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—not even particles and electromagnetic radiation such as light—can escape from inside it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of the region from which no escape is possible is called the event horizon. Although the event horizon has an enormous effect on the fate and circumstances of an object crossing it, no locally detectable features appear to be observed. In many ways, a black hole acts like an ideal black body, as it reflects no light. Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is on the order of billionths of a kelvin for black holes of stellar mass, making it essentially impossible to observe.

Objects whose gravitational fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. The first modern solution of general relativity that would characterize a black hole was found by Karl Schwarzschild in 1916, although its interpretation as a region of space from which nothing can escape was first published by David Finkelstein in 1958. Black holes were long considered a mathematical curiosity; it was during the 1960s that theoretical work showed they were a generic prediction of general relativity. The discovery of neutron stars by Jocelyn Bell Burnell in 1967 sparked interest in gravitationally collapsed compact objects as a possible astrophysical reality.

Black holes of stellar mass are expected to form when very massive stars collapse at the end of their life cycle. After a black hole has formed, it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses (M☉) may form. There is general consensus that supermassive black holes exist in the centers of most galaxies.

Despite its invisible interior, the presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as visible light. Matter that falls onto a black hole can form an external accretion disk heated by friction, forming some of the brightest objects in the universe. If there are other stars orbiting a black hole, their orbits can be used to determine the black hole's mass and location. Such observations can be used to exclude possible alternatives such as neutron stars. In this way, astronomers have identified numerous stellar black hole candidates in binary systems, and established that the radio source known as Sagittarius A*, at the core of the Milky Way galaxy, contains a supermassive black hole of about 4.3 million solar masses.

On 11 February 2016, the LIGO collaboration announced the first direct detection of gravitational waves, which also represented the first observation of a black hole merger. As of December 2018, eleven gravitational wave events have been observed that originated from ten merging black holes (along with one binary neutron star merger). On 10 April 2019, the first ever direct image of a black hole and its vicinity was published, following observations made by the Event Horizon Telescope in 2017 of the supermassive black hole in Messier 87's galactic centre.

Event Horizon Telescope

The Event Horizon Telescope (EHT) is a large telescope array consisting of a global network of radio telescopes. The EHT project combines data from several very-long-baseline interferometry (VLBI) stations around Earth with angular resolution sufficient to observe objects the size of a supermassive black hole's event horizon. The project's observational targets include the two black holes with the largest angular diameter as observed from Earth: the black hole at the center of the supergiant elliptical galaxy Messier 87 (M87), and Sagittarius A* (Sgr A*), at the center of the Milky Way.The Event Horizon Telescope project is an international collaboration launched in 2009 after a long period of theoretical and technical developments. On the theory side, work on the photon orbit and first simulations of what a black hole would look like progressed to predictions of VLBI imaging for the Galactic Center black hole, Sgr A*. Technical advances in radio observing moved from the first detection of Sgr A*, through VLBI at progressively shorter wavelengths, ultimately leading to detection of horizon scale structure in both Sgr A* and M87. The collaboration now comprises over 200 members, 60 institutions, working over 20 countries and regions.The first image of a black hole, at the center of galaxy Messier 87, was published by the EHT Collaboration on April 10, 2019, in a series of six scientific publications. The array made this observation at a wavelength of 1.3 mm and with a theoretical diffraction-limited resolution of 25 microarcseconds. Future plans involve improving the array's resolution by adding new telescopes and by taking shorter-wavelength observations.

Greenland Telescope

The Greenland Telescope is a radio telescope that is currently installed and operating at the Thule Air Base in north-western Greenland. It will later be deployed at the Summit Station research camp, located at the highest point of the Greenland ice sheet at an altitude of 3,210 meters (10,530 feet).

The telescope is an international collaboration between:

The Smithsonian Astrophysical Observatory of the Harvard–Smithsonian Center for Astrophysics (United States)

The National Radio Astronomy Observatory (United States)

The Haystack Observatory of the Massachusetts Institute of Technology (United States)

The Academia Sinica Institute of Astronomy and Astrophysics (Taiwan) (project leaders)In 2011 the U.S. National Science Foundation gave the Smithsonian Astrophysical Observatory a 12-meter radio antenna that had been used as a prototype for the ALMA project in Chile. The antenna was to be deployed in Greenland. Deploying the telescope in the middle of Greenland is ideal for detecting certain radio frequencies.

The telescope will be used to study the event horizons of black holes and to test how general relativity behaves in environments with extreme gravity.

The Greenland Telescope will become part of the global network of telescopes that makes up the Event Horizon Telescope that will study supermassive black holes and explore the origin of the relativistic jet in the active galaxy Messier 87.


HVGC-1 is the first discovered hypervelocity globular cluster. Discovered in 2014, it was found escaping the supergiant elliptical galaxy Messier 87, in the Virgo Cluster. It is one of thousands of globular clusters found in M87. It is the first hypervelocity star cluster so far discovered. The globular is located at decimal degrees (RA,DEC) (187.72791°,+12.68295°).

List of black holes

This is a list of black holes (and stars considered probable candidates) organized by size (including black holes of undetermined mass); some items in this list are galaxies or star clusters that are believed to be organized around a black hole. Messier and New General Catalogue designations are given where possible.


M87 or M-87 may refer to:

Messier 87, a giant elliptical galaxy in the Virgo Cluster

M87*, a supermassive black hole at Messier 87's core

M87 machine gun, a Yugoslav copy of the NSVT machine gun

Tumansky M-87, a Soviet aircraft engine

M-87 Orkan, a Yugoslav rocket-artillery vehicle

M-87 (Michigan highway), a former state highway in the state of Michigan

McDonnell Douglas MD-87, a passenger airplane

M87 Ray (α and β), the signature move of the character Zoffy from the Ultra Series of television shows

Messier 49

Messier 49 (also known as M 49 or NGC 4472) is an elliptical galaxy located about 56 million light-years away in the equatorial constellation of Virgo. This galaxy was discovered by French astronomer Charles Messier on February 16, 1777.

As an elliptical galaxy, Messier 49 has the physical form of a radio galaxy, but it only has the radio emission of a normal galaxy. From the detected radio emission, the core region has roughly 1053 erg (1046 J or 1022 YJ) of synchrotron energy. The nucleus of this galaxy is emitting X-rays, suggesting the likely presence of a supermassive black hole with an estimated mass of 5.65 × 108 solar masses, or 565 million times the mass of the Sun. X-ray emissions shows a structure to the north of Messier 49 that resembles a bow shock. To the southwest of the core, the luminous outline of the galaxy can be traced out to a distance of 260 kpc. The only supernova event observed within this galaxy is SN 1969Q, discovered in June 1969.This galaxy has a large collection of globular clusters, estimated at about 5,900. However, this count is far exceeded by the 13,450 globular clusters orbiting the supergiant elliptical galaxy Messier 87. On average, the globular clusters of M 49 are about 10 billion years old. Between 2000 and 2009, strong evidence for a stellar mass black hole was discovered in an M 49 cluster. A second candidate was announced in 2011.Messier 49 was the first member of the Virgo Cluster of galaxies to be discovered. It is the most luminous member of that cluster and more luminous than any galaxy closer to the Earth. This galaxy forms part of the smaller Virgo B subcluster located 4.5° away from the dynamic center of the Virgo Cluster, centered on Messier 87. Messier 49 is gravitationally interacting with the dwarf irregular galaxy UGC 7636. The dwarf shows a trail of debris spanning roughly 1 × 5 arcminutes, which corresponds to a physical dimension of 6 × 30 kpc.

Messier 99

Messier 99 or M99, also known as NGC 4254, is a grand design spiral galaxy in the northern constellation Coma Berenices approximately 15 megaparsecs (49 megalight-years) in distance from the Milky Way. It was discovered by Pierre Méchain on March 17, 1781. The discovery was then reported to Charles Messier, who included the object in the Messier Catalogue of comet-like objects. Messier 99 was one of the first galaxies in which a spiral pattern was seen. This pattern was first identified by Lord Rosse in the spring of 1846.This galaxy has a morphological classification of SA(s)c, indicating a pure spiral shape with loosely wound arms. It has a peculiar shape with one normal looking arm and an extended arm that is less tightly wound. The galaxy is inclined by 42° to the line-of-sight with a major axis position angle of 68°. Four supernovae have been observed in this galaxy: SN 1967H (type II), 1972Q, 1986I (type II), and 2014L (type Ic).A bridge of neutral hydrogen gas links NGC 4254 with VIRGOHI21, an HI region and a possible dark galaxy. The gravity from the latter may have distorted M99 and drawn out the gas bridge, as the two galaxy-sized objects may have had a close encounter before they went their separate ways. However, VIRGOHI21 may instead be tidal debris from an interaction with the lenticular galaxy NGC 4262 some 280 million years ago. It is expected that the drawn out arm will relax to match the normal arm once the encounter is over.

While not classified as a starburst galaxy, M99 has a star formation activity three times larger than other galaxies of similar Hubble type that may have been triggered by the encounter. M99 is likely entering the Virgo Cluster for the first time and is located at the periphery of the cluster at a projected separation of 3.7°, or around one megaparsec, from the cluster center at Messier 87. The galaxy is undergoing ram-pressure stripping as it moves through the intracluster medium.

NGC 1316

NGC 1316 (also known as Fornax A) is a lenticular galaxy about 60 million light-years away in the constellation Fornax It is a radio galaxy and at 1400 MHz is the fourth-brightest radio source in the sky.

NGC 3311

NGC 3311 is a supergiant elliptical galaxy (a type-cD galaxy) located about 190 million light-years away in the constellation Hydra. The galaxy was discovered by astronomer John Herschel on March 30, 1835. NGC 3311 is the brightest member of the Hydra Cluster and forms a pair with NGC 3309 which along with NGC 3311, dominate the central region of the Hydra Cluster.NGC 3311 is surrounded by a rich and extensive globular cluster system rivaling that of Messier 87 in the Virgo Cluster.

NGC 4476

NGC 4476 is a lenticular galaxy located about 55 million light-years away in the constellation Virgo. NGC 4476 was discovered by astronomer William Herschel on April 12, 1784. The galaxy is a member of the Virgo Cluster.

NGC 4478

NGC 4478 is a elliptical galaxy located about 50 million light-years away in the constellation Virgo. NGC 4478 was discovered by astronomer William Herschel on April 12, 1784. NGC 4478 is a member of the Virgo Cluster.

NGC 4491

NGC 4491 is a dwarf barred spiral galaxy located about 55 million light-years away in the constellation Virgo. NGC 4491 was discovered by astronomer William Herschel on March 15, 1784. NGC 4491 is located in a subgroup of the Virgo Cluster centered on Messier 87 known as the Virgo A subgroup.

NGC 4535

NGC 4535 is a barred spiral galaxy located some 54 million light years from Earth in the constellation Virgo. It is a member of the Virgo Cluster of galaxies and is located 4.3° from Messier 87. The galactic plane of NGC 4535 is inclined by an angle of 43° to the line of sight from the Earth. The morphological classification of NGC 4535 in the De Vaucouleurs system is SAB(s)c, which indicates a bar structure across the core (SAB), no ring (s), and loosely wound spiral arms (c). The inner part of the galaxy has two spiral arms, which branch into multiple arms further away. The small nucleus is of type HII, meaning the spectrum resembles that of an H II region.During 1999, the Hubble Space Telescope was used to observe Cepheid variable stars in NGC 4535. The period-luminosity relationship for these objects yielded a distance modulus of 31.02 ± 0.26 magnitude. This corresponded to a physical distance estimate of 52.2 ± 6.2 Mly (16.0 ± 1.9) Mpc, which was consistent with distance estimates for other members of the Virgo Cluster.

New Earth (Doctor Who)

"New Earth" is the first episode of the second series of the British science fiction television series Doctor Who. It was first broadcast on BBC One on 15 April 2006.

The episode is set five billion years in the future on the planet New Earth, a planet humanity settled on following the destruction of the Earth in the 2005 episode "The End of the World". In the episode, the alien time traveller the Tenth Doctor (David Tennant), his travelling companion Rose Tyler (Billie Piper), and their old enemy Lady Cassandra (Zoë Wanamaker) uncover many artificially-grown humans having been infected with every disease in a hospital by a group of humanoid cat nuns as a way of finding cures for the diseases.

Supermassive black hole

A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, containing a mass of the order of hundreds of thousands, to billions of times, the mass of the Sun (M☉). Black holes are a class of astronomical object that have undergone gravitational collapse, leaving behind spheroidal regions of space from which nothing can escape, not even light. Observational evidence indicates that nearly all large galaxies contain a supermassive black hole, located at the galaxy's center. In the case of the Milky Way, the supermassive black hole corresponds to the location of Sagittarius A* at the Galactic Core. Accretion of interstellar gas onto supermassive black holes is the process responsible for powering quasars and other types of active galactic nuclei.

Virgo Cluster

The Virgo Cluster is a cluster of galaxies whose center is 53.8 ± 0.3 Mly (16.5 ± 0.1 Mpc)

away in the constellation Virgo. Comprising approximately 1300 (and possibly up to 2000) member galaxies, the cluster forms the heart of the larger Virgo Supercluster, of which the Local Group (containing our Milky Way galaxy) is a member. The Local Group actually experiences the mass of the Virgo Supercluster as the Virgocentric flow. It is estimated that the Virgo Cluster's mass is 1.2×1015 M☉ out to 8 degrees of the cluster's center or a radius of about 2.2 Mpc.Many of the brighter galaxies in this cluster, including the giant elliptical galaxy Messier 87, were discovered in the late 1770s and early 1780s and subsequently included in Charles Messier's catalogue of non-cometary fuzzy objects. Described by Messier as nebulae without stars, their true nature was not recognized until the 1920s.The cluster subtends a maximum arc of approximately 8 degrees centered in the constellation Virgo. Although some of the cluster's most prominent members can be seen with smaller instruments, a 6-inch telescope will reveal about 160 of the cluster's galaxies on a clear night. Its brightest member is the elliptical galaxy Messier 49; however its most famous member is the elliptical galaxy Messier 87, which is located in the center of the cluster.

Stars (list)
Star clusters
See also

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