Messier 87 (also known as Virgo A or NGC 4486, generally abbreviated to M87) is a supergiant elliptical galaxy with several trillion stars in the constellation Virgo. One of the largest and most massive galaxies in the local universe, it has a large population of globular clusters — about 15,000 compared with the 150–200 orbiting the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

— and a jet of energetic plasma that originates at the core and extends at least , traveling at a

relativistic speed Relativistic speed refers to speed at which relativistic effects become significant to the desired accuracy of measurement of the phenomenon being observed. Relativistic effects are those discrepancies between values calculated by models consideri ...

. 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 Charles Messier (; 26 June 1730 – 12 April 1817) was a French astronomer. He published an astronomical catalogue consisting of 110 nebulae and star clusters, which came to be known as the ''Messier objects''. Messier's purpose ...

discovered M87 in 1781, and cataloged it as a

nebula A nebula ('cloud' or 'fog' in Latin; pl. nebulae, nebulæ or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regio ...

. M87 is about from Earth and is the second-brightest galaxy within the northern Virgo Cluster, having many satellite galaxies. Unlike a disk-shaped

spiral galaxy Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''dust lanes. Instead, it has an almost featureless,

ellipsoid An ellipsoid is a surface that may be obtained from a sphere by deforming it by means of directional scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface; that is, a surface that may be defined as th ...

al shape typical of most giant elliptical galaxies, diminishing in

luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...

with distance from the center. Forming around one-sixth of its mass, M87's

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

s 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 An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not prod ...

. The black hole was imaged using data collected in 2017 by the Event Horizon Telescope (EHT), with a final, processed image released on 10 April 2019. In March 2021, the EHT Collaboration presented, for the first time, a polarized-based image of the black hole which may help better reveal the forces giving rise to

quasar A quasar is an extremely luminous active galactic nucleus (AGN). It is pronounced , and sometimes known as a quasi-stellar object, abbreviated QSO. This emission from a galaxy nucleus is powered by a supermassive black hole with a mass rangi ...

s. The galaxy is a strong source of multi-wavelength radiation, particularly

radio wave Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz ( GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (sho ...

s. It has an isophotal diameter of , with a diffuse galactic envelope that extends to a radius of about , where it is truncated – possibly by an encounter with another galaxy. Its

interstellar medium In astronomy, the interstellar medium is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstella ...

consists of diffuse gas enriched by elements emitted from evolved stars.

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

comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...

s. In subsequent use, each catalogue entry was prefixed with an "M". Thus, M87 was the eighty-seventh object listed in Messier's catalogue. During the 1880s, the object was included as NGC 4486 in the ''

New General Catalogue The ''New General Catalogue of Nebulae and Clusters of Stars'' (abbreviated NGC) is an astronomical catalogue of deep-sky objects compiled by John Louis Emil Dreyer in 1888. The NGC contains 7,840 objects, including galaxies, star clusters and ...

'' of nebulae and star clusters assembled by the Danish-Irish astronomer

John Dreyer John Dreyer may refer to: *John Louis Emil Dreyer John Louis Emil Dreyer (13 February 1852 – 14 September 1926) was a Danish astronomer who spent most of his career working in Ireland. He spent the last decade of his life in Oxford, Engl ...

, which he based primarily on the observations of the English astronomer

John Herschel Sir John Frederick William Herschel, 1st Baronet (; 7 March 1792 – 11 May 1871) was an English polymath active as a mathematician, astronomer, chemist, inventor, experimental photographer who invented the blueprint and did botanical wo ...

. In 1918, the American astronomer Heber Curtis of

Lick Observatory The Lick Observatory is an astronomical observatory owned and operated by the University of California. It is on the summit of Mount Hamilton, in the Diablo Range just east of San Jose, California, United States. The observatory is managed by t ...

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. The following year, a

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or whe ...

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.

Identification as a galaxy

In 1922, the American astronomer

Edwin Hubble Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer. He played a crucial role in establishing the fields of extragalactic astronomy and observational cosmology. Hubble proved that many objects previousl ...

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. In 1926 he produced a new categorization, distinguishing extragalactic from galactic nebulae, the former being independent star systems. M87 was

classified Classified may refer to: General *Classified information, material that a government body deems to be sensitive *Classified advertising or "classifieds" Music *Classified (rapper) (born 1977), Canadian rapper * The Classified, a 1980s American ro ...

as a type of elliptical extragalactic nebula with no apparent elongation (class E0). In 1931, Hubble described M87 as a member of the Virgo Cluster, and gave a provisional estimate of 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. 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'' was at that time a synonym for the Milky Way. M87 continued to be labelled as an extragalactic nebula at least until 1954.

Modern research

In 1947, a prominent

radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a tr ...

source, Virgo A, was identified overlapping the location of M87. The source was confirmed to be M87 by 1953, and the linear

relativistic jet An astrophysical jet is an astronomical phenomenon where outflows of ionised matter are emitted as an extended beam along the axis of rotation. When this greatly accelerated matter in the beam approaches the speed of light, astrophysical jets bec ...

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″. In 1969–1970, a strong component of the radio emission was found to closely align with the optical source of the jet. In 1966, the

United States Naval Research Laboratory The United States Naval Research Laboratory (NRL) is the corporate research laboratory for the United States Navy and the United States Marine Corps. It was founded in 1923 and conducts basic scientific research, applied research, technological ...

's Aerobee 150 rocket identified Virgo X-1, the first X-ray source in Virgo. 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. Subsequent X-ray observations by the HEAO 1 and

Einstein Observatory 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 ...

showed a complex source that included the active galactic nucleus of M87. However, there is little central concentration of the X-ray emission. 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 mass The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...

es. After the installation of the

COSTAR CoStar Group, Inc. is a Washington, DC-based provider of information, analytics and marketing services to the commercial property industry in the United States, Canada, the United Kingdom, France, Germany, and Spain. Founded in 1987 by Andrew C. ...

corrective-optics module in the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...

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 , with 30% uncertainty. Globular clusters within M87 have been used to calibrate metallicity relations as well. M87 was observed by the Event Horizon Telescope (EHT) during much of 2017. The event horizon of the black hole at the center was directly imaged by the EHT, then revealed in a press conference on the issue date stated, filtering out from this the first image of a black hole's shadow.

Visibility

M87 is near a high

declination In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of th ...

limit of the Virgo constellation, abutting

Coma Berenices Coma Berenices is an ancient asterism in the northern sky, which has been defined as one of the 88 modern constellations. It is in the direction of the fourth galactic quadrant, between Leo and Boötes, and it is visible in both hemisphe ...

. It lies along the line between the stars

Epsilon Virginis Epsilon Virginis (ε Virginis, abbreviated Epsilon Vir, ε Vir), formally named Vindemiatrix , is a star in the zodiac constellation of Virgo. The apparent visual magnitude of this star is +2.8, making it the third-brightest member of V ...

and Denebola (Beta Leonis). The galaxy can be observed using a small telescope with a

aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An ...

, extending across an angular area of at a surface brightness of 12.9, with a very bright, 45

arcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The n ...

core. Viewing the jet is a challenge without the aid of photography. Before 1991, the Ukrainian-American astronomer Otto Struve was the only person known to have seen the jet visually, using the

Hooker telescope The Mount Wilson Observatory (MWO) is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles. The observato ...

. In more recent years it has been observed in larger amateur telescopes under excellent conditions.

Properties

In the modified

Hubble sequence The Hubble sequence is a morphological classification scheme for galaxies invented by Edwin Hubble in 1926. It is often colloquially known as the Hubble tuning-fork diagram because the shape in which it is traditionally represented resembles a tun ...

galaxy morphological classification scheme of the French astronomer

Gérard de Vaucouleurs Gérard Henri de Vaucouleurs (25 April 1918 – 7 October 1995) was a French astronomer. Life and career Born in Paris, he had an early interest in amateur astronomy and received his undergraduate degree in 1939 at the Sorbonne in that city. ...

, M87 is categorized as an E0p galaxy. "E0" designates an elliptical galaxy that displays no flattening — that is, it appears spherical. 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. In the Yerkes (Morgan) scheme, M87 is classified as a

type-cD galaxy The type-cD galaxy (also cD-type galaxy, cD galaxy) is a galaxy morphology classification, a subtype of type-D giant elliptical galaxy. Characterized by a large halo of stars, they can be found near the centres of some rich galaxy clusters. T ...

. A D galaxy has an elliptical-like nucleus surrounded by an extensive, dustless, diffuse envelope. A D type supergiant is called a cD galaxy. The distance to M87 has been estimated using several independent techniques. These include measurement of the luminosity of

planetary nebula A planetary nebula (PN, plural PNe) is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. The term "planetary nebula" is a misnomer because they are unrelate ...

e, comparison with nearby galaxies whose distance is estimated using

standard candles The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects. A ''direct'' distance measurement of an astronomical object is possible o ...

such as cepheid variables, the linear size distribution of globular clusters, and the tip of the red-giant branch method using individually resolved

red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around o ...

stars. These measurements are consistent with each other, and their weighted average yields a distance estimate of . Galactic Chromodynamics

M87 is one of the most massive galaxies in the local Universe. Its diameter is estimated at 132,000 light-years, which is approximately 51% larger than that of the Milky Way. As an elliptical galaxy, the galaxy is a spheroid rather than a flattened disc, accounting for the substantially larger mass of M87. Within a radius of , the mass is times the mass of the Sun, which is double the mass of the

galaxy. 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 ; that is, only about one part in six of the galaxy's mass is in the form of stars that radiate energy. This ratio varies from 5 to 30, approximately in proportion to in the region of from the core. The total mass of M87 may be 200 times that of the Milky Way. The galaxy experiences an infall of gas at the rate of two to three solar masses per year, most of which may be accreted onto the core region. The extended stellar envelope of this galaxy reaches a radius of about , compared with about for the Milky Way. Beyond that distance the outer edge of the galaxy has been truncated by some means; possibly by an earlier encounter with another galaxy. 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. 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. M87 is estimated to have at least 50 satellite galaxies, including NGC 4486B and NGC 4478. The spectrum of the nuclear region of M87 shows the

emission line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to identi ...

s of various ions, including

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...

(HI, HII),

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic ta ...

(HeI),

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

(OI, OII, OIII),

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

(NI),

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...

(MgII), and

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...

(SII). The line intensities for weakly ionized atoms (such as neutral

atomic oxygen There are several known allotropes of oxygen. The most familiar is molecular oxygen (O2), present at significant levels in Earth's atmosphere and also known as dioxygen or triplet oxygen. Another is the highly reactive ozone (O3). Others are ...

, OI) are stronger than those of strongly ionized atoms (such as

doubly ionized oxygen In astronomy and atomic physics, doubly ionized oxygen is the ion O2+ (O III in spectroscopic notation). Its emission forbidden lines in the visible spectrum fall primarily at the wavelength 500.7 nm, and secondarily at 495.9 nm. Befor ...

, OIII). A galactic nucleus with such spectral properties is termed a LINER, for "

low-ionization nuclear emission-line region A low-ionization nuclear emission-line region (LINER) is a type of galactic nucleus that is defined by its spectral line emission. The spectra typically include line emission from weakly ionized or neutral atoms, such as O, O+, N+, and S+. ...

". 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 or photoionization in the inner region powered by the jet. Elliptical galaxies such as M87 are believed to form as the result of one or more mergers of smaller galaxies. They generally contain relatively little cold

interstellar gas In astronomy, the interstellar medium is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstella ...

(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 Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''Very Large Telescope The Very Large Telescope (VLT) is a telescope facility operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. It consists of four individual telescopes, each with a primary mirror 8.2 m acro ...

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 In dynamical system theory, a phase space is a space in which all possible states of a system are represented, with each possible state corresponding to one unique point in the phase space. For mechanical systems, the phase space usually ...

mixing of a disrupted galaxy.

Components

Supermassive black hole M87*

Telescopes Unite in Unprecedented Observations of Famous Black Hole M87

The core of the galaxy contains a supermassive black hole (SMBH), designated M87*, whose mass is billions of times that of the Earth's Sun; estimates had ranged from to , surpassed by in 2016. In April 2019, the Event Horizon Telescope collaboration released measurements of the black hole's mass as . 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, and spans a maximum diameter of . By comparison,

Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the S ...

averages from the Sun. Gas accretes onto the black hole at an estimated rate of one solar mass every ten years (about 90

Earth mass An Earth mass (denoted as M_\mathrm or M_\oplus, where ⊕ is the standard astronomical symbol for Earth), is a unit of mass equal to the mass of the planet Earth. The current best estimate for the mass of Earth is , with a relative uncertainty ...

es per day). The

Schwarzschild radius The Schwarzschild radius or the gravitational radius is a physical parameter in the Schwarzschild solution to Einstein's field equations that corresponds to the radius defining the event horizon of a Schwarzschild black hole. It is a characteri ...

of the black hole is , or 18 billion km, which is around 120 times the Earth–Sun distance (120 AU). The diameter of the accretion disk, as seen from Earth, is 42 μas (

microarcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...

) and the diameter of the black hole itself is 15 μas. By comparison, the diameter of the core of M87 is 45" (as, arcsecond) and the size of M87 is 7.2' x 6.8' (am, arcminute). A 2010 paper suggested that the black hole may be displaced from the galactic center by about . This was claimed to be in the opposite direction of the known jet, indicating acceleration of the black hole by it. Another suggestion was that the offset occurred during the merger of two supermassive black holes. However, a 2011 study did not find any statistically significant displacement, 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. This black hole is the first to be imaged. Data to produce the image were taken in April 2017, the image was produced during 2018 and was published on 10 April 2019. The image shows the

shadow A shadow is a dark area where light from a light source is blocked by an opaque object. It occupies all of the three-dimensional volume behind an object with light in front of it. The cross section of a shadow is a two- dimensional silhouett ...

of the black hole, surrounded by an asymmetric emission ring with a diameter of . The shadow radius is 2.6 times that of the black hole's Schwarzschild radius. The rotation parameter was estimated at corresponding to a rotation speed After the black hole had been imaged, it was named Pōwehi, a Hawai'ian word meaning "the adorned fathomless dark creation", taken from the ancient creation chant Kumulipo. On 24 March 2021, the Event Horizon Telescope collaboration revealed a unprecedented unique view of the M87 black hole shadow: how it looks in polarized light. Polarization is a powerful tool which allows astronomers to probe physics behind the image in more detail. Light polarization informs us about the strength and orientation of magnetic fields in the ring of light around the black hole shadow. Knowing those is essential to understand how M87 supermassive black hole is launching jets of magnetized plasma which expand at relativistic speed beyond the M87 galaxy. On 14 April 2021, astronomers further reported that the M87 black hole and its surrounding was studied during Event Horizon Telescope 2017 observing run also by many multi-wavelength observatories from around the world.

Jet

The

of matter emerging from the core extends at least 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 of the core, to about 16° at , and to 6–7° at . Its base has the diameter of and is probably powered by a prograde accretion disk around the spinning supermassive black hole. 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 A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

. The total energy of these electrons is estimated at

erg The erg is a unit of energy equal to 10−7joules (100 nJ). It originated in the Centimetre–gram–second system of units (CGS). It has the symbol ''erg''. The erg is not an SI unit. Its name is derived from (), a Greek word meaning 'work' o ...

s ( or ). This is roughly times the energy produced in the entire Milky Way in one second, which is estimated at 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 Relativistic beaming (also known as Doppler beaming, Doppler boosting, or the headlight effect) is the process by which relativistic effects modify the apparent luminosity of emitting matter that is moving at speeds close to the speed of ligh ...

. The jet is precessing, causing the outflow to form a helical pattern out to . Lobes of expelled matter extend out to . 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 In astronomy, superluminal motion is the apparently faster-than-light motion seen in some radio galaxies, BL Lac objects, quasars, blazars and recently also in some galactic sources called microquasars. Bursts of energy moving out along the re ...

, 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 Faster-than-light (also FTL, superluminal or supercausal) travel and communication are the conjectural propagation of matter or information faster than the speed of light (). The special theory of relativity implies that only particles with zero ...

speeds, though the jet itself has a velocity of only 80-85% the speed of light. Detection of such motion is used to support the theory that

s, BL Lacertae objects and radio galaxies may all be the same phenomenon, known as

active galaxies An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not pro ...

, viewed from different perspectives. It is proposed that the nucleus of M87 is a BL Lacertae object (of lower luminosity than its surrounds) seen from a relatively large angle. Flux variations, characteristic of the BL Lacertae objects, have been observed in M87.

Close-Up Look at a Jet Near a Black Hole

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 The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space telescope launched aboard the during STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources ...

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 in diameter around the black hole. Other features observed include narrow X-ray-emitting filaments up to 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. M87 is a very strong source of

gamma ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...

s, 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. In general, the smaller the diameter of the emission source, the faster the variation in flux. A knot of matter in the jet (designated HST-1), about 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, while the X-ray emission has since been decaying in a variable manner. The interaction of relativistic jets of plasma emanating from the core with the surrounding medium gives rise to

radio lobe A radio galaxy is a galaxy with giant regions of radio emission extending well beyond its visible structure. These energetic radio lobes are powered by jets from its active galactic nucleus. They have luminosities up to 1039 W at radio wav ...

s in active galaxies. The lobes occur in pairs and are often symmetrical. The two radio lobes of M87 together span about 80 kiloparsecs; the inner parts, extending up to 2 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 intra-cluster medium. At greater distances, both flows diffuse into two lobes. The lobes are surrounded by a fainter halo of radio-emitting gas.

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 In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar He ...

lifetime. Carbon and nitrogen are continuously supplied by stars of intermediate mass as they pass through the

asymptotic giant branch The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses) lat ...

. 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 supernova A Type Ia supernova (read: "type one-A") is a type of supernova that occurs in binary systems (two stars orbiting one another) in which one of the stars is a white dwarf. The other star can be anything from a giant star to an even smaller white ...

e. 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. Since oxygen is produced mainly by core-collapse supernovae, which occur during the early stages of galaxies, and mostly in outer star-forming regions, 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. The contribution of elements from these sources was much lower than in the Milky Way. Examination of M87 at far

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...

wavelengths shows an excess emission at wavelengths longer than 25 μm. Normally, this may be an indication of

thermal emission Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) is ...

by warm dust. In the case of M87, the emission can be fully explained by

synchrotron radiation Synchrotron radiation (also known as magnetobremsstrahlung radiation) is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity (). It is produced artificially in ...

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. This dust may be destroyed by the hostile environment or expelled from the galaxy. The combined mass of dust in M87 is no more than 70,000 times the mass of the Sun. By comparison, the Milky Way's dust equals about a hundred million () solar masses. 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. These filaments have an estimated mass of about 10,000 . Surrounding the galaxy is an extended corona with hot, low-density gas.

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 clusters in orbit around M87, 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. Within a radius of the core, the cluster

metallicity In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as ...

— 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. Clusters with low metallicity are somewhat larger than metal-rich clusters. 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. Almost a hundred ultra-compact dwarfs have been identified in M87. They resemble globular clusters but have a diameter of or more, much larger than the maximum of globular clusters. It is unclear whether they are dwarf galaxies captured by M87 or a new class of massive globular cluster.

Environment

M87 is near (or at) the center of the Virgo Cluster, a closely compacted structure of about 2,000 galaxies. This forms the core of the larger Virgo Supercluster, of which the Local Group (including the Milky Way) is an outlying member. It is organized into at least three distinct subsystems associated with the three large galaxies — M87, M49 and M86 — with the core subgroup including M87 (''Virgo A'') and M49 (''Virgo B''). There is a preponderance of elliptical and S0 galaxies around M87. A chain of elliptical galaxies roughly aligns with the jet. In terms of mass, M87 is likely to be the largest, and coupled with centrality appears to be moving very little relative to the cluster as a whole. It is defined in one study as the cluster center. The cluster has a sparse gaseous medium that emits X-rays, lower in temperature toward the middle. The combined mass of the cluster is estimated to be 0.15 to Measurements of the motion of those intracluster starburst ("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, 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 Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ...

. A third possibility is that the halo's formation was truncated by early feedback from the active galactic nucleus.

Notes

References

External links

Messier 87
SEDS Messier pages
ESA/Hubble images of M87
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