Supermassive black hole

Supermassive black hole

Overview
A supermassive black hole is the largest type of black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...

 in a galaxy, in the order of hundreds of thousands to billions of solar masses. Most, and possibly all galaxies, including the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

, are believed to contain supermassive black holes at their centers
Galactic Center
The Galactic Center is the rotational center of the Milky Way galaxy. It is located at a distance of 8.33±0.35 kpc from the Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius where the Milky Way appears brightest...

.

Supermassive black holes have properties which distinguish them from lower-mass classifications:
  • The average density
    Density
    The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

     of a supermassive black hole (defined as the mass of the black hole divided by the volume within its Schwarzschild radius
    Schwarzschild radius
    The Schwarzschild radius is the distance from the center of an object such that, if all the mass of the object were compressed within that sphere, the escape speed from the surface would equal the speed of light...

    ) can be equal to (for black holes) or less than (for > black holes) the density of water
    Water
    Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

    .
Discussion
Ask a question about 'Supermassive black hole'
Start a new discussion about 'Supermassive black hole'
Answer questions from other users
Full Discussion Forum
 
Recent Discussions
Encyclopedia
A supermassive black hole is the largest type of black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...

 in a galaxy, in the order of hundreds of thousands to billions of solar masses. Most, and possibly all galaxies, including the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

, are believed to contain supermassive black holes at their centers
Galactic Center
The Galactic Center is the rotational center of the Milky Way galaxy. It is located at a distance of 8.33±0.35 kpc from the Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius where the Milky Way appears brightest...

.

Supermassive black holes have properties which distinguish them from lower-mass classifications:
  • The average density
    Density
    The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

     of a supermassive black hole (defined as the mass of the black hole divided by the volume within its Schwarzschild radius
    Schwarzschild radius
    The Schwarzschild radius is the distance from the center of an object such that, if all the mass of the object were compressed within that sphere, the escape speed from the surface would equal the speed of light...

    ) can be equal to (for black holes) or less than (for > black holes) the density of water
    Water
    Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

    . This is because the Schwarzschild radius is directly proportional
    Proportionality (mathematics)
    In mathematics, two variable quantities are proportional if one of them is always the product of the other and a constant quantity, called the coefficient of proportionality or proportionality constant. In other words, are proportional if the ratio \tfrac yx is constant. We also say that one...

     to mass
    Mass
    Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

    , while density is inversely proportional to the volume. Since the volume of a spherical object (such as the event horizon
    Event horizon
    In general relativity, an event horizon is a boundary in spacetime beyond which events cannot affect an outside observer. In layman's terms it is defined as "the point of no return" i.e. the point at which the gravitational pull becomes so great as to make escape impossible. The most common case...

     of a non-rotating black hole) is directly proportional to the cube of the radius, the density of a black hole is inversely proportional to the square of the mass, and thus higher mass black holes have lower average density.
  • The tidal force
    Tidal force
    The tidal force is a secondary effect of the force of gravity and is responsible for the tides. It arises because the gravitational force per unit mass exerted on one body by a second body is not constant across its diameter, the side nearest to the second being more attracted by it than the side...

    s in the vicinity of the event horizon
    Event horizon
    In general relativity, an event horizon is a boundary in spacetime beyond which events cannot affect an outside observer. In layman's terms it is defined as "the point of no return" i.e. the point at which the gravitational pull becomes so great as to make escape impossible. The most common case...

     are significantly weaker. Since the central singularity
    Gravitational singularity
    A gravitational singularity or spacetime singularity is a location where the quantities that are used to measure the gravitational field become infinite in a way that does not depend on the coordinate system...

     is so far away from the horizon, a hypothetical astronaut traveling towards the black hole center would not experience significant tidal force
    Spaghettification
    In astrophysics, spaghettification is the vertical stretching and horizontal compression of objects into long thin shapes in a very strong gravitational field, and is caused by extreme tidal forces...

     until very deep into the black hole.

Formation


There are many models for the formation of black holes of this size. The most obvious is by slow accretion
Accretion (astrophysics)
In astrophysics, the term accretion is used for at least two distinct processes.The first and most common is the growth of a massive object by gravitationally attracting more matter, typically gaseous matter in an accretion disc. Accretion discs are common around smaller stars or stellar remnants...

 of matter starting from a black hole of stellar size. Another model of supermassive black hole formation involves a large gas cloud collapsing into a relativistic star
Relativistic star
A relativistic star is a rotating neutron star whose behavior is well described by general relativity, but not by classical mechanics. Relativistic stars are one possible source to allow gravitational waves to be studied....

 of perhaps a hundred thousand solar masses or larger. The star would then become unstable to radial perturbations because of electron-positron pair production in its core, and may collapse directly into a black hole without a supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...

 explosion, which would eject most of its mass and prevent it from leaving a supermassive black hole as a remnant. Yet another model involves a dense stellar cluster undergoing core-collapse as the negative heat capacity of the system drives the velocity dispersion in the core to relativistic
Theory of relativity
The theory of relativity, or simply relativity, encompasses two theories of Albert Einstein: special relativity and general relativity. However, the word relativity is sometimes used in reference to Galilean invariance....

 speeds. Finally, primordial black hole
Primordial black hole
A primordial black hole is a hypothetical type of black hole that is formed not by the gravitational collapse of a large star but by the extreme density of matter present during the universe's early expansion....

s may have been produced directly from external pressure in the first instants after the Big Bang
Big Bang
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...

.

The difficulty in forming a supermassive black hole resides in the need for enough matter to be in a small enough volume. This matter needs to have very little angular momentum in order for this to happen. Normally the process of accretion involves transporting a large initial endowment of angular momentum outwards, and this appears to be the limiting factor in black hole growth, and explains the formation of accretion disks
Accretion disc
An accretion disc is a structure formed by diffuse material in orbital motion around a central body. The central body is typically a star. Gravity causes material in the disc to spiral inward towards the central body. Gravitational forces compress the material causing the emission of...

.

Currently, there appears to be a gap in the observed mass distribution of black holes. There are stellar-mass black holes, generated from collapsing stars, which range up to perhaps 33 solar masses. The minimal supermassive black hole is in the range of a hundred thousand solar masses. Between these regimes there appears to be a dearth of intermediate-mass black hole
Intermediate-mass black hole
An Intermediate-mass black hole is a black hole whose mass is significantly more than stellar black holes yet far less than supermassive black holes...

s. Such a gap would suggest qualitatively different formation processes. However, some models suggest that ultraluminous X-ray source
Ultraluminous X-ray source
An ultra-luminous X-ray source is an astronomical source of X-rays that is less luminous than an active galactic nucleus but is more consistently luminous than any known stellar process , assuming that it radiates isotropically...

s (ULXs) may be black holes from this missing group.

Doppler measurements


Direct Doppler
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...

 measures of water masers
Astrophysical maser
An astrophysical maser is a naturally occurring source of stimulated spectral line emission, typically in the microwave portion of the electromagnetic spectrum...

 surrounding the nucleus
Active galactic nucleus
An active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...

 of nearby galaxies have revealed a very fast keplerian motion
Kepler's laws of planetary motion
In astronomy, Kepler's laws give a description of the motion of planets around the Sun.Kepler's laws are:#The orbit of every planet is an ellipse with the Sun at one of the two foci....

, only possible with a high concentration of matter in the center. Currently, the only known objects that can pack enough matter in such a small space are black holes, or things that will evolve into black holes within astrophysically short timescales. For active galaxies farther away, the width of broad spectral lines can be used to probe the gas orbiting near the event horizon. The technique of reverberation mapping
Reverberation mapping
Reverberation mapping is to-day a statistical method within astrophysics preferably used in connection with velocity analysis of gaseous discs around supermassive compact objects. The technique is used to measure the size of the broad emission-line region and mass of the alleged central black hole...

 uses variability of these lines to measure the mass and perhaps the spin of the black hole that powers the active galaxy's "engine".

Such supermassive black holes in the center of many galaxies are thought to be the "engine" of active objects such as Seyfert galaxies
Seyfert galaxy
Seyfert galaxies are a class of galaxies with nuclei that produce spectral line emission from highly ionized gas, named after Carl Keenan Seyfert, the astronomer who first identified the class in 1943...

 and quasar
Quasar
A quasi-stellar radio source is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than...

s.

Supermassive black hole hypothesis



Astronomers are confident that our own Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

 galaxy has a supermassive black hole at its center, 26,000 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...

s from the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

, in a region called Sagittarius A* because:
  • The star S2
    S2 (star)
    S2, also known as S0—2 , is a star that is located close to the radio source Sagittarius A*, orbiting it with an orbital period of 15.56 ± 0.35 years and a pericenter distance of 17 light hours — about 4 times the distance of Neptune from the Sun.Its changing apparent position has been...

     follows an elliptical orbit with a period
    Orbital period
    The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...

     of 15.2 years and a pericenter (closest distance) of 17 light hours ( or 120 AU) from the center of the central object.
  • From the motion of star S2, the object's mass can be estimated as 4.1 million solar masses.
  • The radius of the central object must be significantly less than 17 light hours, because otherwise, S2 would either collide with it or be ripped apart by tidal forces. In fact, recent observations indicate that the radius is no more than 6.25 light-hours, about the diameter of Uranus' orbit.
  • Only a black hole is dense enough to contain 4.1 million solar masses in this volume of space.

The Max Planck Institute for Extraterrestrial Physics
Max Planck Institute for Extraterrestrial Physics
The Max Planck Institute for Extraterrestrial Physics is a Max Planck Institute, located in Garching, near Munich, Germany.In 1991 the Max Planck Institute for Physics and Astrophysics split up into the Max Planck Institute for Extraterrestrial Physics, the Max Planck Institute for Physics and the...

 and UCLA Galactic Center Group have provided the strongest evidence to date that Sagittarius A* is the site of a supermassive black hole, based on data from the ESO
ESO
ESO, as a three-letter abbreviation, may stand for:* European Southern Observatory* Ensemble Studios Online* English Symphony Orchestra* Edmonton Symphony Orchestra* Executive Stock Options...

 and the Keck telescope. Our galactic central black hole is calculated to have a mass of approximately 4.1 million solar masses, or about 8.2 × 1036 kg.

Supermassive black holes outside the Milky Way


It is now widely accepted that the center of nearly every galaxy contains a supermassive black hole. The close observational correlation between the mass of this hole and the velocity dispersion of the host galaxy's bulge, known as the M-sigma relation
M-sigma relation
The M-sigma relation is an empirical correlation between the stellar velocity dispersion \sigma of a galaxy bulge and the mass M of the supermassive black hole atthe galaxy's center.The relation can be expressed mathematically as...

, strongly suggests a connection between the formation of the black hole and the galaxy itself.

The explanation for this correlation remains an unsolved problem in astrophysics. It is believed that black holes and their host galaxies coevolved between 300-800 million years after the Big Bang
Big Bang
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...

, passing through a quasar
Quasar
A quasi-stellar radio source is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than...

 phase and developing correlated characteristics, but models differ on the causality of whether black holes triggered galaxy formation or vice versa, and sequential formation cannot be excluded. The unknown nature of dark matter
Dark matter
In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...

 is a crucial variable in these models.

The nearby Andromeda Galaxy
Andromeda Galaxy
The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years from Earth in the constellation Andromeda. It is also known as Messier 31, M31, or NGC 224, and is often referred to as the Great Andromeda Nebula in older texts. Andromeda is the nearest spiral galaxy to the...

, 2.5 million light-years away, contains a (1.1–2.3) × 108 solar mass central black hole, significantly larger than the Milky Way's. The largest supermassive black hole in the Milky Way's neighborhood appears to be that of M87
Messier 87
Messier 87 is a supergiant elliptical galaxy. It was discovered in 1781 by the French astronomer Charles Messier, who cataloged it as a nebulous feature. The second brightest galaxy within the northern Virgo Cluster, it is located about 16.4 million parsecs from Earth...

, weighing in at solar masses at a distance of 53.5 million light years.

Some galaxies, such as Galaxy 0402+379
Galaxy 0402+379
4C +37.11 or Galaxy 0402+379 is a radio galaxy and elliptical galaxy with the binary supermassive black holes with the least separation of any directly observed binaries, as of 2006...

, appear to have two supermassive black holes at their centers, forming a binary system. If they collided, the event would create strong gravitational waves. Binary supermassive black holes are believed to be a common consequence of galactic mergers
Galaxy merger
Galaxy mergers can occur when two galaxies collide. They are the most violent type of galaxy interaction. Although galaxy mergers do not involve stars or star systems actually colliding, due to the vast distances between stars in most circumstances, the gravitational interactions between galaxies...

. , the binary pair in OJ 287
OJ 287
OJ 287 is a BL Lac object located 3.5 billion light years away that has produced quasi-periodic optical outbursts going back approximately 120 years, as first apparent on photographic plates from 1891...

, 3.5 billion light years away, contains the most massive black hole known, with a mass estimated at 18 billion solar mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...

es.

A supermassive black hole was recently discovered in the dwarf galaxy Henize 2-10
Henize 2-10
Henize 2-10 is a dwarf galaxy located 34 million light years away in the constellation of Pyxis. It is the first dwarf galaxy ever discovered that contains, at its center, a supermassive black hole...

, which has no bulge. The precise implications for this discovery on black hole formation are unknown, but may indicate that black holes formed before bulges.

On March 28, 2011, a supermassive black hole was for the first time seen tearing a mid-size star apart. That is, according to astronomers, the only likely explanation of the observations that day of sudden X-ray radiation.

See also

  • Active galactic nucleus
    Active galactic nucleus
    An active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...

  • Black hole
    Black hole
    A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...

  • Galaxy
    Galaxy
    A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...

  • Galactic center
    Galactic Center
    The Galactic Center is the rotational center of the Milky Way galaxy. It is located at a distance of 8.33±0.35 kpc from the Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius where the Milky Way appears brightest...

  • Hypercompact stellar system
    Hypercompact stellar system
    A hypercompact stellar system is a dense cluster of stars around a supermassive black hole that has been ejected from the centre of its host galaxy...

  • Neutron star
    Neutron star
    A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...

  • Quasar
    Quasar
    A quasi-stellar radio source is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than...

  • M-sigma relation
    M-sigma relation
    The M-sigma relation is an empirical correlation between the stellar velocity dispersion \sigma of a galaxy bulge and the mass M of the supermassive black hole atthe galaxy's center.The relation can be expressed mathematically as...

  • Sagittarius A*
  • Spin-flip
    Spin-flip
    A black hole spin-flip occurs when the spin axis of a rotating black hole undergoes a sudden change in orientation due to absorption of a second black hole....


External links