Are there black holes near the galactic nucleus?
7901784#5
The Milky Way and Andromeda galaxies each contain a central supermassive black hole (SMBH), these being Sagittarius A* (ca. ) and an object within the P2 concentration of Andromeda's nucleus (). These black holes will converge near the centre of the newly formed galaxy over a period that may take millions of years, due to a process known as dynamical friction: As the SMBHs move relative to the surrounding cloud of much less massive stars, gravitational interactions lead to a net transfer of orbital energy from the SMBHs to the stars, causing the stars to be "slingshotted" into higher-radius orbits, and the SMBHs to "sink" toward the galactic core. When the SMBHs come within one light-year of one another, they will begin to strongly emit gravitational waves that will radiate further orbital energy until they merge completely. Gas taken up by the combined black hole could create a luminous quasar or an active galactic nucleus, releasing as much energy as 100 million supernova explosions. As of 2006, simulations indicated that the Sun might be brought near the centre of the combined galaxy, potentially coming near one of the black holes before being ejected entirely out of the galaxy. Alternatively, the Sun might approach one of the black holes a bit closer and be torn apart by its gravity. Parts of the former Sun would be pulled into the black hole.
Andromeda–Milky Way collision
48732137#1
The radio continuum emission along the galaxy's major axis is asymmetrical, being brighter in the southwestern part than in the northeast. But the overall radio surface brightness is on the low side. In the mid-infrared range, the spectrum shows indications of high ionization levels usually associated with an active galactic nucleus. However, optical observations show no signs of an active nucleus, which may just mean it is heavily obscured. Indeed, the amount of ionized matter appears to increase near the core. Although this galaxy lacks a bulge that could supply mass to a supermassive black hole, a large black hole was detected at the core by the Chandra X-ray Observatory in 2012. It is inferred to have a mass of around 10 to 10 times the mass of the Sun. This makes it one of the lowest mass nuclear black holes known.
NGC 4178
864424#4
The nucleus of the Sombrero galaxy is classified as a low ionization nuclear emission region (LINER). These are nuclear regions where ionized gas is present, but the ions are only weakly ionized (i.e. the atoms are missing relatively few electrons). The source of energy for ionizing the gas in LINERs has been debated extensively. Some LINER nuclei may be powered by hot, young stars found in star formation regions, whereas other LINER nuclei may be powered by active galactic nuclei (highly energetic regions that contain supermassive black holes). Infrared spectroscopy observations have demonstrated that the nucleus of the Sombrero Galaxy is probably devoid of any significant star formation activity. However, a supermassive black hole has been identified in the nucleus (as discussed in the subsection below), so this active galactic nucleus is probably the energy source that weakly ionizes the gas in the Sombrero Galaxy.
Sombrero Galaxy
12558#38
The standard model for an active galactic nucleus is based upon an accretion disc that forms around a supermassive black hole (SMBH) at the core region of the galaxy. The radiation from an active galactic nucleus results from the gravitational energy of matter as it falls toward the black hole from the disc. In about 10% of these galaxies, a diametrically opposed pair of energetic jets ejects particles from the galaxy core at velocities close to the speed of light. The mechanism for producing these jets is not well understood.
Galaxy
59714879#2
The nucleus of the galaxy is active and hosts a low luminosity transition Active Galactic Nucleus (AGN). The most accepted theory for the energy source of AGNs is the presence of an accretion disk around a supermassive black hole. The mass of the black hole in the centre of NGC 3665 is estimated to be based on the velocity dispersion of the molecular gas around the nucleus , or based on the M-sigma relation.
NGC 3665
43948#5
A supermassive black hole at the core of a galaxy may serve to regulate the rate of star formation in a galactic nucleus. A black hole that is accreting infalling matter can become active, emitting a strong wind through a collimated relativistic jet. This can limit further star formation. Massive black holes ejecting radio-frequency-emitting particles at near-light speed can also block the formation of new stars in aging galaxies. However, the radio emissions around the jets may also trigger star formation. Likewise, a weaker jet may trigger star formation when it collides with a cloud.
Star formation
215706#11
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. This is a major component of the theory of accretion disks. Gas accretion is the most efficient and also the most conspicuous way in which black holes grow. The majority of the mass growth of supermassive black holes is thought to occur through episodes of rapid gas accretion, which are observable as active galactic nuclei or quasars. Observations reveal that quasars were much more frequent when the Universe was younger, indicating that supermassive black holes formed and grew early. A major constraining factor for theories of supermassive black hole formation is the observation of distant luminous quasars, which indicate that supermassive black holes of billions of solar masses had already formed when the Universe was less than one billion years old. This suggests that supermassive black holes arose very early in the Universe, inside the first massive galaxies.
A vacancy exists in the observed mass distribution of black holes. Black holes that spawn from dying stars have masses . The minimal supermassive black hole is approximately a hundred thousand solar masses. Mass scales between these ranges are dubbed intermediate-mass black holes. Such a gap suggests a different formation process. However, some models suggest that ultraluminous X-ray sources (ULXs) may be black holes from this missing group.
Supermassive black hole
215706#0
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 times, the mass of the Sun (). This is a class of astronomical objects that has undergone gravitational collapse, leaving behind a spheroidal region of space from which nothing can escape; not even light. Observational evidence indicates that all, or nearly all, massive 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.
Supermassive black hole
37939765#2
Supermassive black holes reside in galactic nuclei. The total mass of the stars in a nucleus is roughly equal to the mass of the supermassive black hole. In the case of the Milky Way, the mass of the supermassive black hole is about 4 million Solar masses, and the number of stars in the nucleus is about ten million.
Bahcall–Wolf cusp
510060#6
In November 2004 a team of astronomers reported the discovery of GCIRS 13E, the first intermediate-mass black hole in our galaxy, orbiting three light-years from Sagittarius A*. This medium black hole of 1,300 solar masses is within a cluster of seven stars, possibly the remnant of a massive star cluster that has been stripped down by the Galactic Center. This observation may add support to the idea that supermassive black holes grow by absorbing nearby smaller black holes and stars. However, in 2005, a German research group claimed that the presence of an IMBH near the galactic center is doubtful, based on a dynamical study of the star cluster in which the IMBH was said to reside. An IMBH near the galactic center could also be detected via its perturbations on stars orbiting around the supermassive black hole.
Intermediate-mass black hole
177092#9
For a long time it has been argued that an AGN must be powered by accretion of mass onto massive black holes (10 to 10 times the Solar mass). AGN are both compact and persistently extremely luminous. Accretion can potentially give very efficient conversion of potential and kinetic energy to radiation, and a massive black hole has a high Eddington luminosity, and as a result, it can provide the observed high persistent luminosity. Supermassive black holes are now believed to exist in the centres of most if not all massive galaxies since the mass of the black hole correlates well with the velocity dispersion of the galactic bulge (the M-sigma relation) or with bulge luminosity. Thus AGN-like characteristics are expected whenever a supply of material for accretion comes within the sphere of influence of the central black hole.
Active galactic nucleus
59800990#1
NGC 4278 is an elliptical galaxy. Its nucleus has been found to be active (AGN) and based on its spectrum has been identified as a LINER. The most accepted theory for the power source of active galactic nuclei is the presence of an accretion disk around a supermassive black hole. In the centre of NGC 4278 lies a supermassive black hole with an estimated mass based on stellar velocity dispersion. The X-ray emission of the nucleus is consistent with one of a black hole fed by a low radiative efficiency accretion flow.
NGC 4278