M87 Galaxy & Black Hole

M87 Galaxy

           M87 or the Messier87 galaxy  (also known as M87, Virgo A or NGC 4486) is a supergiant elliptical galaxy. It was discovered in 1781 by the French astronomer Charles Messier, who cataloged it as a nebulous feature. The M87 is located within the north Virgo Cluster and is about 53.5 million light years from Earth & is about 3 times as large as our own Milky Way.

 This deep image of the Virgo Cluster shows the diffuse light between the galaxies belonging to the cluster. The dark spots indicate where bright foreground stars were removed from the image. Messier 87 is the largest galaxy in the picture (lower left).

Photo of the Center of the Virgo Cluster of Galaxies with names and magnitudes.

           

          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 is an outlying member. It is estimated that its mass is 1.2×10¹⁵ M out to 8 degrees of the cluster's center or a radius of about 2.2 Mpc. This cluster consists of approx. 1500 Galaxies.

                Above is the M87 Galaxy. the blue beam of light is the radiation given out from the black hole at its center.

                 Active elliptical galaxies of a form similar to Messier 87 are believed to form as a result of one or more mergers between smaller galaxies. There is now little dust remaining to form the diffuse nebulae where new stars are created, so the stellar population is dominated by old, population II stars that contain relatively low abundances of elements other than hydrogen and helium. The elliptical shape of this galaxy is maintained by random orbital motions of its member stars, in contrast to the more orderly rotational motions found in a spiral galaxy such as the Milky Way.

                Unlike a disk-shaped spiral galaxy, Messier 87 has no distinctive dust lanes and it has an almost featureless,ellipsoidal shape that diminishes in luminosity with distance from the center. At the core is a supermassive black hole, which forms the primary component of an active galactic nucleus. This object is a strong source of multiwavelength radiation, particularly radio waves. A jet of energetic plasmaoriginates at the core and extends outward at least 5,000 light-years.

virgo constellation map

                  The stars in this galaxy form about one sixth of Messier 87's mass. They have a nearly spherically symmetric distribution, while the density of stars decreases with increasing distance from the core. The galactic envelope extends out to a radius of about 150 kpc (490 kly), where it has been truncated—possibly by an encounter with another galaxy. Between the stars is a diffuse interstellar medium of gas that has been chemically enriched by elements emitted from evolved stars. Any dust formed within the galaxy is destroyed within 46 million years by the X-ray emission from the core, although optical filaments of dust have been observed. Orbiting the galaxy is an abnormally large population of about 12,000 globular clusters, compared to 150-200 globular clusters orbiting the Milky Way. The M87 is one of the most massive giant elliptical galaxies near Earth and one of the brightest radio sources in the sky. 

Discovery

                 Using European Space Observatory's (ESO) Very Large Telescope, astronomers measured the giant galaxy Messier 87 (M87). They were surprised to find that its outer parts have been stripped away by still unknown effects. The galaxy also appears to be on a collision course with another giant galaxy in this dynamic cluster.

The new observations reveal that M87's halo of stars has been cut short, with a diameter of about a million light-years, despite being about three times the extent of the halo surrounding our Milky Way. Beyond this zone only few intergalactic stars are seen."This is an unexpected result," said coauthor Ortwin Gerhard. "Numerical models predict that the halo around M87 should be several times larger than our observations have revealed. Clearly, something must have cut the halo off early on."The team used the Fibre Large Array Multi Element Spectrograph (FLAMES), the super-efficient spectrograph at ESO's Very Large Telescope at the Paranal Observatory in Chile, to make ultra-precise measurements of a host of planetary nebulae in the outskirts of M87 and in the intergalactic space within the Virgo Cluster of galaxies, to which M87 belongs. FLAMES can simultaneously take spectra of many sources, spread over an area of the sky about the size of the Moon.The new result is quite an achievement. The observed light from a planetary nebula in the Virgo Cluster is as faint as that from a 30-Watt light bulb at a distance of about 3.7 million miles (6 million kilometers) — about 15 times the Earth-Moon distance. Furthermore, planetary nebulae are thinly spread throughout the cluster so even FLAMES' wide field of view could only capture a few tens of nebulae at a time."It is a little bit like looking for a needle in a haystack, but in the dark," said team member Magda Arnaboldi. "The FLAMES spectrograph on the VLT was the best instrument for the job".At a distance of approximately 50 million light-years, the Virgo Cluster is the nearest galaxy cluster. It is located in the constellation Virgo and is a relatively young and sparse cluster. The cluster contains many hundreds of galaxies, including giant and massive elliptical galaxies, as well as more spirals like our own Milky Way.Astronomers have proposed several explanations for the discovered "cut-off" of M87's halo, such as collapse of dark matter nearby in the galaxy cluster. It might also be that another galaxy in the cluster, M84, came much closer to M87 in the past and dramatically perturbed it about a billion years ago. "At this stage, we can't confirm any of these scenarios," said Arnaboldi. "We will need observations of many more planetary nebulae around M87."One thing the astronomers are sure about, however, is that M87 and its neighbor M86 are falling towards each other. "We may be observing them in the phase just before the first close pass," said Gerhard. "The Virgo Cluster is still a very dynamic place and many things will continue to shape its galaxies over the next billion years."

The M87 Super Massive Black Hole

                    At the core of this galaxy is a supermassive black hole (SMBH) with an estimated (6.6 ± 0.4) × 10⁹ times the mass of the Sun and a diameter larger than the orbit of Pluto. This is one of the highest masses known for such an object. Surrounding the black hole is a rotating disk of ionized gas that is oriented roughly perpendicular to a relativistic jet. This disk is rotating at velocities of up to roughly 1,000 km/s, and spans a maximum diameter of 0.12 pc (0.39 ly).Gas is accreting onto the black hole at an estimated rate equal to the mass of the Sun every ten years.

             It is large enough to swallow our entire solar system and has the same mass as 6.8 billion suns. This black hole M87 is almost twice as big as scientists had previously thought.

Even its event horizon - the edge from within nothing can escape, not even light - is four times as large as the orbit of Neptune.

             As gas spirals into the black hole, it's heated to millions of degrees, so it produces enormous amounts of X-rays. Some of the hot gas around the black hole shoots back into the galaxy in powerful jets that span thousands of light-years into the black hole, it's heated to millions of degrees, so it produces enormous amounts of X-rays. Some of the hot gas around the black hole shoots back into the galaxy in powerful jets that span thousands of light-years into the black hole, it's heated to millions of degrees, so it produces enormous amounts of X-rays. Some of the hot gas around the black hole shoots back into the galaxy in powerful jets that span thousands of light-years.

               Messier 87 is a very strong source of gamma rays, which are the most energetic rays of the electromagnetic spectrum; more than a million times as powerful as visible light. Gamma rays coming from Messier 87 have been observed since the late 1990s, but in 2006, using the HESS Cherenkov telescopes, scientists have measured the variations of the gamma ray flux coming from Messier 87, and found that the flux changes over a matter of days. This short period makes the immediate vicinity of the supermassive black hole in Messier 87 the most promising source for these gamma rays.In general, the smaller the diameter of the emission source, the faster the variation in flux, and vice versa.

Video - 

Fast Facts for M87:
Credit -	X-ray (NASA/CXC/KIPAC/N. Werner, E. Million et al); Radio (NRAO/AUI/NSF/F. Owen) Volcano image: Omar Ragnarsson
Scale -	Image is 14 arcmin across (about 200,000 light years)
Category -	Quasars & Active Galaxies, Groups & Clusters of Galaxies
Coordinates (J2000) -	RA 12h 30m 49.40s | Dec +12° 23' 28.00"
Constellation -	Virgo
Observation Dates -	2 pointings in Jul 2002, and 7 between Jan and Nov 2005
Observation Time -	159 hours (6 days 15 hours)
Obs. IDs -	2707, 3717, 5826-5828, 6186, 7210-7212
Color Code -	X-ray (blue), Radio (red-orange)
Instrument -	ACIS
Also Known As -	NGC 4486
References -	Werner, N. et al, 2010, MNRAS, in press. Million, E. et al. 2010, MNRAS, in press.
Distance Estimate -	About 50 million light years *source - chandra