18 Jan. 2011

 

Weighed: the super black hole in M87

 

6.6 billion solar masses. This is the mass of the super-massive black hole nested in the nucleus of the enormous elliptical galaxy M87, visible in the constellation of Virgo and about 50 million light years away.
The determination of the mass of this cosmic monster was accomplished by a team of researchers led by Karl Gebhardt, of the University of Texas, Austin. To do it they took advantage of the optical quality of the Gemini North telescope in Hawaii and the McDonald Observatory in Texas, to measure the speeds of groups of stars in orbit at various distances from the centre of the galaxy.
The increasing speeds of star clusters at decreasing distances from the black hole was used to provide a measure of the gravitational field, and this leads to a value for its mass.
At 6.6 billion solar masses, the super-massive black hole in M87 is the most massive in the local Universe, and gets close to the 10 billion solar mass giants observed in the more remote cosmos.
The mass derived is about twice as large as thought until now, and confirms previous computer simulations carried out by the same team, according to which numerous other super-massive black holes would also have double the mass of current estimates.
But having measured the mass of the black hole in M87 has wider implications, in fact, such a large black hole at a relatively modest distance from us could provide the telescopes of the near future with a fascinating possibility: directly observing it.
In the meantime the observations of Gebhardt at Gemini North continue, with the objective of measuring the masses of other super black holes in much more distant galaxies, in an attempt to demonstrate that there exists an upper limit to their mass.

 

by Michele Ferrara & Marcel Clemens

credit: Gemini Observatory/AURA illustration by Lynette Cook