How would two recently discovered monster black holes be described? Massive? Supermassive?
Somehow, adding “super” before “massive” is an understatement for the Goliaths living in the centers of the NGC 3842 and NGC 4889 — two galaxies located 320 million and 335 million light-years away, in the Leo and Coma clusters of galaxies.
A team of astronomers, headed by Nicholas McConnell of the University of California, Berkeley, used data collected by the Hubble Space Telescope, the Keck and Gemini observatories in Hawaii, and the McDonald Observatory in Texas to observe the stars orbiting around the central nuclei of both galaxies and calculated the mass of the black holes hidden in their cores.
By measuring the speed at which these stars were traveling around the invisible mass in the center, an accurate gauge on the black holes’ masses could be arrived at.
The research can be found in the Dec. 8 edition of the journal Nature.
Up until this point, the largest known supermassive black hole was living in the center of the elliptical galaxy M87, 54 million light-years from Earth. That heavyweight weighs in at 6.3 billion times the mass of our sun.
As a comparison, the supermassive black hole residing in the center of our galaxy is a positively featherweight 4.3 million solar masses.
So how do the black holes in NGC 3842 and NGC 4889 measure up? Both weigh in at over 9 billion times the mass of our sun. These super-supermassive black holes are over 2,000 times more massive than the supermassive black hole in the center of the Milky Way.
Their event horizons are also huge. The event horizon is the point at which even light cannot escape the black hole’s gravitational grasp, and in the case of these two black holes, their event horizons would reach five-times further than the orbit of Pluto from the sun. The event horizon of the Milky Way’s piddly black hole is one-fifth the distance from the sun to Mercury.
The existence of black holes with such gargantuan proportions have been long theorized, and are thought to have provided the awesome power behind the quasars that lit up space in the early history of the Universe.
When the Universe was less than half its current age, large quantities of interstellar gas would be drawn into the centers of galaxies, eventually falling into the central black holes, releasing vast quantities of energy in the process. Quasars were born.
However, as the Universe aged, this gas was used in the production of stars — therefore the fuel supply for quasars dried up.
The quasars may have died in the modern Universe, but the large black hole relics remain behind, lurking silently in the centers of the galaxies they used to terrorize during their “quasar phase.”
Although we now know that most galaxies contain supermassive black holes in their cores, none appear to be massive enough to generate the energy the most powerful quasars generated.
But now, with the discovery of two black holes nearing 10 billion solar masses, have astronomers found the missing link? Possibly.
The relationship between the black holes and the galactic bulges surrounding them has also been investigated by McConnell’s team. It would appear that the two super-supermassive black holes are too big to be explained solely by the accretion model — i.e. growing purely from the gas supplied by their host galaxies.
By analyzing the velocities of the stars in the galaxies’ central bulges, the researchers think that they were more likely formed through the merging of smaller galaxies. The central black holes then merged some time afterward to reach their current, mammoth sizes.
So, in the wake of this fascinating study, how should these super-supermassive black holes be described? To be honest, rather than trying to wrap my brain around all that mass, I think I’ll just let Muse sing us out:
Publication: McConnell, N. J. et al. Nature 480, 215–218 (2011) doi:10.1038/nature10636
Images: Top: A supermassive black hole, plus “aurora” (Ian O’Neill/Discovery News). Middle: Artist’s impression of stars orbiting close to a supermassive black hole (Gemini Observatory/AURA artwork by Lynette Cook)