Artist's View of a Binary Black Hole
Optical-to-Ultraviolet Spectrum of Markarian 231
This simplified spectral plot shows the radiation emitted from the
center of a nearby galaxy that hosts a quasar. Visible and infrared
light coming from a disk surrounding a central black hole in the middle
of the galaxy is measured. Surprisingly, ultraviolet light from the
disk, as measured by the Hubble Space Telescope, shows a drop in
radiation from the disk. This is evidence for a large gap in the center
of the disk that is likely carved out by a second black hole orbiting
the primary black hole. Credit: NASA, ESA, and P. Jeffries (STScI)
Astronomers using NASA's Hubble Space Telescope have found that Markarian 231 (Mrk 231), the nearest galaxy to Earth that hosts a quasar, is powered by two central black holes furiously whirling about each other.
The finding suggests that quasars — the brilliant cores of active
galaxies — may commonly host two central supermassive black holes that
fall into orbit about one another as a result of the merger between two
galaxies. Like a pair of whirling skaters, the black-hole duo
generates tremendous amounts of energy that makes the core of the host
galaxy outshine the glow of the galaxy's population of billions of
stars, which scientists then identify as quasars.
Scientists looked at Hubble archival observations of ultraviolet
radiation emitted from the center of Mrk 231 to discover what they
describe as "extreme and surprising properties."
If only one black hole were present in the center of the quasar, the
whole accretion disk made of surrounding hot gas would glow in
ultraviolet rays. Instead, the ultraviolet glow of the dusty disk
abruptly drops off towards the center. This provides observational
evidence that the disk has a big donut hole encircling the central black
hole. The best explanation for the observational data, based on
dynamical models, is that the center of the disk is carved out by the
action of two black holes orbiting each other. The second, smaller
black hole orbits in the inner edge of the accretion disk, and has its
own mini-disk with an ultraviolet glow.
"We are extremely excited about this finding because it not only
shows the existence of a close binary black hole in Mrk 231, but also
paves a new way to systematically search binary black holes via the
nature of their ultraviolet light emission," said Youjun Lu of the
National Astronomical Observatories of China, Chinese Academy of
Sciences.
"The structure of our universe, such as those giant galaxies and
clusters of galaxies, grows by merging smaller systems into larger
ones, and binary black holes are natural consequences of these mergers
of galaxies," added co-investigator Xinyu Dai of the University of
Oklahoma.
The central black hole is estimated to be 150 million times the mass
of our sun, and the companion weighs in at 4 million solar masses. The
dynamic duo completes an orbit around each other every 1.2 years.
The lower-mass black hole is the remnant of a smaller galaxy that
merged with Mrk 231. Evidence of a recent merger comes from the host
galaxy's asymmetry, and the long tidal tails of young blue stars.
The result of the merger has been to make Mrk 231 an energetic
starburst galaxy with a star-formation rate 100 times greater than that
of our Milky Way galaxy. The infalling gas fuels the black hole
"engine," triggering outflows and gas turbulence that incites a
firestorm of star birth.
The binary black holes are predicted to spiral together and collide within a few hundred thousand years.
Mrk 231 is located 581 million light-years away.
The results were published in the August 14, 2015, edition of The Astrophysical Journal.
Contact
Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4514
villard@stsci.edu
Jana Smith
University of Oklahoma, Norman, Ok.
405-325-1701
jana.smith@ou.edu
Xinyu Dai
University of Oklahoma, Norman, Ok.
405-325-3961
xdai@ou.edu
Source: HubbleSite
