Six hundred million light years away, a pair of black holes spiral furiously about one another at the brilliant core of a starburst galaxy.
Black holes are usually lone wolves, devouring light and matter at centres of their galaxies. But when galaxies collide, two black holes can in theory become locked in a gravitational embrace, much like a binary star. This is the first confirmed instance of the phenomena.
The dynamic duo in question lives at the centre of Markarian 231, the nearest galaxy to host a bright star-forming core known as a quasar. Astronomers discovered the black hole pair using Hubble data on the quasar’s UV light spectra:
If only one black hole were present in the centre 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 toward the centre. This provides observational evidence that the disk has a big doughnut hole encircling the central black hole.
The best explanation for the doughnut hole in the disk, based on dynamical models, is that the centre 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.
The binary system seems to have formed when a small galaxy bumped into Mk 231, adding a black hole of four million solar masses to a system whose resident black hole weighs 150 million Suns. As the swirling binary swallows nearby gases, it releases tremendous outflows of energy, amping up star formation in the surrounding region of space.
Eventually, the two black holes are going spiral into one another in an epic cosmic collision that will certainly spell doom for any Cylons foolish enough to have set up base on the event horizon. But for astronomer, the distant demise of this system is no great tragedy: After all, there could be plenty of other double-hearted quasars out there waiting to be discovered.
[NASA]
Top image: Artist’s concept of the binary black hole found in the center of Markarian 231, via NASA, ESA, and G. Bacon (STScI)