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Starts With A Bang

Meet the most supermassive pair of black holes ever found

Binary black holes eventually inspiral and merge. That’s why the OJ 287 system is destined for the most energetic event in history.
Although most galaxies have only a single supermassive black hole at their centers, some galaxies have two: a binary supermassive black hole. When these black holes inspiral and merge, they represent the most energetic events to occur in our cosmos since the Big Bang, and can outshine all the stars in the sky, combined, by a factor of many millions.
(Credit: NASA, ESA, and G. Bacon (STScI))
Key Takeaways
  • Black holes don’t just exist in isolation, but often come in pairs known as binary black holes.
  • While LIGO has detected merging stellar mass black holes, supermassive ones often come in pairs as well, which are also destined to merge.
  • The pair found in OJ 287 is the most extreme pair ever discovered, and when they merge, they’ll release more energy than any known event ever.

The closest supermassive black hole pair, in NGC 7727, was only recently discovered.

The galaxy NGC 7727 shows extended spiral arms: likely the aftermath of a recent major merger. The presence of two supermassive black holes inside this galaxy may be a prelude to the most major merger to occur in our local neighborhood in some time. (Credit: ESO/VST ATLAS team. Acknowledgment: Durham University/CASU/WFAU)

Just 89 million light-years away, these 154,000,000- and 6,300,000-solar-mass black holes are just 1,600 light-years apart.

A close-up (left) and wider-field (right) view of the central nucleus of the nearby galaxy NGC 7727. Just 89 million light-years away, it houses the closest pair of binary supermassive black holes known, with a separation of 1,600 light-years. These black holes ought to merge in just a few hundred million years, we think. (Credit: ESO/Voggel et al.; ESO/VST ATLAS team. Acknowledgment: Durham University/CASU/WFAU)

We’ve also discovered pairs of “double quasars,” with two supermassive black holes each.

The two quasar pairs seen above, when examined in detail by the Hubble Space Telescope, reveal that there isn’t a single supermassive black hole at the core of each, but rather two supermassive black holes separated by about 10,000 light-years each. This may be common in the early Universe; the merger timescale for these black holes should be less than a billion years according to the estimates of the study’s authors. (Credit: NASA, ESA, H. Hwang and N. Zakamska (Johns Hopkins University), and Y. Shen (University of Illinois, Urbana-Champaign))

Approximately 0.1% of young quasars are expected to be doubles, with typical separations of ~10,000 light-years.

This artist’s conception shows the brilliant light of two quasars residing in the cores of two galaxies that are in the chaotic process of merging. Although most galaxies possess only a single supermassive black hole, binaries may be present in a substantial fraction of galaxies, particularly young, early galaxies. (Credit: NASA, ESA, and J. Olmsted (STScI))

Until 2015, when PKS 1302-102‘s was identified, only one double supermassive black hole was known.

This simulation shows the radiation emitted from a binary black hole system. Although we’ve detected many pairs of black holes through gravitational waves, they’re all restricted to black holes of ~200 solar masses or below. The supermassive ones remain out of reach until a longer baseline gravitational wave detector is established. (Credit: NASA’s Goddard Space Flight Center)

That’s OJ 287, still the most extreme supermassive binary, 3.5 billion light-years away.

OJ 287
This image shows X-ray (emissions) and radio (contoured) data for OJ 287. This bright, face-on quasar is actually powered by not one, but two supermassive black holes. (Credit: A.P. Marscher & S. G. Jorstad, ApJ, 2011; NASA/Chandra and Very Large Array)

First spotted in 1887, it flares with a double burst every 12 years.

OJ 287
This view of the sky in the direction of OJ 287 shows what appears to be a single point of light indistinguishable from a star. However, it is no star, but a BL Lacertae object 3.5 billion light-years away, which is now identified as a pair of supermassive black holes, including one of the largest ever known. (Credit: Ramon Naves/Observatorio Montcabrer)

Its main black hole is enormous: 18.35 billion solar masses.

We typically measure black holes in solar masses, for stellar mass black holes, or in millions of solar masses, for supermassive ones. But some black holes, like OJ 287, extend into the billions of solar masses, making them the most massive individual objects of all-time. (Credit: NASA/JPL-Caltech)

Its event horizon is 12 times the size of Neptune’s orbit.

OJ 287
This diagram shows the relative sizes of the event horizons of the two supermassive black holes orbiting one another in the OJ 287 system. The larger one, of ~18 billion solar masses, is 12 times the size of Neptune’s orbit; the smaller, of 150 million solar masses, is about the size of the asteroid Ceres’s orbit around the Sun. (Credit: NASA/JPL-Caltech/R. Hurt (IPAC))

It also has a companion black hole of “merely” 150,000,000 solar masses.

When multiple black holes appear in the same vicinity as one another, they will interact with their environment via dynamical friction. As the matter gets either swallowed or expelled, the black holes become more tightly gravitationally bound. If the black holes are of unequal masses, the smaller one will lose more orbital energy than the larger one. (Credit: Mark Garlick/SPL)

The periodic double burst arises when the smaller black hole punches through the larger’s accretion disk.

OJ 287
This animation shows a lower-mass black hole punching through the accretion disk generated around a larger supermassive black hole. When the smaller black hole crosses through the disk, a flare emerges. (Credit: NASA/JPL-Caltech)

With a 12-year orbit, it varies from 0.05 to 0.28 light-years away from the primary.

OJ 287
The double peaks of the flare seen from OJ 287 is consistent with the smaller black hole punching through the larger’s accretion disk. The flare is thoroughly predictable with Einstein’s General Relativity. (Credit: L. Dey et al., ApJ, 2018)

The secondary black hole precesses 39° with every orbit: a fantastic confirmation of General Relativity’s predictions.

This illustration shows the precession of a planet’s orbit around the Sun. A very small amount of precession is due to General Relativity in our Solar System; Mercury precesses by 43 arc-seconds per century, the greatest value of all our planets. OJ 287’s secondary black hole precesses by 39 degrees per orbit, a tremendous effect! (Credit: WillowW/Wikimedia Commons)

In only ~10,000 years, these behemoths should merge.

Numerical simulations of the gravitational waves emitted by the inspiral and merger of two black holes. The colored contours around each black hole represent the amplitude of the gravitational radiation; the blue lines represent the orbits of the black holes and the green arrows represent their spins. The physics of binary black hole mergers is mass-independent. (Credit: C. Henze/NASA Ames Research Center)

Hopefully, humanity will be watching when it happens.

With three equally spaced detectors in space connected by laser arms, periodic changes in their separation distance can reveal the passing of gravitational waves of appropriate wavelengths. LISA will be humanity’s first detector capable of detecting spacetime ripples from supermassive black holes. (Credit: NASA/JPL-Caltech/NASAEA/ESA/CXC/STScl/GSFCSVS/S.Barke (CC BY 4.0))

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.