Two massive black holes are about to collide.  If they do, the explosion will be incalculable

Two massive black holes are about to collide. If they do, the explosion will be incalculable

Two massive black holes are about to collide. If they do, the explosion will be incalculable

Stars like our sun are violent creatures that constantly spew radiation, gamma rays and all sorts of nasty things (although luckily Earth’s ozone layer and the atmosphere protect us from the worst.) But when stars die, especially large ones, their wrath becomes even more ruthless. End-of-life stars of sufficient size will collapse and form a black hole. These singularities are defined by their gravitational pull, which is so incredibly strong that nothing – not even light – can escape. In other words, what happens in a black hole stays in a black hole.

But black holes aren’t too limited by size or number. On average, a standard black hole is about three to ten times the size of our sun. As massive as “ordinary” black holes can get, supermassive black holes – which probably form over billions of years when black holes merge – can reach a size millions or billions that of our nearest star. And the universe could be filled with billions of supermassive black holes. In fact, there is one at the center of our galaxy, the Milky Way, called Sagittarius A*, around which all things in the galaxy revolve.

The closest two supermassive black holes ever recorded are each about 200 million and 125 million times the mass of our sun.

Supermassive black holes really live up to their name, but if two collided and mutually enveloped each other, it would cause one of the most insanely large explosions in the universe – sending out reflections in the form of gravity waves that would ripple throughout the universe. Scientists recently announced the discovery of just such a situation: the closest two supermassive black holes on a collision course, at least that humans have detected so far. The discovery also suggests that black hole mergers are more common than previously believed.

Despite their relative frequency and inscrutable size, finding a supermassive black hole is no easy task. They don’t generate light, of course; so scientists have to deduce the size and location of black holes using indirect clues, such as how they distort spacetime, their effect on nearby stars, the speed of their orbit nearby starsand the detection of huge gravity waves which are created when black holes slam into each other. When this happens, two become one even bigger black hole.

To find these two supermassive black holes, a team of 29 scientists had to process a lot of data. They analyzed data from a dozen instruments across seven telescopes located around the globe and in orbit, including the Hubble Space Telescope, the Keck Observatory in Hawaii and the cluster of 66 radio telescopes in a desert in Chile known as the Atacama Large Millimeter Array. They looked at UGC 4211, a galaxy tucked away in the constellation Cancer.

The gap between them “is pretty close to the limit of what we can detect, which is why this is so exciting.”

No single observation was enough to locate these giant dead stars, but taken together the data paints a clear picture. At the center of UGC 4211 – technically two galaxies colliding into each other – is an extremely bright blob of matter called the active galactic nuclei (AGN). Astronomers believe that AGNs are caused by supermassive black holes, but as they looked more closely at the center of UGC 4211, they found not one black hole, but two. Their research was published this month in Astrophysical Journal Letters.

Both are about the same size, and they appear to be super close together — again, the closest two supermassive black holes ever recorded — and are each about 200 million and 125 million times the mass of our sun. Fortunately, these monstrosities are nowhere near us, some 480 million light-years away from the Milky Way.


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The gap between them “is pretty close to the limit of what we can detect, which is why this is so exciting,” Chiara Mingarelli, one of the study’s authors and an associate research scientist at the Flatiron Institute’s Center for Computational Astrophysics in New York City, said in a pronunciation.

“It’s important that with all these different images you get the same story — that there are two black holes,” Mingarelli added, comparing this new multi-observation study to previous efforts. “This is where other studies [of close-proximity supermassive black holes] have fallen in the past. When people followed them, it turned out that there was only one black hole. [This time we] have many observations, all in agreement.”

Eventually, the two supermassive black holes will collide, but it won’t happen anytime soon. Although these two giant dead stars are closer together than any of the other supermassive black holes we’ve detected, they’re still about 750 light-years apart. This inevitable collision will probably not occur for another hundred million years.

But when it does, the surge of energy it will blast into space will be beyond comprehension. First, the two former stars will orbit closer and closer, eventually colliding and emitting gravitational waves greater than anything humans have ever recorded before. Currently, the largest black hole merger ever detected by Earth’s gravitational wave observatories has led to a new black hole with a mass of 142 solar masses (or 142 times the mass of our sun). Upon merging, eight solar masses were removed from the universe and immediately converted to energy in the form of gravitational waves. When these two supermassive black holes merge, the energy release will be exponentially greater.

This research is about much more than just finding cool space objects. It could help us better understand the evolution and life cycles of stars and could help astronomers locate more black holes in the nearby universe. In turn, this information could help researchers better calibrate gravitational wave-detection devices. Black holes may be mysterious and hard to find, but it just got a little easier to know how and where to look.

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