By Michael D. Lemonick
They’re huge. They’revoracious. They’re blacker than a panther on a moonless night. They’re black holes, the mind-bending, space-warping cosmic objects with gravity so insanely powerful that even a beam of light that wanders too close will be sucked in, never to emerge. Einstein’s theory of general relativity predicted they might exist, but the great physicist himself doubted it would really happen.
Einstein was wrong. Over the past decade or two, black holes have been discovered all over the place — small ones peppered around the Milky Way and huge ones, impressively called “supermassive” black holes, lurking the centers of galaxies. The one at the core of Milky Way weighs as much as a couple of million stars, and it could swallow the sun without even noticing, the way you’d swallow a pistachio.
But that’s positively puny compared with the two new black holes, each about 330 million light-years away or so, just announced in the journal Nature. The smaller one, located inside a galaxy known as NGC 3842, is as massive as 9.7 billion suns, and the other, in a galaxy called NGC 4889, is more than twice as large: if you put it on a very large balance, it would take at least 21 billion stars to even things out. Another way to think about things: even the smaller of the two is nearly 30% bigger than the previous record holder, announced last winter, and it would make for a great storyline if astronomers were surprised, amazed, flabbergasted, blown away by the awesome giganticness of these monsters. Truthfully, though, they kind of expected it. “If we infer the existence of quasar black holes of ten billion solar masses at early cosmic times,” Harvard theorist Avi Loeb told Nature’s Ron Cowen for the journal’s online news blog, “we’d better find their counterparts in the present-day Universe.”
Loeb is referring to quasars — beacons of light so intensely bright they can be seen halfway across the universe. When astronomers first spotted them in the late 1950s, nobody knew what they were. Nowadays, everyone pretty much agrees that quasars are supermassive black holes at the cores of young galaxies. The holes themselves aren’t visible, of course, but when they suck in surrounding matter, the stuff heats up to millions of degrees, sending bursts of energy shooting across the cosmos.
Back when the universe was young, there was plenty of gas floating around to feed these monsters. Nowadays, much of it the gas is gone, and so are the quasars — but the black holes that powered them should, as Loeb says, still be around (where would they go, after all?). Now, thanks to some of the world’s most powerful telescopes, astronomers know that indeed they are. While scientists can’t see the black holes directly, they can see stars whipping around at high speeds in the two galaxies’ cores — and by clocking those speeds carefully, the astronomers can calculate how big and how dense the object they’re orbiting must be. In each of these cases, nothing but a supermassive black hole fits the bill.
Such observations are technically difficult, so in one sense the latest black-hole discoveries are extraordinary. Still, astronomers expected to find such things all along, so it might not seem like such a big deal to space experts. Indeed, Martin Rees, the British astronomer royal, dubbed the new results “an incremental step” in the New York Times, with nary a word about shock or awe. If you’ve got a professional interest in how black holes were born and how they evolved, this is more grist for the mill.
For the rest of us — well, they’re just kind of awesome.