Unlucky stars serve as brilliant but short-lived snacks when they wander too close to supermassive black holes. But one such black hole is still gnawing on its stellar meal after a decade.
More than a decade ago, a million-solar-mass black hole lurking in the center of an unremarkable galaxy, known only as SDSS J150052.07+015453.8, snagged itself a nearby star for a snack. But unlike most such tidal disruption events, where a black hole's extreme gravity tears a star apart before swallowing its gas in the next year or two, this was the snack that kept on giving.
Astronomers caught the event serendipitously — its light traveled 1.8 billion years to the XMM-Newton X-ray telescope, which snapped it by chance while imaging a galaxy group in the foreground. The Chandra X-ray Observatory and Swift space telescope also kept tabs on the source too. Though it brightened quickly, to astronomers' surprise the flare has been slow to fade. Even 10 years after its discovery, it's still ten times brighter in X-rays than it was before the flare.
So what does it mean that this star-killer is a record-breaker? Dacheng Lin (University of New Hampshire) and colleagues have two theories: one is simply that the star is bigger and so took longer for the black hole to tear apart. If that were true, the star might have had the mass of 10 Suns. But such massive stars are rare (less than 1% of the stellar population), so an alternative is more likely: the black hole simply took its time to make the kill, ripping the star apart completely before devouring it.
Whatever the means of the decade-long meal, Lin and colleagues can see from the X-rays this object is emitting that the supermassive black hole is feeding at a tremendous rate — so high that pressure from the emitted radiation ought to blow away the gas that's flowing inward. In astrospeak, this gorging is known as super-Eddington accretion. Yet somehow, the black hole is not only feeding at a super-Eddington rate, it has kept up that rate for most of the past ten years.
Astronomers have long wondered how the universe can grow supermassive black holes so fast. We see black holes containing the mass of 1 billion Suns when the universe is just 1 billion years old — numbers that are hard to replicate in calculations based on the Eddington limit. Now we have evidence that these beasts can feed faster than we thought for prolonged periods, so there's a good chance that supermassive black holes in the early universe fed in this way too.
To read more about this intriguing black hole and its decennary dining habits, see the press release issued by the Chandra X-ray Observatory:
Black Hole Meal Sets Record for Length and Size
A giant black hole ripped apart a star and then gorged on its remains for about a decade, according to astronomers. This is more than ten times longer than any observed episode of a star's death by black hole. . . . Read more or watch their video here.