Astronomers have detected a supermassive black hole ripping a passing star to shreds. Not only was this cataclysm closer to Earth than ever seen before, but its location and light emissions were unusual, hinting at a large unseen population of these events.
Black holes are notorious for gobbling up anything that gets too close, and that includes stars. But it’s not a neat little slurp – black holes are far messier eaters than you might expect, stretching objects out and throwing matter all over the place. When stars are on the menu, they give off bright flashes of light that can be seen across the cosmos, in what astronomers call a tidal disruption event (TDE).
These TDEs are thought to be fairly common occurrences, with around 100 of them detected so far, but the new detection, designated WTP14adbjsh, is significant for a few reasons. First and foremost, it’s the closest event seen yet, at a distance of 137 million light-years. That might not sound very close, but the previous record-holder was over 200 million light-years away, and most are much farther.
It also came from a different type of galaxy than usual. Most TDEs are detected in relatively quiet galaxies, but WTP14adbjsh occurred in a galaxy that’s actively forming new stars. It would make sense that these kinds of galaxies would regularly host TDEs, since there’s an increasing amount of food for black holes, but strangely enough, these detections remain elusive.
However, the new TDE hints at why that might be the case. The death throes of these stars are usually bright in optical and X-ray light, but WTP14adbjsh didn’t stand out in those wavelengths – instead, it was bright in infrared. Star-forming galaxies tend to be dusty places, so the usual optical and X-ray light would be blocked, while infrared can pierce the veil just fine.
The scientists weren’t specifically looking for TDEs. Instead, they were studying short-lived signals in data captured by the NEOWISE mission, which scans the sky in infrared. In doing so, they spotted a celestial flash that began in late 2014, peaked in 2015, and then started dimming again. The clean light curve and timing told the team it was a TDE, after eliminating other possibilities like supernovae.
The discovery could shed some light on why these events seem much rarer than they should be – astronomers have been looking for them in the wrong ways.
“Finding this nearby TDE means that, statistically, there must be a large population of these events that traditional methods were blind to,” said Christos Panagiotou, lead author of the study. “So, we should try to find these in infrared if we want a complete picture of black holes and their host galaxies.”
The research was published in The Astrophysical Journal Letters.
Source: MIT
