Astronomers have detected a supermassive black hole tearing apart a passing star. Not only is the catastrophe closer to Earth than ever before, but its location and light emission are also unusual, suggesting a large unseen crowd at these events.
Black holes are notorious for devouring anything that comes too close, including stars. But it’s not a clean little thing — a black hole is a lot messier than you might think, sticking things out and throwing matter all over the place. When stars come on the menu, they emit bright flashes that can be seen throughout the universe in what astronomers call tidal disruption events (TDEs).
These TDEs are considered to be fairly common occurrences, with around 100 detected so far, but the new detection, designated WTP14adbjsh, is significant for a few reasons. First and foremost, it is the closest event ever observed, at a distance of 137 million light-years. That may not sound very close, but previous record holders were more than 200 million light-years away, and most were farther.
It also comes from a different type of galaxy than usual. Most TDEs are detected in relatively quiet galaxies, but WTP14adbjsh occurred in a galaxy that was actively forming new stars. It makes sense that these types of galaxies would host TDEs on a regular basis, as black holes are increasingly fed, but oddly enough, these detections have remained elusive.
However, the new TDE hints at why this is the case. The dying throes of these stars are usually bright in visible light and X-rays, but WTP14adbjsh doesn’t stand out at these wavelengths — instead, it’s bright in the infrared. Star-forming galaxies tend to be dusty places, so the usual optical and X-rays are blocked, while infrared light penetrates well through the veil.
Scientists aren’t specifically looking for TDEs. Instead, they are studying ephemeral signals in data captured by the NEOWISE mission, which scans the sky in infrared light. In doing so, they detected a celestial flash that began in late 2014, peaked in 2015, and then began to dim again. After ruling out other possibilities like a supernova, the clean light curve and timing told the team it was a TDE.
The discovery could explain why these events appear to occur far less often than they should — astronomers have been looking for them the wrong way.
“Finding this TDE nearby means that, statistically speaking, there must be a large number of these events that cannot be detected by traditional methods,” said Christos Panagiotou, lead author of the study. “So, if we want a complete picture of a black hole and its host galaxy, we should try to find these in the infrared.”
The study was published in The Astrophysical Journal Letters.