A team of astronomers at the McDonald Observatory have reported a remarkable discovery – a black hole choking on a star.
The discovery came as the team was searching for supernovae – exploding stars that produce an extremely bright flash in the sky. They were using the ROTSE IIIb – a small telescope by the McDonald Observatory standards.
“You take a picture, you go back a couple of days or a week later, you take another picture and you see whether any galaxy in the field of view has erupted with a new light in it,” says Craig Wheeler, professor of astronomy at the University of Texas at Austin.
But one day in 2009, the telescope captured an event that didn’t quite fit the bill of a supernovae.
“It went off, it got very bright, it was up into the luminosity of what we would call a super luminous supernovae, but as we studied it and collected data, with the big Hobby-Eberly Telescope – it just didn’t have the properties of a supernovae, it didn’t show the kind of light signals and specific features,” says Wheeler.
The astronomers were in the habit of naming the events they captured, and this one got the name “Dougie.”
“We used Star Wars characters, we were running through South Park at this point and named this one after the character, ‘Dougie’,” says Wheeler.
Over the next five years, Dr. Wheeler and his colleagues analyzed Dougie, and just last week they published their results. It turns out that Dougie was something special.
“We ruled out a whole bunch of other things, but very early on in the game, we suspected that it might be a black hole pulling a star apart, a tidal disruption,” says Wheeler.
We’re familiar with tidal forces here on Earth; the mass of the Moon and Sun pull on our oceans and cause the tides. But a black hole can be millions of times more massive than our Sun, so its effect on nearby objects is extreme.
“If a star gets near a black hole, the black hole will pull harder on one side of the star, the near side, than it will the far side, and you stretch the star out into a noodle and you can completely tear it apart,” explains Wheeler.
And this is what was happening with Dougie.
“Gas from the disrupted star spirals around and falls down into the black hole and produces light in the process, before it falls down into the black hole and disappears. So what we saw was the flash of light as the star came apart,” says Wheeler.
Dr. Wheeler says these events are rare, perhaps a dozen have been witnessed, but Dougie was unique. The destroyed star was falling into the black hole so fast that the black hole was essentially choking on the star matter.
“As matter falls into a gravitating object, it will get hot, and it will create radiation, and if that radiation is intense enough, it will push back outward on the matter, and prevent it from falling inward. That’s where the choking process is,” explains Wheeler.
A cosmic event like Dougie is rare enough that Wheeler doesn’t expect to see another one with the small ROTSE IIIb telescope. But, advancements in new technologies may allow for astronomers to see more tidal disruption events in the future.
– Ian Lewis