Breaking News on Black Holes: They “Waltz” in Pairs, Rip Stars Apart
Waltzing black holes, star-destroying black holes; it’s a black hole bonanza as the American Astronomical Society meets this week in Washington DC.
First, the orbiting pairs: Just about every galaxy has a supermassive black hole at its heart that is millions if not billions the size of our sun. Logic would suggest that when two galaxies merge, astronomers would see the two great black holes orbiting each other, but so far they’ve had tough luck, astronomer Julie Comerford says. “We expect the universe to be littered with these waltzing black holes,” Comerford said. “But until recently, only a few had ever been found.” Those missing black hole pairs posed problems for theories of how galaxies merge and grow [Wired.com].
Comerford, however, announced at the meeting that her team has found 33 new pairs of black holes in galactic centers. When the black hole dances toward Earth, its light is blueshifted — meaning it has a shorter wavelength. The team identified waltzing pairs by looking for instances when one black hole was blueshifted and the other redshifted [Wired.com]. Those black holes orbit each other at 200 km per second, but they’re not in a close embrace—several thousand light years separate each pair.
Next, the star destroyers: Astronomers see plenty of supermassive black holes, whether paired or not. And they see lots of black holes close to our sun in mass, like the kind a single star’s supernovae creates. But what about the black holes in between? Black holes measuring in the range of hundreds to thousands of solar masses have only existed in theory up till now and observational evidence of these “medium-sized” singularities has been very hard to come by [Discovery News].
The Chandra X-Ray Observatory, however, just discovered one of these intermediate black holes. Not only did Chandra catch a black hole in the missing size hanging around a globular cluster, it also caught the black hole in the process of ripping apart a star. In this case, that star was probably a white dwarf: The observations suggest oxygen is in abundance, but there is a deficiency in hydrogen, suggesting that the material was being stripped from an old, white dwarf star. (The lack of hydrogen shows that the stellar object has burnt up its fuel) [Discovery News].
For more on the Chandra discovery, check out Phil Plait’s Bad Astronomy post. And for more about how black holes could have shaped the early universe, read the DISCOVER story “Are Black Holes the Architects of the Universe?”
Image: NASA / Chandra