New Possibilities for Black Holes

by Clifford Johnson     Department: Physics & Chemistry

There's been a rather interesting discovery announced recently, by a team of scientists led by Jerome Orosz of San Diego State University. It is a black hole about 16 times the mass of our sun. You might say in response to this "big deal, aren't we already aware of black holes millions of times the mass of our sun, lurking at the cores of galaxies?" (Have a look here at Andrea Ghez's group's website here for information about  a big one at the centre of our very own Milky Way!)  So sure, if those are already known about, what's the fuss about one that's 16 times the solar mass?

Well, the issue is that these smaller holes (sometimes called "stellar" black holes) form from the collapse of stars, when their normal phase of operation (supporting themselves against gravitational collapse through nuclear processes) stops. There's a complicated process of collapse of a lot of stellar material (typically from stars more than 20 times or so the mass of our sun) into a black hole that involves the ejection of a lot of the material, forming stellar black holes that are considerably less massive - up to about ten times the mass of our sun. A  lot of computer simulations of the processes give results consistent with these sorts of numbers.

The significance of the new discovery (through observations that reportedly give rather reliable estimates of the mass) of a sixteen solar mass hole is that it lies outside expectations and current understanding of how stellar black holes form. Puzzles of this sort are exciting, as they point to new science - new processes not thought of or yet appreciated. So the quest is to understand why and how such large stellar black holes can form. This is a new conundrum for Astrophysicists. The very process by which the black hole has been studied (by observations of a partner star  that orbits it, passing in front of it creating a blink every three days or so) is probably a clue to what's going on. The presence of and interaction with the companion star may well give clues to the new formation process, although there's probably going to have to be a lot of new ideas explored (and tested via simulations) before the details are pinned down. Of course, this also means that there'll be keen eyes looking for new examples of this sort of stellar black hole. More examples will give more clues to pinning down exactly what's going on.

For more information, have a look at this space.com article,  this this AFP article (via Yahoo News), and especially this press release from the Chandra X-ray Observatory. The scientific paper on this result came out  today in the journal Nature.

-cvj

Tags: astronomy, black holes

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