

Talk about problems with obesity. Astronomers have discovered a massive, record-setting black hole in a nearby galaxy that is confounding theories of how such objects should form.

The 3-million-light-year-distant M33 X-7 is apparently about 15.7 times the mass of our Sun, making it the most massive black hole created from the collapse of a star yet observed, researchers say. But as part of a binary star system, orbiting a star fully 70 times the mass of the Sun, it presents a whole range of puzzles, and a fascinating future. Says Jeffrey McClintock, of the Harvard-Smithsonian Center for Astrophysics:

"This is a huge star that is partnered with a huge black hole. … "Eventually, the companion will also go supernova and then we’ll have a pair of black holes."

The ponderous star-black hole system is so far leaving scientists scrambling to explain how it could exist.

Under normal theories of star evolution, the black hole must have originally had a mass larger than its chunky companion, in order to collapse first. But if that was true, the now-collapsed star should also have had a radius larger than the current distance between the two companions, so that the two would have shared a common outer atmosphere.

But if that was true, scientists would ordinarily expect a huge quantity of mass to have been lost from the binary system – so much so that the black hole observed today shouldn’t now be as large as it seems to be. To wind up with what researchers see, the original giant star must have shed material about 10 times slower than predicted before going supernova, and collapsing.

So, Americans, take comfort. Dieting is tricky even in outer space.

Along with setting all kinds of records, and promising a deliciously explosive future, the binary system offers the first look at a black hole that undergoes eclipses from our point of view, as it rotates around its companion star. That’s giving researchers using NASA’s

Chandra X-ray Observatory and the Gemini telescope on Mauna Kea, Hawaii the ability to make unusually precise estimates of its mass.



Heaviest Stellar Black Hole Discovered in Nearby Galaxy [Chandra press release]

(Image: Artist’s representation of binary system, with inset composite image of M33 X-7. Source: Illustration: NASA/CXC/M.Weiss; X-ray:

NASA/CXC/CfA/P.Plucinsky et al.; Optical: NASA/STScI/SDSU/J.Orosz et al.)