Oddly Quiet Black Hole Spotted Around Fast-Spinning Star

Astronomers have found a quiescent black hole orbiting a massive, fast-rotating star, suggesting that these strange binary systems may be common throughout the Milky Way galaxy.

The huge star MWC 656, known as a “B-emission” or “Be” star, shares space with a companion stellar-mass black hole, researchers report in a study published today (Jan. 15) in the journal Nature. Surprisingly, the black hole emits no X-ray radiation, explaining how the object had eluded detection until now.

“It is important to note that only black hole with a massive stellar companion is known in the galaxy — the bright X-ray source Cyg X-1,” study lead author Jorge Casares, of the Instituto de Astrofisica de Canarias in the Canary Islands, told SPACE.com via email. “Our discovery suggests many more black holes with massive companions may exist in the form of quiescent Be binaries.”

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You don’t normally think of gravitationally collapsed objects orbiting gravitationally uncollapsed objects.

Bubblecar said:

You don’t normally think of gravitationally collapsed objects orbiting gravitationally uncollapsed objects.

You are right you know.

Bubblecar said:

You don’t normally think of gravitationally collapsed objects orbiting gravitationally uncollapsed objects.

Yes and no. :) Consider, Sirius B is a white dwarf (so it’s composed of electron-degenerate matter and not totally gravitationally collapsed) in mutual orbit with the more massive Sirius A. However, Sirius B was originally the more massive but shed a lot of matter in the process of turning into a WD; some of that matter was consumed by Sirius A.

http://en.wikipedia.org/wiki/Sirius

>It is predicted that Sirius A will have completely exhausted the store of hydrogen at its core within a billion (109) years of its formation. At this point it will pass through a red giant stage, then settle down to become a white dwarf.

I wonder which will be orbiting which by then.

I wonder which will be orbiting which by then.

they will be orbiting a common barycentre and its position will depend on the mass of the two objects.

Bubblecar said:

>It is predicted that Sirius A will have completely exhausted the store of hydrogen at its core within a billion (109) years of its formation. At this point it will pass through a red giant stage, then settle down to become a white dwarf.

I wonder which will be orbiting which by then.

Well, the mass ratio is currently roughly 2:1, so even now it’s sensible to say they orbit each other. It’s not obvious from the orbit diagrams on that Wiki page, and I can’t find an orbit diagram that uses their mutual centre of mass as the origin, but the diagram at the bottom of this page is pretty good, although it does have some distortion because it’s looking at the Sirius system at an angle instead of perpendicular to the orbital plane.

PM 2Ring said:

Bubblecar said:

>It is predicted that Sirius A will have completely exhausted the store of hydrogen at its core within a billion (109) years of its formation. At this point it will pass through a red giant stage, then settle down to become a white dwarf.

I wonder which will be orbiting which by then.

Well, the mass ratio is currently roughly 2:1, so even now it’s sensible to say they orbit each other. It’s not obvious from the orbit diagrams on that Wiki page, and I can’t find an orbit diagram that uses their mutual centre of mass as the origin, but the diagram at the bottom of this page is pretty good, although it does have some distortion because it’s looking at the Sirius system at an angle instead of perpendicular to the orbital plane.

Good thing I read to the end of the thread because you answered my question.

It’s true of everything though, isn’t it? Just that often the centre is not within either object.

yes, see my answer. just add an es to the end of mass.

It’s true of everything though, isn’t it?
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Yes everything is balanced on a pivot.

The pivot of course… jumps all over the frecken place.