The Silent Black Hole

[Radical Edward]

There is a really interesting looking article in http://sciencenow.sciencemag.org/

 

could someone with access and interest have a look at it and maybe do a summary?

 

 

thanks

 

there is also one on titan somewhere too.

[fafalone]

http://sciencenow.sciencemag.org/cgi/content/full/2003/424/2

 

Supernovas, the explosive deaths of massive stars, often herald the births of black holes. But a rare breed of black hole may enter the universe with a phffft, not a boom. Astronomers have found one of them drifting so slowly through space that they believe its parent star morphed into a black hole without blowing up.

 

According to theory, a black hole arises when a giant star runs out of fuel for thermonuclear fusion. The star's core collapses, igniting a shock wave that blasts the rest of the star into space. If the collapsing core is a few times the mass of our sun, gravity will crush it into an infinitely dense speck. However, models predict that rare stars at least 40 times heftier than our sun should plummet directly into black holes without exploding, because their massive outer layers snuff the shock wave like the heavy lid of a pressure cooker. Until now, astronomers had no firm evidence that was true.

 

To trace the origins of black holes in our galaxy, astronomer I. Félix Mirabel of the French Atomic Energy Commission in Saclay and colleagues have observed the motions of binary systems in which suspected black holes rip gas off companion stars. X-rays and radio waves from the hot gas pinpoint the holes. Recently, Mirabel detected one binary jetting through space at 120 kilometers per second--a sure sign that a supernova drastically boosted its speed (ScienceNOW, 19 November 2002. His group's newest discovery, published online 24 April in Science, reveals the opposite: a binary poking along at a sluggish 9 kilometers per second.

 

This binary system, called Cygnus X-1, appears to be part of an association of massive stars drifting through the Milky Way at about the same pace, Mirabel says. His calculations show that the parent star ejected no more than one sun's worth of mass when the black hole formed--far too small for a supernova blast. A bigger boom would have booted the binary system at higher speed--and probably not in the same direction as its peers, Mirabel notes. The original star probably contained between 40 and 100 times our sun's mass and then lost most of it during intense winds, he says. When the star died, its remaining gas vanished silently into a black hole of about 10 solar masses.

 

The argument is convincing, says supernova modeler Chris Fryer of Los Alamos National Laboratory in New Mexico. For a star of this size, a nonexplosive collapse would be expected, he says, "and this is probably the strongest case." Still, Fryer thinks that only about one in 10 black holes should form in this way, because most stars are less massive--and far more likely to detonate.

--ROBERT IRION

 

BELOW: Adrift. A slowly moving black hole revealed by bright x-rays (inset) moves at the same rate as other stars, suggesting a supernova did not explode.

CREDIT: I. F. MIRABEL AND I. RODRIGUES, CEA-SACLAY/NASA MSFC (INSET)