Astronomers have started monitoring about a million massive stars to see if any suddenly vanish, seemingly without a trace. Such a disappearing act would support a theory that some massive stars simply implode when they die, rather than exploding in brilliant supernovae or gamma-ray bursts.
As a massive star ages, it accumulates iron in its core. Eventually, this iron core grows so massive that it is crushed by its own gravity, forming a black hole.
Sometimes the process is accompanied by a supernova, when the star's outer layers explode outwards to produce a brilliant flash of light at visible wavelengths. In rare cases, black hole births are even more spectacular, with the star firing out powerful jets of high-energy radiation as it dies – a phenomenon known as a gamma-ray burst.
But as many as half of black hole births may happen more stealthily, with no explosion to mark the event. A new survey led by Christopher Kochanek of Ohio State University in Columbus, US, may detect these events by watching massive stars suddenly wink out.
The survey, which uses the 8.4-metre Large Binocular Telescope (LBT) on Mount Graham, Arizona, US, took its first images in early 2008. It is monitoring about 1 million red supergiant stars – massive stars in the final stage of their lives – in 30 nearby galaxies.
The team plans to take images of the galaxies twice per year, watching for the sudden disappearance of the red supergiants. By watching 1 million stars, the team hopes to catch about one stellar death per year in their survey, which will last five years.
"There's no guarantee that you'll find these things – because it could just be that they all do a supernova at some level," Kochanek told New Scientist. "But that's no reason not to give it a try."
Stan Woosley of the University of California in Santa Cruz, US, who does theoretical studies of stellar deaths, agrees. "My own view is that it is impossible to make a black hole without some sort of electromagnetic display," he told New Scientist.
But perhaps there are cases where the radiation comes out in the form of X-rays or gamma rays, he says, rather than the visible light astronomers normally look for when searching for supernovae. "In any case, it is worth looking."
If a star seems to disappear, the team will try to confirm the formation of a black hole by looking for X-rays emitted by stray bits of matter falling into the black hole, Kochanek says.
In addition to clarifying what proportion of black holes are born without fanfare, the survey may also detect rare, giant outbursts from massive stars that are close to going supernova. Such an outburst in the 1840s temporarily made a star called Eta Carinae the second brightest star in the sky.
Journal reference: Astrophysical Journal (in press)
By Nick
Sat May 10 00:43:44 BST 2008
Fans of British SF author Peter F. Hamilton will recognise the significance of this.By Greg
Sat May 10 06:26:10 BST 2008
Dyson spheres would require a stable star with a long lifespan. Most importantly if such a thing were to exist we would not see it at all since the sphere would block all of the radiation from the star it surrounds.By Nick
Sat May 10 08:06:28 BST 2008
Precisely, which is why I refer to Hamilton's writings, and not Freeman Dyson's ;)By Anon
Sat May 10 06:31:42 BST 2008
"By watching 1 million stars, the team hopes to catch about one stellar death per year ..." would they therefore predict no red giants visible in the universe in about a thousand years?By Mader
Sat May 10 12:00:01 BST 2008
First, you wanted to say "about a milion years". Funny that you complaint of somebody other math.By Koalabeer
Sat May 10 16:36:12 BST 2008
Well, Mader and anon, it's 1,000,000 red giants in 30 nearby galaxies- a piffling amount of the universe. To look at it another way, if the project finds (ahem, I mean loses) one star in 10 years, then there's probably something of the order of 100,000,000...... Red giants imploding with a whimper that just disappeared with no-one to mourn them.By William Smith
Sun May 11 22:34:36 BST 2008
This survey is of red supergiant stars which only last from 100,000 to one million years before they collapse into a black hole so in one million years all the stars being surveyed will indeed have disappeared.All comments should respect the New Scientist House Rules. If you think a particular comment breaks these rules then please use the "Report" link in that comment to report it to us.
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