Posted on 03/12/2005 11:53:27 AM PST by LibWhacker
The corpses of three "dead" galaxies - which to the surprise of astronomers stopped forming stars long ago - have been identified by the Spitzer Space Telescope during a survey of the distant, early universe. The find bolsters a theory that colossal black holes can starve galaxies of the gas needed to create new stars.
An infrared telescope on Earth first found the galaxies two years ago. They appeared red - a sign that most of their stars were old. But our planet's own heat clouded the observations, making it impossible to rule out whether dust was obscuring the light from younger stars.
Now, using NASA's Spitzer telescope, which trails behind the Earth in the coldness of space, astronomers have determined the galaxies are red because they are dead - no stars appear to have formed for 1.5 billion years. That arrested development happened early in the history of the universe - their distance means Spitzer is viewing them just 2 billion to 3 billion years after the big bang.
"We think galaxies form over tens of billions of years," says lead researcher Ivo Labbé, an astronomer at the Carnegie Observatories in Pasadena, California, US. For example, he notes the 13 billion-year-old Milky Way is still forming stars today. "Surprisingly, we found galaxies that are fully formed and dead when the universe was only one-fifth its present age."
No freak monsters
The researchers estimate a significant fraction of galaxies in the early universe were dead - just 10 times as many exist today. "It means these are not freak monsters," Labbé told New Scientist.
David Hogg, a cosmologist at New York University, who is not part of the team, agrees. "What is most impressive to me is that a significant fraction of the galaxies look 'long dead', which does suggest that some kinds of galaxies could be fully in place at very early times," he says.
Labbé believes that black holes lurking inside the galaxies were their undoing. The galaxies appear to be as massive as the Milky Way and like our galaxy, may harbour "supermassive" black holes containing the mass of millions of Suns. Gas falling into these black holes may have spawned powerful outpourings of energy, creating what astronomers call "active" galaxies.
This enormous energy is thought to heat the gas remaining throughout the galaxy to tens of millions of degrees.
Turned off
Lars Hernquist, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, recently published computer simulations of this heating phenomenon.
"Eventually the gas is so hot, it is no longer bound to the galaxy and simply starts to flow out to space," Hernquist told New Scientist, a process that takes about 10 million years. When it is over "star formation is turned off", says Hernquist. "The galaxy will just sit there and the stars will become older. I think this is a very likely explanation of what's being seen in these galaxies."
Another possibility is that supernovae exploding within the galaxies blow gas out to space, but both Labbé and Hernquist say this is a less efficient mechanism.
The research will be published in a future issue of the Astrophysical Journal Letters.
Ping!!
Just like Ted Kennedy.
"no stars appear to have formed for 1.5 billion years"
It's those damned "go growth" enviros. Made it darn-near impossible to get a new star permit.
"no stars appear to have formed for 1.5 billion years"
Course, same can be said of Hollywood for the past few decades.
Or "lite flight" maybe.
Better dead then red. But it sucks even more to be both.
ET, pay your bills next time!
Have they dropped this info into the Kyoto Treaty yet?
Must... not... make... bad... political... joke...
Fascinating. Bump for later reading.
...no stars appear to have formed for 1.5 billion years.
Given the first statement, how can they determine the second? Heck, how can they determine that no stars have formed in that period at all?
Calculated by the amount of time it takes light to travel the distance from the red galaxy. The farther away somthing is, the older its immage.
What'd you expect with all that "galactic warming".
Actually, I'm curious how you heat galactic gasses to the extent described. Don't the gasses have to exist in some concentration to heat up (and stay heated)? I'm no physicist, so just wondering.
Gravity clumping.
" Gravity clumping."
Sounds like a cat litter.
They are relying on the standard model of stellar evolution. Young stars have a range of characteristic spectra and old stars have another. If they see only spectra of older stars and none younger than 1.5 billion years, then they assume by the model that there are no stars younger than 1.5 billion years, or at least not enough young stars to show up to our instruments at that distance.
ping
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