Spitzer finds distant galaxies grazed on gas

June 30, 2011
This split view shows how a normal spiral galaxy around our local universe (left) might have looked back in the distant universe, when astronomers think galaxies would have been filled with larger populations of hot, bright stars (right). Image credit: NASA/JPL-Caltech/STScI

(PhysOrg.com) -- Galaxies once thought of as voracious tigers are more like grazing cows, according to a new study using NASA's Spitzer Space Telescope.

Astronomers have discovered that galaxies in the distant, continuously ingested their star-making fuel over long periods of time. This goes against previous theories that the galaxies devoured their fuel in quick bursts after run-ins with other galaxies.

"Our study shows the merging of was not the dominant method of galaxy growth in the ," said Ranga-Ram Chary of NASA's Spitzer Science Center at the California Institute of Technology in Pasadena, Calif. "We're finding this type of galactic cannibalism was rare. Instead, we are seeing evidence for a mechanism of galaxy growth in which a typical galaxy fed itself through a steady stream of gas, making stars at a much faster rate than previously thought."

Chary is the principal investigator of the research, appearing in the Aug. 1 issue of the . According to his findings, these grazing galaxies fed steadily over periods of hundreds of millions of years and created an unusual amount of plump stars, up to 100 times the mass of our sun.

"This is the first time that we have identified galaxies that supersized themselves by grazing," said Hyunjin Shim, also of the Spitzer Science Center and lead author of the paper. "They have many more than our ."

Galaxies like our Milky Way are giant collections of stars, gas and dust. They grow in size by feeding off gas and converting it to . A long-standing question in astronomy is: Where did distant galaxies that formed billions of years ago acquire this stellar fuel? The most favored theory was that galaxies grew by merging with other galaxies, feeding off gas stirred up in the collisions.

Chary and his team addressed this question by using Spitzer to survey more than 70 remote galaxies that existed 1 to 2 billion years after the Big Bang (our universe is approximately 13.7 billion years old). To their surprise, these galaxies were blazing with what is called H alpha, which is radiation from hydrogen gas that has been hit with ultraviolet light from stars. High levels of H alpha indicate stars are forming vigorously. Seventy percent of the surveyed galaxies show strong signs of H alpha. By contrast, only 0.1 percent of galaxies in our local universe possess this signature.

Previous studies using ultraviolet-light telescopes found about six times less star formation than Spitzer, which sees infrared light. Scientists think this may be due to large amounts of obscuring dust, through which infrared light can sneak. Spitzer opened a new window onto the galaxies by taking very long-exposure infrared images of a patch of sky called the GOODS fields, for Great Observatories Origins Deep Survey.

Further analyses showed that these galaxies furiously formed stars up to 100 times faster than the current star-formation rate of our Milky Way. What's more, the star formation took place over a long period of time, hundreds of millions of years. This tells astronomers that the galaxies did not grow due to mergers, or collisions, which happen on shorter timescales. While such smash-ups are common in the universe -- for example, our Milky Way will merge with the Andromeda galaxy in about 5 billion years -- the new study shows that large mergers were not the main cause of galaxy growth. Instead, the results show that distant, giant galaxies bulked up by feeding off a steady supply of gas that probably streamed in from filaments of dark matter.

Chary said, "If you could visit a planet in one of these , the sky would be a crazy place, with tons of bright stars, and fairly frequent supernova explosions."

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5 comments

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kevinrtrs
2 / 5 (8) Jul 01, 2011
Further analyses showed that these galaxies furiously formed stars up to 100 times faster than the current star-formation rate of our Milky Way. What's more, the star formation took place over a long period of time, hundreds of millions of years.

So is this now the explanation for why there are OLD looking galaxies far out in space, instead of the expected youngish looking ones that the Big Bang predicts? Or is there now a strange correlation of distance from us to speed of galaxy formation?

Also, where are the remnants of the super novas that should have accumulated over these supposed hundreds of millions of years? There is far, far fewer than the expected number that is supposed to have occurred.
Tuxford
1 / 5 (3) Jul 01, 2011
Would not the galaxies sampled consist generally of the largest brightest most actively forming galaxies at such distances? In LaViolette's core ejection model, the larger galaxies with the more massive cores which nucleate and eject new gas much more rapidly as seed material than in smaller galaxies. These bigger galaxies would naturally experience much more rapid growth. I suspect the conclusions reached are based somewhat on natural data selection effects.

And how did these massive galaxies condense slowly so soon after the BB 'non'-event? Accepted cosmological 'conclusions' and a few physics 'laws' need to be re-visited. Nature, please obey the law!
TheRedComet
3 / 5 (2) Jul 01, 2011

So is this now the explanation for why there are OLD looking galaxies far out in space, instead of the expected youngish looking ones that the Big Bang predicts? Or is there now a strange correlation of distance from us to speed of galaxy formation?

Also, where are the remnants of the super novas that should have accumulated over these supposed hundreds of millions of years? There is far, far fewer than the expected number that is supposed to have occurred.

Read about Einsteins theory of general relativity if you want to explore that thought further.

Super novas created a large percentage of the atoms above oxygen through nucleosynthesis.
frajo
1 / 5 (3) Jul 01, 2011
Instead, the results show that distant, giant galaxies bulked up by feeding off a steady supply of gas that probably streamed in from filaments of dark matter.
Sometimes I'm wondering whether there's any cosmological question which will not immediately be answerable by that magical ingredient called "dark matter".
omatumr
1 / 5 (4) Jul 01, 2011
Galaxies once thought of as voracious tigers are more like grazing cows


Thanks, Ranga-Ram Chary and associates of NASA's Spitzer Science Center at the California Institute of Technology, for backing away from the story that galaxies "voraciously" consume hydrogen.

They do not.

Galaxies of neutron stars (future stellar cores) produced by fragmentation generate and gravitationally retain a cloud of decay products (mostly H and He) that emits photons and glows brightly as stellar photosphere, thus hiding the neutron star from view.

See: "Neutron Repulsion", The APEIRON Journal, in press, 19 pages (2011)

http://arxiv.org/...2.1499v1

With kind regards,
Oliver K. Manuel

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