The faint blue yonder – Hubble telescope survey indicates most galaxies in universe are faint blue blobs containing new stars

The faint blue yonder – Hubble telescope survey indicates most galaxies in universe are faint blue blobs containing new stars – Brief Article

WHAT DOES A “TYPICAL” GALAXY look like? If you imagine a gleaming white spiral, you might be disappointed to learn that the average galaxy is far less majestic. A new survey of galaxies by the Hubble Space Telescope shows that the most common galaxies in the universe are humble faint blue blobs.

The results come from an ongoing project called the Medium Deep Survey, which uses the Hubble to examine galaxies up to 10 billion light-years from Earth. When the project started, shortly after the telescope was launched in 199(), one of its main goals was to study faint bluish objects that had been showing up on astronomical plates since the 1970s. These objects are so faint that they were difficult to see clearly through Earth’s atmosphere, so the Hubble telescope was the perfect instrument for the job. The survey was in full swing even before the Hubble was repaired in 1993. The Hubble telescope found that the objects were very faint galaxies. And they were unusual. For one thing, their blue color indicated that many new hot stars were being formed. Also, the galaxies weren’t in the familiar spiral or elliptical shapes but were small blobs about a tenth the size of Milkt Way. But perhaps the most surprising find was that there were more of these faint blue galaxies than all other galaxies combined–surprising in part because such faint galaxies with new stars are uncommon closer to home.

Astronomers believe these blue galaxies were born from dust and gas left over from the formation of larger elliptical and spiral galaxies. Shortly after the giant galaxies formed, quasars erupted inside their cores, spewing out radiation that heated intergalactic gas, making it so energetic that the gas could not organize into galaxies for 7 or 8 billion years. Only after the quasars died did the small blue galaxies form.

Why don’t we see many blue galaxies closer to home? One theory suggests that they merged to form larger spiral galaxies. Or they may have died off due to their puny size. With such a small mass, they may not have had the gravitational pull to hold on to the dust formed in supernova explosions. Without the stellar raw material of dust and gas, there could be no new star formation and the galaxies would grow dimmer and dimmer as each star died. In theory, then, the faint blue galaxies near us would have died off by now. Only by looking billions of light-years into space, as the Hubble did–and thus farther back in time–can they be seen, says Richard Griffiths, the Johns Hopkins astronomer who heads the Hubble survey. And in fact, he says, “we see them everywhere we look. And we see an increasing fraction of them the fainter we go.”

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