Weirdly big galaxy found in young universe

How did that get there?

Astronomers have identified a very weird galaxy, floating around in space some 800m years after the Big Bang. Nothing wrong with that, except that it is much bigger, and more mature than theory predicts, prompting scientists to consider new models of galaxy formation.

Bahram Mobasher of the European Space Agency and the Space Telescope Science Institute said: "This galaxy appears to have bulked up amazingly quickly. It made about eight times more mass in terms of stars than are found in our own Milky Way today, and then, just as suddenly, it stopped forming new stars. It appears to have grown old prematurely."

The galaxy was found among 10,000 others in an infra-red picture taken in 2004 by Hubble during its ultra deep field sky survey. The same patch of sky was then surveyed by the Spitzer telescope.

Spitzer observes at even longer infrared wavelengths than does Hubble, so it can see the older, redder stars that give astronomers an idea about how mature a particular galaxy is.

In Hubble's image, taken with its Near Infrared Camera (NICMOS), the galaxy is relatively faint. But at the longer wavelengths Spitzer can see with its Infrared Array Camera, it is surprisingly bright.

"This would be quite a big galaxy even today," said the National Optical Astronomy Observatory's Mark Dickinson. "At a time when the Universe was only 800 million years-old, it's positively gigantic."

Spitzer can also look at wavelengths 15 times longer than Hubble can see. Researchers found that even in this region of the spectrum the galaxy is blazing, suggesting that it has, at its centre, a super massive black hole.

The standard, and currently most widely accepted, theory of galaxy formation has most galaxies gradually being built up by the merging of smaller galaxies. But this newly identified galaxy must have formed differently, as it appeared so early in the history of the universe.

Some older theories of galaxy formation made room for large, monolithic galaxies to form. This discovery suggests that in some cases at least, this could well be what happened. ®

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