Ultra-dense Galaxies in the Early Universe

In today’s universe, a galaxy about 100,000 light years across containing 200 billion stars is considered typical, something like our Milky Way Galaxy.

But that was not the case for galaxies in the early universe.

Astronomers, using the Hubble Space Telescope and Keck Observatory to study galaxies as they existed 11 billion years ago, found that galaxies are surprisingly compact. The nine compact galaxies that they found, each about the mass of our Galaxy, instead of hundred thousand light years across, are only 5,000 light years across.

MilkyWay & Compact Galaxy

This is a puzzle to astronomers. No massive galaxy at that distance has ever been observed to be so compact. Over the 11 billion years, these baby galaxies must have grown a lot, to about five times bigger than it previously were. They might comprise half of all galaxies of that mass 11 billion years ago, forming the building blocks of today’s largest galaxies.

Ultra-dense Galaxies

These baby galaxies are only a fraction of the size of today’s grown-up galaxies, but contain approximately the same numbers of stars.  Credit: Hubble Space Telescope.

So, how do these ultra-dense galaxies form?

One hypothesis is that the early universe contains pockets of dark matter (an invisible form of matter that accounts for about 23% of the universe’s mass), where hydrogen gas became trapped there. The gas then began spinning rapidly in the dark matter’s gravitational whirlpool, forming stars at a furious rate. The new-formed galaxies would have been very small because they are constrained in the dark matter pockets.

These galaxies are ideal targets for the Wide Field Camera 3, which is scheduled to be installed aboard Hubble during Servicing Mission 4 in the fall of 2008. “We hope to use the Wide Field Camera 3 to find thousands of these galaxies. The Hubble images, together with the laser adaptive optics at Keck and similar large telescopes, should lead to a better understanding of the evolution of galaxies early in the life of the universe,” said Garth Illingworth of the University of California, Santa Cruz, and Lick Observatory.

Source: HubbleSite NewsCentre


~ by thChieh on May 1, 2008.

One Response to “Ultra-dense Galaxies in the Early Universe”

  1. The age of the universe is estimated to be 13.73 billion years old. This gives a perspective of how young these compact galaxies are. Wow, they are young!

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