Hubble Spots Tiny, Ancient Ghost Galaxies

By Chelsea Whyte on July 12, 2012 10:08 PM EDT

galaxy
Ghost galaxies show astronomers what the early universe was like. (Photo: Creative Commons: Flickr/theba)

Astronomers have solved one of the mysteries of the early universe: why some small, faint, ancient galaxies have so few stars.

Using the Hubble Telescope, NASA astronomers were able to see that three of these puny galaxies are roughly the same age. The stars all started forming more than 13 billion years ago and then abruptly stopped. This screeching halt to their growth happened within the first billion years after the Big Bang.

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"These galaxies are all ancient and they're all the same age, so you know something came down like a guillotine and turned off the star formation at the same time in these galaxies," said study leader Tom Brown of the Space Telescope Science Institute in Baltimore, Md. "The most likely explanation is reionization."

In the early universe, radiation from the formation of the first stars knocked electrons off hydrogen atoms, ionizing the cool hydrogen gas, which then became transparent to ultraviolet light. The reionization period marks a time when the cosmos transformed from being filled with cool neutral hydrogen (which carried no charge) into a universe with ionized hydrogen that had been split into its component electrons and protons, reports Fox News.

"These galaxies are fossils of the early universe: they have barely changed for 13 billion years," scientists explained in an announcement on Tuesday, according to MSNBC. "The discovery could help explain the so-called 'missing satellite' problem, where only a handful of satellite galaxies have been found around the Milky Way, against the thousands that are predicted by theories."

These low rates of star formation would even help answer why so few of these ghost galaxies have been found. Without starlight, these dwarf galaxies would be rendered virtually invisible from telescopes on or near Earth, reports Wired UK.

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