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Probing the Dark Galaxies

What is 200,000 light years across, 153 million light years from Earth, and invisible to normal telescopes? The answer is, a newly-discovered ‘dark galaxy’, one of a number of new galaxies identified by a project called the Arecibo Galaxy Environment Survey (AGES). The enigmatic dark galaxy is located near NGC1156, a normal enough (though irregularly shaped) galaxy near the constellation Aries.

Dark galaxies are made up primarily of gas and dark matter, making the job of finding them problematic. After all, without stars or other radiation sources, such a galaxy remains hidden from normal observation. But the AGES survey focused on hydrogen, for the interactions between hydrogen atoms in gas clouds within the galaxy create emissions at the 21 cm neutral hydrogen wavelength.

Led by Jonathan Davies (Cardiff University), the AGES team used Arecibo’s giant radio dish in conjunction with ground and space-based telescopes to pick up the dark galaxy’s unique signature. Robbie Auld (also at Cardiff) presented their results at the recent Royal Astronomical Society meeting. The next step for AGES is to make follow-up observations at other wavelengths to see how many stars the new galaxy may contain, and what percentage of it is dark matter.

Centauri Dreams‘ note: In conjunction with VIRGOHI21, a similar dark galaxy detected earlier, the discovery leads to the supposition that there are similar objects scattered throughout the universe. Studying them is heady stuff because it’s widely believed that most matter in the universe is dark; these dark galaxies are therefore one way we can gain clues about the mystery of what the cosmos is made of. Figuring out how much dark matter hides in them, and how widely distributed they are, will go a long way toward refining current models.