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Universe Has Many More Galaxies Than Previously Thought


From and today:

A new headcount of galaxies in the observable universe turned up 10- to 20 times more galaxies than previous estimates, bringing the tally up to as many as 2 trillion, a new study shows.

And from Science News yesterday:

Not all galaxies sparkle with stars. Galaxies as wide as the Milky Way but bereft of starlight are scattered throughout our cosmic neighborhood. Unlike Andromeda and other well-known galaxies, these dark beasts have no grand spirals of stars and gas wrapped around a glowing core, nor are they radiant balls of densely packed stars. Instead, researchers find just a wisp of starlight from a tenuous blob.

“If you took the Milky Way but threw away about 99 percent of the stars, that’s what you’d get,” says Roberto Abraham, an astrophysicist at the University of Toronto.

A new telescope called the Dragonfly that is designed to mimic the compound eyes of insects is able to pick up these ultrafaint galaxies that are full of gas and dark matter but aren’t forming stars.  The Dragonfly, with 48 telephoto lenses, has an advantage over larger, single lens telescopes because faint images aren’t blotted out by internal reflections that plague larger lenses.  In 2014, astronomers pointed the Dragonfly at the Coma cluster, which has been observed in depth for 80   years.  The Dragonfly found 48 galaxies that had never been seen before, some as large as the Milky Way.  These substantial galaxies have very few stars, so they are very faint, but they appear to have been present as long as normal galaxies, and they appear to be as large.  Astronomers are concluding that these galaxies are composed of mostly dark matter, which lurks in an invisible halo around all galaxies but composes a much larger proportion of these faint galaxies.

After studying older photographs of Coma, astronomers realized that there were nearly a thousand of these faint galaxies, just as big and heavy as their brighter cousins but bereft of visible stars.  Some of these “ultradiffuse” galaxies are small, but some are as heavy as the Milky Way and composed almost entirely of dark matter.  The mystery now is how these galaxies formed; there are many theories but no definite answers.

What is important is that astronomers are finding new things constantly, even when looking at the same parts of the sky.  New and better telescopes discover new and more interesting stars and galaxies.  The answer to the puzzles of dark matter may lie in some of these new galaxies.

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