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Astronomers Find Ancient Galaxy Rich With Dark Matter

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Astronomers at the University of Texas in Austin have found an ancient galaxy rich with dark matter in a recent incidental discovery that supports a long-held theory about its evolution.

Researchers who studied spiral galaxies in the 1970s theorized that dark matter is at least five times as much as the normal dark matter visible in the universe. This theory was contested by a few studies suggesting that galaxies that evolved some 10 billion years ago may not necessarily have that much amount of dark matter at its birth.

Long-Held Theory

A new study published Dec. 12 in the journal American Astronomical Society corroborated with the long-held traditional theory on the formation of galaxies. Austin Caitlin Casey, an associate professor at the Department of Astronomy in UT, and her graduate student Patrick Drew refuted the notion that some galaxies have little dark matter in the beginning and only gained it later on.

"The galaxy we found is a clear counter-example of that, where it seems to have dark matter behaving in the normal way, as it does in the present-day universe," Casey said.

Their findings contradicted a 2017 study published in Nature stating that galaxies that formed 10 billion years ago are different than present-day galaxies.

Drew added that their discovery confirms the long-held theory that what happens in current galaxies are the same as what happened to ancient galaxies.

Serendipitous Finding

Casey's discovery of galaxy DSFG850.95 is incidental to their survey of the so-called dusty star-forming galaxies. They wanted to understand why these galaxies are able to produce stars at a rapid rate.

Using the Keck Telescope, the scientists measured the galaxy's rotation curve to determine the amount of dark matter present in DSFG850.95. Susan Kassin, an associate astronomer at the Space Telescope Science Institute, saw that the amount of dark matter in this ancient galaxy is what is expected of galaxies from 9 billion years ago.

"Our results point to DSFG850.95 being a massive, rotationally supported disk galaxy with a high dark-matter-to-baryon fraction in the outer galaxy," the study authors reported.

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