Ancient Galaxy in the 'Sea Serpent' Has More Dark Matter Than Expected

X-ray observations of a peculiar galaxy deep within the constellation Hydra (the Sea Serpent) have revealed more dark matter at its core than expected.

The galaxy is almost as old as the universe itself, representatives from NASA's Chandra X-Ray Observatory said in a statement published Monday (June 3). This celestial body, Markarian 1216, went through a different evolution than typical galaxies and is home to stars that are within 10% of the age of the universe.

To study the dark matter within this compact, elliptically shaped galaxy about 295 million light- years from Earth, researchers conducted new observations with the Chandra spacecraft. Markarian 1216 is packed with more dark matter in its core than researchers expected, according to their findings published June 1. 

Related: 4 Dark Matter Searches to Watch in 2019

Two views of galaxy Markarian 1216. The red image on the left shows X-ray observations conducted by NASA's Chandra X-Ray Observatory, and the yellowish image on the right is composed of optical observations taken by the Hubble Space Telescope. The brighter colors at the center of the Chandra image represent the increased density of hot gas in the galaxy's core.

(Image: © X-ray: NASA/CXC/Univ. of CA Irvine/D. Buote; Optical: NASA/STScI )

Dark matter is like the invisible puppeteer of the universe: Astronomers see the movement of baryonic matter (protons and neutrons) and can indirectly detect that something is acting upon the more massive configurations, like stars and galaxies — but little is known about the dark matter itself. 

If Markarian 1216 descended from "red nuggets," the reddish, compact galaxies that formed a billion years after the Big Bang that later stopped growing, the researchers said, the dark matter in this galaxy should be tightly packed, too. To test this idea, two astronomers studied the X-ray brightness and temperature of hot gas at different distances from this galaxy's core to effectively weigh the dark matter.. 

"When we compared the Chandra data to our computer models, we found a much stronger concentration of dark matter was required than we find in other galaxies of similar total mass," David Buote, a researcher at University of California at Irvine and co-author of the study said in the statement. 

Some scientists wonder whether dark matter exists at all since it has never been observed directly. But this paper seems to provide another leg for dark matter to stand on. Buote and university colleague Aaron Barth chose to interpret the Chandra data using two separate models — the standard model of gravity and MOND (Modified Newtonian Dynamics), which accounts for mass discrepancies in the universe without including dark matter in certain types of galaxies — and found that both theories required the same amount of dark matter at Markarian 1216's center.

"In the future we hope to go a step further and study the nature of dark matter," Buote said. '"The dense accumulation of dark matter in the middle of Mrk 1216 may provide an interesting test for non-standard theories that predict less centrally concentrated dark matter, such as for dark matter particles that interact with each other by an additional means other than gravity."

The new work was detailed June 1 in The Astrophysical Journal, and can be read in full on ArXiv.org.

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