Dense, distant and full of dark matter

This is a lonely, stunted, ancient galaxy, full to bursting with dark matter.

Its name is Markarian 1216, and it formed as a compact galaxy of a type known as a “red nugget” about a billion years after the Big Bang. Yet while other red nuggets went on to grow and absorb other, smaller galaxies over time, this one didn’t. It stalled, its growth retarded, and it was left isolated in deep space.

And now, a pair of astronomers using NASA’s Chandra X-ray Observatory have concluded that it is also packed to the gills with dark matter.

David Boute and Aaron Barth from the University of California, Irvine, used Chandra to measure the x-ray brightness and temperature of hot gas at different distances from the centre of the galaxy, and used the results to estimate how much dark matter was present.

“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,” explains Buote.

“This tells us the history of Markarian 1216 is very different from the typical galaxy. Essentially all of its stars and dark matter was assembled long ago with little added in the past 10 billion years.”

The findings are detailed in a paper published in The Astrophysical Journal, and are also available on the Cornell University preprint site, arXiv.