A Tour of Mrk 1216

Narrator (April Jubett, CXC): Isolated for billions of years, a galaxy with more dark matter packed into its core than expected has been identified by astronomers using data from NASA's Chandra X-ray Observatory.

The galaxy, known as Markarian 1216, contains stars that are within 10% the age of the universe. In other words, the stars are almost as old as the universe itself. Scientists have found that Markarian 1216 has gone through a different evolution than typical galaxies. This includes dark matter that, through gravity, holds the galaxy together. Dark matter is a mysterious substance that accounts for about 85% of the matter in the universe, yet does not give off or reflect light. Therefore, scientists have only been able to detect it indirectly so far, making it a challenge to learn about.

Markarian 1216 belongs to a family of elliptically shaped galaxies that are more densely packed with stars in their centers than most other galaxies. Astronomers think they have descended from reddish, compact galaxies called "red nuggets" that formed about a billion years after the Big Bang, but then stalled in their growth about 10 billion years ago.

If this explanation is correct, then the dark matter in Markarian 1216 and its galactic cousins should be tightly packed. To test this idea for the first time, a pair of astronomers studied the X-ray brightness and temperature of hot gas from Chandra at different distances from Markarian 1216's center. This allowed them to, in a sense, weigh, how much dark matter exists in the middle of the galaxy.

The researchers found a high concentration of dark matter in the center of Markarian 1216, confirming that Markarian 1216 descended from a red nugget galaxy. This tells us about the evolution of Mrk 1216 going back in time about ten billion years. Further studies of this galaxy may provide astronomers with the opportunity to test ideas about the nature of dark matter.