Data from NASA's Chandra X-ray Observatory (left) have helped astronomers reveal that a galaxy has more dark matter packed into its core than expected after being isolated for billions of years, as reported in our press release. The image on the right shows the galaxy called Markarian 1216 (abbreviated as Mrk 1216) in visible light from NASA's Hubble Space Telescope over the same field of view.
Mrk 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 red, 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 evolution is correct, then the dark matter in Mrk 1216 and its galactic cousins should also 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 at different distances from Mrk 1216's center, so they could "weigh" how much dark matter exists in the middle of the galaxy. The brighter colors at the center of the Chandra image represent the increased density of hot gas in the galaxy's core.
According to the new study, a halo, or fuzzy sphere, of dark matter formed around the stars in the center of Mrk 1216 about 3 or 4 billion years after the Big Bang. The formation of such a red nugget was typical for a wide range of elliptical galaxies seen today. However, unlike Mrk 1216, most giant elliptical galaxies continued to gradually grow in size when smaller galaxies merged with them over cosmic time.
Previously, astronomers estimated that the supermassive black hole in Mrk 1216 is more massive than expected for a galaxy of its mass. This most recent study, however, concluded that the black hole mass is likely to be less than about four billion times the mass of the Sun, which means it may not be unusually massive for a galaxy as large as Mrk 1216.
Researchers also searched for signs of outbursts from the supermassive black hole in the center of the galaxy. They saw hints of cavities in the hot gas similar to those observed in other massive galaxies and galaxy clusters like Perseus, but more data are needed to confirm their presence.
A paper by David Buote and Aaron Barth (both of the University of California at Irvine) describing these results appeared in the June 1st issue of The Astrophysical Journal and is available online. NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.
|
||||||||||||||||||||||||||||||
The main panel of this graphic is an artist's illustration of a supermassive black hole and there is an inset containing an X-ray image of the red nugget galaxy Mrk 1216. The center of the illustration is dominated by a large, swirling black hole surrounded by an accretion disk and shows material falling towards black holes that can be redirected outward at high speeds due to intense gravitational and magnetic fields. These high-speed jets can tamp down the formation of stars. This happens because the blasts from the vicinity of the black hole provide a powerful source of heat, preventing the galaxy's hot interstellar gas from cooling enough to allow large numbers of stars to form. The X-ray inset with data from NASA's Chandra X-ray Observatory is a small clump of red. A study using Chandra data indicates that black holes have squelched star formation in small, yet massive galaxies known as "red nuggets". The results suggest some red nugget galaxies may have used some of the untapped stellar fuel to grow their central supermassive black holes to unusually massive proportions.
