New Observations Illuminate the Middle of the Milky Way

Located 26,000 light years away from Earth and surrounded by clouds of dust, the center of the Milky Way galaxy is a hard thing for scientists to get a good look at. In fact, for nearly 20 years astronomers have been wondering about the origin of x-rays seen emanating from the core of our galaxy. Originally it was unclear whether the radiation came from widely dispersed hot interstellar gas or from multiple individual sources. Now new research suggests that it may be a combination of both. According to a report published today in the journal Nature, some of the emissions come from discrete sources representing hundreds of never-before-seen white dwarf stars, neutron stars and black holes.

Using data from the Chandra X-ray Observatory, Q. Daniel Wang of the University of Massachusetts, Amherst, and colleagues identified nearly 1,000 point-like sources that contribute to the x-ray emission, only 20 of which were previously known. Focusing on the spectral features associated with the presence of iron in the central galaxy, the team determined that the majority of the emissions from highly ionized iron can be attributed to discrete sources. Specifically, the most energetic iron emission they studied is characteristic of so-called x-ray binary starsduos comprised of a dense stellar object such as a white dwarf star, a neutron star or a black hole that collects matter from a less dense companion, emitting x-rays in the process. The classification of these new sources of x-rays has allowed the scientists to revise their temperature estimates of the interstellar gas: according to study co-author Eric Gotthelf of Columbia University, the gas appears to be a mere 10 million degrees, 10 times cooler than previously thought.

The celestial survey also found large amounts of diffuse x-ray- emitting material distributed assymetrically around the Galatic Center. Together, the new findings provide the most detailed x-ray map yet of objects near the middle of the Milky Way. "A detailed picture of the physical processes that influence this extraordinary region is key to understanding all other galactic nuclei in the universe," Andreas Eckart of the University of Cologne in Germany writes in an accompanying commentary. These results, he further notes, "finally settle important aspects of the twenty-year-old debate surrounding the origin of x-ray emission from the Galactic Center."