Dewald's Astronomy Blog - A Look at the Heart of the Milky Way

Job 22:12 "Is not God high in the heavens? See the highest stars, how lofty they are! The image on your right hand displays an area of our galactic centre 26,000 lightyears away from earth and a few hundred lightyears across. If you click on the image to enlarge it you will notice a very bright, white patch to the bottom of the picture - this white patch is, in fact, the very core, the very heartbeat of our galaxy, the Milky Way, and is named Sagittarius A. Of course, even if you were to employ a very powerful optical telescope, such as, say, the Hubble space telescope, you would not be able to see the heart of our galaxy. The reason for this is simple: we inhabit a dense, spiral galaxy - gas and dust blocks most visible light along our line of sight. Fortunately, X-ray telescopes, like NASAs Chandra X-ray Observatory, can detect higher-energy radiation that penetrates this veil of galactic debris. Chandra's elliptical orbit takes the spacecraft to an altitude of approximately 139,000 km - more than a third of the distance to the Moon. Operating in space since July 23, 1999, Chandra detects and images X-ray sources that lie within our Solar System to those billions of light years away. In fact, Chandra was launched from the famous Columbia space shuttle that subsequently, on February 1, 2003, disintegrated over Texas during re-entry into the Earth's atmosphere. The Chandra Observatory is presently one of the flagships for X-Ray Astronomy, and the results from Chandra help explore high-energy phenomena and provide insights into the Universe's structure and formation. After its launch in 1999 we were able, for the first time in the history of the world to gaze directly and clearly into the heart of our own galaxy (barring of course radio images of this region). "What does Chandra see when it looks at the heart of the Galaxy? It finds a sea of hot gas enveloping thousands of white dwarfs (a type of star), neutron stars and black holes. Chandra also finds regions aglow with the light of massive young stars. And thats not all; at the very core of the Milky Way lies a supermassive black hole that has a mass of nearly four million suns. This black hole is named Sagittarius A*, or Sgr A* for short, due to its location in the direction of the constellation Sagittarius. Sgr A* is continually growing as it pulls in gas. Infalling gas is heated to millions of degrees and gives off X-rays, which have been detected by Chandra. Sometimes gas outside the black hole can become super-heated and expelled from the region at millions of [kilometres] per hour." (http://chandra.harvard.edu/resources/podcasts/ts/ts300806.html) "As the high energy X rays stream away from the vicinity of the black hole, they heat the blanketing gas to temperatures of a few million degrees, and the blanket absorbs some of the X rays from the central source [in the image you can observe patches of this blanket surrounding the white patch to the bottom]. This produces dark stripes, or absorption lines in the X-ray spectrum. Bright stripes or emission lines due to emission from the blanketing gas are also present. Since each element has its own unique structure, these lines can be read like a cosmic bar code to take inventory of the gas. [Dr. Frederick K. Baganoff of the Massachusetts Institute of Technology, who has been using Chandra to study our Galactic Center for several years] was able to determine what atoms the gas contains and how many, the number of electrons each atom has retained in the hostile environment of the black hole, and how the gas is moving there. They found lines from eight different elements including carbon, nitrogen, oxygen, and iron." http://science.nasa.gov/headlines/y2000/ast29feb_1m.htm