Intense X-Rays Produced by Gas falling into Black Holes

Author:  Kost Jeffery
Institution:  Physics/Mathematics
Date:  October 2007

Scientists from the Chandra X-Ray Observatory (a NASA satellite) have observed stellar gas falling into black holes producing intense X-rays. Although light cannot escape the gravitational effects of a black hole, when gas succumbs to gravitational forces, intense X-Rays ignite violently before the gas disappears. An assistant professor of Astronomy at University of Michigan, John Miller, who is a part of the NASA research project, explains the observed process: "Just before stellar gas falls into the black hole, it can glow very brightly in X-rays."

The astronomers are able to determine the gas's temperature and chemical make-up as it falls into the black hole by using a process called spectroscopy. This is a process that determines light's unique "fingerprint" by looking at the colors it contains and their corresponding energy levels. Through this type of measurement the gasses have been found to approach temperatures up to 1000X that of the sun. This is quite an extreme temperature, and it is shared with many other extreme qualities of black holes. And knowing some of the background on these sometimes perplexing objects can demonstrate where these extreme qualities come from.

A black hole is a collapsed star with such a huge density that it creates a "rip" in space-time fabric. This means the collapsed star's gravitational field has become too large to be contained like a normal star, and just to understand how this happens can be a puzzling task. Black holes usually begin as stars that don't have enough fuel to keep their temperature at an adequate level. When the star loses its temperature like this, its volume also decreases; and since stellar masses, temperatures, and volumes are so extreme this shrinkage causes the star to eventually collapse in on itself. Sometimes, depending on the amount of mass in the star, a supernova will occur where the outer shell of the star will explode in an immense display of energy. After this, a black hole is formed. The new gravitational field is so strong that no matter or light can escape. However, black holes are not as common forming, as it may seem. In order for a black hole to be created, there are certain prerequisites for the star. The remnants of the supernova (or what is left of the candidate star in any other case) must exceed 3 times the mass of our sun to form a black hole. Due to this, our sun (or any star around its mass) will never be able to form a black hole; there is just not enough mass in that case to cause the havoc that creates these astronomical phenomena.

Artist rendition of X-Rays emitted by gas falling into a black hole Image Courtesy: Miller, University of Michigan, Ann Arbor

Artist rendition of X-Rays emitted by gas falling into a black hole Image Courtesy: Miller, University of Michigan, Ann Arbor

There are many interesting implications of black holes that make them rather mysterious research subjects (but usually only in theoretical research). Black Holes are difficult to study from an experimental perspective, because they are not naturally visible. However, as in this case that the Chandra X-Ray observatory has studied, black holes may be observed indirectly, through the effects they have on their surroundings. NASA's observation of gas falling into black holes is a good example of this, and one of many methods that astronomers are beginning to use to monitor the behavior of black holes. After all, any scientific research would not be complete without the presence of both theory and observation.

This research is along the same lines as many astronomical observations in recent memory. X-Ray emissions have given strong evidence for the confirmation of many theories on Black Holes and have given further clues as to how they function. As with any endeavor in science, technology drastically improves research efforts. We may all hope that improvements in observational astronomy will allow us to learn more about the darkest and most mysterious parts of our universe.

Written by Jeffrey Kost.

Reviewed by Nira Datta.