MadSci Network: Astronomy

Re: According to the article can black holes produce UECRS?

Date: Sun Oct 18 05:57:42 2009
Posted By: Donald Terndrup, Faculty, Astronomy, Ohio State University
Area of science: Astronomy
ID: 1252524270.As

Black holes are very compact, massive objects. As a result, particles that orbit near them or fall in can be moving at very high speeds.

It now seems that all large galaxies have a massive black hole at their center. In our galaxy the Milky Way, the central black hole has a mass of about 3 or 4 million solar masses. One solar mass is the mass of the Sun, which is 2 times 1030 kg.

In a few cases, astronomers have directly detected high energy gamma rays (light) from the central regions of a galaxy. These are inevitably "active galaxies", in which we see a bright nucleus, complicated emission lines, and sometimes brightness variations over short time scales. The gamma rays are signatures of high energy processes taking place near the black hole.

Cosmic rays are charged particles (usually protons) which come from space. There is a good Wikipedia article on cosmic rays. Since the particles are charged, they can be affected by magnetic fields in space. Consequently, we generally do not have a good idea of the sources of cosmic rays, and there have been few direct detections of cosmic rays from individual objects. Based on statistical studies, astronomers have argued that many cosmic rays are associated with the nearest active galaxies - those closer than about 250 million light years.

Compared to active galaxies, the central region of the Milky Way is quiescent. The black hole does not have a large amount of gas orbiting it. Nevertheless, cosmic rays have been detected from regions near the galactic center.

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