Friday, June 22, 2012
From the center of the galaxy Ghost beams of gamma rays rising
The center of the Milky Way shows little activity in contrast. It was not always so peaceful. New evidence of ghost beams of gamma rays suggests that the central black hole of our galaxy was much more active in the past.
"These jets are faint ghost or just a sequel to what existed for millions of years," said Meng Su, an astronomer at the Harvard-Smithsonian Center for Astrophysics (CfA), and author of a new article in the Astrophysical Journal. "But it reinforces the evidence that there was an active galactic nucleus in the relatively recent past of the Milky Way," he added.
The two beams, or jets, were revealed by the Fermi Space Telescope for NASA. They extend from the center of the galaxy at a distance of 27,000 light years above and below the galactic plane. They are the first gamma-ray jets of this type have been found and the only ones close enough to be captured with Fermi.
May be related to mysterious gamma rays Fermi bubbles detected in 2010. The bubbles also extend to 27,000 light years from the center of the Milky Way. However, when the bubbles are perpendicular to the plane galactic gamma ray jets are inclined at an angle of 15 degrees. This may reflect an inclination of the accretion disk around the supermassive black hole.
"The core accretion disk may be distorted, spiraling toward the black hole under the influence of rotation of the black hole," said co-author Douglas Finkbeiner, CfA. "The magnetic field included on the disk, therefore, accelerates the injection material along the axis of rotation of the black hole, which may not be aligned with the Milky".
The two structures are also formed differently. The jets were produced when the plasma is extended from the galactic center, due to a magnetic field shaped like a corkscrew that had a strong orientation. Gamma-ray bubbles were probably creaas by a "wind" blowing hot matter outward from the accretion disk of the black hole. As a result, are much broader than the narrow jets.
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