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MPE News November 18, 2010

Fermi telescope finds giant gamma-ray bubbles in the Milky Way

A team of scientists has found a previously unseen structure in the Milky Way by processing publicly available data from Fermi's Large Area Telescope (LAT). The LAT is the most sensitive and highest-resolution gamma-ray detector ever launched and the MPE is involved in scientific analysis of the LAT data. The newly detected feature spans 50,000 light-years and may be the remnant of an eruption from a supersized black hole at the centre of our galaxy. A paper about the findings has been accepted for publication in the Astrophysical Journal.
Fermi sky
A giant gamma-ray structure was discovered by processing Fermi all-sky data at energies from 1 to 10 billion electron volts, shown here. The dumbbell-shaped feature (centre) emerges from the galactic centre and extends 50 degrees north and south from the plane of the Milky Way.
Credit: NASA/DOE/Fermi LAT/D. Finkbeiner et al..

Scientists are now conducting more analyses to better understand how the giant structure was formed. The bubble emissions are much more energetic than the gamma-ray "fog" seen elsewhere in the Milky Way; this fog happens when particles moving near the speed of light interact with light and interstellar gas. The bubbles also appear to have well-defined edges. The structure's shape and emissions suggest that it was formed as a result of a large and relatively rapid energy release.

One possible source for this energy is a particle jet from the supermassive black hole at the galactic centre. In many other galaxies, astronomers see fast particle jets powered by matter falling toward a central black hole. While there is no evidence that the Milky Way's black hole has such a jet today, it may have had in the past. The bubbles also may have formed as a result of gas outflows from a burst of star formation, perhaps the one that produced many massive star clusters in the Milky Way's centre several million years ago.

Hints of the bubbles also appear in earlier internal linkROSAT data and from WMAP, which detected an excess of radio signals at the position of the gamma-ray bubbles. The combination of this data suggests that the energy injection in the galactic centre could be due to a combination of different mechanisms. To help discriminate between the different scenarios, however, the authors conclude that improved measurements with internal linkeROSITA and Planck will be necessary.

Original paper :
  Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
Meng Su, Tracy R. Slatyer, Douglas P. Finkbeiner
external link arXiv:1005.5480v3 [astro-ph.HE] (2010)

Press releases :
  external link NASA press release

Links :
  internal linkFermi
internal linkeROSITA
internal linkROSAT

externer Verweis Why is the Milky Way Blowing Bubbles? (Blog in Sky & Telescope)

Contakt :
  internal link Dr. Hannelore Hämmerle
Press Officer
Max-Planck-Institut für extraterrestrische Physik
phone: +49 89 30000-3980
email: hanneh@mpe.mpg.de
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