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
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
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
and Planck will be necessary.