No Gamma rays from a dwarf galaxy solve an astronomical puzzle with the help of NASA
A glowing blob known as “the cocoon”, which appears to be inside one of the enormous gamma-ray emanations from the centre of our galaxy dubbed the “Fermi bubbles”, has puzzled astronomers since it was discovered in 2012.
In new research published in Nature Astronomy, we show the cocoon is caused by gamma rays emitted by fast-spinning extreme stars called “millisecond pulsars” located in the Sagittarius dwarf galaxy, which orbits the Milky Way. While our results clear up the mystery of the cocoon, they also cast a pall over attempts to search for dark matter in any gamma-ray glow it may emit.
Thankfully for life on Earth, our atmosphere blocks gamma rays. These are particles of light with energies more than a million times higher than the photons we detect with our eyes.
Because our ground-level view is obscured, scientists had no idea of the richness of the gamma-ray sky until instruments were lofted into space. But, starting with the serendipitous discoveries made by the Vela satellites (put into orbit in the 1960s to monitor the Nuclear Test Ban), more and more of this richness has been revealed.
The state-of-the-art gamma-ray instrument operating today is the Fermi Gamma Ray Space Telescope, a large NASA mission in orbit for more than a decade. Fermi's ability to resolve fine detail and detect faint sources has uncovered a number of surprises about our Milky Way and the wider cosmos.
One of these surprises emerged in 2010, soon after Fermi's launch: something in the Milky Way's centre is blowing what look like a pair of giant, gamma-ray-emitting bubbles. These completely unanticipated “Fermi bubbles” cover fully 10% of the sky.
A prime suspect for the source of the bubbles is the Galaxy's resident supermassive black hole.
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