Star formation drives huge bubbles in the Milky way

Fermi gamma ray image of the huge bubbles originated at the center of the Milky Way. Follow-up radio and microwave observations revealed magnetic fields and ridgelike structures in these bubbles.

NASA/DOE/Fermi LAT/D. Finkbeiner et al.

In 2010, data from the Fermi Gamma-Ray Space Telescope revealed two huge gamma-ray-emitting bubbles extending 25,000 light-years in each direction from the Milky Way's center. Since this region of the galaxy is home both to a supermassive black hole and star formation activity, it was uncertain which of them produced the structures. A new analysis of radio and microwave observations has confirmed these bubbles exist—but found additional features suggestive of star formation, rather than black hole activity.

The new results looked at the polarization of the radio emission coming from the lobes. As reported by Ettore Carretti and colleagues, the polarized light revealed relatively strong magnetic fields. These are of a kind associated with rapid star formation, which is known to occur in the region 700 light-years around the galactic center. Additionally, the bubbles contain spiraling ridges that indicate fluctuations in the history of the star formation, which may be used to study the evolution of the Milky Way's nucleus over the last 10 million years.

Gamma rays and radio waves are on the opposite ends of the energy spectrum, but they are often produced by the same physical phenomena. However, they convey different information about their source. In particular, when electrons are accelerated by magnetic fields, they emit synchrotron radiation, radio light with a distinctive polarization signature—information not carried by gamma radiation.