The galactic haze that surrounds the Milky Way is a baffling mystery

Back in late 2010, astrophysicists spotted two gargantuan, gamma-ray emitting bubbles mysteriously coming out of the galactic center. Now the bubbles have an equally baffling companion: a strange haze of microwaves that extends through the galaxy, and "defies explanation."

The haze was detected by the European Space Agency's Planck mission, a space observatory located at the second Lagrangian point in the Earth-Sun system. (For a quick explanation of the Lagrangian points, check out this recent post.) Planck's primary mission is to study the cosmic microwave background, the thermal radiation left over from the Big Bang found throughout the universe. But to do that, it first must identify and remove all other microwave sources, which is where this haze enters the picture.


According to the ESA, this "mysterious haze of microwaves presently defies explanation." It seems to originate in the region around the galactic center. It most closely resembles a natural phenomenon known as synchrotron emission. This type of radiation occur when supernovas accelerate electrons to relativistic speeds. These electrons then pass through magnetic fields, which causes them to spiral violently.

Such radiation isn't totally unknown in the galaxy, but we've never seen anything quite like this before. In particular, this is the only such emission that shows what's known as a "hard spectrum", meaning the emission doesn't rapidly decline as the energy increases. There are a few possible explanations for this, including a ton of unexpected supernova explosions, fierce galactic winds, and - perhaps most intriguingly - dark matter particles smashing into each other.


But all theses possibilities remain tantalizingly unconfirmed, which means this galactic haze is the latest addition to the long list of cosmic mysteries. For more of Planck's findings, check out the ESA website here.

Image of Milky Way by GFSC/NASA. Image of galactic haze via Planck.


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