Giant energy bubbles discovered in Milky Way galaxy

Images of the Milky Way – our home galaxy – typically show an immense, dusty band of stars. But we might have to revise the picture. That’s because, in November of 2010, a team led by Harvard astrophysicist Doug Finkbeiner discovered two giant, energy-filled bubbles extending from the galaxy’s center. He said each bubble is about a third of the size of the visible Milky Way. They contain high energy particles that produce gamma radiation.

Doug Finkbeiner Gamma radiation is very high energy light. These photons have about a billion times as much energy as visible light.

Dr. Finkbeiner’s team found these bubbles with the aid of NASA’s Fermi telescope. He said the bubbles have very distinct edges – in fact, put together, they look like a giant number “8” painted in the center of the galaxy.

Doug Finkbeiner: The edges are quite sharp compared to the overall structure, and so it looks to me like something that’s currently exploding, it looks like a shock wave propagating out from some burst of energy.

Finkbeiner said scientists are throwing around two ideas about how these bubbles formed. One is that the black hole at the center of our galaxy ‘burped’, spewing out light and electric particles at incredibly high speeds. Another idea is that a group of giant stars near the center of the Milky Way exploded all at once. EarthSky asked Dr. Finkbeiner how old these bubbles are.

Doug Finkbeiner: What seems clear is that they were caused by some huge energy injection at some point in the past. Whether they were caused one million or ten million years ago, we don’t know – some point in the past.

He said scientists haven’t spotted these bubbles before because they didn’t have the right telescope. The Fermi Telescope – which is floating out in space – specializes in gamma rays.

Doug Finkbeiner: Astrophysicists have been looking at Gamma Rays for years, decades, but the machinery gets better with each generation of course, and so this current Gamma ray telescope is about 100 times more powerful than it’s predecessor using this telescope is kind of like putting on your glasses for the first time.

He talked about the moment his team spotted the bubbles.

Doug Finkbeiner: Well there’s a great quote from Isaac Asimov which is that the sound of discovery is not “Eureka, I found it!’ but “Hmm, that looks funny!” And that’s really how it was! We were staring at the computer screen and said, “Hmm..that looks funny…is that really an edge?”

The edge of these bubbles, that is.

Doug Finkbeiner: It was a progressive thing. But there was a particular day when I went from thinking they weren’t real to thinking they were real. And that just had to do with looking at the data, getting more data – because the telescope is always getting more data – and analyzing it more carefully.

Finkbeiner and his team published their findings in November 2010 in The Astrophysical Journal.

EarthSky’s extended podcast, EarthSky22, features more on Doug Finkbeiner’s discovery

November 29, 2010

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Beth Lebwohl

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