You’d think it would be hard to hide a structure half the size of the Milky Way sticking straight out of its centre. Yet, that’s precisely what researchers say they have uncovered: two giant, previously undetected bubbles 50,000 light years across, emanating from either side of the galactic plane. The discovery, based on data from NASA’s orbiting Fermi telescope, was unveiled today at a NASA press briefing in Washington DC.
“My first response when I saw these figures was ‘Wow!’” said David Spergel, an astronomer at Princeton University in New Jersey. The striking find challenges astronomers to do further observational and theoretical work to better understand unseen processes within the Milky Way, he added.
The dual, mammoth lobes first appeared in gamma-ray sky maps that are part of the publicly available Fermi database. A galactic gamma-ray fog that arises when swiftly-moving particles hit gas and photons hid the structures, said their discoverer, Doug Finkbeiner, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. Finkbeiner and his team were able to subtract the fog to reveal the two bubbles.
“They have performed a nice analysis of the data,” said Fermi team member Simona Murgia, a physicist at SLAC National Accelerator Laboratory in Menlo Park, California. “This result is very exciting.”
The structures appear to have sharp edges, suggesting they formed from a single rapid energy release—roughly equivalent to that of 100,000 supernovae, said Finkbeiner. This has led to the hypothesis that a burst of star formation in the center of the galaxy produced short-lived, massive stars that exploded and ejected a great deal of gas and dust over millions of years, he said. Another possibility is that the 4 million solar mass black hole at the center of the galaxy shot a jet of particles out into the galaxy over shorter time-scales, around 10,000 to 100,000 years.
Finkbeiner says locating structures like this around other galaxies could shed light on their formation, though current technology limits the resolution of gamma-ray telescopes. X-ray telescopes like Chandra might have already seen evidence of them, though that data will have to be reassessed, he says.
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Image: NASA Goddard