Astrophysics Professor Discovers Celestial ‘Bubbles’

A Harvard professor recently discovered two large bubble-shaped structures around the center of our galaxy, identifying a phenomenon that could facilitate scientists’ research into galaxy formation and black holes.

The discovery, made by Associate Professor of Astronomy and of Physics Douglas P. Finkbeiner and his team of Harvard researchers, was published in The Astrophysical Journal earlier this month.

The bubbles—each of which is approximately 30,000 light years long—extend perpendicular to the galaxy, one upward and one downward.

“They look to me almost like an infinity symbol tipped at 90 degrees, or like two teardrops,” said Finkbeiner.

The structures’ origin has not yet been determined. Finkbeiner said that the most likely explanation is that the bubbles were formed when matter that encountered the black hole in the center of the Milky Way was converted into a jet of energy.

Finkbeiner said another possible explanation­—one he is more skeptical of—is that the energy was released when a large number of stars exploded into supernovas around 7 million years ago.

The bubbles’ composition has not been determined, but Finkbeiner said he believes they are made of highly excited electrons, which emit gamma rays.

Finkbeiner—aloing with graduate assistants Meng Su and Tracy Slayter—discovered the structures by analyzing data from NASA’s Fermi Gamma-Ray Space Telescope.

Researchers had previously detected evidence that may support presence of the bubbles both in our galaxy and beyond. But Finkbeiner’s discovery marks the first time such structures have been definitively.

Su said that the discovery might make it more difficult to find dark matter, the elusive substance that likely makes up 80 percent of the universe but remains undiscovered, because the black hole’s emissions would sweep away gamma rays that dark matter may also produce near the center of the galaxy.

Although dark matter emissions might otherwise have been identifiable, it appears that the bubble is pushing those emissions out of the galaxy, according to Su.

However, some scientists searching for dark matter are not discouraged by Finkbeiner’s discovery.

“If you want to look for gamma ray signals where the bubble happens to be, that might complicate things,” said Dan W. Hooper, an assistant professor of astronomy and astrophysics at the University of Chicago. “But if you want to look in the galactic center itself, I don’t think the bubbles are relevant...There still are places to look for dark matter that won’t be negatively impacted by the bubble.”

The discovery will be certain to spur further research at Harvard.

“At the center for astrophysics at Harvard, we have probably a couple hundred people who work on x-ray astronomy, and lot of what they do is study energetic outbursts of black holes in other galaxies,” Finkbeiner said. “It would be really neat for people who work on this kind of thing to have an example of some of those phenomena right in their face.”