Our first story of the day taught me a new term: Fermi bubbles. Named after the gamma-ray telescope that discovered them, these dramatic regions of heated gas extend above and below the disc of our Milky Way galaxy, and were created during high-energy events involving our galaxy’s supermassive black hole (SMBH). First discovered in 2010, we’re still trying to understand these structures, what formed them, and how far-reaching an effect that source event may have had. It’s currently thought they most likely formed when 100,000 solar masses of material formed an accretion disk near our SMBH. As the material orbited rapidly toward its death, flashes were released that energized the surrounding gas that formed these globes.  

New research shared yesterday at the AAS meeting shows that the event related to the Fermi bubble formation had much more distant effects than previously realized. Beyond energizing the Fermi bubbles, the light ionized gas as far away as the Magellanic Stream: the stream of material pulled off the Magellanic Clouds as these galaxies race past the Milky Way. According to project Principal Investigator Andrew Fox, “The flash was so powerful that it lit up the stream like a Christmas tree—it was a cataclysmic event! This shows us that different regions of the galaxy are linked—what happens in the galactic center makes a difference to what happens out in the Magellanic Stream. We’re learning about how the black hole impacts the galaxy and its environment.” 

The ionized gas can’t be directly seen. Instead, it was mapped out by taking spectra of distant quasars and looking for absorption lines in the quasar light from the relatively nearby gas. Since every atom, and every ionization state of atoms, has a unique fingerprint of absorption or emission lines, the team was able to get not just the composition of the absorbing gas, but also its ionization state. This is a nice clean result, and scientists are even able to figure out roughly when the high-energy flare in our Milky Way took place. It turns out that had you been an early hominid on the Earth 3.5 to 2.5 million years ago, you would have seen the galactic core in Sagittarius shine with the ghostly glow of this likely million-year long event. This is one of the few times we know that a galaxy shaping event would have been visible to the unaided eye.

Our Earth was unaffected by this particular event, but other worlds, closer to the core of the galaxy, may not have been so lucky. Once again we are reminded, it’s all about location location location.

More Information

HubbleSite news release 

“Kinematics of the Magellanic Stream and Implications for Its Ionization,” Andrew J. Fox, Elaine M. Frazer et al., 2020, to appear in the Astrophysical Journal (Preprint)