Fermi Bubbles

The Fermi Bubbles are two massive plasma bubbles that extend about 25,000 light years both above and below the Milky Way disk. These biconical outflows are detected in many different parts of the electromagnetic spectrum including gamma rays, X-rays, ultraviolet absorption, and microwaves.

The Fermi Bubbles. Image Credit: NASA's Goddard Space Flight Center

The Fermi Bubbles. Image Credit: NASA's Goddard Space Flight Center

There are two leading theories on how the Fermi Bubbles formed. One theory states that they formed recently (a few Myr ago) due to an outburst from the Milky Way’s supermassive black hole, Sagittarius A* (references). The other theory suggests that they are outflows resulting from intense star formation activity in the center of our galaxy. In order to understand which mechanism (or combination of mechanisms) has formed the Fermi Bubbles, we have to first fully characterize the Fermi Bubbles.

While the Fermi Bubbles are most famously known for their gamma ray emission, the maps of the gamma ray emission cannot tell us how gas is moving within the Fermi Bubbles. Ultraviolet absorption gives us the advantage of measuring the kinematics of the cool/warm gas entrained within the bubbles. These kinematics can help distinguish between formation scenarios since a black hole outburst would be expected to take a short amount of time and the outflows from star formation should take much longer. We can also use the ultraviolet radiation to characterize the ion levels of the cool gas entrained in the bubbles. These ion levels tell us what kind of gas is entrained in the bubbles.

We use background quasars (distant galaxies) with suitably high ultraviolet continuum as our background sources for the ultraviolet radiation. To date we have Hubble Space Telescope (HST) data from _________ background quasars that have sightlines through the Fermi Bubbles. Currently I am analyzing five new sightlines associated with the Fermi Bubbles and combining the information from the total ___________ sightlines to search for trends in the kinematics and ion levels with Longitude and Latitude.

Image Credit: NASA, ESA, and Z. Levy (STScI)

Image Credit: NASA, ESA, and Z. Levy (STScI)

References