Free Astronomy Magazine November-December 2022

NOVEMBER-DECEMBER 2022 ! “There’re lots of predictions from computer simulations about what they should look like, how they should interact over billions of years, but observationally we can’t really test most of them because dwarf galaxies are typically just too hard to detect,” said Krishnarao. Because they are right on our doorstep, the Magellanic Clouds provide an ideal opportunity to study how dwarf galaxies interact and evolve. In search of direct evi- dence of the Magellanic Corona, the team combed through the Hub- ble and FUSE archives for ultravio- let observations of quasars located billions of light-years behind it. Quasars are the extremely bright cores of galaxies harboring massive active black holes. The team rea- soned that although the corona would be too dim to see on its own, it should be visible as a sort of fog obscuring and absorbing distinct patterns of bright light from quasars in the background. Hubble observations of quasars were used in the past to map the corona sur- rounding the Andromeda galaxy. By analyzing patterns in ultraviolet light from 28 quasars, the team was able to detect and characterize the material surrounding the Large Magellanic Cloud and confirm that the corona exists. As predicted, the quasar spectra are imprinted with the distinct signatures of carbon, oxygen, and silicon that make up the halo of hot plasma that sur- rounds the galaxy. The ability to detect the corona re- quired extremely detailed ultravio- let spectra. “The resolution of Hubble and FUSE were crucial for this study,” explained Krishnarao. “The corona gas is so diffuse, it’s barely even there.” In addition, it is mixed with other gases, including the streams pulled from the Magel- lanic Clouds and material originat- ing in the Milky Way. By mapping the results, the team also discovered that the amount of gas decreases with distance from the center of the Large Magellanic Cloud. “It’s a per- fect telltale signature that this co- rona is really there,” said Krish- narao. “It really is cocooning the galaxy and protecting it.” How can such a thin shroud of gas protect a galaxy from destruction? “Anything that tries to pass into the galaxy has to pass through this material first, so it can absorb some of that impact,” explained Krish- narao. “In addition, the corona is the first material that can be ex- tracted. While giving up a little bit of the corona, you’re protecting the gas that’s inside the galaxy it- self and able to form new stars.” NASA, ESA, Leah Hustak (STScI)