A Tour of Sagittarius A*

Narrator (April Hobart, CXC): Since NASA's Chandra X-ray Observatory was launched over 15 years ago, it has frequently turned its gaze to the center of the Milky Way galaxy. One of the reasons is that at the center of our Galaxy there is a black hole, which astronomers now estimate contains about four and a half million times the mass of the Sun. This makes this object, called Sagittarius A*, the closest supermassive black hole to us. Over the years, astronomers have learned many things about Sagittarius A* and it continues to surprise and intrigue scientists to this day. On September 13, 2013, astronomers saw a flare from Sagittarius A* that was 400 times brighter than its usual X-ray output. A little more than a year later, astronomers again used Chandra to see another flare from Sagittarius A* that was 200 times brighter than its normal state in October 2014.

What's going on with the Milky Way’s biggest black hole? Astronomers have two theories about what could be causing these “megaflares” from Sagittarius A*. The first idea is that the intense gravity around the black hole ripped apart an asteroid that wandered too close. As the asteroid’s debris swirled around the black hole, it would have been heated to temperatures that cause it to emit X-rays before passing over the edge of the black hole. The other proposed explanation involves the strong magnetic fields that exist around Sagittarius A*. If the magnetic field lines reconfigured themselves and reconnected, this could also create a large burst of X-rays. Scientists see flares happen regularly on the Sun and the events around Sgr A* appear to have a similar pattern in intensity levels to those. Whatever the final explanation is for these flares, scientists will continue to observe Sagittarius A* with Chandra and will undoubtedly make more fascinating discoveries about our Galaxy’s supermassive black hole.