Chandra Discovers Light Echo from the Milky Way's Black Hole
This set of Chandra images shows evidence for a light echo
generated by the Milky Way's supermassive black hole, a.k.a.
Sagittarius A* (pronounced "A-star"). Astronomers believe a mass
equivalent to the planet Mercury was devoured by the black hole
about 50 years earlier, causing an X-ray outburst which then
reflected off gas clouds near Sagittarius A*. The large image
shows a Chandra view of the middle of the Milky Way, with
Sagittarius A* labeled. The smaller images show close-ups of the
region marked with ellipses. Clear changes in the shapes and
brightness of the gas clouds are seen between the 3 different
observations in 2002, 2004 and 2005. This behavior agrees with
theoretical predictions for a light echo produced by Sagittarius
A* and helps rule out other interpretations. While the primary
X-rays from the outburst would have reached Earth about 50 years
ago, before X-ray observatories were in place to see it, the
reflected X-rays took a long