Cool black hole. Chandra X-ray telescope image of an anomalously cool black hole (blue) at the heart of the Andromeda galaxy (M31). The yellow dots are X-ray binary stars, which contain gases at temperatures of tens of millions of degrees Celsius. The cool central black hole is at a mere few million degrees. The cool black hole has a mass 30 million times that of the Sun, and is the central object in M31. M31 is similar to our galaxy (the Milky Way), and lies 2.9 million light years away. Studying M31 will aid the under- standing of our own galaxy. This image was made by the Advanced CCD Imaging Spectrometer (ACIS) on Chandra, an observatory in orbit around the Earth.