 There are three classifications for black holes based on their mass, stellar, with masses up to ten times the mass of our sun, supermassive, with millions or even billions of times the mass of our sun, and intermediate, with masses somewhere in between. SAGA star is a supermassive black hole. In March 2018, the Japanese instrument MAXI aboard the International Space Station recorded an extremely strong X-ray outburst. NASA's NICER neutron star instrument, also on the space station, focused on the outburst for days and watched it fade. In addition, the Gaia mission was able to locate the X-ray source companion star and determine its distance at 10,000 light years. Analysis showed that the X-ray object is a black hole, with a mass of around 10 suns. The X-rays are generated as matter from the star feeds the accretion disk around the black hole. Some astronomers calculate that there are as many as 100 million stellar mass black holes like this one in our galaxy. Most of these are invisible to us, and only about a dozen have been identified. For more information on black holes, see the General Relativity Effects segment of the How Fast Is It? video book.