Types of Black Holes
Astronomers generally divide black holes into three categories according to their mass: stellar-mass, supermassive, and intermediate-mass. The mass ranges that define each group are approximate, and scientists are always reassessing where the boundaries should be set. Cosmologists suspect a fourth type, primordial black holes formed during the birth of the universe, may also lurk undetected in the cosmos. A swirling vortex of hot gas glows in this multiwavelength composite, marking the approximate location of the supermassive black hole Sagittarius A* (pronounced ey-star) at the heart of our Milky Way galaxy. NASA, ESA, SSC, CXC, STScI Stellar When a star with more than eight times the Sun’s mass runs out of fuel, its core collapses, rebounds, and explodes as a supernova. What’s left behind depends on the star’s mass before the explosion. If it was near the threshold, it creates a city-sized, superdense neutron star. If it had around 20 times the Sun’s mass or more, the star’s cor...