Every few weeks we'll get an announcement for the biggest, farthest, or brightest something in the universe. The latest finding from astronomers is the biggest medium-size black hole. Think of it this way: researchers didn't find the largest dog, but the largest Boston terrier.
Black holes come in two main size classes. The largest-known "supermassive" black holes lie at the cores of galaxies and have masses of billions of Suns. Scattered around the galaxy are "stellar-mass" black holes, the remnants of exploding stars that probably grow as they sweep up material.
On Tuesday, astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) announced finding a black hole in the nearby dwarf galaxy, designated IC 10, that weighs in between 24 and 33 times the mass of the Sun.
The black hole made itself known through X-ray emission as it swallows material from the large, hot star it orbits. Data from NASA's Chandra X-ray Observatory and Swift satellite revealed that the black hole and star pass in front of each other as they revolve. By timing the "eclipses" of the X-ray binary, the research team was able to estimate the black hole's mass. Observations in visible light should be able to refine the size further.