At the heart of a star metropolis, a strong force that is invisible to the eye is present. With a distance of roughly 6,000 light-years from Earth, the brilliant star cluster Messier 4 is the closest of its kind. It is home to hundreds of thousands of stars. A sight to behold. The center of the star cluster appears to be a black hole that is about 800 times as massive as the sun, as revealed by NASA’s renowned Hubble Space Telescope. According to Eduardo Vitral of the Space Telescope Science Institute, which runs the instrument’s science missions, “You can’t do this kind of science without Hubble”
This is a rare black hole. It’s not the kind of rogue object that roams our galaxy—a small black hole (scientists estimate there are a whopping 100 million of these in our Milky Way galaxy alone). And it’s not one of the enormous “supermassive” black holes, like Sagittarius A*, that reside at the centers of galaxies and are millions of times heavier than the sun (astronomers captured a rare picture of this giant Milky Way object). Instead, the new discovery is a strange “intermediate mass” black hole, about which scientists still don’t fully understand why they are so uncommon. Unimaginable mass and gravitational pulls prevent even light from escaping from black holes. So how did researchers find proof of an invisible object?