Millions of stars that are held together by gravitational attraction form a galaxy. Certain galaxy centers emit lots of energy. Astronomers think that this energy is created by a black hole. Such galaxies are known as active galaxies.
Black holes are so dense that even light cannot escape their gravity. An active galaxy’s energy doesn’t come from inside a black hole but from the realm directly outside it, instead. The area around the black hole is a disk constructed of torn-apart stars and clouds of gas. The disk is squeezed with extreme force, thereby heating it to hundreds of thousands of degrees. Energy and hot gas shoot from the disks creating jets that stretch for thousands of light years.
A stellar black hole is formed after a star goes supernova. These black holes have the mass of a star but are comparatively lighter than galactic black holes, which can have the mass of a billion stars.
Astronomers cannot see black holes directly because they trap in light. So, to locate them, astronomy experts look for the effects of extremely strong gravity. Depending on the size of the black hole, the effects could vary from minimal to catastrophic.
Black holes are complex, enigmatic parts of our world. While we have unearthed many important facts about them, astronomers still have much to uncover in this realm.
[Source: Children’s Atlas of the Universe]