Black Hole
A black hole is an astronomical object whose gravity is so strong that nothing—even light—can escape from within its event horizon. It forms when a massive star’s core collapses or through other processes, and may have an accretion disk of infalling matter that emits radiation. Supermassive black holes at galaxy centers influence stellar orbits, and mergers produce gravitational waves.
Source: nasa.gov
APODs including "Black Hole"
X-Ray Stars of 47 Tucanae
24/05/2001
A deep optical image (left) of 47 Tucanae shows an ancient globular star cluster so dense and crowded that individual stars can not be distinguished in its closely packed core. An x-ray image of its central regions (inset right) from the Chandra Observatory reveals a wealth of x-ray stars hidden there. Color-coded by energy, low energies are red, medium are green, and high energy cosmic x-ray sources are blue, while whitish sources are bright across the x-ray energy bands. The x-ray stars here are double stars or "compact" binary star systems. They are so called because one of the pair of stellar companions is a normal star and the other a compact object -- a white dwarf, neutron star, or possibly a black hole. Chandra's x-ray vision detects the presence of an unexpectedly large number of these exotic star systems within 47 Tucanae, but it also indicates the apparent absence of a large central black hole. The finding suggests that compact binary star systems of 47 Tucanae may be ejected from the cluster before coalescing to form a large black hole at its core.