It is 21 billion times the mass of the sun!
Don’t let the calm appearance of the giant elliptical galaxy NGC 4889 fool you! Although it is the brightest and largest galaxy seen in the above image, in its center lies the largest black hole ever observed.
Located roughly 300 million light-years away in the Coma Cluster, the supermassive black hole is 21 billion times the mass of the sun, and it has an event horizon — the distance at which even light cannot escape its gravitational pull — with a diameter of approximately 80 billion miles (130 billion kilometers). In other words, it is 15 times larger than the diameter of Neptune’s orbit around the sun.
If we compare it to the supermassive black hole located at the center of our galaxy, the Milky Way, Sagittarius A* only has a mass 4 million times that of the sun and an event horizon just one-fifth the orbit of Mercury — a substantial size difference!
It is impossible to directly observe a black hole since light cannot escape its pull, but its mass can be indirectly determined. Astronomers measured the velocity of the stars moving around NGC 4889’s center, and these velocities, which depend on the mass of the object they orbit, revealed the black holes immense size.
However, this enormous black hole is no longer gobbling up stars and dust — it is currently resting after having fed on a large amount of cosmic entrees once found in NGC 4889. In fact, the galaxy is so peaceful that stars are forming and orbiting undisturbed around the black hole.
When the black hole was active, it was fuelled by a process known as hot accretion. When gas, dust and other debris slowly fell towards the black hole, it accumulated and formed an accretion disc — a disk of material emitting energy as it falls into a black hole. This spinning disc of material was accelerated by the black hole’s gravitational pull and heated to millions of degrees causing the material to expel large, energetic jets.
Astronomers would have classified NGC 4889 as a quasar when the black hole was active, because the disc around it would have emitted up to a thousand times the energy output of the Milky Way.
Quasars are massive and elusive objects that emit large of amounts of energy. Although still an area of research, it has been suggested that quasars contain massive black holes, which could represent a stage in the evolution of some galaxies.
For now, the supermassive black hole in the center of NGC 4889 is full and dormant — in other words, it is taking a nap! Luckily, now that astronomers know it even exists, it allows them to learn more about how and where mysterious quasars formed in the early stages of the universe.
You can watch this video which zooms into the galaxy NGC 4889!