The most mystifying black holes in the universe

Nearly all galaxies are thought to harbor at their cores supermassive black holes millions to billions of times the mass of Earth's sun. In 2011, scientists discovered the largest black holes known in two nearby galaxies.

One of these galaxies, known as NGC 3842 — the brightest galaxy in the Leo cluster nearly 320 million light years away — has a central black hole containing 9.7 billion solar masses. The other, NGC 4889, the brightest galaxy in the Coma cluster more than 335 million light years away, has a black hole of comparable or larger mass.

The gravitational range, or "event horizon," of these black holes is about five times the distance from the sun to Pluto. For comparison, these black holes are 2,500 times as massive as the black hole at the center of the Milky Way galaxy, whose event horizon is one-fifth the orbit of Mercury.