How Big Is the Biggest Black Hole?

"That changed when observers used some clever techniques to glimpse a faint blue star sitting at the radio source's exact position. Eventually they were able to determine that this object, called 3C 273, was not a star at all but rather something much stranger located a staggering two billion light-years from Earth. To be visible at all across such vast stretches of space, the quasi-stellar object (quasar for short) 3C 273 had to be overwhelmingly bright."

"Since that time we've found many more such supermassive black holes. In fact, by the 1980s astronomers were starting to suspect that every big galaxy had a supermassive black hole in its center. Thanks to observations from the Hubble Space Telescope and other facilities, we now know that to be truewhich means there could be as many as a trillion such giants in the observable universe."

In the early 1960s astronomers detected a powerful radio source in Virgo that lacked an obvious visible counterpart. Observers later identified a faint blue object at the same position and determined it was a quasar, 3C 273, located about two billion light-years away. The quasar's luminosity requires a feeding supermassive black hole, estimated around 900 million solar masses. By the 1980s astronomers suspected that most large galaxies host central supermassive black holes. Hubble and other observations have confirmed that and imply there could be as many as a trillion such giants in the observable universe, with many exceeding a billion solar masses. Determining an upper mass limit remains challenging and relies on difficult, often indirect measurements.

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