Imagine if you could see something the size of a coin at the distance of the moon.
That’s roughly the equivalent of what an international team of astronomers did by combining four of the most powerful telescopes in the world — the Very Large Telescopes at the European Southern Observatory in Chile — in a super-instrument called GRAVITY and directing it at the quasar 3C 273, which is about 2.5 billion light-years away from Earth in the constellation Virgo.
For the first time, the scientists were able to observe the motion of gas clouds swirling around the supermassive black hole at the center of the quasar. Doing so allowed them to measure the black hole’s mass with unprecedented precision.
“In terms of technology, this was a huge breakthrough,” said Bradley Peterson, professor emeritus of astronomy at The Ohio State University and a key collaborator on the GRAVITY study, which was released Nov. 29 in Nature. “I never thought this would happen in my lifetime.”
Zoom from an optical image of quasar 3C 273 to an artist’s impression of the surroundings of its central supermassive black hole. (Credit: L. Calçada/ESO)
Studying black holes in quasars — the extremely active centers of far-away galaxies that typically appear 10 times brighter than all the stars in the Milky Way combined — is key to understanding galaxy formation, as their evolution is intricately tied to galaxy growth, Peterson explained.
“There are supermassive black holes at the center of every large galaxy, but about one in 10 is accreting gas at a high enough rate that it develops a quasar,” added Peterson, who pioneered a widely used method to determine black hole masses in quasars called reverberation mapping. Until now, the technique has been the only way for astronomers to understand the physics occurring at the threshold of a quasar’s black hole, which are too far away to directly image.