For quasars and other objects that existed many billions of years ago, it’s meaningless to express their distances in terms of light-years. The universe has expanded so much between then and now that astronomers instead refer to an object’s redshift, which is a measurement of how much cosmic expansion has stretched the object’s light toward redder (longer) wavelengths.
For years, astronomers such as the University of Arizona’s Xiaohui Fan have been identifying quasars at redshifts as high as 6, when the universe was about 900 million years old. They’ve even found a few around redshift 7, which corresponds to an era when the universe was about 735 million years old. But in late 2017, an international team led by Eduardo Bañados of the Carnegie Institution for Science announced a quasar at a record-shattering redshift of 7.54. This quasar, designated J1342+0928 (J1342 for short), based on its sky coordinates in Boötes, was radiating 40 trillion Suns’ worth of energy at a time when the universe was only 690 million years old.
The team found J1342 by mining data from NASA’s Wide-field Infrared Survey Explorer satellite, the United Kingdom Infrared Telescope Deep Sky Survey Large Area Survey, and the DECam Legacy Survey. They used the 6.5-meter Magellan Telescope in Chile to measure the quasar’s redshift, while observations with the 8-meter Gemini North Telescope in Hawaii enabled the team to estimate the black hole’s mass: around 800 million Suns.
“Gathering all this mass in under 690 million years is an enormous challenge for theories of supermassive black hole growth,” said Bañados in the discovery announcement. “The finding shows that a process obviously existed in the early universe to make this monster. What that process is? Well, that will keep theorists very busy!”
Theorists had a difficult enough time accounting for the redshift-6 and redshift-7 quasars. But a supermassive black hole beyond redshift 7.5 borders on the absurd. And, as it turns out, the discovery was not a fluke.
In June 2020, a team with many of the same astronomers, this time led by Jinyi Yang of the University of Arizona, announced the discovery of a second quasar at a redshift greater than 7.5. This quasar, designated J1007+2115, lies at a redshift of 7.515. Its black hole engine weighs a whopping 1.5 billion solar masses at a time when the universe was barely 700 million years old.