Astrophysicists scanning the heavens have clocked a new cosmological record: the two biggest black holes ever detected -- one about 10 billion times the mass of our sun and the second as much as twice that mass.
As described in the journal Nature, these behemoth black holes are nearly double the size of the previous record-holder and, strangely, are far more massive than they should be given the size of the galaxies they reside within.
For that reason, they stand to teach scientists much about how galaxies form and grow, astronomers said.
The finds were made using the Gemini North and Keck 2 telescopes in Hawaii, the McDonald Observatory in Texas and the Earth-orbiting Hubble space telescope. The first sits 320 million light years away in a huge elliptical galaxy within the Leo galaxy cluster. It contains a mass equivalent to 9.7 billion suns.
The second resides 336 million light years away at the center of a galaxy within the Coma galaxy cluster, in the direction of the constellation Coma Berenices. It may be far more massive than the first -- in the neighborhood of 20 billion solar masses.
The excitement at the find goes beyond the two black holes' record-breaking size and the weirdness of entities so massive even light cannot escape their pull.
"Black holes are not just curiosities," said Michele Cappellari, an astrophysicist at the University of Oxford who was not involved in the study and wrote a commentary accompanying the report. "They're really a part of the theory of how we think galaxies form."
Astronomers are fairly certain that every galaxy -- our own included -- has a supermassive black hole at its center. These black holes' existence was proposed four decades ago to account for the high-energy bursts of radiation, known as quasars, from very distant and ancient galaxies.
In recent years, the search for supermassive black holes has heated up and scientists have thus far uncovered more than five dozen of the cosmic behemoths.
The two newly discovered black holes dwarf the recent former record-holder, a heavyweight of 6.3 billion solar masses that sits in the M87 galaxy, about 50 million light years from Earth.
The largest black holes are most likely to be found at the center of very large galaxies. That's because as a black hole's gravity pulls gas toward it, gobbling the gas and growing larger, it allows the galaxy to grow, too, from gas that gets pulled into the galactic sphere from space.
But finding extremely large black holes is difficult, because such massive galaxies -- prime places to fish for the most massive black holes -- are very rare, and often located far away at the center of a cluster of galaxies.
And even though such galaxies may be large and bright enough to be seen, astronomers need to be able to peer at the part of the galaxy very close to the black hole itself -- hard to do from so far away.
Because they emit no light, black holes must be detected indirectly. As material moves in toward the black hole, it speeds up. Astrophysicists can use the speed of the material close to the black hole as a measure of how massive the hole must be.
"There was no guarantee we could actually measure anything, so it was very exciting that we found something," said study co-author Chung-Pei Ma, an astrophysicist at the University of California, Berkeley.
The scientists did more than luck out -- they found the stars and gas near the centers of the two far-off galaxies were moving much faster than they had anticipated. That meant the black holes were larger than they should be, even taking into account the large size of the galaxies they sat within.
Only very massive black holes, at least twice as massive as predicted by the galaxies' properties, could be inducing that kind of speed, the researchers calculated. They don't yet fully understand the reason for the discrepancy. One possibility is that the big galaxies the researchers chose to study are the result of two galaxies slamming together and combining, Cappellari said.
The findings show that the relationship between the masses of galaxies and their black holes may be more complicated than scientists had thought, Ma said.
"We didn't expect to find such massive black holes. These were kind of extraordinary," she said -- and it's too soon to tell how common they may be. "We don't know if it's a rare find, or the tip of the iceberg."