Quasars are the giants of the early cosmos – and pose a puzzle. Because so far it is difficult to explain how these supermassive black holes in the center of distant galaxies could get so big so early. Now astronomers have discovered the most distant and oldest quasar to date – it already existed 670 million years after the Big Bang. Nevertheless, the black hole of this quasar has 1.6 billion solar masses and is therefore twice as massive as the previous record holder. This deepens the mystery of the origin of these gravitational giants and largely rules out two common theories.
Quasistellar objects, or quasars for short, are supermassive black holes in distant galaxies that actively suck in matter. In doing so, they release enormous amounts of radiation that can be seen for billions of light years. Quasars are therefore among the brightest objects in the cosmos. But for several years astronomers have been puzzling over how the black holes of such early gravity giants could have formed. The reason: Some of the previously known quasars are more than twelve billion years old – they therefore come from the early days of the cosmos. But that means that their black holes had little time to grow to hundreds of millions of solar masses. According to current theory, supermassive black holes gradually grow by consuming surrounding stars and gas and also by merging smaller predecessors.
13.03 billion light years away
But now researchers around Feige Wang from the University of Arizona have discovered a quasar that torpedoed many popular ideas. They tracked him down with the 6.5-meter telescope at the Las Campanas Observatory in Chile. The object, named J0313-1806, is around 13.03 billion light years away from Earth, and therefore as far as no other known quasar. The previous record holder, discovered in 2017, is 20 million light years closer, the researchers report. At the same time, J0313-1806 is the oldest representative of these exceptional objects, because it already existed 670 million years after the Big Bang – at a time when the universe was only five percent of its present age. The researchers will present their find today at the American Astronomical Society’s annual meeting.
Although this quasar existed so shortly after the Big Bang, it shines around a thousand times brighter than the Milky Way and its black hole comprises around 1.6 billion solar masses, as Wang and his team report. It is twice as massive as the black hole of the previous record quasar. This again raises the question of how these objects could accumulate so much mass in such a short time back then. The black hole of J0313-1806 did not have enough time for slow growth from stellar black holes or by sucking in nearby stars. Even assuming the earliest possible point in time for the formation of the predecessor object, these common scenarios cannot explain how this quasar got its enormous mass. According to the calculations of the astronomers, the predecessor of J0313-1806 must have been around 10,000 solar masses, even if it was created 100 million years after the Big Bang.
How did the black hole get its enormous mass?
However, this initial mass cannot be reconciled with stellar black holes as predecessors or with growth through the engulfing of stars: “These values tell us that the seedling of this black hole must have been formed by another mechanism,” says co-author Xiaohui University of Arizona fan. Because so early after the Big Bang there were simply not enough stars to adequately “feed” the predecessor of the quasar. The astronomers therefore suspect that this black hole could have been created directly by the collapse of a large, dense cloud of primordial hydrogen gas. The gas was compressed so much that a black hole formed in the center of the cloud. “Only in such a direct collapse scenario could a previous object of at least 10,000 solar masses have been created”, says Fan.
The newly discovered quasar opens up new insights into the prehistory of some of the most extreme objects in the cosmos. At the same time, however, it also provides information on how the first galaxies in the cosmos grew. Images with the Atacama Large Millimeter / submillimeter Array (ALMA) in Chile show that the home galaxy of quasar J0313-1806 has a star formation rate that is 200 times higher than that of the Milky Way today. “This indicates that this galaxy is growing very quickly,” explains Wang’s colleague Jinyi Yang. At the same time, the supermassive black hole in the heart of the galaxy devours the mass equivalent of around 25 suns every year. Part of the energy that is released during this “feeding orgy” drives a strong wind of ionized gases that rushes out of the center of the galaxy at around 20 percent the speed of light. “This is the earliest evidence of how a supermassive black hole affects its host galaxy,” says Wang.
Quelle: University of Arizona, 237th Meeting of the American Astronomical Society