What’s a quasar? Astronomical discovery could reveal how massive black holes, galaxies formed in early universe
An international team of astronomers has observed the most distant quasar yet found: a cosmic monster more than 13.03 billion light-years from Earth. Called J0313-1806, it is powered by a supermassive black hole equivalent to the combined mass of 1.6 billion suns. The mass of the Sun is often used as a convenient unit for describing the mass of stars, galaxies and other celestial objects.
Fully formed 670 million years after the Big Bang, when the universe was only 5% its current age, the quasar is more than 1,000 times brighter than the entire Milky Way Galaxy. Observations with the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile confirmed the distance measurement to high precision. The discovery beats the previous distance record for a quasar set three years ago. The detection is providing scientists with valuable insight on how massive galaxies, and the supermassive black holes at their cores, formed in the early universe.
“Besides being the most distant, and by extension, earliest quasar known, the object is the first of its kind to show evidence of an outflowing wind of super-heated gas escaping from the surroundings of the black hole at a fifth of the speed of light. The new observations also show intense star formation activity in the host galaxy where the quasar, formally designated J0313-1806, is located,” say researchers. Their findings have been accepted for publication in Astrophysical Journal Letters.
Remote celestial objects
Quasars occur when the powerful gravity of a supermassive black hole at a galaxy's core draws in surrounding material that forms an orbiting disk of superheated material around the black hole. The process releases tremendous amounts of energy, making the quasar extremely bright, often outshining their host galaxies.
“Quasars are extremely remote celestial objects, emitting exceptionally large amounts of energy. Quasars contain supermassive black holes fueled by infalling matter that can shine 1,000 times brighter than their host galaxies of hundreds of billions of stars,” explains NASA. It adds, “As the black hole devours matter, hot gas encircles it and emits intense radiation, creating the quasar. Winds, driven by blistering radiation pressure from the vicinity of the black hole, push material away from the galaxy’s center. These outflows accelerate to breathtaking velocities that are a few percent of the speed of light.”
Black hole swallowing equivalent of 25 suns every year
The newly discovered quasar appears to offer a rare glimpse into the life of a galaxy at the dawn of the universe when many of the galaxy-shaping processes that have since slowed or ceased in galaxies that have been around for much longer were still in full swing.
By measuring the quasar’s luminosity, the experts calculated that the supermassive black hole at its center is ingesting the mass equivalent of 25 suns each year, on average, which is thought to be the main reason for its high-velocity hot plasma wind blowing into the galaxy around it at relativistic speed. For comparison, the black hole at the center of the Milky Way has become mostly dormant.
The energy released by that rapid feeding is probably powering a strong “outflow of ionized gas seen moving at about 20 percent of the speed of light,” according to scientists. Such outflows are thought to be what ultimately stops star formation in the galaxy.
“We think those supermassive black holes were the reason why many of the big galaxies stopped forming stars at some point. We observe this ‘quenching’ at later times, but until now, we didn’t know how early this process began in the history of the universe. This quasar is the earliest evidence that quenching may have been happening at very early times,” explains co-author Xiaohui Fan, Regents professor and associate head of the University of Arizona Department of Astronomy.
The analysis reveals that while the Milky Way forms stars at the leisurely pace of about one solar mass each year, J0313-1806 churns out 200 solar masses in the same period. “This is a relatively high star formation rate, similar to that observed in other quasars of similar age, and it tells us the host galaxy is growing very fast,” notes lead author Feige Wang, a Hubble Fellow at the University of Arizona’s Steward Observatory.
According to Fan, this process will also leave the black hole with nothing left to eat and halt its growth. “These quasars presumably are still in the process of building their supermassive black holes. Over time, the quasar’s outflow heats and pushes all the gas out of the galaxy, and then the black hole has nothing left to eat anymore and will stop growing. This is evidence about how these earliest massive galaxies and their quasars grow,” he says.
Findings challenge existing theories
J0313-1806 is only 20 million light-years farther away than the previous record holder. But the black hole at the core of J0313-1806 is twice as massive as that of the previous record holder. This marks a significant advancement for cosmology and provides astronomers with a valuable clue about such black holes and their effect on their host galaxies.
“This is the earliest evidence of how a supermassive black hole is affecting the galaxy around it. From observations of less distant galaxies, we know that this has to happen, but we have never seen it happening so early in the universe,” emphasizes Wang.
The huge mass of J0313-1806’s black hole at such an early time in the universe's history rules out two current models of how supermassive black holes form in such short timescales, notes the team. In the first model, massive stars that consist largely of hydrogen and lack most other elements that makeup later stars, including metals, form the first generation of stars in a young galaxy and provide the food for the nascent black hole. The second model involves dense star clusters, which collapse into a massive black hole right from the outset.
In both cases, however, the process takes too long to produce a black hole as massive as the one in J0313-1806 by the age at which it is seen. The team calculated that if the black hole at its center formed as early as 100 million years after the Big Bang and grew as fast as possible, it still would have had to have at least 10,000 solar masses, to begin with.
“This tells you that no matter what you do, the seed of this black hole must have formed by a different mechanism. In this case, it’s a mechanism that involves vast quantities of primordial, cold hydrogen gas directly collapsing into a seed black hole,” emphasizes Fan.
The researchers hope to uncover more about the quasar’s secrets with future observations, especially with NASA’s James Webb Space Telescope, currently slated for launch in 2021. “With ground-based telescopes, we can only see a point source. Future observations could make it possible to resolve the quasar in more detail, show the structure of its outflow and how far the wind extends into its galaxy, and that would give us a much better idea of its evolutionary stage,” says Wang.