Voracious eater at the cosmic dawn
Astronomers found a distant galaxy vigorously spewing material from its core. It is the farthest known galaxy of its kind to shine in radio wavelengths. The discovery of this ravenous beast provides researchers with a novel tool to study galaxies and black holes in the young, unapproachable Universe.
Meet PSO J172.3556+18.7734 or, as it is known among friends, P172+18. At first sight, there is not much to it—a faint speck of light visible only to the largest telescopes on Earth. However, don’t let its shy demeanor fool you. P172+18 is a hungry beast howling at us from the time when the Universe was only 800 million years old. It took 13 billion years for its light to reach us.
P172+18 is a quasar, a special class of galaxies with an active supermassive black hole in their center. As the black hole consumes the surrounding gas, it produces light directed into a narrow cone or jet. Quasars show an incredibly diverse set of properties. Only about ten percent of them shine brightly at radio wavelengths and classify as “radio-loud”1Yes, you guessed it. The other class comprises the “radio-quiet” members. At some point, the quasar classification system got out of hand. Check Table 1 in this paper to see a list of no less than 51 different classes. It is… complicated.. P172+18 is not the first radio-loud quasar discovered in the young Universe, but it is a record breaker.
Quasar’s defining features are its black hole and the amount of material falling into it. The black hole in the center of P172+18 is about 300 million times more massive than our Sun. Impressive, but far from the stupendously large specimens that boast masses hundred times as high. P172+18’s black hole appears to be very hungry. It is consuming gas at a stunning rate.
The eating habits of our friend may be the reason why the galaxy is broadcasting across the Universe. There might be a link between the black hole’s rapid growth and the appearance of radio jets. The jets themselves could disturb the surrounding gas and cause more of it to fall into the black hole, creating a positive loop in which the black hole eats faster and radiates more light.
But nothing lasts forever. A time comes when the food source is gone and a black hole goes to sleep. Astronomers found evidence that P172+18 may actually be in the state of shutting down—it was likely brighter in the past. The variability of quasars’ emission is not a new insight. It is well known that supermassive black holes show periods of activity and inactivity. Even the Milky Way’s central black hole, which appears so calm and quiescent, had a much more turbulent past.
Discoveries of distant quasars enable us to study the Universe’s distant past, the period close to the formation of the first stars and galaxies. The existence of supermassive black holes in a young Universe is a mystery. How could they have grown so fast? And how did they influence their surroundings and subsequent growth of galaxies? P172+18 is just the first of many distant quasars that will help us answer such questions in the not-so-distant future.
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