THE UNIVERSE’S OLDEST BLACK HOLE IS MUCH TOO MASSIVE

About 13 billion light years away, scientists have discovered a mysterious, supermassive black hole. It is much too big to have formed according to existing theories, so scientists have rephrased the genesis of massive black holes, allowing them to grow faster.

The supermassive black hole that cosmologists call J1342+0928 is the oldest and remotest object that has so far been observed. The hole is surrounded by a rotating disc of gas, and it is constantly attracting large, swirling gas clouds beyond the event horizon, where gravity is so extreme that not even light can escape.

The hole is the centre of a quasar – the heart of the most active, bright galaxies of space. Most quasars had their heyday about four billion years after the Big Bang, after enough time had passed for their central black holes to grow to monster sizes. However, J1342+0928 lit up the sky as soon as 690 million years after the Big Bang, but somehow, the former quasar includes a monster hole of 800 million solar masses, scientists have calculated.

The discovery of J1342+0928 in 2017 has caused astrophysicists problems, because according to the classical theory about the origin of the universe’s first supermassive black holes, the hole should not have been able to grow so huge in such a short time. Rotating gas emits radiation The light from quasars emerges, because gas clouds are accelerated to such high energy levels around the black hole at the centre that more than one third of the gas’ mass is converted into light. Moreover, the rotating gas disc creates extremely forceful magnetic

fields, which send two jet streams of electrically charged particles out through the surrounding galaxy at a speed of 99 % of that of light. In combination, the disc and the jet streams emit more light that dozens of ordinary galaxies. The light is so bright that telescopes can detect it, although the light waves have travelled through the universe for billions of years on their way towards Earth. If a jet stream points at Earth, the quasar can be seen like a floodlight.

It was the discovery of quasars that finally proved that black holes are not just a theoretical phenomenon, they actually exist. In the early 1960s, astronomers observed several mysterious sources of radio waves. They named them quasi-stars, because the radio waves from the sources were different from the radiation that comes from ordinary stars.

In 1963, American astronomer Maarten Schmidt studied one of the sources using a radio telescope in California, and he found that the radiation did not come from a star, rather from a remote, unknown object that emitted short-wave radiation. The telescope saw long radio waves instead of shorter light waves, because the light from the object had travelled through space for a billion years and had been stretched into radio waves en route due to the expansion of the universe.

The light source that Schmidt observed outshone 100 galaxies, but was not any bigger than the Solar System. There was only one

800 million solar masses is the weight of a supermassive black hole that formed 690 million years after the Big Bang.

possible explanation of the phenomenon. The cosmic beacon had to have been formed by such swirling hydrogen gases around a supermassive black hole. Following Schmidt’s observation, the objects were named quasars instead of quasi-stars.

Black holes are too large

Today, astronomers know that super-massive black holes of sizes of two million-several billion solar masses exist at the centres of all major galaxies. The biggest black holes in the modern universe have not only grown by consuming gas from the surroundings, rather by galaxy collisions, in which supermassive black holes of colliding galaxies attract each other and merge.

In 2000, astronomers spotted a quasar, which existed already 900 million years after the Big Bang. And in 2012, they observed a huge quasar with a black hole of two billion solar masses, which lit up the sky only 770 million years after the formation of the universe. The two discoveries are inconsistent with the classical theory about the formation of the first supermassive black holes, but scientists thought that the quasars had to be the exceptions that confirm the rule. A few years later, they however found the quasar with the monster hole of 800 million solar masses only 690 million years after the Big Bang, and they realized that their theory is not correct.

For decades, astronomers thought that seed corns, from which early black giants emerged, came from the first stars that were lit a few hundred million years after the Big Bang. The stars were huge as compared to modern stars, and when they had consumed all the fuel in their cores, they exploded into supernovas, leaving black holes of up to 100 solar masses. According to the classical theory, the original small black holes ( star size) grew into supermassive black holes over billions of years by consuming gas. However, the model cannot explain the monster hole of J1342+0928. Even if a star size seed corn is constantly fed gas, the hole will not be able to reach a size of some 800 million solar masses until one billion years after the Big Bang.

So, in the first place, scientists were forced to adjust the theory slightly. The huge stars were born in clusters, and the black holes they created were located close to one another. Hence, it is likely that some of the holes attracted each other, merging into black holes of around 1,000 solar masses, which immediately began to grow by consuming gas.

Holes pause from feast

Even with scientists’ extra large seed corns, it still seems almost impossible to form monster holes such as J1342+0928 in less than one billion years after the Big Bang. In principle, the old monster hole could be formed in this way, but only if the black hole always has free access to gas, and that is not realistic. When a black hole consumes gas from a rotating disc, the swirling gases around the hole emit lots of radiation, which pushes the gases further away from the hole, so after a while, there is not access to any more gas. Consequently, the growth of the hole stops for millions of years, until the hole’s huge mass has once again attracted gas to the event horizon, and the growth can start again. The many long "lunch breaks" makes it impossible for the newlydiscovered, supermassive black hole to build 800 million solar masses in just 690 million years with the method desribed by the classical theory.

So, the three quasars have made scientists search for a new explanation of how the holes grew so large.

Collapse causes huge seed corns

In order for the first supermassive black holes to be formed so quickly after the Big Bang, scientists need a theory, in which larger seed corns make up the starting points of the holes.

The leading model involves that in the young universe, huge gas clouds collapsed directly into black holes with masses of up to one million solar masses. If such heavy seed corns existed some 270 million years after the Big Bang, the early monster hole could be explained by the hole immediately starting to vacuum clean the surroundings of gas. However, the theory involves a major challenge: it must explain why the gas cloud is not cooled and gives birth to stars as usual instead of remaining hot and collapsing.

According to Priyamvada Natarajan from the US Yale University, intense radiation from a galaxy close by could prevent the cooling. The huge gas clouds of the young universe primarily consisted of hydrogen, which is most efficiently cooled, when the atoms combine with hydrogen molecules. The radiation