Hi, I’m Marley, the astronomer here at the Space Centre. To end off this year, we are going to take one last look at the James Webb Space Telescope (JWST). So far, we have explored stars, other worlds, and galaxies. This month, I thought we could take a look at the early universe.
Being an infrared telescope, it was built specifically to be able to study the early universe and the mysteries that come with it. One of these mysteries happen to be the size of supermassive black holes bound at the centres of early galaxies. Sgr A* (pronounced sadge-ay-star) is the supermassive black hole at the centre of our Milky Way Galaxy. Its mass is approximately 4 million times that of the Sun, and it is on the smaller side. The supermassive black hole at the centre of galaxy M87 has a mass of about 5 billion Suns.
Some observations of distant galaxies have shown scientists that some supermassive black holes have formed in the first billion years after the universe began. It is possible that the collapse of supermassive stars in the early universe is what led to these black holes. They would have had a head start in terms of mass. Scientists also know that supermassive black holes can grow by merging with smaller objects. These include other, smaller, black holes, and neutron stars. They can even merge with other supermassive black holes when galaxies collide! But seeing them so large, so early on is what is puzzling to scientists.
Using JWST, that puzzle became a bit clearer. On November 6th, a team of scientists published their discovery of a supermassive black hole from when the universe was only 3% of its current age! This black hole lives in a galaxy named UHZ1, which is in the direction of the galaxy cluster Abell 2744. JWST has looked at this galaxy cluster before, as its gravity acts as a giant magnifying glass. It magnifies the light from galaxies behind it, allowing scientists to see galaxies that would otherwise be too faint. One of these galaxies is UHZ1.
Finding the black hole inside of UHZ1 required the use of the Chandra X-Ray Observatory. X-rays are a marker of black hole accretion, and x-rays with shorter wavelengths can be used to detect the accreting black holes, even if those black holes are surrounded by large amounts of gas and dust. Over two weeks, scientists gathered data from this galaxy. The observations showed intense X-ray emitting gas coming from the galaxy – a sign of an accreting supermassive black hole. Without the magnifying effects of Abell 2744, the x-rays would have been too faint for Chandra to detect them. The light from UHZ1 and the X-rays from the supermassive black hole were magnified by a factor of 4, thanks to the gravitational lensing effects of the cluster.
There are limits on how fast black holes can grow once they have formed, thanks to physics. From the X-ray data, the mass of the black hole in UHZ1 is estimated to be between 10 and 100 million Suns. This is close to the mass of all the stars in UHZ1, which is not something that we see in galaxies in the nearby universe. In the nearby universe, the mass of the supermassive black hole at the centre of the galaxy is usually closer to ~0.1% of the mass coming from the stars.
The brightness of the galaxy, the amount of X-rays detected, and of course the extremely large mass of the black hole in UHZ1 point to the black hole having formed from the collapse of a huge cloud of gas, instead of other formation methods mentioned earlier. This theoretical formation prediction comes from Priyamvada Natarajan, a professor in the departments of astronomy and physics of Yale University, who co-authored a paper on this. This black hole might be the first ever detection of one of these black holes, and scientists were able to see it before the mass of the stars in the galaxy begin to overpower that of the black hole.
It is still early days for figuring out the supermassive black hole formation puzzle, but discoveries like this help guide scientists on their journey. The data from this discovery and others will help paint a larger picture of what exactly was going on in our universe. Until then, see you all in the New Year!