The James Webb Space Telescope (JWST) has observed light from stars around some of the universe’s former supermassive black holes – black holes as they appeared less than a billion years after the Big Bang.
The observations from a team at the Massachusetts Institute of Technology (MIT) address the question of how these cosmic titans, located at the hearts of galaxies, grew into enormous masses, equivalent to millions (sometimes even billions) of suns. More specifically, how did they grow so quickly? The findings could also answer the riddle: which came first: the galaxy or the supermassive black hole?
The supermassive black holes observed by the MIT team feed insatiably on surrounding material and generate enormous tidal forces in a disk of matter called an accretion disk, causing the disk itself to glow. This feeding situation powers objects called quasars, which reside at the hearts of active galaxies. Quasars are among the brightest objects in the cosmos, and some are so bright that they outshine the combined light of every star in the galaxies around them.
Supermassive black holes are also shrouded in mystery – especially if they are observed earlier than 1 billion years in the universe’s 13.8 billion year history. That’s because the ongoing black hole merger process, in which scientists believe supermassive black holes grow over time, should take many billions of years. How can these gigantic voids exist only about 1 billion years after the Big Bang?
One suggestion is that they got a head start, having formed from so-called ‘heavy seed’ black holes.
Related: New view of the supermassive black hole at the heart of the Milky Way hints at an exciting hidden feature
By using the JWST to observe faint light coming from stars in the host galaxies of six ancient quasars, the MIT team has collected the first evidence that supermassive black holes in the early Universe did indeed grow from heavy seeds.
“These black holes are billions of times more massive than the Sun, at a time when the universe is still in its infancy,” Anna-Christina Eilers, team member and assistant professor of physics at MIT, said in a statement. ‘Our results imply that in the early Universe, supermassive black holes may have reached their mass earlier than their host galaxies, and that the initial seeds of black holes could have been more massive than they are today.’
What came first? The black hole or its galaxy?
The intense brightness of quasars, discovered in the 1960s, was initially thought to come from a single star-like point. This led to the name ‘quasar’, a portmanteau of the term ‘quasi-stellar’ object. However, researchers soon discovered that quasars are actually caused by enormous amounts of matter accumulating in supermassive black holes at the hearts of galaxies.
However, these objects are also surrounded by stars, which are much fainter and more difficult to observe. That’s because this stellar light is washed out by the brighter light from the quasar around which the stars orbit. So separating light from quasars and light from stars around them is no small feat, akin to seeing the light from fireflies sitting on the lamp of a lighthouse about a mile away.
However, the JWST’s ability to look further back in time than any previous telescope, combined with its high sensitivity and resolution, has made this challenge less difficult. For example, the MIT team managed to observe light that has been traveling to Earth from six quasars in ancient galaxies for about 13 billion years.
“The quasar outshines its host galaxy by orders of magnitude. And previous images were not sharp enough to distinguish what the host galaxy and all its stars look like,” said team member Minghao Yue, a postdoc at MIT’s Kavli Institute for Astrophysics and Space Research , said. “Now, for the first time, we are able to reveal the light from these stars by very carefully modeling JWST’s much sharper images of those quasars.”
The JWST data includes measurements of the light emissions from each of the six quasars over a range of wavelengths. This information was then introduced into a computer model that detailed how much of this light could be attributed to a compact point source – the accretion disk around the black hole – and how much could be attributed to a more diffuse source – the stars scattered throughout the galaxy. .
By splitting the light into two sources, the team was also able to deduce the masses of both elements of these galaxies. This showed that the supermassive black holes have a mass equal to about 10% of the mass of the stars around them.
While this may sound like a huge imbalance in the stars’ favor, consider that central supermassive black holes in modern galaxies have a mass of only 0.1% that of the stars in the surrounding galaxies.
“This tells us something about what grows first: is it the black hole that grows first, and then the galaxy catches up? Or is it the galaxy and its stars that grow first, and they dominate and regulate the growth of the black hole?” Eilers said. ‘We see that black holes in the early universe appear to grow faster than their host galaxies.
“That is preliminary evidence that the original seeds of a black hole could have been more massive at the time.”
related stories
— James Webb Space Telescope discovers an ‘extremely red’ supermassive black hole growing in the early universe
– The brightest quasar ever seen is powered by a black hole that eats ‘a sun a day’
—Black hole-like “gravastars” can be stacked like Russian tea dolls
“After the universe came into existence, there were black holes that then consumed material and grew in a very short time. One of the big questions is to understand how those monstrous black holes could grow so fast and so big,” Yue concluded. ‘There must have been a mechanism that ensured that a black hole gained mass earlier in those first billion years than the galaxy in which it was located.
“It’s kind of the first evidence we’re seeing for this, and that’s exciting.”
The team’s results will be published in the Astrophysical Journal.