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The James Webb Space Telescope (JWST) has observed light from stars surrounding some of the universe’s former supermassive black holes, black holes seen as they were less than a billion years after the Big Bang.
Observations by a team from the Massachusetts Institute of Technology (MIT) address the question of how these cosmic giants at the cores of galaxies grow into massive masses, equivalent to millions (sometimes billions) of suns. More specifically, how did it grow so quickly? The results could also answer the puzzle: What came first, the galaxy or the supermassive black hole?
The supermassive black holes observed by the MIT team feed insatiably on the material surrounding them, generating enormous tidal forces in a disk of matter called an accretion disk, causing the disk itself to glow. This feeding state powers objects called quasars, which are located at the hearts of active galaxies. Quasars are some of the brightest objects in the universe, and some are so bright that they outshine the combined light of every star in the galaxies surrounding them.
Supermassive black holes are also shrouded in mystery, especially when viewed a billion years before the 13.8 billion year history of the universe. This is because the process of continuous black hole mergers, which scientists believe supermassive black holes grow over time, must take several billion years to begin. So, how could these giant voids exist only about a billion years after the Big Bang?
Well, one suggestion is that they got a head start, forming from so-called “heavy seed” black holes.
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Using the James Webb Space Telescope to observe faint light coming from stars in galaxies hosting six ancient quasars, the MIT team has, for the first time, gathered evidence that supermassive black holes in the early universe actually grew 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,” said Anna-Christina Ehlers, a team member and assistant professor of physics at MIT. He said in a statement. “Our results suggest that in the early universe, supermassive black holes may have gained mass before their host galaxies did, and primordial black hole seeds could have been more massive than they are today.”
What came first? Black hole or its galaxy?
Discovered in the 1960s, the intense brightness of quasars was initially thought to arise from a single star-like point. This gave rise to the name “quasar”, which is a translation of the term “quasar” object. However, researchers soon discovered that quasars are actually caused by the accumulation of massive amounts of matter in supermassive black holes located at the cores of galaxies.
However, these objects are also surrounded by stars, which are much fainter and more difficult to observe. This is because this stellar light is washed out by the brighter light of the quasar around which the star orbits. Thus, separating the light from the quasars and the light from the surrounding stars is not easy, it is like seeing the light of fireflies sitting on a lighthouse lamp about a mile away.
However, the James Webb Space Telescope’s ability to travel further back in time than any previous telescope, coupled with its high sensitivity and resolution, made this challenge less daunting. Thus, the MIT team was able to observe light traveling to Earth about 13 billion years ago from six quasars in ancient galaxies.
“The quasar outshines the host galaxy by many orders of magnitude. Previous images were not sharp enough to discern the shape of the host galaxy with all its stars,” said team member Minghao Yu, a postdoctoral researcher at MIT’s Kavli Institute for Astrophysics and Space Research. He said. “Now, for the first time, we are able to detect the light from these stars by carefully crafting the sharpest JWST images of these quasars.”
The JWST data included measurements of each of the six quasars’ light emissions over a range of wavelengths. This information was then fed 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 — stars scattered around the galaxy.
By splitting the light into two sources, the team was also able to deduce the masses of both elements in these galaxies. This revealed that supermassive black holes have masses equivalent to about 10% of the mass of the stars surrounding them.
While this may seem like a huge imbalance in favor of stars, consider how central supermassive black holes in modern galaxies have a mass of only 0.1% of the mass of stars in the galaxies surrounding them.
“This tells us something about what grows first: Is it the black hole that grows first, and then the galaxy follows? Or is it the galaxy and its stars that grow first, dominating and regulating the growth of the black hole?” Ehlers said. “We see that black holes in the early universe appear to grow faster than their host galaxies.
“This is preliminary evidence that the primordial black hole seeds could have been much larger at that time.”
“After the universe appeared, there were primordial black holes that then consumed matter and grew in a very short time. One of the big questions is understanding how these giant black holes could grow so large and so quickly,” Yu concluded. “There must be some mechanism to make the black hole gain mass earlier than its host galaxy in those first billion years.
“It’s kind of the first evidence we’re seeing of this, which is exciting.”
The team’s results are published in Astrophysical Journal.
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