JWST has allowed astronomers to look further into the past than any other infrared or optical telescope, observing infrared light emitted by distant galaxies just 300 million years after the Big Bang.
With the infrared telescope, we hoped to learn more about galaxy formation and solve the mysteries of the size of supermassive black holes. But we got some surprises as we went further back in time.
One such surprise is the appearance of tiny, bright red points of light that seem to dot the early universe, about 600 to 800 million years after its birth. When they were first detected and analyzed, astronomers thought they might be massive galaxies. But that assumption was at odds with how cosmological models expect galaxies to form — small clouds of dust and stars that grow larger over long periods of time.
“The revelation that massive galaxies began to form very early in the history of the universe upends what many of us thought was settled science,” Joel Leja, assistant professor of astronomy and astrophysics at Penn State, said in a statement following the initial observations. “We’ve informally called these objects ‘universe breakers’ — and so far they’ve lived up to their name.”
Of course, seeing objects that could upend our models of galaxy formation, the team wanted to be sure of what they were seeing and sought to take spectral images of these galaxies to get a better idea of the galaxies’ distance, composition, and true mass. From this analysis, they discovered that these objects are indeed quite strange, in several ways.
First, despite being only 600 to 800 million years old, the galaxies appear to be teeming with ancient stars, hundreds of millions of years old. Aside from the strangeness of their formation, this means the team has studied the first signatures of light from ancient stars ever discovered.
“These early galaxies would be so dense with stars — stars that must have formed in ways we’ve never seen, under conditions we never expected at a time when we never expected to see them,” Leja said in a statement following the latest work. “And for some reason, the universe stopped creating objects like these after just a few billion years. They’re unique to the early universe.”
But there are still more mysteries to be solved. The team estimates that galaxies have surprisingly large supermassive black holes at their centers, between 100 and 1,000 times larger than Sagittarius A* at the center of the Milky Way. That’s far too big for the galaxy around it. If the galaxy were compressed to the size of the Milky Way, the team says the closest star would be just outside our solar system, and the supermassive black hole at the center would be just 26 light-years from Earth, visible as a huge pillar of light.
“Normally, supermassive black holes are associated with galaxies,” Leja added. “They grow together and have all their major experiences together. But here we have a fully formed adult black hole living inside what should be a small galaxy. That doesn’t really make sense, because these things should grow together, or at least that’s what we thought.”
The supermassive black holes we observe in the nearby (newer) universe are, as their name suggests, quite large. Cosmologists would like to know how these supermassive black holes, which are found at the centers of most (but not all) galaxies, became so large.
There are a number of theories, including the merger of black holes and the theory that black holes grew by feeding. These early black holes, and others discovered by JWST, appear to be too large to be explained by these theories, and much larger than cosmologists expected relative to the galaxies around them.
One idea, which is perhaps becoming more favorable in light of recent observations, is that of “direct collapse” or “heavy seed” black holes. Typically, to obtain a stellar-mass black hole (in the current era of the universe), a star undergoes collapse. In the case of heavy seed black holes, the idea is that supermassive black holes would have started at about 10,000 to 100,000 solar masses, by the direct gravitational collapse of gigantic gas clouds, with no intervening stellar phase.
Several factors could also make this scenario unlikely. The gas cloud would have to collapse without fragmenting or forming clumps, although astronomers have suggested that this could be avoided if the cloud was heated by nearby young stars in pregalactic gas disks, or if the gas cloud moved at supersonic speeds in “streams” in the early universe, allowing it to grow for longer, until gravity was sufficient to begin the cloud’s collapse into an original black hole.
It is currently difficult to distinguish the precise mass of the supermassive black holes at the centers of these galaxies from that of the stars surrounding them. Further observations are planned, taking spectra over a longer period of time, to get a better picture.
“It’s very puzzling,” Leja added. “We can get this to fit poorly into our current model of the universe, but only if we’re talking about an exotic, incredibly rapid formation at the beginning of time. This is, without a doubt, the most peculiar and interesting set of objects I’ve seen in my career.”
The latest study is published in The Astrophysical Journal Letters.
.jpg)
.webp)
0 Comments