Discovery of ‘red monster’ galaxy

Strange little red dots may really be 'black hole stars', challenges astronomers’ understanding of the early universe

"Black hole stars" are clouds of gas energized by a supermassive black hole hidden within them. A tiny black hole discovered with a white-blue disk around it. There are reddish hues all around revealing the supermassive black hole within. The discovery of an X-ray signal coinciding with the location of one of the mysterious 'little red dots' found by the James Webb Space Telescope (JWST) has strengthened the theory that the dots are 'black hole stars', huge, dense clumps of gas energized by the presence of a growing supermassive black hole within them. Astronomers puzzle over early origins of mysterious ‘red monster’ galaxy. Researchers are perplexed by a galaxy which seems too large and too dusty for its place in cosmic history. Astronomers studying the early universe with NASA’s James Webb Space Telescope (JWST) have found what seems to be a time traveler from the future: a large galaxy so chock-full of dust that the light from its bountiful blue stars has turned a crimson hue. Such heavy loads of dust are generally thought to arise much later in cosmic history than circa 400 million years after the big bang, the epoch at which this newfound galaxy appears. Although the work has yet to be peer-reviewed, a preprint study that analyzed this “red monster” galaxy, officially called EGS-z11-R0, is already making waves in the astronomical community. “It’s astonishing to think about how short these timescales are,” says Pieter van Dokkum, an astrophysicist at Yale University, who was not involved in the study. “Sharks and turtles have been around for about that long.”

The little red dots may be the biggest cosmological discovery made so far by the JWST, and possibly the most important since the discovery of dark energy. If they are what astronomers think they are, then they would act as a crucial missing link in the formation of not only supermassive black holes but also the galaxies that grow around them. The newly discovered "X-ray dot" was recognized when the JWST's observations of an area of sky containing little red dots was compared to archival observations of the same area by NASA's Chandra X-ray Observatory. For perspective, seeing such a big, dusty galaxy less than a half-billion years into the universe’s 13.8-billion-year history is a bit like finding a redwood tree towering over saplings in a recently plowed field; it’s hard to explain how something so giant reached maturity so quickly, in a cosmic blink of an eye. Clues could come from studying other behemoths lurking in the galactic vicinity, “blue monster” galaxies, also uncovered by JWST but lacking the red-inducing buildup of dust. (Red monsters shouldn’t be conflated with JWST’s “little red dots,” an entirely different but no less mysterious type of object that the observatory has spied in the early universe and that are now thought to indicate still-forming supermassive black holes.)

Chandra has identified millions of X-ray sources across the sky, but the importance of this one, only became apparent when it was noticed that it was in exactly the same location as a little red dot seen by the JWST. The X-ray source carries an energy not dissimilar to the X-ray energy of quasars, which are galaxies which host an extremely active black hole, often as the result of a galaxy merger stirring up gas and prompting that material to fall towards the black hole. Giulia Rodighiero, the study’s lead author and an astronomer at the University of Padua in Italy, had wondered whether other large objects, perhaps obscured by their own dust, might be dwelling among JWST’s blue monsters. So she and her colleagues scoured through the Dawn JWST Archive, a repository of public JWST galaxy data, for possible contenders. EGS-z11-R0 was the sole clear candidate that emerged. The telltale signature of abundant dust lies within the galaxy’s continuum of ultraviolet light, which has a relatively flat slope as a result of absorption from the dust. Rodighiero notes that while the researchers’ analysis indicates that the reddening effect comes primarily from dust, they’re still after more direct evidence because light emanating from clumps of ionized gas within the galaxy may also be involved. By obtaining a spectrum from EGS-z11-R0, that is, by gathering and parsing its light into constituent colors, or wavelengths, the team also found evidence of carbon as another sign of galactic maturity. “There’s a whole cycle that has to happen before you get to a very dust-obscured, red galaxy like this,” van Dokkum says. “It’s surprising this happened so fast and so early.” The study is a “tour de force” in extracting such indicative signatures, he adds.

Little red dots are compact, being at most just a few hundred light-years across. They are also very red, meaning they are rather cool, the existence of which tells us how cool the little red dots must be, in the range of 3,092 to 6,692 degrees Fahrenheit (1,700 to 3,700 degrees Celsius). This sounds hot to us, but it is cooler than our sun and indeed most stars except for the least massive red dwarfs. Furthermore, little red dots are very distant objects, measured to have existed 12 billion years ago, or even older still. The discovery of little red dots potentially also fulfills one of the JWST's primary science goals, which is to try and trace the origins of supermassive black holes and the galaxies that assemble around them. The new red monster is just one of a growing group, with others usually spotted at times closer to about a billion years after the big bang. Such galaxies had already surprised astronomers because of their surprising maturity. But with its placement at just 400 million years into the universe’s history, the new monster is a sort of anomaly among anomalies. Still, JWST’s keen gaze can peer back even further into the past. So far, the telescope has managed to spot galaxies as early as about 280 million years after the big bang.

The new finding, however, seems to push the universe’s earliest epochs of galaxy formation even further back than astronomers had once thought. Given the time it takes for stars to churn out such atoms and dust, van Dokkum says, EGS-z11-R0’s existence suggests astronomers could spot galaxies as early as 200 million years after the big bang. How supermassive black holes are born has been a mystery that has confounded astronomers. Do they form from the bottom up, as smaller stellar-mass black holes produced in supernova explosions combine with each other? Or, do they form from the top down, via the collapse of a vast gas cloud containing hundreds of thousands or even millions of times the mass of our sun? Little red dots are thought to be huge gas clouds hiding a burgeoning supermassive black hole within them that is feeding off the cloud, eating it from the inside-out. The gas cloud glows from the heat and energy radiated from the material swirling around the black hole, and via magnetically collimated jets of charged particles that can escape the black hole's maw. As the new class of ancient red monsters emerges, so do some key questions: How does the dust build up so fast, and why do only some galaxies have it? Finding answers will likely entail assembling a larger sample of these early-onset red monsters, as well as observing them through different instruments onboard JWST, which can detect shorter and longer infrared wavelengths, says Callum Donnan, an expert on galactic evolution at the National Science Foundation’s National Optical-Infrared Astronomy Research Laboratory.

Rodighiero and her team already have their suspicions about how the red and blue monsters can coexist in the early universe, perhaps the blue galaxies are in fact born from the red ones as the dust disperses. “We think that they are connected by the same evolutionary story,” she says. “It’s just that we catch galaxies in different periods, and it’s much easier to detect a blue monster.” She and her team hope that discovering more objects might help astronomers understand these galactic phases, and they also plan to look at a larger range of infrared light to fully confirm that EGS-z11-R0’s redness comes from its dust. Although little red dots are not yet definitive proof that supermassive black holes form through the top-down process, they do strongly indicate that. But new discovery strengthens that hypothesis even further. Furthermore, although the X-ray signal is weak at such great distances. This would happen as the huge cloud of gas rotates and different windows, some large and some smaller in size, spin into view. If this hypothesis is confirmed, then little red dots would become a crucial piece in the jigsaw of how galaxies and their supermassive black holes form, allowing astronomers to figure out the early history of galaxies such as our own Milky Way in the universe.

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