In its first year of operation, the James Webb Space Telescope made one of its most unexpected discoveries: a large number of faint little red dots in the distant universe that may change our understanding of the cause of supermassive black holes. The research, led by Jorryt Matthee, assistant professor of astrophysics at the Institute of Science and Technology Austria (ISTA), has been published in The Astrophysical Journal.
In what may have been an unexpected breakthrough, the James Webb Space Telescope (JWST) discovered a cluster of tiny red dots in a tiny area of our night sky during its first year of service. Through the "eyes" of the old Hubble Space Telescope, these objects are indistinguishable from ordinary galaxies.
"JWST was not developed for this specific purpose, but it helped us determine that faint little red dots found in the universe's distant past are small versions of extremely massive black holes. These special objects may change our view of the origin of black holes," said Jorryt Matthee, assistant professor at the Institute of Science and Technology Austria (ISTA) and first author of the study.
"The current discovery could bring us one step closer to solving one of the biggest mysteries in astronomy: According to current models, some supermassive black holes in the early universe simply grew 'too fast'. So how did they form?"
Giant quasar and little red dot. NASA/ESA/CSA James Webb Space Telescope (JWST) NIRCam image of the luminous quasar J1148+5251, an extremely rare 10 billion solar mass active supermassive black hole. Quasar light is an orange star-like source with six clear diffraction spikes that was emitted 13 billion years ago. The presence of such massive black holes in the young universe poses important challenges to theories of black hole and galaxy formation. At the same time, the image also captured small dot-like red objects, so-called red dots. Several such objects appear in almost every JWST deep-sky image. Like quasar J1148+5251, the light from these objects (in these cases emitted 12.5 billion years ago) is driven by supermassive black holes. However, these black holes are a hundred to a thousand times less massive and heavily obscured by dust (making them appear red). These small red dots may represent galaxies in a stage of evolution before the quasar-luminous stage, and therefore help researchers understand the formation and role of supermassive black holes in distant galaxies.
This image is part of the EIGER project. Source: NASA, ESA, CSA, J.Matthee (ISTA), R.Mackenzie (ETH Zurich), D.Kashino (National Astronomical Observatory of Japan), S.Lilly (ETH Zurich)
The point of no return of the universe
Scientists long thought black holes were a mathematical curiosity until their existence became increasingly apparent. These strange cosmic bottomless pits may have such compact mass and strong gravity that nothing can escape their pull—they suck in everything, including cosmic dust, planets, and stars, and distort space and time around them so that not even light can escape.
Einstein's general theory of relativity, published more than a century ago, predicts that black holes can have any mass. Some of the most fascinating black holes are supermassive black holes (SMBHs), which can reach millions to billions of times the mass of the sun. Astrophysicists agree that nearly every large galaxy has a supermassive black hole at its center. Evidence that Sagittarius A* is an SMBH at the center of the Milky Way with a mass more than 4 million times that of the Sun won the 2020 Nobel Prize in Physics.
Too massive to exist
However, not all SMBHs are created equal. Sagittarius A* can be likened to a sleeping volcano, while some SMBHs grow rapidly by devouring astronomical amounts of material. As a result, they become so bright that they are visible all the way to the edge of the expanding universe. These SMBHs are called quasars and are among the brightest objects in the universe.
"One of the problems with quasars is that some of them appear to be too massive, judging from the age of the universe at which the quasars are observed. We call them 'problem quasars,'" Matthee said. "If we take into account that quasars originate from the explosion of massive stars - and that we know their maximum growth rate from the general laws of physics - it looks like some of them are growing faster than is possible. It's like a five-year-old child growing to two meters tall," he explains.
Could SMBH be growing faster than we first thought? Or are they formed differently?
Smaller versions of giant space monsters
Now, Matthee and his colleagues have identified a cluster of objects that appear as small red dots in JWST images. At the same time, they also proved that these objects are SMBHs, but not excessively massive SMBHs. The key to identifying these objects as SMBHs lies in the detection of Hα spectral emission lines with broad line profiles. The Hα line is a spectral line in the deep red region of visible light, which is emitted when hydrogen atoms are heated. The width of the spectrum tracks the movement of the gas.
"The wider the base of the Hα line, the higher the velocity of the gas. So these spectra tell us that we are looking at a very small cloud of gas that is moving very fast and orbiting something very massive like an SMBH," Matthee said.
However, these little red dots are not the giant cosmic monsters found in supermassive SMBHs. "The 'problem quasars' are blue, very bright and billions of times more massive than the Sun, while the little red dots are more like 'baby quasars'. Their masses range from 10 million to 100 million solar masses. Also, they appear red because they are filled with dust. The dust obscures the black hole, giving it a reddish color," Matthee said.
But eventually, the gas flowing from the black hole will puncture the dust cocoon, and giant planets will evolve from these little red dots. Therefore, the ISTA astrophysicist and his team believe that these little red dots are small red versions of the giant blue SMBH, in a stage that preceded the emergence of the quasar in question. "Studying the baby version of a supermassive SMBH in more detail will give us a better understanding of how the quasar in question came to exist."
A "breakthrough" technology
Matthee and his team were able to find baby quasars thanks to a data set obtained by the EIGER (Emission Line Galaxies and Intergalactic Gas in the Epoch of Reionization) and FRESCO (First Reionization Era Spectral Complete Observations) collaborative projects. These are one large and one medium JWST program that Matthee is involved with. In December last year, Physics World magazine listed EIGER as one of the top ten breakthroughs of 2023.
"EIGER was designed to specifically study rare blue supermassive quasars and their environments. It was not designed to find the little red dot. But we stumbled across them in the same data set. That's because, by using JWST's near-infrared camera, EIGER acquires the emission spectra of all objects in the universe," said Matthee. "If you hold your index finger up and extend your arm fully, the area of the night sky we've explored is about one-twentieth the surface of your fingernail. So far, we've probably only scratched the surface."
Matthee believes the current research will open up many avenues and help answer some of the biggest questions about the universe. "Black holes and SMBHs are probably the most interesting things in the universe. It's hard to explain why they exist, but they do. We hope this work will help us unravel one of the universe's greatest mysteries.
Compiled from /scitechdaily