James Webb Space Telescope finds dwarf galaxies packed enough punch to reshape the entire early universe
"The main surprise is that these small faint galaxies had so much power, their cumulative radiation could transform the entire universe."
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By Robert Lea
Astronomers have used the James Webb Space Telescope (JWST) and an effect predicted by Albert Einstein over 100 years ago to discover that small galaxies in the early cosmos packed a massive punch, shaping the entire universe when it was less than 1 billion years old.
The international team found the galaxies, which resemble dwarf galaxies that exist today, played a vital role during a crucial stage of cosmic evolution that occurred between 500 and 900 million years after the Big Bang. These small galaxies also vastly outnumbered larger galaxies in the infant universe, the scientists say, adding that it's likely the realms supplied most of the energy needed for a process called cosmic reionization. Cosmic reionization was critical to the growth and progression of the universe.
"We're really talking about the global transformation of the entire universe," Hakim Atek, research lead author and an astronomer at the Institut d'Astrophysique de Paris, told Space.com. "The main surprise is that these small, faint galaxies had so much power, their cumulative radiation could transform the entire universe."
Small driving forces behind major changes
Prior to around 380 million years after the Big Bang happened, during a period called the epoch of recombination, the now 13.8 billion-year-old universe had been opaque and dark. This was because, in its dense and ultra-hot state, free electrons endlessly bounced around particles of light, called photons.
Later, during the epoch of recombination, however, the universe had expanded and cooled enough to allow electrons to bond with protons and create the first atoms of hydrogen, the lightest and simplest element in the cosmos. This disappearance of free electrons meant photons were suddenly free to travel, and as a result, the "dark age" of the universe ended. The cosmos suddenly became transparent to light. This "first light" can seen today in the form of a cosmic fossil that uniformly fills the universe called the "cosmic microwave background" or "CMB."
Because electrons and protons have equal but opposite electric charges, these first atoms were electrically neutral, but they would soon undergo yet another transformation.
After 400 million years, the first stars and galaxies formed — then, during the era of reionization, neutral hydrogen, the predominant element in the universe, was transformed into charged particles. These particles are called ions. Ionization is caused by electrons absorbing photons and increasing their energy, breaking free from atoms. Until now, scientists weren't sure where this ionizing radiation came from.
Suspects for the radiation source behind reionization had included supermassive black holes feeding on gas from accretion disks surrounding them — causing these regions to eject high-energy radiation — large galaxies with masses in excess of 1 billion suns, and smaller galaxies with masses less than this.
"We've been debating this issue for decades, actually, whether it's massive black holes or massive galaxies. There are even exotic explanations, like dark matter annihilation that creates ionizing radiation," Atek said, "One of the best candidates was galaxies, and now we've shown that the contribution of small galaxies is huge.
"We didn't think small galaxies would be so efficient at producing ionizing radiation. It's four times higher than what we expected, even for normal-sized galaxies."
Identifying smaller dwarf galaxies as main sources of this ionizing radiation was a challenge for a long time, because of how faint they are.
"It was hard to get this kind of information and these observations, but the JWST has spectroscopic capabilities in the infrared. In fact, one of the reasons we built the JWST is to understand what happened during the epoch of reionization," Arek said.
Even with the impressive infrared observing power of the JWST, spotting these dwarf galaxies wouldn't have been possible without the help of Albert Einstein — more specifically, without the help of his 1915 theory of general relativity, and an effect on light it predicts.
A helping hand from Albert Einstein
General relativity suggests all objects of mass warp the very fabric of space and time, which are, in truth, united as a single entity called "spacetime." Our perception of gravity, the theory says, arises as a result of that curvature. The greater the mass of an object, the more "extreme" the curvature of spacetime is. Thus, the stronger its gravitational effects are.
Not only does this curvature tell planets how to move in orbits around stars and, in turn, tell those stellar bodies how to orbit the supermassive black holes at the centers of their home galaxies, but it also changes paths of light coming from the stars.
Light from a background source can take different paths around a foreground object as it travels toward Earth, and the closer that path is to an object of great mass, the more it gets "bent." Thus, light from the same object can arrive to Earth at different times as a result of the foreground, or "lensing," object.
This lensing can shift the location of the background object in the sky, or it can cause the background object to appear in multiple places in the same image of the sky. Other times, light from the background object is amplified, and thus that object is magnified in the sky.
This effect is known as "gravitational lensing," and the JWST has been using it to great effect to observe ancient galaxies near the dawn of time, which it would otherwise have had no chance of seeing.
To observe the newly studied distant and early dwarf galaxies, and analyze the light they emit, the JWST used a galaxy cluster called Abell 2744 as a gravitational lens. "Even for the JWST, these small galaxies are very faint, so we needed to add gravitational lensing to amplify the flux of from them," Atek said.
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With the mystery of reionization potentially solved, the team now aims to extend this study to a larger scale with another JWST project called GLIMPSE. The researchers will first try to confirm that the particular location studied in this research is representative of the average distribution of galaxies in the universe.
Then, beyond studying the reionization process, Atek and colleagues will aim to better understand the formation of the very first galaxies, which, over the course of 12 billion years, grew into present-day galaxies.
"So far, we've been really studying mostly bright, massive galaxies, but they are not very typical in the early universe," Atek concluded. "So if we want to understand the formation of the first galaxies, we really need to understand the formation of tiny, low-mass galaxies. And this is what we will be trying to do with this upcoming program."
The team's research was published on Wednesday (Feb. 28) in the journal Nature.
Using the James Webb Space Telescope (JWST), astronomers have discovered an "extremely red" supermassive black hole growing in the shadowy, early universe.
The red hue of the supermassive black hole, seen as it was around 700 million years after the Big Bang, is the result of the expanding universe. As the universe balloons outward in all directions, light traveling toward us gets "redshifted," and the redshifted light in this case indicates a cloak of thick gas and dust shrouding the black hole.
Examining JWST data, the astronomy team led by Lukas Furtak and Adi Zitrin of the Ben-Gurion University of the Negev, was also able to determine the mass of the supermassive black hole. At around 40 million times the mass of the sun, it is unexpectedly massive in comparison to the galaxy in which it resides.
The team also found that the supermassive black hole, which is located around 12.9 billion light-years away from Earth, is rapidly feasting on the gas and dust around it. In other words, it's growing.
Related: Brightest quasar ever seen is powered by black hole that eats a 'sun a
"We were very excited when JWST started sending its first data. We were scanning the data that arrived for the UNCOVER program, and three very compact yet red-blooming objects prominently stood out and caught our eyes," Furtak said in a statement. "Their 'red-dot' appearance immediately led us to suspect that it was a quasar-like object."
The 'three red dots'
Quasars are created when copious amounts of matter surround supermassive black holes like this one. This matter forms a disk of gas and dust called an accretion disk that gradually feeds the black hole. The immense gravitational influence of the black hole churns this matter, generating intense temperatures and causing it to glow.
Additionally, matter that doesn't fall into the supermassive black hole is channeled to the cosmic titan's poles. Particles in these regions are accelerated to speeds approaching that of light as highly collimated jets. As these relativistic jets are blasted out, the eruptions are accompanied by bright electromagnetic emissions.
As a result of these phenomena, quasars powered by supermassive black holes in active galactic nuclei (AGN) are often so bright that the light they emit often outshines the combined light of every star in the galaxy that surrounds them.
The vast amount of radiation being emitted from around this particular supermassive black hole caused it to take on a small point-like appearance in JWST data.
"Analysis of the object's colors indicated that it was not a typical star-forming galaxy. This further supported the supermassive blackhole hypothesis," Rachel Bezanson, from the University of Pittsburgh and co-lead of the UNCOVER program, said in the statement. "Together with its compact size, it became evident this was likely a supermassive black hole, although it was still different from other quasars found at those early times."
The early quasar wouldn't have been visible even to the powerful infrared eye of the JWST without a little help from an effect predicted by Albert Einstein in 1915.
Einstein's lens
Einstein's theory of general relativity suggests objects of mass warp the very fabric of space and time, which are truly united as a single entity called "spacetime." The theory continues on that gravity arises as a result of that curvature. The greater the mass of an object, the more "extreme" the curvature of spacetime is.
Not only does this curvature therefore tell planets how to move around stars and stars and how to move around the centers of their home galaxies, but it also changes paths of light coming from those stars.
The closer to the object of mass that light travels, the more its path is "bent." Different paths of light from a single background object can thus be bent by a foreground, or "lensing object," and shift the appearance of the background object's location. Sometimes, the effect can even cause the background object to appear in multiple places in the same image of the sky. Other times, light from the background object is simply amplified, and that object is magnified.
This phenomenon is known as "gravitational lensing."
In this case, the JWST used a galaxy cluster called Abell 2744 as a foreground lensing body to amplify light from background galaxies, which are otherwise too distant to see. This revealed the extremely red quasar they zeroed-in on, originally in the form of three red dots.
"We used a numerical lensing model that we had constructed for the galaxy cluster to determine that the three red dots had to be multiple images of the same background source, seen when the universe was only some 700 million years old," Zitrin said
Further analysis of the background source revealed its light must have come from a compact region.
"All the light of that galaxy must fit within a tiny region the size of a present-day star cluster. The gravitational lensing magnification of the source gave us exquisite limits on the size," team member and Princeton University researcher Jenny Greene said in the statement. "Even packing all the possible stars into such a small region, the black hole ends up being at least 1% of the total mass of the system."
The discovery further adds to the mystery of how supermassive black holes, which can be millions (or even billions) of times as massive as the sun, grew to such huge sizes during the universe's infancy.
"Several other supermassive black holes in the early universe have now been found to show a similar behavior, which leads to some intriguing views of the black hole and host galaxy growth, and the interplay between them, which is not well understood," Greene said.
The JWST has detected a wealth of "little red dots" over time. These could also indicate feeding supermassive black hole-powered quasars in the early universe, maybe meaning a striking black hole growth conundrum could soon be solved.
"In a way, it's the astrophysical equivalent of the chicken and egg problem," Zitrin concluded. "We do not currently know which came first — the galaxy or black hole, how massive the first black holes were, and how they grew."
The team's research was published on Feb. 14 in the journal Nature.
