Astronomers have used the James Webb Space Telescope (JWST) and predicted an effect by Albert Einstein more than 100 years ago to discover that small galaxies packed a huge punch in the early cosmos, forming the entire universe when it was less than 1 billion years old.
The international team found that the galaxies, which resemble dwarf galaxies that exist today, played a crucial role during a crucial phase of cosmic evolution that occurred between 500 and 900 million years after the Big Bang. These small galaxies also easily outnumbered the larger galaxies in the early universe, the scientists say. They add that these areas likely provided 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 actually talking about the global transformation of the entire universe,” Hakim Atek, principal investigator and astronomer at the Institut d’Astrophysique de Paris, told Space.com. “The biggest surprise is that these small, faint galaxies had so much power that their cumulative radiation could transform the entire universe.”
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Small driving forces behind big changes
Before about 380 million years after the Big Bang, during a period called the epoch of recombination, the now 13.8 billion-year-old universe was opaque and dark. This was because free electrons in their dense and ultra-hot state bounced endlessly around light particles called photons.
Later, however, during the Age of Recombination, the universe expanded and cooled enough for 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 suddenly allowed photons to travel freely, and as a result, the universe’s “Dark Age” ended. The cosmos suddenly became transparent to light. This ‘first light’ can be observed today in the form of a cosmic fossil that uniformly fills the universe and is called the ‘cosmic microwave background’ or ‘CMB’.
Because electrons and protons have equal but opposite electrical charges, these first atoms were electrically neutral, but would soon undergo another transformation.
After 400 million years, the first stars and galaxies were formed. During the era of reionization, neutral hydrogen, the predominant element in the universe, was converted into charged particles. These particles are called ions. Ionization is caused by electrons absorbing photons and increasing their energy, causing them to detach from atoms. Until now, scientists weren’t sure where this ionizing radiation came from.
Suspects for the radiation source behind reionization included supermassive black holes that feed on gas from accretion disks around them – causing these regions to emit high-energy radiation – large galaxies with a mass of more than 1 billion suns, and smaller galaxies with a mass of less then this one. .
‘We’ve been debating this issue for decades, whether it’s about huge black holes or huge galaxies. There are even exotic explanations, such as the destruction of dark matter causing ionizing radiation,” Atek said. ‘One of the best candidates was galaxies. and now we have shown that the contribution of small galaxies is enormous.
“We didn’t think small galaxies would be so efficient at producing ionizing radiation. It’s four times higher than we expected, even for normal-sized galaxies.”
Identifying smaller dwarf galaxies as main sources of this ionizing radiation has long been a challenge, due to their faintness.
“It was difficult to obtain this kind of information and these observations, but the JWST has spectroscopic capabilities in the infrared. One of the reasons we built the JWST is to understand what happened during the epoch of reionization,” said Arek.
Even with the impressive infrared observing power of the JWST, observing these dwarf galaxies would not 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 predicted by it.
A helping hand from Albert Einstein
General relativity suggests that all mass objects distort the fabric of space and time, which in reality are unified 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. The stronger the gravitational effects are.
This curvature not only tells planets how to orbit stars, and in turn tells those stellar bodies how to orbit the supermassive black holes at the centers of their home systems, but also changes the paths of light coming from the stars come.
Light from a background source can follow different paths around a foreground object as it travels toward Earth, and the closer that path is to a large-mass object, the more it is “bent.” Light from the same object can therefore arrive at Earth at different times due to the object in the foreground, or ‘lensing’.
This lensing can shift the location of the background object in the sky, or can cause the background object to appear in multiple places in the same image of the sky. Other times the light from the background object is amplified, and so that object in the sky is magnified.
This effect is known as “gravitational lensing,” and the JWST has used it with great success to observe ancient galaxies near the beginning of time that would otherwise have had no chance of seeing them.
To observe the newly studied distant and early dwarf galaxies and analyze the light they emit, the JWST used a cluster of galaxies called Abell 2744 as a gravitational lens. “Even for the JWST, these small galaxies are very faint, so we had to add gravitational lenses to amplify their flow,” Atek said.
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With the mystery of reionization potentially solved, the team now wants to expand this research on a larger scale with another JWST project called GLIMPSE. The researchers will first try to confirm that the specific location studied in this study is representative of the average distribution of galaxies in the universe.
Then, in addition to studying the reionization process, Atek and colleagues will try to better understand the formation of the very first galaxies, which grew into current galaxies over 12 billion years.
“So far we have mainly studied bright, massive galaxies, but these are not very typical of 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 small, low-mass galaxies. And this is what we will try to do with this upcoming program.”
The team’s research was published Wednesday (Feb. 28) in the journal Nature.