NASA’s Webb Space Telescope proves that galaxies changed the early universe
The stars of early galaxies allowed light to travel freely by heating and ionizing intergalactic gas, clearing large regions around them.
Cave divers equipped with fancy headlamps often explore cavities in the rocks less than a mile below our feet. It’s easy to be completely unaware of these cave systems—even if you’re sitting in a meadow above them—because the rock between you and the cave explorers blocks the light of your headlights from disturbing your otherwise idyllic afternoon.
Apply this view to conditions in the early universe, but switch from focusing on rocks to focusing on gas. After only a few hundred million years the great explosionThe universe was filled with opaque hydrogen gas that trapped light at certain wavelengths coming from stars and galaxies. Over the first billion years, the gas became completely transparent, allowing light to travel freely. Researchers have long sought conclusive evidence to explain this reversal.
New data from James Webb Space Telescope We recently determined the answer using a group of galaxies that existed when the universe was only 900 million years old. The stars in these galaxies emit enough light to ionize and heat the gas surrounding them, forming huge, transparent “bubbles.” Eventually, those bubbles met and merged, giving rise to today’s clear and expanded views.
Webb Space Telescope proves that galaxies changed the early universe
In the early universe, the gas between stars and galaxies was opaque, and energetic starlight was unable to penetrate it. But a billion years after the Big Bang, the gas became completely transparent. Why? New data from NASA’s James Webb Space Telescope has determined why: galaxy stars emit enough light to heat and ionize the gas surrounding them, elucidating our collective view over hundreds of millions of years.
The findings, by a research team led by Simon Lilly from ETH Zürich in Switzerland, are the latest insights into a time period known as the Era of Reionization (see image below), when the universe underwent radical changes. After the Big Bang, the gas in the universe was incredibly hot and dense. Over hundreds of millions of years, the gas cooled. Then the universe hit “Repeat”. The gas became hot and ionized again – likely due to early star formation in galaxies, and over millions of years, it became transparent.
Researchers have long sought conclusive evidence to explain these shifts. The new results effectively pull back the curtain on the end of this reionization period. “Not only did Webb clearly show that these transparent regions exist around galaxies, but we also measured their size,” explained Daiichi Kashino of Nagoya University in Japan, lead author of the team’s first paper. “Thanks to Webb’s data, we see galaxies reionizing the gas around them.”
These regions of transparent gas are very massive compared to galaxies – imagine a hot air balloon with a pea hanging inside. Webb’s data shows that these relatively small galaxies drove the reionization process, clearing huge regions of space around them. Over the next 100 million years, these transparent “bubbles” continued to grow larger and larger, eventually merging and causing the entire universe to become transparent.
Lilly’s team deliberately targeted a time just before the end of the reionization era, when the universe was neither completely clear nor completely opaque — it contained a mixture of gas in different states. Scientists aimed Webb in the direction of a quasar, a massive, active, and extremely luminous object Black hole It acts like a giant light bulb, shining light on the gas between the quasar and our telescopes. (You can find it in the center of this view: it’s small, pink, and has six prominent diffraction spikes.)
As the quasar light traveled toward us through different patches of gas, it was absorbed by opaque gas or moved freely through transparent gas. The team’s groundbreaking findings were only possible by pairing Webb’s data with observations of the central quasar from the WM Keck Observatory in Hawaii, and observations from the European Southern Observatory. Very large telescope and the Magellan Telescope at Las Campanas Observatory.
“By illuminating the gas along our line of sight, the quasar gives us comprehensive information about the composition and state of the gas,” explained Anna-Christina Ehlers of the Massachusetts Institute of Technology in Cambridge, Massachusetts, lead author of another paper.
The researchers then used Webb to identify galaxies near this line of sight and showed that the galaxies are generally surrounded by transparent regions with a radius of about 2 million light-years. In other words, Webb witnessed galaxies evacuating the space around them at the end of the epoch of reionization. To put that in perspective, the area covered by these galaxies is roughly the same as the distance between our own galaxy milky way The galaxy and our closest neighbour, Andromeda.
Until now, researchers haven’t had such conclusive proof of what’s causing the reionization, and before Webb, they weren’t exactly sure why.
What do these galaxies look like? “They are more chaotic than those in the neighboring universe,” explained Jorrit Mathy, also of ETH Zürich and lead author of the team’s second paper. “Webb shows that they were actively forming stars, and must have launched many supernovae. They had a very adventurous youth!”
Along the way, Ehlers used Webb’s data to confirm that the black hole in the quasar at the center of the field is the most massive hole currently known in the early universe, weighing 10 billion times the mass of the Sun. “We still cannot explain how quasars were able to grow so large so early in the history of the universe,” she said. “This is another puzzle to solve!” Webb’s stunning images also revealed no evidence that the light from the quasar had been gravitationally reflected, ensuring that the mass measurements were definitive.
The team will soon delve deeper into galaxy research in five additional fields, each centered on a central quasar. Webb’s results from the first field were so clear that they couldn’t wait to share them. “We expected to identify a few dozen galaxies that existed during the epoch of reionization, but we were easily able to select 117 galaxies,” Kashino explained. “Webb has exceeded our expectations.”
Lilly’s research team, Emission Line Galaxies and Intergalactic Gas in the Epoch of Reionization (EIGER), has demonstrated the unique power of combining conventional images from Webb’s NIRCam (near infrared camera) with data from aperture-free wide-field spectroscopy of the same instrument. mode, which gives a spectrum of every object in the images, turning Webb into what the team calls an “amazing spectral redshift machine.”
The team’s first publications include “EIGER I. A large sample of galaxies emitting O iii at 5.3 the Astrophysical Journal.
“Eiger. I. A large sample of (O iii)-emitting galaxies at 5.3 < z < 6.9 and direct evidence for local reionization by galaxies” by Daiichi Kashino, Simon J. Lilly, Jorit Mathie, Anna-Christina Ehlers, Ruari McKenzie, Rongmon Bordoloi, and Robert A. Simcoe, June 12, 2023, Astrophysical Journal.
“Eiger II. First spectroscopic characterization of young stars and ionized gas associated with strong Hβ and (O iii) line emission in galaxies at z = 5–7 with JWST” by Jorit Mathie, Ruari McKenzie, Robert A. Simcoe, Daiichi Kashino, Simon J. Lily, Rongmun Bordoloi and Anna Cristina Ehlers, June 12, 2023, Astrophysical Journal.
“Eiger III. JWST/NIRCam observations of the ultraluminous high-redshift quasar J0100+2802” by Anna-Kristina Ehlers, Robert A. June 2023, Astrophysical Journal.
The James Webb Space Telescope is the world’s leading space science observatory. Webb will solve the mysteries of our solar system, look beyond distant worlds around other stars, and explore the mysterious structures and origins of our universe and our place in it. WEB is an international led programme NASA With its partners the European Space Agency (ESA)European Space Agency) and the Canadian Space Agency.