̽��ֱ�� of Cambridge - Big Bang

Webb Telescope sees galaxy in mysteriously clearing fog of early Universe

sc604 — Wed, 26 Mar 2025 16:00:00 +0000

A key goal of the NASA/ESA/CSA James Webb Space Telescope has been to see further than ever before into the distant past of our Universe, when the first galaxies were forming after the Big Bang, a period know as cosmic dawn.

Researchers studying one of those very early galaxies have now made a discovery in the spectrum of its light, that challenges our established understanding of the Universe’s early history. Their results are reported in the journal Nature.

Webb discovered the incredibly distant galaxy JADES-GS-z13-1, observed at just 330 million years after the Big Bang. Researchers used the galaxy’s brightness in different infrared filters to estimate its redshift, which measures a galaxy’s distance from Earth based on how its light has been stretched out during its journey through expanding space.

̽��ֱ��NIRCam imaging yielded an initial redshift estimate of 12.9. To confirm its extreme redshift, an international team led by Dr Joris Witstok, previously of the ̽��ֱ�� of Cambridge’s Kavli Institute for Cosmology, observed the galaxy using Webb’s Near-Infrared Spectrograph (NIRSpec) instrument.

̽��ֱ��resulting spectrum confirmed the redshift to be 13.0. This equates to a galaxy seen just 330 million years after the Big Bang, a small fraction of the Universe’s present age of 13.8 billion years.

But an unexpected feature also stood out: one specific, distinctly bright wavelength of light, identified as the Lyman-α emission radiated by hydrogen atoms. This emission was far stronger than astronomers thought possible at this early stage in the Universe’s development.

“ ̽��ֱ��early Universe was bathed in a thick fog of neutral hydrogen,” said co-author Professor Roberto Maiolino from Cambridge’s Kavli Institute for Cosmology. “Most of this haze was lifted in a process called reionisation, which was completed about one billion years after the Big Bang.

“GS-z13-1 is seen when the Universe was only 330 million years old, yet it shows a surprisingly clear, telltale signature of Lyman-α emission that can only be seen once the surrounding fog has fully lifted. This result was totally unexpected by theories of early galaxy formation and has caught astronomers by surprise.”

Before and during the epoch of reionisation, neutral hydrogen fog surrounding galaxies blocked any energetic ultraviolet light they emitted, much like the filtering effect of coloured glass. Until enough stars had formed and were able to ionise the hydrogen gas, no such light — including Lyman-α emission — could escape from these fledgling galaxies to reach Earth.

̽��ֱ��confirmation of Lyman-α radiation from this galaxy has great implications for our understanding of the early Universe. “We really shouldn’t have found a galaxy like this, given our understanding of the way the Universe has evolved,” said co-author Kevin Hainline from the ̽��ֱ�� of Arizona. “We could think of the early Universe as shrouded with a thick fog that would make it exceedingly difficult to find even powerful lighthouses peeking through, yet here we see the beam of light from this galaxy piercing the veil.”

̽��ֱ��source of the Lyman-α radiation from this galaxy is not yet known, but it may include the first light from the earliest generation of stars to form in the Universe. “ ̽��ֱ��large bubble of ionised hydrogen surrounding this galaxy might have been created by a peculiar population of stars — much more massive, hotter and more luminous than stars formed at later epochs, and possibly representative of the first generation of stars,” said Witstok, who is now based at the Cosmic Dawn Center at the ̽��ֱ�� of Copenhagen. A powerful active galactic nucleus, driven by one of the first supermassive black holes, is another possibility identified by the team.

̽��ֱ��team plans further follow-up observations of GS-z13-1, aiming to obtain more information about the nature of this galaxy and origin of its strong Lyman-α radiation. Whatever the galaxy is concealing, it is certain to illuminate a new frontier in cosmology.

JWST is an international partnership between NASA, ESA and the Canadian Space Agency (CSA). ̽��ֱ��data for this result were captured as part of the JWST Advanced Deep Extragalactic Survey (JADES).

Reference:
Joris Witstok et al. ‘Witnessing the onset of reionization through Lyman-α emission at redshift 13.’ Nature (2025). DOI: 10.1038/s41586-025-08779-5

Adapted from an ESA media release.

Astronomers have identified a bright hydrogen emission from a galaxy in the very early Universe. ̽��ֱ��surprise finding is challenging researchers to explain how this light could have pierced the thick fog of neutral hydrogen that filled space at that time.

This result was totally unexpected by theories of early galaxy formation and has caught astronomers by surprise

Roberto Maiolino

ESA/Webb, NASA, STScI, CSA, JADES Collaboration

JADES-GS-z13-1 in the GOODS-S field

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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Galaxy mergers solve early Universe mystery

sc604 — Thu, 18 Jan 2024 16:28:39 +0000

This has solved one of the most puzzling mysteries in astronomy – why astronomers detect light from hydrogen atoms that should have been entirely blocked by the pristine gas that formed after the Big Bang.

These new observations have found small, faint objects surrounding the galaxies that show the ‘inexplicable’ hydrogen emission. In conjunction with state-of-the-art simulations of galaxies in the early Universe, the observations have shown that the chaotic merging of these neighbouring galaxies is the source of this hydrogen emission. ̽��ֱ��results are reported in the journal Nature Astronomy.

Light travels at a finite speed (300 000 km a second), which means that the further away a galaxy is, the longer it has taken the light from it to reach our Solar System. As a result, not only do observations of the most distant galaxies probe the far reaches of the Universe, but they also allow us to study the Universe as it was in the past.

To study the early Universe, astronomers require exceptionally powerful telescopes that are capable of observing very distant – and therefore very faint – galaxies. One of Webb’s key capabilities is its ability to observe these galaxies, and probe the early history of the Universe.

̽��ֱ��earliest galaxies were sites of vigorous and active star formation, and were rich sources of a type of light emitted by hydrogen atoms called Lyman-α emission. However, during the epoch of reionisation, an immense amount of neutral hydrogen gas surrounded these stellar nurseries. Furthermore, the space between galaxies was filled by more of this neutral gas than is the case today. ̽��ֱ��gas can effectively absorb and scatter this kind of hydrogen emission, so astronomers have long predicted that the abundant Lyman-α emission released in the early Universe should not be observable today.

This theory has not always stood up to scrutiny, however, as examples of early hydrogen emission have previously been observed by astronomers. This has presented a mystery: how is it that this hydrogen emission – which should have long since been absorbed or scattered – is being observed?

“One of the most puzzling issues that previous observations presented was the detection of light from hydrogen atoms in the very early Universe, which should have been entirely blocked by the pristine neutral gas that was formed after the Big Bang,” said lead author Callum Witten from Cambridge’s Institute of Astronomy. “Many hypotheses have previously been suggested to explain the great escape of this ‘inexplicable’ emission.”

̽��ֱ��team’s breakthrough came thanks to Webb’s combination of angular resolution and sensitivity. ̽��ֱ��observations with Webb’s NIRCam instrument were able to resolve smaller, fainter galaxies that surround the bright galaxies from which the ‘inexplicable’ hydrogen emission had been detected. In other words, the surroundings of these galaxies appear to be a much busier place than we previously thought, filled with small, faint galaxies.

These smaller galaxies were interacting and merging with one another, and Webb has revealed that galaxy mergers play an important role in explaining the mystery emission from the earliest galaxies.

“Where Hubble was seeing only a large galaxy, Webb sees a cluster of smaller interacting galaxies, and this revelation has had a huge impact on our understanding of the unexpected hydrogen emission from some of the first galaxies,” said co-author Sergio Martin-Alvarez from Stanford ̽��ֱ��.

̽��ֱ��team then used computer simulations to explore the physical processes that might explain their results. They found that the rapid build-up of stellar mass through galaxy mergers both drove strong hydrogen emission and facilitated the escape of that radiation via channels cleared of the abundant neutral gas. So, the high merger rate of the previously unobserved smaller galaxies presented a compelling solution to the long-standing puzzle of the ‘inexplicable’ early hydrogen emission.

̽��ֱ��team is planning follow-up observations with galaxies at various stages of merging, to continue to develop their understanding of how the hydrogen emission is ejected from these changing systems. Ultimately, this will enable them to improve our understanding of galaxy evolution.

Reference:
Callum Witten et al. ‘Deciphering Lyman-α emission deep into the epoch of reionization.’ Nature Astronomy (2024). DOI: 10.1038/s41550-023-02179-3

Adapted from an ESA press release.

A team of astronomers, led by the ̽��ֱ�� of Cambridge, has used the NASA/ESA/CSA James Webb Space Telescope to reveal, for the first time, what lies in the local environment of galaxies in the very early Universe.

ESA/Webb, NASA & CSA, S. Finkelstein (UT Austin), M. Bagley (UT Austin), R. Larson (UT Austin), A. Pagan (STScI), C. Witten, M.

Zooming in on three neighbouring galaxies (NIRCam image)

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Astronomers detect oldest black hole ever observed

sc604 — Wed, 17 Jan 2024 15:59:26 +0000

̽��ֱ��international team, led by the ̽��ֱ�� of Cambridge, used the NASA/ESA/CSA James Webb Space Telescope (JWST) to detect the black hole, which dates from 400 million years after the big bang, more than 13 billion years ago. ̽��ֱ��results, which lead author Professor Roberto Maiolino says are “a giant leap forward”, are reported in the journal Nature.

That this surprisingly massive black hole – a few million times the mass of our Sun – even exists so early in the universe challenges our assumptions about how black holes form and grow. Astronomers believe that the supermassive black holes found at the centre of galaxies like the Milky Way grew to their current size over billions of years. But the size of this newly-discovered black hole suggests that they might form in other ways: they might be ‘born big’ or they can eat matter at a rate that’s five times higher than had been thought possible.

According to standard models, supermassive black holes form from the remnants of dead stars, which collapse and may form a black hole about a hundred times the mass of the Sun. If it grew in an expected way, this newly-detected black hole would take about a billion years to grow to its observed size. However, the universe was not yet a billion years old when this black hole was detected.

“It’s very early in the universe to see a black hole this massive, so we’ve got to consider other ways they might form,” said Maiolino, from Cambridge’s Cavendish Laboratory and Kavli Institute for Cosmology. “Very early galaxies were extremely gas-rich, so they would have been like a buffet for black holes.”

Like all black holes, this young black hole is devouring material from its host galaxy to fuel its growth. Yet, this ancient black hole is found to gobble matter much more vigorously than its siblings at later epochs.

̽��ֱ��young host galaxy, called GN-z11, glows from such an energetic black hole at its centre. Black holes cannot be directly observed, but instead they are detected by the tell-tale glow of a swirling accretion disc, which forms near the edges of a black hole. ̽��ֱ��gas in the accretion disc becomes extremely hot and starts to glow and radiate energy in the ultraviolet range. This strong glow is how astronomers are able to detect black holes.

GN-z11 is a compact galaxy, about one hundred times smaller than the Milky Way, but the black hole is likely harming its development. When black holes consume too much gas, it pushes the gas away like an ultra-fast wind. This ‘wind’ could stop the process of star formation, slowly killing the galaxy, but it will also kill the black hole itself, as it would also cut off the black hole’s source of ‘food’.

Maiolino says that the gigantic leap forward provided by JWST makes this the most exciting time in his career. “It’s a new era: the giant leap in sensitivity, especially in the infrared, is like upgrading from Galileo’s telescope to a modern telescope overnight,” he said. “Before Webb came online, I thought maybe the universe isn’t so interesting when you go beyond what we could see with the Hubble Space Telescope. But that hasn’t been the case at all: the universe has been quite generous in what it’s showing us, and this is just the beginning.”

Maiolino says that the sensitivity of JWST means that even older black holes may be found in the coming months and years. Maiolino and his team are hoping to use future observations from JWST to try to find smaller ‘seeds’ of black holes, which may help them untangle the different ways that black holes might form: whether they start out large or they grow fast.

̽��ֱ��research was supported in part by the European Research Council, the Royal Society, and the Science and Technology Facilities Council (STFC), part of UK Research and Innovation (UKRI).

Reference:
Roberto Maiolino et al. ‘A small and vigorous black hole in the early Universe.’ Nature (2024). DOI: 10.1038/s41586-024-07052-5

Researchers have discovered the oldest black hole ever observed, dating from the dawn of the universe, and found that it is ‘eating’ its host galaxy to death.

It’s a new era: the giant leap in sensitivity, especially in the infrared, is like upgrading from Galileo’s telescope to a modern telescope overnight

Roberto Maiolino

NASA, ESA, and P. Oesch (Yale ̽��ֱ��)

̽��ֱ��GN-z11 galaxy, taken by the Hubble Space Telescope

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Early universe crackled with bursts of star formation, Webb Telescope shows

sc604 — Tue, 06 Jun 2023 00:52:41 +0000

One of the largest programmes in Webb’s first year of science is the JWST Advanced Deep Extragalactic Survey, or JADES, which will devote about 32 days of telescope time to uncover and characterise faint, distant galaxies. While data is still coming in, JADES has already discovered hundreds of galaxies that existed when the universe was less than 600 million years old. ̽��ֱ��international team, including researchers from the ̽��ֱ�� of Cambridge, also has identified galaxies sparkling with a multitude of young, hot stars.

̽��ֱ��extragalactic research group at the Cavendish Laboratory co-led by Professor Roberto Maiolino and Dr Sandro Tacchella is playing a leadership role in JADES, which is a partnership between the science team of NIRCam — JWST’s primary imager — and NIRSpec — JWST’s primary spectrograph.

In the autumn of 2022, JADES took deep imaging and spectroscopy in and around the iconic Hubble Ultra Deep Field. ̽��ֱ��JADES imaging is deep, extends further into the infrared, and covers a wider area than any previous imaging with the Hubble Space Telescope. Results based on this data, which have not yet been peer-reviewed, are being reported at the 242nd meeting of the American Astronomical Society in Albuquerque, New Mexico.

“With JADES, we want to answer a lot of questions, like: How did the earliest galaxies assemble themselves? How fast did they form stars? Why do some galaxies stop forming stars?” said Marcia Rieke of the ̽��ֱ�� of Arizona, co-lead of the JADES programme.

For hundreds of millions of years after the big bang, the universe was filled with a gaseous fog. By one billion years after the big bang, the fog had cleared and the universe became transparent, a process known as reionisation. Scientists have debated whether active, supermassive black holes or galaxies full of hot, young stars were the primary cause of reionisation.

As part of the JADES programme, researchers studied these galaxies to look for signatures of star formation – and found them in abundance. “Almost every single galaxy that we are finding shows these unusually strong emission line signatures indicating intense recent star formation. These early galaxies were very good at creating hot, massive stars,” said Ryan Endsley from the ̽��ֱ�� of Texas at Austin.

These bright, massive stars pumped out ultraviolet light, which transformed surrounding gas from opaque to transparent by ionising the atoms, removing electrons from their nuclei. Since these early galaxies had such a large population of hot, massive stars, they may have been the main driver of the reionisation process. ̽��ֱ��later reuniting of the electrons and nuclei produces distinctively strong emission lines.

̽��ֱ��team also found evidence that these young galaxies underwent periods of rapid star formation interspersed with quiet periods where fewer stars formed. These fits and starts may have occurred as galaxies captured clumps of the gaseous raw materials needed to form stars. Alternatively, since massive stars quickly explode, they may have injected energy into the surrounding environment periodically, preventing gas from condensing to form new stars.

Another JADES result released today concerns the structural evolution of galaxies. ̽��ֱ��team used imaging and spectroscopy data to tackle a key unknown in extragalactic astrophysics, which is how the structural diversity of galaxies we observe today came to be.

̽��ֱ��team discovered a galaxy in the infant universe – just 700 million years after the big bang – but with the structure of a far more mature galaxy. ̽��ֱ��galaxy is 100 times less massive than the Milky Way, but it is highly compact. Most of the young stars of this galaxy are in the outskirts, indicating that this galaxy is growing from the inside out.

“I was surprised to find such a compact galaxy this early in the universe,” said Tacchella, from Cambridge’s Cavendish Laboratory and Kavli Institute for Cosmology. “I’m excited that the telescope works so well, allowing us to do such detailed measurements of galaxies that are so distant.”

Another element of the JADES programme involves the search for the earliest galaxies that existed when the universe was less than 400 million years old. By studying these galaxies, astronomers can explore how star formation in the early years after the big bang was different from what is seen in current times.

̽��ֱ��light from faraway galaxies is stretched to longer wavelengths and redder colours by the expansion of the universe – a phenomenon called redshift. By measuring a galaxy’s redshift, astronomers can learn how far away it is and, therefore, when it existed in the early universe. Before Webb, there were only a few dozen galaxies observed above a redshift of 8, when the universe was younger than 650 million years old, but JADES has now uncovered nearly a thousand of these extremely distant galaxies.

̽��ֱ��gold standard for determining redshift involves looking at a galaxy’s spectrum, which measures its brightness at closely spaced wavelengths. But a good approximation can be determined by taking photos of a galaxy using filters that each cover a narrow band of colours to get a handful of brightness measurements. In this way, researchers can determine estimates for the distances of many thousands of galaxies at once.

Kevin Hainline of the ̽��ֱ�� of Arizona in Tucson and his colleagues used Webb’s NIRCam (Near-Infrared Camera) instrument to obtain these measurements, called photometric redshifts, and identified more than 700 candidate galaxies that existed when the universe was between 370 million and 650 million years old. ̽��ֱ��sheer number of these galaxies was far beyond predictions from observations made before Webb’s launch. ̽��ֱ��observatory’s resolution and sensitivity are allowing astronomers to get a better view of these distant galaxies than ever before.

“Previously, the earliest galaxies we could see just looked like little smudges. And yet those smudges represent millions or even billions of stars at the beginning of the universe,” said Hainline. “Now, we can see that some of them are actually extended objects with visible structure. We can see groupings of stars being born only a few hundred million years after the beginning of time.”

“We’re finding star formation in the early universe is much more complicated than we thought,” said Rieke.

Adapted from a NASA press release.

Among the most fundamental questions in astronomy is: How did the first stars and galaxies form? ̽��ֱ��James Webb Space Telescope (JWST), a partnership between NASA, the European Space Agency and the Canadian Space Agency, is already providing new insights into this question.

I’m excited that the telescope works so well, allowing us to do such detailed measurements of galaxies that are so distant

Sandro Tacchella

NASA, ESA, CSA, Brant Robertson, Ben Johnson, Sandro Tacchella, Marcia Rieke, Daniel Eisenstein

This infrared image from NASA’s James Webb Space Telescope (JWST) was taken for the JWST Advanced Deep Extragalactic Survey, or JADES, programme.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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Webb telescope reaches new milestone in its search for distant galaxies

sc604 — Fri, 09 Dec 2022 14:50:15 +0000

An international team of astronomers, including scientists at the Universities of Cambridge, Hertfordshire and Oxford, has reported the discovery of the earliest galaxies ever confirmed in our Universe.

Using data from the James Webb Space Telescope (JWST), scientists have confirmed observations of galaxies dating back to the earliest days of the Universe, less than 350 million years after the Big Bang – when the Universe was just 2% of its current age.

Images from JWST had previously suggested possible candidates for such early galaxies. Now, their age has been confirmed using long spectroscopic observations, which measure light to determine the speed and composition of objects in space.

These observations have revealed distinctive patterns in the tiny amount of light coming from these incredibly faint galaxies, allowing scientists to establish that the light they are emitting has taken 13.4 billion years to reach us, and corroborating their status as some of the earliest galaxies ever observed.

Scientists can also now confirm that two of these galaxies are further away than any observations made by the Hubble telescope – underlining JWST’s incredible power and ability to detect never-before-seen parts of the earliest Universe.

“It was crucial to prove that these galaxies do indeed inhabit the early Universe, as it’s very possible for closer galaxies to masquerade as very distant galaxies,” said Dr Emma Curtis-Lake from the ̽��ֱ�� of Hertfordshire, lead author on one of two papers on the findings. “Seeing the spectrum revealed as we hoped, confirming these galaxies as being at the true edge of our view, some further away than Hubble could see – it is a tremendously exciting achievement for the mission!”

̽��ֱ��findings have been achieved by an international collaboration of more than 80 astronomers from ten countries via the JWST Advanced Deep Extragalactic Survey (JADES) programme. ̽��ֱ��team were allocated just over a month of observation on the telescope, using the two on-board instruments: the Near-Infrared Spectrograph (NIRSpec) and the Near-Infrared Camera (NIRCam). These instruments were developed with the primary purpose of investigating the earliest and faintest galaxies.

“It is hard to understand galaxies without understanding the initial periods of their development,” said Dr Sandro Tacchella from Cambridge’s Cavendish Laboratory and Kavli Institute for Cosmology, co-lead author on the second paper. “Much as with humans, so much of what happens later depends on the impact of these early generations of stars. So many questions about galaxies have been waiting for the transformative opportunity of Webb, and we’re thrilled to be able to play a part in revealing this story.”

“For the first time, we have discovered galaxies only 350 million years after the big bang, and we can be absolutely confident of their fantastic distances,” said Brant Robertson from the ̽��ֱ�� of California Santa Cruz, co-lead author on the second paper. “To find these early galaxies in such stunningly beautiful images is a special experience.”

Across 10 days of their observation time, the JADES team of astronomers focused on a small patch of sky in and around Hubble Space Telescope’s Ultra Deep Field, which for over 20 years has been a favourite of astronomers and has been analysed at the limit of nearly every large telescope to have existed. However, with JWST, the team were able to observe in nine different infrared wavelength ranges, providing an exquisitely sharp and sensitive picture of the field. ̽��ֱ��image reveals nearly 100,000 galaxies, each billions of light years away, in a pinprick of the sky equivalent to looking at a mobile phone screen across a football field.

̽��ֱ��very earliest galaxies were identifiable by their distinctive banded colours, visible in infrared light but invisible in other wavelengths. In one rare continuous 28-hour observation window, the Near-Infrared Spectrograph was used to spread out the light emitting from each galaxy into a rainbow spectrum. This allowed astronomers to measure the amount of light received at each wavelength and study the unique light patterns created by the properties of the gas and stars within each galaxy.

Crucially, four of the galaxies were revealed to originate earlier in the Universe than any previous observations.

“Our observations suggest that the formation of the first stars and galaxies started very early in the history of the Universe,” said Professor Andrew Bunker from the ̽��ֱ�� of Oxford.

“This is a major leap forward in our understanding of how the first galaxies formed,” said Professor Roberto Maiolino from Cambridge’s Cavendish Laboratory and Kavli Institute for Cosmology, co-author on one of the two papers. “We have been able to dissect the light coming from these galaxies in the very early universe and, for the first time, characterise in detail their properties. It’s really fascinating and intriguing to discover how young these systems were and that stellar processes hadn’t yet managed to pollute these galaxies with chemical elements heavier than helium.”

Astronomers in the JADES team now plan to focus on another area of the sky to conduct further spectroscopy and imaging, hoping to reveal more about the earliest origins of our Universe and how these first galaxies evolve with cosmic time.

More information about the findings can be found in a newly-published NASA blog. Pre-prints of the team’s two papers, which have not yet been peer-reviewed, are available online.

̽��ֱ��James Webb Space Telescope is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency). Sandro Tacchella is a Fellow of St Edmund’s College, Cambridge.

Adapted from a ̽��ֱ�� of Hertfordshire media release.

New findings confirm that JWST has surpassed the Hubble telescope in its ability to observe the early Universe

So many questions about galaxies have been waiting for the transformative opportunity of Webb, and we’re thrilled to be able to play a part in revealing this story

Sandro Tacchella

NASA, ESA, CSA, M. Zamani (ESA/Webb)

This image taken by the James Webb Space Telescope highlights the region of study by the JWST Advanced Deep Extragalactic Survey (JADES).

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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Non-detection of key signal allows astronomers to determine what the first galaxies were – and weren’t – like

sc604 — Mon, 28 Nov 2022 16:00:00 +0000

Using data from India’s SARAS3 radio telescope, researchers led by the ̽��ֱ�� of Cambridge were able to look at the very early Universe – just 200 million years after the Big Bang – and place limits on the mass and energy output of the first stars and galaxies.

Counterintuitively, the researchers were able to place these limits on the earliest galaxies by not finding the signal they had been looking for, known as the 21-centimetre hydrogen line.

This non-detection allowed the researchers to make other determinations about the cosmic dawn, placing restraints on the first galaxies, and enabling them to rule out scenarios including galaxies that were inefficient heaters of cosmic gas and efficient producers of radio emissions.

While we cannot yet directly observe these early galaxies, the results, reported in the journal Nature Astronomy, represent an important step in understanding how our Universe transitioned from mostly empty to one full of stars.

Understanding the early Universe, when the first stars and galaxies formed, is one of the major goals of new observatories. ̽��ֱ��results obtained using the SARAS3 data are a proof-of-concept study that paves the way to understanding this period in the development of the Universe.

̽��ֱ��SKA project – involving two next-generation telescopes due to be completed by the end of the decade – will likely be able to make images of the early Universe, but for current telescopes, the challenge is to detect the cosmological signal of the first stars re-radiated by thick hydrogen clouds.

This signal is known as the 21-centimetre line – a radio signal produced by hydrogen atoms in the early Universe. Unlike the recently launched JWST, which will be able to directly image individual galaxies in the early Universe, studies of the 21-centimetre line, made with radio telescopes such as the Cambridge-led REACH (Radio Experiment for the Analysis of Cosmic Hydrogen), can tell us about entire populations of even earlier galaxies. ̽��ֱ��first results are expected from REACH early in 2023.

To detect the 21-centimetre line, astronomers look for a radio signal produced by hydrogen atoms in the early Universe, affected by light from the first stars and the radiation behind the hydrogen fog. Earlier this year, the same researchers developed a method that they say will allow them to see through the fog of the early universe and detect light from the first stars. Some of these techniques have been already put to practice in the current study.

In 2018, another research group operating the EDGES experiment published a result that hinted at a possible detection of this earliest light. ̽��ֱ��reported signal was unusually strong compared to what is expected in the simplest astrophysical picture of the early Universe. Recently, the SARAS3 data disputed this detection: the EDGES result is still awaiting confirmation from independent observations.

In a re-analysis of the SARAS3 data, the Cambridge-led team tested a variety of astrophysical scenarios which could potentially explain the EDGES result, but they did not find a corresponding signal. Instead, the team was able to place some limits on properties of the first stars and galaxies.

̽��ֱ��results of the SARAS3 analysis are the first time that radio observations of the averaged 21-centimetre line have been able to provide an insight to the properties of the first galaxies in the form of limits of their main physical properties.

Working with collaborators in India, Australia and Israel, the Cambridge team used data from the SARAS3 experiment to look for signals from cosmic dawn, when the first galaxies formed. Using statistical modelling techniques, the researchers were not able to find a signal in the SARAS3 data.

"We were looking for a signal with a certain amplitude,” said Harry Bevins, a PhD student from Cambridge’s Cavendish Laboratory and the paper’s lead author. “But by not finding that signal, we can put a limit on its depth. That, in turn, begins to inform us about how bright the first galaxies were.”

“Our analysis showed that the hydrogen signal can inform us about the population of first stars and galaxies,” said co-lead author Dr Anastasia Fialkov from Cambridge’s Institute of Astronomy. “Our analysis places limits on some of the key properties of the first sources of light including the masses of the earliest galaxies and the efficiency with which these galaxies can form stars. We also address the question of how efficiently these sources emit X-ray, radio and ultraviolet radiation.”

“This is an early step for us in what we hope will be a decade of discoveries about how the Universe transitioned from darkness and emptiness to the complex realm of stars, galaxies and other celestial objects we can see from Earth today,” said Dr Eloy de Lera Acedo from Cambridge’s Cavendish Laboratory, who co-led the research.

̽��ֱ��observational study, the first of its kind in many respects, excludes scenarios in which the earliest galaxies were both more than a thousand times as bright as present galaxies in their radio-band emission and were poor heaters of hydrogen gas.

“Our data also reveals something which has been hinted at before, which is that the first stars and galaxies could have had a measurable contribution to the background radiation that appeared as a result of the Big Bang and which has been travelling towards us ever since,” said de Lera Acedo, “We are also establishing a limit to that contribution.”

“It’s amazing to be able to look so far back in time – to just 200 million years after the Big Bang- and be able to learn about the early Universe,” said Bevins.

̽��ֱ��research was supported in part by the Science and Technology Facilities Council (STFC), part of UK Research & Innovation (UKRI), and the Royal Society. ̽��ֱ��Cambridge authors are all members of the Kavli Institute for Cosmology in Cambridge.

Reference:
H T J Bevins et al. ‘Astrophysical constraints from the SARAS 3 non-detection of the cosmic dawn sky-averaged 21-cm signal.’ Nature Astronomy (2022). DOI: 10.1038/s41550-022-01825-6

Researchers have been able to make some key determinations about the first galaxies to exist, in one of the first astrophysical studies of the period in the early Universe when the first stars and galaxies formed, known as the cosmic dawn.

This is an early step for us in what we hope will be a decade of discoveries about how the Universe transitioned from darkness and emptiness to the complex realm of stars and galaxies we can see today

Eloy de Lera Acedo

NASA Goddard

Early galaxies capture by the NASA/ESA Hubble Telescope

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Licence type:

Public Domain

Can cosmic inflation be ruled out?

sc604 — Thu, 03 Nov 2022 11:59:51 +0000

̽��ֱ��astrophysicists, from the ̽��ֱ�� of Cambridge, the ̽��ֱ�� of Trento, and Harvard ̽��ֱ��, say that there is a clear, unambiguous signal in the cosmos that could eliminate inflation as a possibility. Their paper, published in ̽��ֱ��Astrophysical Journal Letters, argues that this signal – known as the cosmic graviton background (CGB) – can feasibly be detected, although it will be a massive technical and scientific challenge.

“Inflation was theorised to explain various fine-tuning challenges of the so-called hot Big Bang model,” said the paper’s first author Dr Sunny Vagnozzi, from Cambridge’s Kavli Institute for Cosmology, and who is now based at the ̽��ֱ�� of Trento. “It also explains the origin of structure in our Universe as a result of quantum fluctuations.

“However, the large flexibility displayed by possible models for cosmic inflation which span an unlimited landscape of cosmological outcomes raises concerns that cosmic inflation is not falsifiable, even if individual inflationary models can be ruled out. Is it possible in principle to test cosmic inflation in a model-independent way?”

Some scientists raised concerns about cosmic inflation in 2013, when the Planck satellite released its first measurements of the cosmic microwave background (CMB), the universe's oldest light.

“When the results from the Planck satellite were announced, they were held up as a confirmation of cosmic inflation,” said Professor Avi Loeb from Harvard ̽��ֱ��, Vagnozzi’s co-author on the current paper. “However, some of us argued that the results might be showing just the opposite.”

Along with Anna Ijjas and Paul Steinhardt, Loeb was one of those who argued that results from Planck showed that inflation posed more puzzles than it solved, and that it was time to consider new ideas about the beginnings of the universe, which, for instance, may have begun not with a bang but with a bounce from a previously contracting cosmos.

̽��ֱ��maps of the CMB released by Planck represent the earliest time in the universe we can ‘see’, 100 million years before the first stars formed. We cannot see farther.

“ ̽��ֱ��actual edge of the observable universe is at the distance that any signal could have travelled at the speed-of-light limit over the 13.8 billion years that elapsed since the birth of the Universe,” said Loeb. “As a result of the expansion of the universe, this edge is currently located 46.5 billion light years away. ̽��ֱ��spherical volume within this boundary is like an archaeological dig centred on us: the deeper we probe into it, the earlier is the layer of cosmic history that we uncover, all the way back to the Big Bang which represents our ultimate horizon. What lies beyond the horizon is unknown.”

In could be possible to dig even further into the universe’s beginnings by studying near-weightless particles known as neutrinos, which are the most abundant particles that have mass in the universe. ̽��ֱ��Universe allows neutrinos to travel freely without scattering from approximately a second after the Big Bang, when the temperature was ten billion degrees. “ ̽��ֱ��present-day universe must be filled with relic neutrinos from that time,” said Vagnozzi.

Vagnozzi and Loeb say we can go even further back, however, by tracing gravitons, particles that mediate the force of gravity.

“ ̽��ֱ��Universe was transparent to gravitons all the way back to the earliest instant traced by known physics, the Planck time: 10 to the power of -43 seconds, when the temperature was the highest conceivable: 10 to the power of 32 degrees,” said Loeb. “A proper understanding of what came before that requires a predictive theory of quantum gravity, which we do not possess.”

Vagnozzi and Loeb say that once the Universe allowed gravitons to travel freely without scattering, a relic background of thermal gravitational radiation with a temperature of slightly less than one degree above absolute zero should have been generated: the cosmic graviton background (CGB).

However, the Big Bang theory does not allow for the existence of the CGB, as it suggests that the exponential inflation of the newborn universe diluted relics such as the CGB to a point that they are undetectable. This can be turned into a test: if the CGB were detected, clearly this would rule out cosmic inflation, which does not allow for its existence.

Vagnozzi and Loeb argue that such a test is possible, and the CGB could in principle be detected in future. ̽��ֱ��CGB adds to the cosmic radiation budget, which otherwise includes microwave and neutrino backgrounds. It therefore affects the cosmic expansion rate of the early Universe at a level that is detectable by next-generation cosmological probes, which could provide the first indirect detection of the CGB.

However, to claim a definitive detection of the CGB, the ‘smoking gun’ would be the detection of a background of high-frequency gravitational waves peaking at frequencies around 100 GHz. This would be very hard to detect, and would require tremendous technological advances in gyrotron and superconducting magnets technology. Nevertheless, say the researchers, this signal may be within our reach in future.

Reference:
Sunny Vagnozzi and Abraham Loeb. ‘ ̽��ֱ��Challenge of Ruling Out Inflation via the Primordial Graviton Background.’ ̽��ֱ��Astrophysical Journal Letters (2022). DOI: 10.3847/2041-8213/ac9b0e

Adapted in part from a piece on Medium by Avi Loeb.

Astrophysicists say that cosmic inflation – a point in the Universe’s infancy when space-time expanded exponentially, and what physicists really refer to when they talk about the ‘Big Bang’ – can in principle be ruled out in an assumption-free way.

Is it possible in principle to test cosmic inflation in a model-independent way?

Sunny Vagnozzi

A Ijjas, PJ Steinhardt and A Loeb (Scientific American, February 2017)

Cosmic inflation is a popular scenario for the earliest phase in the evolution of the Universe

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Variations in the ‘fogginess’ of the universe identify a milestone in cosmic history

sc604 — Mon, 15 Apr 2019 23:00:25 +0000

̽��ֱ��results, reported in the Monthly Notices of the Royal Astronomical Society, have enabled astronomers to zero in on the time when reionisation ended and the universe emerged from a cold and dark state to become what it is today: full of hot and ionised hydrogen gas permeating the space between luminous galaxies.

Hydrogen gas dims light from distant galaxies much like streetlights are dimmed by fog on a winter morning. By observing this dimming in the spectra of a special type of bright galaxies, called quasars, astronomers can study conditions in the early universe.

In the last few years, observations of this specific dimming pattern (called the Lyman-alpha Forest) suggested that the fogginess of the universe varies significantly from one part of the universe to another, but the reason behind these variations was unknown.

“We expected the light from quasars to vary from place to place at most by a factor of two at this time, but it is seen to vary by a factor of about 500,” said lead author Girish Kulkarni, who completed the research while a postdoctoral researcher at the ̽��ֱ�� of Cambridge. “Some hypotheses were put forward for why this is so, but none were satisfactory.”

̽��ֱ��new study concludes that these variations result from large regions full of cold hydrogen gas present in the universe when it was just one billion years old, a result which enables researchers to pinpoint when reionisation ended.

During reionisation, when the universe transitioned out of the cosmic ‘dark ages’, the space between galaxies was filled with a plasma of ionised hydrogen with a temperature of about 10,000˚C. This is puzzling because fifty million years after the big bang, the universe was cold and dark. It contained gas with temperatures only a few degrees above absolute zero, and no luminous stars and galaxies. How is it then that today, about 13.6 billion years later, the universe is bathed in light from stars in a variety of galaxies, and the gas is a thousand times hotter?

Answering this question has been an important goal of cosmological research over the last two decades. ̽��ֱ��conclusions of the new study suggest that reionisation occurred 1.1 billion years after the big bang (or 12.7 billion years ago), quite a bit later than previously thought.

̽��ֱ��team of researchers from India, the UK, Canada, Germany, and France drew their conclusions with the help of state-of-the-art computer simulations performed on supercomputers based at the Universities of Cambridge, Durham, and Paris, funded by the UK Science and Technology Facilities Council (STFC) and the Partnership for Advanced Computing in Europe (PRACE).

“When the universe was 1.1 billion years old there were still large pockets of the cosmos where the gas between galaxies was still cold and it is these neutral islands of cold gas that explain the puzzling observations,” said Martin Haehnelt of the ̽��ֱ�� of Cambridge, who led the group that conducted this research, supported by funding from the European Research Council (ERC).

“This finally allows us to pinpoint the end of reionisation much more accurately than before,” said Laura Keating of the Canadian Institute of Theoretical Astrophysics.

̽��ֱ��new study suggests that the universe was reionised by light from young stars in the first galaxies to form.

“Late reionisation is also good news for future experiments that aim to detect the neutral hydrogen from the early universe,” said Kulkarni, who is now based at the Tata Institute of Fundamental Research in India. “ ̽��ֱ��later the reionisation, the easier it will be for these experiments to succeed.”

One such experiment is the ten-nation Square Kilometre Array (SKA) of which Canada, France, India, and the UK are members.

Reference:
Girish Kulkarni et al. ‘Large Ly α opacity fluctuations and low CMB τ in models of late reionisation with large islands of neutral hydrogen extending to z < 5:5.’ Monthly Notices of the Royal Astronomical Society (2019). DOI: 10.1093/mnrasl/slz025

Large differences in the ‘fogginess’ of the early universe were caused by islands of cold gas left behind when the universe heated up after the big bang, according to an international team of astronomers.

These neutral islands of cold gas explain the puzzling observations

Martin Haehnelt

Amanda Smith, Institute of Astronomy

Artist's impression of reionisation period

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