̽��ֱ�� of Cambridge - Department of Physics

AI can be good for our health and wellbeing

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UCAS evaluation shows the most engaged sixth formers saw their results jump by a grade on average, were up to four times as successful in achieving an A*, and around twice as successful in securing an Oxbridge place.

10 Cambridge AI spinouts

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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.

Yes

Spinning, twisted light could power next-generation electronics

sc604 — Thu, 13 Mar 2025 18:09:28 +0000

̽��ֱ��researchers, led by the ̽��ֱ�� of Cambridge and the Eindhoven ̽��ֱ�� of Technology, have created an organic semiconductor that forces electrons to move in a spiral pattern, which could improve the efficiency of OLED displays in television and smartphone screens, or power next-generation computing technologies such as spintronics and quantum computing.

̽��ֱ��semiconductor they developed emits circularly polarised light—meaning the light carries information about the ‘handedness’ of electrons. ̽��ֱ��internal structure of most inorganic semiconductors, like silicon, is symmetrical, meaning electrons move through them without any preferred direction.

However, in nature, molecules often have a chiral (left- or right-handed) structure: like human hands, chiral molecules are mirror images of one another. Chirality plays an important role in biological processes like DNA formation, but it is a difficult phenomenon to harness and control in electronics.

But by using molecular design tricks inspired by nature, the researchers created a chiral semiconductor by nudging stacks of semiconducting molecules to form ordered right-handed or left-handed spiral columns. Their results are reported in the journal Science.

One promising application for chiral semiconductors is in display technology. Current displays often waste a significant amount of energy due to the way screens filter light. ̽��ֱ��chiral semiconductor developed by the researchers naturally emits light in a way that could reduce these losses, making screens brighter and more energy-efficient.

“When I started working with organic semiconductors, many people doubted their potential, but now they dominate display technology,” said Professor Sir Richard Friend from Cambridge’s Cavendish Laboratory, who co-led the research. “Unlike rigid inorganic semiconductors, molecular materials offer incredible flexibility—allowing us to design entirely new structures, like chiral LEDs. It’s like working with a Lego set with every kind of shape you can imagine, rather than just rectangular bricks.”

̽��ֱ��semiconductor is based on a material called triazatruxene (TAT) that self-assembles into a helical stack, allowing electrons to spiral along its structure, like the thread of a screw.

“When excited by blue or ultraviolet light, self-assembled TAT emits bright green light with strong circular polarisation—an effect that has been difficult to achieve in semiconductors until now,” said co-first author Marco Preuss, from the Eindhoven ̽��ֱ�� of Technology. “ ̽��ֱ��structure of TAT allows electrons to move efficiently while affecting how light is emitted.”

By modifying OLED fabrication techniques, the researchers successfully incorporated TAT into working circularly polarised OLEDs (CP-OLEDs). These devices showed record-breaking efficiency, brightness, and polarisation levels, making them the best of their kind.

“We’ve essentially reworked the standard recipe for making OLEDs like we have in our smartphones, allowing us to trap a chiral structure within a stable, non-crystallising matrix,” said co-first author Rituparno Chowdhury, from Cambridge’s Cavendish Laboratory. “This provides a practical way to create circularly polarised LEDs, something that has long eluded the field.”

̽��ֱ��work is part of a decades-long collaboration between Friend’s research group and the group of Professor Bert Meijer from the Eindhoven ̽��ֱ�� of Technology. “This is a real breakthrough in making a chiral semiconductor,” said Meijer. “By carefully designing the molecular structure, we’ve coupled the chirality of the structure to the motion of the electrons and that’s never been done at this level before.”

̽��ֱ��chiral semiconductors represent a step forward in the world of organic semiconductors, which now support an industry worth over $60 billion (about £45 billion). Beyond displays, this development also has implications for quantum computing and spintronics—a field of research that uses the spin, or inherent angular momentum, of electrons to store and process information, potentially leading to faster and more secure computing systems.

̽��ֱ��research was supported in part by the European Union’s Marie Curie Training Network and the European Research Council. Richard Friend is a Fellow of St John’s College, Cambridge. Rituparno Chowdhury is a member of Fitzwilliam College, Cambridge.

Reference

Rituparno Chowdhury, Marco D Preuss et al. ‘Circularly polarized electroluminescence from chiral supramolecular semiconductor thin films.’ Science (2025). DOI:10.1126/science.adt3011

Researchers have advanced a decades-old challenge in the field of organic semiconductors, opening new possibilities for the future of electronics.

It’s like working with a Lego set with every kind of shape you can imagine, rather than just rectangular bricks

Richard Friend

Samarpita Sen, Rituparno Chowdhury

Confocal microscopy image of a chiral semiconductor

Yes

Tributes paid to first British-Pakistani Head of House

Anonymous — Fri, 24 Jan 2025 16:02:28 +0000

Professor Ahmed, the first British-Pakistani Head of House, had a distinguished academic career centred on research interests in the physics and technology of nanoscale electronic devices, nanotechnology and electron beam lithography. Master of Corpus Christi College from 2000 to 2006, he remained actively involved as a Life Fellow and later an Honorary Fellow.

Born in Calcutta in 1936, after the partition of India Professor Ahmed and his family were forced to flee to Karachi in the newly formed Pakistan. ̽��ֱ��family later moved to London where Professor Ahmed read Electrical Engineering at Imperial College, graduating with a First Class degree. After a brief spell working for General Electric Company in Birmingham, he realised his passion was for research. Encouraged by a friend, he successfully applied for a PhD scholarship at King’s College Cambridge. After a formative sabbatical year in New York state where he worked at the Thomas J Watson Research Centre of IBM, he returned to Cambridge where his research activity grew rapidly. He moved to the Cavendish Laboratory where he joined the Department of Engineering and established the Microelectronics Research Centre, sponsored by Hitachi. In 1990, he was elected a Fellow of the Royal Academy of Engineering, in 1992 he was promoted to Professor of Microelectronics, and in 1996 he was awarded a Doctor of Science degree from the ̽��ֱ�� of Cambridge.

Professor Ahmed died peacefully at home, surrounded by his wife and family on 23 October 2024. He is survived by his wife, Anne; his children, Ayesha, Rehana and Imran; his grandchildren, Max, Jem, Keir and Maya; and his sister, Zubaida.

Read his full obituary on the Corpus Christi website and on the Department of Physics website.

Tributes have been paid to former Master of Corpus Christi College Professor Haroon Ahmed, who has died aged 88.

Professor Haroon Ahmed

Yes

Massive black hole in the early universe spotted taking a ‘nap’ after overeating

sc604 — Wed, 18 Dec 2024 16:00:00 +0000

Like a bear gorging itself on salmon before hibernating for the winter, or a much-needed nap after Christmas dinner, this black hole has overeaten to the point that it is lying dormant in its host galaxy.

An international team of astronomers, led by the ̽��ֱ�� of Cambridge, used the NASA/ESA/CSA James Webb Space Telescope to detect this black hole in the early universe, just 800 million years after the Big Bang.

̽��ֱ��black hole is huge – 400 million times the mass of our Sun – making it one of the most massive black holes discovered by Webb at this point in the universe’s development. ̽��ֱ��black hole is so enormous that it makes up roughly 40% of the total mass of its host galaxy: in comparison, most black holes in the local universe are roughly 0.1% of their host galaxy mass.

However, despite its gigantic size, this black hole is eating, or accreting, the gas it needs to grow at a very low rate – about 100 times below its theoretical maximum limit – making it essentially dormant.

Such an over-massive black hole so early in the universe, but one that isn’t growing, challenges existing models of how black holes develop. However, the researchers say that the most likely scenario is that black holes go through short periods of ultra-fast growth, followed by long periods of dormancy. Their results are reported in the journal Nature.

When black holes are ‘napping’, they are far less luminous, making them more difficult to spot, even with highly sensitive telescopes such as Webb. 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 black hole’s edges. When black holes are actively growing, the gas in the accretion disc becomes extremely hot and starts to glow and radiate energy in the ultraviolet range.

“Even though this black hole is dormant, its enormous size made it possible for us to detect,” said lead author Ignas Juodžbalis from Cambridge’s Kavli Institute for Cosmology. “Its dormant state allowed us to learn about the mass of the host galaxy as well. ̽��ֱ��early universe managed to produce some absolute monsters, even in relatively tiny galaxies.”

According to standard models, black holes form from the collapsed remnants of dead stars and accrete matter up to a predicted limit, known as the Eddington limit, where the pressure of radiation on matter overcomes the gravitational pull of the black hole. However, the sheer size of this black hole suggests that standard models may not adequately explain how these monsters form and grow.

“It’s possible that black holes are ‘born big’, which could explain why Webb has spotted huge black holes in the early universe,” said co-author Professor Roberto Maiolino, from the Kavli Institute and Cambridge’s Cavendish Laboratory. “But another possibility is they go through periods of hyperactivity, followed by long periods of dormancy.”

Working with colleagues from Italy, the Cambridge researchers conducted a range of computer simulations to model how this dormant black hole could have grown to such a massive size so early in the universe. They found that the most likely scenario is that black holes can exceed the Eddington limit for short periods, during which they grow very rapidly, followed by long periods of inactivity: the researchers say that black holes such as this one likely eat for five to ten million years, and sleep for about 100 million years.

“It sounds counterintuitive to explain a dormant black hole with periods of hyperactivity, but these short bursts allow it to grow quickly while spending most of its time napping,” said Maiolino.

Because the periods of dormancy are much longer than the periods of ultra-fast growth, it is in these periods that astronomers are most likely to detect black holes. “This was the first result I had as part of my PhD, and it took me a little while to appreciate just how remarkable it was,” said Juodžbalis. “It wasn’t until I started speaking with my colleagues on the theoretical side of astronomy that I was able to see the true significance of this black hole.”

Due to their low luminosities, dormant black holes are more challenging for astronomers to detect, but the researchers say this black hole is almost certainly the tip of a much larger iceberg, if black holes in the early universe spend most of their time in a dormant state.

“It’s likely that the vast majority of black holes out there are in this dormant state – I’m surprised we found this one, but I’m excited to think that there are so many more we could find,” said Maiolino.

̽��ֱ��observations were obtained as part of the JWST Advanced Deep Extragalactic Survey (JADES). ̽��ֱ��research was supported in part by the European Research Council and the Science and Technology Facilities Council (STFC), part of UK Research and Innovation (UKRI).

Reference:
Ignas Juodžbalis et al. ‘A dormant overmassive black hole in the early Universe.’ Nature (2024). DOI: 10.1038/s41586-024-08210-5

Scientists have spotted a massive black hole in the early universe that is ‘napping’ after stuffing itself with too much food.

Jiarong Gu

Artist’s impression of a black hole during one of its short periods of rapid growth

Yes

10 Cambridge spinouts forging a future for our planet

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10 companies taking Cambridge ideas out of the lab and into the real world to address the climate emergency.