Physicists working on the Antihydrogen Laser Physics Apparatus (ALPHA) experiment at CERN have trapped and accumulated 15,000 antihydrogen atoms in less than 7 h. This accumulation rate is more than 20 times the previous record. Large ensembles of antihydrogen could be used to search for tiny, unexpected differences between matter and antimatter – which if discovered could point to physics beyond the Standard Model.

According to the Standard Model every particle has an antimatter counterpart – or antiparticle. It also says that roughly equal amounts of matter and antimatter were created in the Big Bang. But, today there is much more matter than antimatter in the visible universe, and the reason for this “baryon asymmetry” is one of the most important mysteries of physics.

The Standard Model predicts the properties of antiparticles. An antiproton, for example, has the same mass as a proton and the opposite charge. The Standard Model also predicts how antiparticles interact with matter and antimatter. If physicists could find discrepancies between the measured and predicted properties of antimatter, it could help explain the baryon asymmetry and point to other new physics beyond the Standard Model.

Powerful probe

Just as a hydrogen atom comprises a proton bound to an electron, an antihydrogen antiatom comprises an antiproton bound to an antielectron (positron). Antihydrogen offers physicists several powerful ways to probe antimatter at a fundamental level. Trapped antiatoms can be released in freefall to determine if they respond to gravity in the same way as atoms. Spectroscopy can be used to make precise measurements of how the electromagnetic force binds the antiproton and positron in antihydrogen with the aim of finding differences compared to hydrogen.

So far, antihydrogen’s gravitational and electromagnetic properties appear to be identical to hydrogen. However, these experiments were done using small numbers of antiatoms, and having access to much larger ensembles would improve the precision of such measurements and could reveal tiny discrepancies. However, creating and storing antihydrogen is very difficult.

Today, antihydrogen can only be made in significant quantities at CERN in Switzerland. There, a beam of protons is fired at a solid target, creating antiprotons that are then cooled and stored using electromagnetic fields. Meanwhile, positrons are gathered from the decay of radioactive nuclei and cooled and stored using electromagnetic fields. These antiprotons and positrons are then combined in a special electromagnetic trap to create antihydrogen.

This process works best when the antiprotons and positrons have very low kinetic energies (temperatures) when combined. If the energy is too high, many antiatoms will be escape the trap. So, it is crucial that the positrons and antiprotons to be as cold as possible.

Sympathetic cooling

Recently, ALPHA physicists have used a technique called sympathetic cooling on positrons, and in a new paper they describe their success.  Sympathetic cooling has been used for several decades to cool atoms and ions. It originally involved mixing a hard-to-cool atomic species with atoms that are relatively easy to cool using lasers. Energy is transferred between the two species via the electromagnetic interaction, which chills the hard-to-cool atoms.

The ALPHA team used beryllium ions to sympathetically cool positrons to 10 K, which is five degrees colder than previously achieved using other techniques. These cold positrons boosted the efficiency of the creation and trapping of antihydrogen, allowing the team to accumulate 15,000 antihydrogen atoms in less than 7 h. This is more than a 20-fold improvement over their previous record of accumulating 2000 antiatoms in 24 h.

Science fiction

“These numbers would have been considered science fiction 10 years ago,” says ALPHA spokesperson Jeffrey Hangst, who is a Denmark’s Aarhus University.

Team member Maria Gonçalves, a PhD student at the UK’s Swansea University, says, “This result was the culmination of many years of hard work. The first successful attempt instantly improved the previous method by a factor of two, giving us 36 antihydrogen atoms”.

The effort was led by Niels Madsen of the UK’s Swansea University. He enthuses, “It’s more than a decade since I first realized that this was the way forward, so it’s incredibly gratifying to see the spectacular outcome that will lead to many new exciting measurements on antihydrogen”.

The cooling technique is described in Nature Communications.

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“Drain the swamp!”

In the intense first few months of his second US presidency, Donald Trump has been enacting his old campaign promise with a vengeance. He’s ridding all the muck from the American federal bureaucracy, he claims, and finally bringing it back under control.

Scientific projects and institutions are particular targets of his, with one recent casualty being the High Energy Physics Advisory Panel (HEPAP). Outsiders might shrug their shoulders at a panel of scientists being axed. Panels come and go. Also, any development in Washington these days is accompanied by confusion, uncertainty, and the possibility of reversal.

But HEPAP’s dissolution is different. Set up in 1967, it’s been a valuable and long-standing advisory committee of the Office of Science at the US Department of Energy (DOE). HEPAP has a distinguished track record of developing, supporting and reviewing high-energy physics programmes, setting priorities and balancing different areas. Many scientists are horrified by its axing.

The terminator

Since taking office in January 2025, Trump has issued a flurry of executive orders – presidential decrees that do not need Congressional approval, legislative review or public debate. One order, which he signed in February, was entitled “Commencing the Reduction of the Federal Bureaucracy”.

It sought to reduce parts of the government “that the President has determined are unnecessary”, seeking to eliminate “waste and abuse, reduce inflation, and promote American freedom and innovation”. While supporters see those as laudable goals, opponents believe the order is driving a stake into the heart of US science.

Hugely valuable, long-standing scientific advisory committees have been axed at key federal agencies, including NASA, the National Science Foundation, the Environmental Protection Agency, the National Oceanic and Atmospheric Administration, the US Geological Service, the National Institute of Health, the Food and Drug Administration, and the Centers for Disease Control and Prevention.

What’s more, the committees were terminated without warning or debate, eliminating load-bearing pillars of the US science infrastructure. It was, as the Columbia University sociologist Gil Eyal put it in a recent talk, the “Trump 2.0 Blitzkrieg”.

Then, on 30 September, Trump’s enablers took aim at advisory committees at the DOE Office of Science. According to the DOE’s website, a new Office of Science Advisory Committee (SCAC) will take over functions of the six former discretionary (non-legislatively mandated) Office of Science advisory committees.

“Any current charged responsibilities of these former committees will be transferred to the SCAC,” the website states matter-of-factly. The committee will provide “independent, consensus advice regarding complex scientific and technical issues” to the entire Office of Science. Its members will be appointed by under secretary for science Dario Gil – a political appointee.

Apart from HEPAP, others axed without warning were the Nuclear Science Advisory Committee, the Basic Energy Sciences Advisory Committee, the Fusion Energy Sciences Advisory Committee, the Advanced Scientific Computing Advisory Committee, and the Biological and Environmental Research Advisory Committee.

Over the years, each committee served a different community and was represented by prominent research scientists who were closely in touch with other researchers. Each committee could therefore assemble the awareness of – and technical knowledge about – emerging promising initiatives and identify the less promising ones.

Many committee members only learned of the changes when they received letters or e-mails out of the blue informing them that their committee had been dissolved, that a new committee had replaced them, and that they were not on it. No explanation was given.

Closing HEPAP and the other Office of Science committees will hamper both the technical support and community input that it has relied on to promote the efficient, effective and robust growth of physics

Physicists whom I have spoken to are appalled for two main reasons. One is that closing HEPAP and the other Office of Science committees will hamper both the technical support and community input that it has relied on to promote the efficient, effective and robust growth of physics.

“Speaking just for high-energy physics, HEPAP gave feedback on the DOE and NSF funding strategies and priorities for the high-energy physics experiments,” says Kay Kinoshita from the University of Cincinnati, a former HEPAP member. “The panel system provided a conduit for information between the agencies and the community, so the community felt heard and the agencies were (mostly) aligned with the community consensus”.

As Kinoshita continued: “There are complex questions that each panel has to deal with. even within the topical area. It’s hard to see how a broader panel is going to make better strategic decisions, ‘better’ meaning in terms of scientific advancement. In terms of community buy-in I expect it will be worse.”

Other physicists cite a second reason for alarm. The elimination of the advisory committees spreads the expertise so thinly as to increase the likelihood of political pressure on decisions. “If you have one committee you are not going to get the right kind of fine detail,” says Michael Lubell, a physicist and science-policy expert at the City College of New York, who has sat in on meetings of most of the Office of Science advisory committees.

“You’ll get opinions from people outside that area and you won’t be able to get information that you need as a policy maker to decide how the resources are to be allocated,” he adds. “A condensed-matter physicist for example, would probably have insufficient knowledge to advise DOE on particle physics. Instead, new committee members would be expected to vet programs based on ideological conformity to what the Administration wants.”

The critical point

At the end of the Second World War, the US began to construct an ambitious long-range plan to promote science that began with the establishment of the National Science Foundation in 1950 and developed and extended ever since. The plan aimed to incorporate both the ability of elected politicians to direct science towards social needs and the independence of scientists to explore what is possible.

US presidents have, of course, had pet scientific projects: the War on Cancer (Nixon), the Moon Shot (Kennedy), promoting renewable energy (Carter), to mention a few. But it is one thing for a president to set science to producing a socially desirable product and another to manipulate the scientific process itself.

“This is another sad day for American science,” says Lubell. “If I were a young person just embarking on a career, I would get the hell out of the country. I would not want to waste the most creative years of my life waiting for things to turn around, if they ever do. What a way to destroy a legacy!”

The end of HEPAP is not draining a swamp but creating one.

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The LIGO–Virgo–KAGRA collaboration has detected strong evidence for second-generation black holes, which were formed from earlier mergers of smaller black holes. The two gravitational wave signals provide one of the strongest confirmations to date for how Einstein’s general theory of relativity describes rotating black holes. Studying such objects also provides a testbed for probing new physics beyond the Standard Model.

Over the past decade, the global network of interferometers operated by LIGO, Virgo, and KAGRA have detected close to 300 gravitational waves (GWs) – mostly from the mergers of binary black holes.

In October 2024 the network detected a clear signal that pointed back to a merger that occurred 700 million light-years away. The progenitor black holes were 20 and 6 solar masses and the larger object was spinning at 370 Hz, which makes it one of the fastest-spinning black holes ever observed.

Just one month later, the collaboration detected the coalescence of another highly imbalanced binary (17 and 8 solar masses), 2.4 billion light-years away. This signal was even more unusual – showing for the first time that the larger companion was spinning in the opposite direction of the binary orbit.

Massive and spinning

While conventional wisdom says black holes should not be spinning at such high rates, the observations were not entirely unexpected. “With both events having one black hole, which is both significantly more massive than the other and rapidly spinning, [the observations] provide tantalizing evidence that these black holes were formed from previous black hole mergers,” explains Stephen Fairhurst at Cardiff University, spokesperson of the LIGO Collaboration. If this were the case, the two GW signals – called GW241011 and GW241110 – are first observations of second-generation black holes. This is because when a binary merges, the resulting second-generation object tends to have a large spin.

The GW241011 signal was particularly clear, which allowed the team to make the third-ever observation of higher harmonic modes. These are overtones in the GW signal that become far clearer when the masses of the coalescing bodies are highly imbalanced.

The precision of the GW241011 measurement provides one of the most stringent verifications so far of general relativity. The observations also support Roy Kerr’s prediction that rapid rotation distorts the shape of a black hole.

Kerr and Einstein confirmed

“We now know that black holes are shaped like Einstein and Kerr predicted, and general relativity can add two more checkmarks in its list of many successes,” says team member Carl-Johan Haster at the University of Nevada, Las Vegas. “This discovery also means that we’re more sensitive than ever to any new physics that might lie beyond Einstein’s theory.”

This new physics could include hypothetical particles called ultralight bosons. These could form in clouds just outside the event horizons of spinning black holes, and would gradually drain a black hole’s rotational energy via a quantum effect called superradiance.

The idea is that the observed second-generation black holes had been spinning for billions of years before their mergers occurred. This means that if ultralight bosons were present, they cannot have removed lots of angular momentum from the black holes. This places the tightest constraint to date on the mass of ultralight bosons.

“Planned upgrades to the LIGO, Virgo and KAGRA detectors will enable further observations of similar systems,” Fairhurst says. “They will enable us to better understand both the fundamental physics governing these black hole binaries and the astrophysical mechanisms that lead to their formation.”

Haster adds, “Each new detection provides important insights about the universe, reminding us that each observed merger is both an astrophysical discovery but also an invaluable laboratory for probing the fundamental laws of physics”.

The observations are described in The Astrophysical Journal Letters.

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