Gravitational waves—ripples in spacetime predicted by Einstein—have been observed at high frequencies by ground-based interferometers such as LIGO and Virgo, and at ultra-low frequencies by pulsar timing arrays. However, the mid-band range has remained a scientific blind spot.  

Developed by researchers at the Universities of Birmingham and Sussex, the new detector concept uses cutting-edge optical cavity and atomic clock technologies to sense gravitational waves in the elusive milli-Hertz frequency band (10⁻⁵ – 1 Hz).  

Publishing their proposal today (Oct. 3) in Classical and Quantum Gravity, the scientist reveal a detector that uses advances in optical resonator technology, originally developed for optical atomic clocks, to measure tiny phase shifts in laser light caused by passing gravitational waves. Unlike large-scale interferometers, these detectors are compact, relatively immune to seismic and Newtonian noise.  

Co-author Dr Vera Guarrera, from the University of Birmingham, commented: “By using technology matured in the context of optical atomic clocks, we can extend the reach of gravitational wave detection into a completely new frequency range with instruments that fit on a laboratory table. This opens the exciting possibility of building a global network of such detectors and searching for signals that would otherwise remain hidden for at least another decade.” 

The milli-Hertz frequency band – sometimes called the ‘mid-band’ – is expected to host signals from a variety of astrophysical and cosmological sources, including compact binaries of white dwarfs and black hole mergers. Ambitious space missions such as LISA also target this frequency band, but they are scheduled for launch in the 2030s. The proposed optical resonator detectors could begin exploring this territory now. 

Co-author Professor Xavier Calmet, from the University of Sussex, commented: “This detector allows us to test astrophysical models of binary systems in our galaxy, explore the mergers of massive black holes, and even search for stochastic backgrounds from the early universe. With this method, we have the tools to start probing these signals from the ground, opening the path for future space missions.” 

While future space-based missions like LISA will offer superior sensitivity, their operation is over a decade away. The proposed optical cavity detectors provide an immediate, cost-effective means to explore the milli-Hz band.  

The study also suggests that integrating these detectors with existing clock networks could extend gravitational wave detection to even lower frequencies, complementing high-frequency observatories like LIGO. 

Each unit consists of two orthogonal ultrastable optical cavities and an atomic frequency reference, enabling multi-channel detection of gravitational wave signals. This configuration not only enhances sensitivity but also allows for the identification of wave polarisation and source direction. 

Staying home is critical to preventing the spread of infectious diseases like influenza; however, people with the flu are contagious before they develop symptoms. Current flu diagnostics like nasal swab-based PCR tests are accurate, but they are slow and expensive. At-home lateral flow tests, akin to those used to test for COVID-19, are convenient and generally low-cost, but don’t catch pre-symptomatic infections.

As written in their published study, Lorenz Meinel and colleagues address these flu detection shortcomings “by switching away from complex detectors and machinery and toward a detector that is available for anyone, everywhere and anytime: the tongue.”

The team developed a molecular sensor that releases a flavor that human tongues can detect — thymol, found in the spice thyme. The sensor is based on a substrate of the influenza virus glycoprotein called neuraminidase (the “N” in H1N1). Influenza viruses use neuraminidase to break certain bonds on the host’s cell to infect it. So, the researchers synthesized a neuraminidase substrate and attached a thymol molecule to it. Thymol registers as a strong herbal taste on the tongue. Theoretically, when the synthesized sensor is in the mouth of someone infected with the flu, the viruses lob off the thymol molecules, and their flavor is detected by the tongue.

After developing their molecular sensor, the researchers conducted lab tests with it. In vials with human saliva from people diagnosed with the flu, the sensor released free thymol within 30 minutes. When they tested the sensor on human and mouse cells, it didn’t change the cells’ functioning. Next, Meinel and team hope to start human clinical trials in about two years to confirm the sensor’s thymol taste sensations in people with pre- and post-symptomatic influenza.

If incorporated into chewing gums or lozenges, “this sensor could be a rapid and accessible first-line screening tool to help protect people in high-risk environments,” says Meinel.

The authors acknowledge funding from the Federal Ministry of Research and Education (now called the Federal Ministry of Research, Technology and Space) and have registered a patent with the European Patent Office on this technology.

The Great Oxygenation Event (GOE) occurred around 2.3 billion years ago and marked the rise of atmospheric oxygen, likely triggered by green Cyanobacteria that used sunlight to split water, subsequently converting carbon dioxide into oxygen through photosynthesis. The result is that the current atmosphere is around 78% nitrogen and 21% oxygen, with only traces of other gases such as methane and carbon dioxide, which might have played a greater role before the rise of oxygen. The GOE fundamentally changed the course of life on Earth. This high amount of oxygen allows us animals to breathe, but it also complicates life for ancient life forms, which were almost unaware of the O₂ molecule. Understanding how these ancient microbes adapted to the presence of oxygen remains a major question.

To answer this, the team studied five hot springs in Japan, which are rich in varied water chemistries. Those five springs (one in Tokyo, two each in Akita and Aomori prefectures) are naturally rich in ferrous iron (Fe²⁺). They are rare in today’s oxygen-rich world because ferrous iron quickly reacts with oxygen and turns into an insoluble ferric iron form (Fe³⁺). But in these springs, the water still contains high levels of ferrous iron, low levels of oxygen, and a near-neutral pH, conditions thought to resemble parts of the early Earth’s oceans.

“These iron-rich hot springs provide a unique natural laboratory to study microbial metabolism under early Earth-like conditions during the late Archean to early Proterozoic transition, marked by the Great Oxidation Event. They help us understand how primitive microbial ecosystems may have been structured before the rise of plants, animals, or significant atmospheric oxygen,” says Shawn McGlynn, who supervised Li-Hau during her dissertation work.

In four of the five hot springs, the team found microaerophilic iron-oxidising bacteria to be the dominant microbes. These organisms thrive in low-oxygen conditions and use ferrous iron as an energy source, converting it into ferric iron. Cyanobacteria, known for producing oxygen through photosynthesis, were also present but in relatively small numbers. The only exception was one of the Akita hot springs, where non-iron-based metabolisms were surprisingly dominant.

Using metagenomic analysis, the team assembled over 200 high-quality microbial genomes and used them to analyse in detail the functions of microbes in the community. The same microbes that coupled iron and oxygen metabolism converted a toxic compound into an energy source and helped maintain conditions that allowed oxygen-sensitive anaerobes to persist. These communities carried out essential biological processes such as carbon and nitrogen cycling, and the researchers also found evidence of a partial sulfur cycle, identifying genes involved in sulfide oxidation and sulfate assimilation. Given that hot springs contained very little sulfur compounds, this was a surprising discovery. The researchers propose that this may indicate a “cryptic” sulfur cycle, where microbes recycle sulfur in complex ways that are not yet fully understood.

“Despite differences in geochemistry and microbial composition across sites, our results show that in the presence of ferrous iron and limited oxygen, communities of microaerophilic iron oxidisers, oxygenic phototrophs, and anaerobes consistently coexist and sustain remarkably similar and complete biogeochemical cycles,” says Li-Hau.

The research suggests a shift in our understanding of early ecosystems, showing that microbes may have harnessed energy from iron oxidation and oxygen produced by early phototrophs. The study proposes that, similar to these hot springs, early Earth hosted ecosystems were composed of diverse microbes, including iron-oxidising bacteria, anaerobes, and Cyanobacteria living alongside one another and modulating oxygen concentrations.

“This paper expands our understanding of microbial ecosystem function during a crucial period in Earth’s history, the transition from an anoxic, iron-rich ocean to an oxygenated biosphere at the onset of the GOE. By understanding modern analogue environments, we provide a detailed view of metabolic potentials and community composition relevant to early Earth’s conditions,” says Li-Hau.

Together, these insights deepen our understanding of life’s early evolution on Earth and have implications for the search for life on other planets with geochemical conditions similar to those of early Earth.

More information

Earth-Life Science Institute (ELSI) is one of Japan’s ambitious World Premiere International research centers, whose aim is to achieve progress in broadly inter-disciplinary scientific areas by inspiring the world’s greatest minds to come to Japan and collaborate on the most challenging scientific problems. ELSI’s primary aim is to address the origin and co-evolution of the Earth and life.

Institute of Science Tokyo (Science Tokyo) was established on October 1, 2024, following the merger between Tokyo Medical and Dental University (TMDU) and Tokyo Institute of Technology (Tokyo Tech), with the mission of “Advancing science and human wellbeing to create value for and with society.”

World Premier International Research Center Initiative (WPI) was launched in 2007 by Japan’s Ministry of Education, Culture, Sports, Science and Technology (MEXT) to foster globally visible research centers boasting the highest standards and outstanding research environments. Numbering more than a dozen and operating at institutions throughout the country, these centers are given a high degree of autonomy, allowing them to engage in innovative modes of management and research. The program is administered by the Japan Society for the Promotion of Science (JSPS).

Poor sleep has been linked to dementia, but it is unclear whether unhealthy sleep habits contribute to the development of dementia or whether they are rather early symptoms of the disease. In a new study, researchers at Karolinska Institutet have investigated the link between sleep characteristics and how old the brain appears in relation to its chronological age.

The study includes 27,500 middle-aged and older people from the UK Biobank who underwent magnetic resonance imaging (MRI) of the brain. Using machine learning, the researchers estimated the biological age of the brain based on over a thousand brain MRI phenotypes.

Low-grade inflammation

The participants’ sleep quality was scored based on five self-reported factors: chronotype (being a morning/evening person), sleep duration, insomnia, snoring, and daytime sleepiness. They were then divided into three groups: healthy (≥4 points), intermediate (2-3 points), or poor (≤1 point) sleep.

“The gap between brain age and chronological age widened by about six months for every 1-point decrease in healthy sleep score,” explains Abigail Dove, researcher at the Department of Neurobiology, Care Sciences and Society, Karolinska Institutet, who led the study. “People with poor sleep had brains that appeared on average one year older than their actual age.”

To understand how poor sleep can affect the brain, the researchers also examined levels of low-grade inflammation in the body. They found that inflammation could explain just over ten per cent of the link between poor sleep and older brain age.

“Our findings provide evidence that poor sleep may contribute to accelerated brain aging and point to inflammation as one of the underlying mechanisms,” says Abigail Dove. “Since sleep is modifiable, it may be possible to prevent accelerated brain aging and perhaps even cognitive decline through healthier sleep.”

Several possible explanations

Other possible mechanisms that could explain the association are negative effects on the brain’s waste clearance system, which is active mainly during sleep, or that poor sleep affects cardiovascular health, which in turn can have a negative impact on the brain.

Participants in the UK Biobank are healthier than the general UK population, which could limit the generalisability of the findings. Another limitation of the study is that the results are based on self-reported sleep.

The study was conducted in collaboration with researchers from the Swedish School of Sport and Health Sciences, and Tianjin Medical University and Sichuan University in China, among others. It was funded by the Alzheimer’s Foundation, the Dementia Foundation, the Swedish Research Council, the Loo and Hans Osterman Foundation for Medical Research, and the Knowledge Foundation. The researchers report no conflicts of interest.