Research by PhD student Jonathan Dodd and Professor René Oudmaijer, from the University’s School of Physics and Astronomy, points to intriguing new evidence that massive Be stars — until now mainly thought to exist in double stars — could in fact be “triples.”

The remarkable discovery could revolutionise our understanding of the objects — a subset of B stars — which are considered an important “test bed” for developing theories on how stars evolve more generally.

These Be stars are surrounded by a characteristic disc made of gas — similar to the rings of Saturn in our own Solar System. And although Be stars have been known for about 150 years — having first been identified by renowned Italian astronomer Angelo Secchi in 1866 — until now, no one has known how they were formed.

Consensus among astronomers so far has said the discs are formed by the rapid rotation of the Be stars, and that itself can be caused by the stars interacting with another star in a binary system.

Triple systems

Mr Dodd, corresponding author of the research, said: “The best point of reference for that is if you’ve watched Star Wars, there are planets where they have two Suns.”

But now, by analysing data from the European Space Agency’s Gaia satellite, the scientists say they have found evidence these stars actually exist in triple systems — with three bodies interacting instead of just two.

Mr Dodd added: “We observed the way the stars move across the night sky, over longer periods like 10 years, and shorter periods of around six months. If a star moves in a straight line, we know there’s just one star, but if there is more than one, we will see a slight wobble or, in the best case, a spiral.

“We applied this across the two groups of stars that we are looking at — the B stars and the Be stars — and what we found, confusingly, is that at first it looks like the Be stars have a lower rate of companions than the B stars. This is interesting because we’d expect them to have a higher rate.”

However, Principal Investigator Prof Oudmaijer said: “The fact that we do not see them might be because they are now too faint to be detected.”

Mass transfer

The researchers then looked at a different set of data, looking for companion stars that are further away, and found that at these larger separations the rate of companion stars is very similar between the B and Be stars.

From this, they were able to infer that in many cases a third star is coming into play, forcing the companion closer to the Be star — close enough that mass can be transferred from one to the other and form the characteristic Be star disc. This could also explain why we do not see these companions anymore; they have become too small and faint to be detected after the “vampire” Be star has sucked in so much of their mass.

The discovery could have huge impacts on other areas of astronomy — including our understanding of black holes, neutron stars and gravitational wave sources.

Prof Oudmaijer said: “There’s a revolution going on in physics at the moment around gravitational waves. We have only been observing these gravitational waves for a few years now, and these have been found to be due to merging black holes.

“We know that these enigmatic objects — black holes and neutron stars — exist, but we don’t know much about the stars that would become them. Our findings provide a clue to understanding these gravitational wave sources.”

He added: “Over the last decade or so, astronomers have found that binarity is an incredibly important element in stellar evolution. We are now moving more towards the idea it is even more complex than that and that triple stars need to be considered.”

“Indeed,” Oudmaijer said, “triples have become the new binaries.”

The team behind the discovery includes PhD student Mr Dodd and Prof Oudmaijer from Leeds, along with University of Leeds PhD student Isaac Radley and two former Leeds academics Dr Miguel Vioque of the ALMA Observatory in Chile and Dr Abigail Frost at the European Southern Observatory in Chile. The team received funding from the Science and Technology Facilities Council (STFC).

Why California and why this time period? In 2020 and 2021, California experienced fire activity unlike anything recorded in the modern record. When the smoke cleared, the amount of burned forest totaled ten times more than the annual average going back to the late 1800s. Nearly half of the forests that burned experienced high-severity fire, killing 75-100% of the vegetation, and much of this fire covered large continuous areas, rather than a patchy mosaic. California’s Department of Fish and Wildlife curates a comprehensive wildlife database, mapping habitat suitability of hundreds of species across the state. Coupling that with Forest Service records of wildfires and some fancy computer footwork gave researchers an opportunity to take a broad look at how these types of “megafires” are shaping wildlife habitat within the state.

Jessalyn Ayars, the lead author, said, “Our intent was to take a broad look to gain a better understanding of the impacts of these kinds of fires on wildlife habitat as a whole.” She continued, “and since each species is different, this study provides a good jumping-off point for others to be able to focus on a single species of interest or small group of species that share similar habitats.”

The fires and habitat studied were mostly located in the Sierra Nevada, southern Cascades, and Klamath mountain regions of California. Researchers looked at more than 600 wildlife species and found that for 50 species, fires spanned 15-30% of habitat within their range in the state. One hundred species experience high severity fire over more than 10% of their geographic range within California. Sixteen of those species are considered species of management concern, such as the great gray owl, wolverine, Pacific marten, and northern rubber boa.

Previous research shows that some species such as great gray owls may benefit from fire in terms of foraging habitat and can be somewhat resilient, but again, the unknown is whether that benefit holds true with this magnitude of habitat change in such a short time.

Some good news is that by looking more closely at some of the details around habitat change by species, scientists learned that these fires are not disproportionately impacting habitats for species of conservation concern compared to wildlife species in general, a finding that suggests that where these species live may serve as refugia for them.

Gavin Jones, senior author and Ayars’ advisor, has conducted research on how proactive forest management can offset risks over the long term of California spotted owl habitat loss from increased wildfire size and severity. Given the impacts of large-scale habitat shifts in a short period of time, coupled with the likelihood that extreme fires will be more common in the future, this new paper adds to the body of research and underscores the importance of increasing the pace and scale of proactive forest management.

“From the soldier on the battlefield to people involved in car crashes the long-term effects of nerve injuries can severely affect sufferers,” said the University of Adelaide’s Professor Giuseppe Tettamanzi, Senior Lecturer, School of Chemical Engineering.

“Transcutaneous Electric Nerve Stimulation (TENS) is a commonly used electrical stimulation method in implants. Many of the current implants are quite invasive so it’s important to understand how to maximise their effectiveness.

“Simple electrical circuitry in an implant can be applied to damaged nerves to help repair and reconstruct them.”

This technology was invented by Professor Antonio Lauto from UWS, Sydney. The implants are surgically placed under the skin around the damaged nerve with power in early versions provided externally. Innovative graft-antenna implants that are powered wirelessly, are increasingly being used. They are minimally invasive devices that function both as a wireless stimulator and a structure around which nerves can rebuild. The implants use a gold band which produces an electrical field around it.

The team has used several sophisticated Computational Electromagnetic techniques incorporated in a mouse model to hypothetically examine the effect of the circuitry implanted via patches inserted near affected nerves. They published their work in the journal Bioelectromagnetics.

Luke Smith, who is leading author in this research, undertook an honours project in his final year of his bachelor’s degree project at the University of Adelaide under the supervision of Professor Tettamanzi and Professor Christophe Fumeaux, to explain the microscopic nature of the effect of electrical stimulation. He is currently undertaking a PhD at the University’s Australian Institute for Machine Learning.

“Our work shows that when the simple metallic circuitry in the patch inserted near the neuronal materials, is irradiated with the commonly used Transcranial Magnetic Stimulation (TMS), it acts as a focaliser for the electromagnetic signal that ultimately activates neurons in the neural material,” he said.

“This ultimately speeds up tremendously the process of repairing damaged neuronal material.

“Electrical stimulation of nerves is due primarily to the electric fields created at the edge of the ring which sets up high-intensity field gradients in a small region around it.

“Our computational model demonstrates that direct contact between the ring and nerve ensures neural activation.”

Nerve damage usually takes longer than three months to repair and sufferers are at increased risk of depression because of the debilitating effects of conditions like sciatica.

People suffering from pain due to nerve damage may need to resort to opioids for pain relief with all the associated risks of addiction and extra burden on health systems.

“This work, which is currently evolving, could benefit people with injuries and with neurodegenerative diseases. The knowledge that we have generated may help in future research,” said Professor Tettamanzi.