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Pulsating white dwarf spotted

From up in orbit, NASA’s Transiting Exoplanet Survey Satellite (TESS) has recorded an extremely rare sight: a white dwarf star suddenly turning on and off.

White dwarfs are stellar corpses, formed when stars like our Sun run out of fuel to burn and slowly begin to cool and die. This particular star – called TW Pictoris, about 1,400 light-years away – is part of a binary system, and it’s greedily feeding off of its companion. As the white dwarf “eats”, it becomes brighter.

But as astronomers watched, the star lost brightness in just half an hour – which they think might be because its feeding process was interrupted.

Lead author Simone Scaringi from Durham University, UK, says this is “extraordinary”.

“The brightness variations seen in accreting white dwarfs are generally relatively slow, occurring on timescales of days to months,” she says.

“To see the brightness of TW Pictoris plummet in 30 minutes is in itself extraordinary as it has never been seen in other accreting white dwarfs and is totally unexpected from our understanding of how these systems are supposed to feed through the accretion disc.”

The study is published in Nature Astronomy.

Lab-grown “mini brains”

Researchers at the University of Cambridge, UK, have developed “mini brains” in the lab, which they say can help them study a common form of motor neurone disease.

Organoids are three-dimensional cell structures derived from stem cells. They are like miniaturised, simplified versions of actual organs, and they function in an organ-like way. They are being increasingly used to study things like infectious diseases, genetic disorders and cancers in the lab – such as being used to study SARS-Cov-2 infection in the lungs.

Now, in a study reported in Nature Neuroscience, researchers have grown brain organoids using stem cells from patients with a neurological disorder called amyotrophic lateral sclerosis (ALS). This affects the nerve cells of the brain and spinal cord, causing loss of muscle control, and it commonly occurs at the same time as frontotemporal dementia (FTD).

The team grew these organoids for 240 days – much longer than previous research had managed – allowing them to observe what happens at the earliest stages of ALS/FTD.

“Not only can we see what may happen early on in the disease – long before a patient might experience any symptoms – but we can also begin to see how the disturbances change over time in each cell,” says senior author András Lakatos from Cambridge.

“While there is much more work to be done following our discovery, it at least offers hope that it may in time be possible to prevent or to slow down the disease process.”

Mystery of Arctic krill solved

Most animals use the guiding light of the Sun to sync up their body clocks – but what about animals who live at the extremes of the Earth, like the polar winter where the Sun never rises about the horizon?

Marine scientists have now figured out how Arctic krill set their daily rhythms. The team measured the light intensity during the Arctic winter on the Svalbard archipelago, and found the midday light was only twice as bright as the midnight light – and yet krill still exhibited a strong biological rhythm, coming to the surface to feed at night and sinking back deep to avoid predators in the day.

Back in the lab, the researchers discovered that krill are much more sensitive to light at night, allowing them to pick up tiny visual cues.

“We found that the light environment during the high Arctic polar night has a complex timing of ‘light’ and ‘dark’ due to light coming from the Sun below the horizon, the Moon, and the aurora borealis,” says lead researcher Jonathan Cohen from the University of Delaware, US.

“While this light is dim and unlike the typical photoperiod at lower latitudes, we show that it is sufficient to set a biological clock in krill, showing this animal has one of the more sensitive biological rhythms studied to date.”

New skinks on the block

Last week we celebrated Reptile Awareness Day, and now two skink species have been discovered in mid-eastern Queensland. One of them might even have a hearing aid.

“The two new species are quite rare and only occur in limited areas and have managed to go completely unnoticed until now,” says Mark Hutchinson from the South Australian Museum, who co-authored the study.

The limbless, burrowing skinks are just 12cm long, and were found using new technology – including molecular comparisons and micro-CT scanning of skeletons.

“One of the species is particularly odd as it has an extra bone in its middle ear,” Hutchinson says. “We don’t know for sure what it does, but it is evidently connected with modified hearing in some way…This little extra bonelet may improve low frequency sound transmission.”

He adds that lizards have evolved a snake-like body multiple different times throughout their evolution.

“By looking at independent cases of leglessness we can look at the common features of the ecological factors that promote it, and the anatomical and developmental changes that make it happen. Every new discovery allows us to test ideas that have already been proposed, and to discover new twists and turns.”

Ancient driftwood tracks 500 years of sea ice change

The beaches of Svalbard in the Arctic are littered with driftwood, originating from boreal forests that have surrounded the Arctic Ocean, where they were borne by rivers to the ocean and frozen in sea ice. Now, scientists have traced the path of these ancient trees back over the past 500 years.

The new study, published in the Journal of Geophysical Research: Oceans, allowed the researchers to reconstruct sea ice over time – as well as the currents that propelled the frozen trees across the ocean. They found that new driftwood arrivals have steeply decreased in the past 30 years, reflecting a drop in sea ice coverage as the Arctic warms.

“This is the first time driftwood has been used to look at large-scale changes in Arctic sea ice dynamics and circulation patterns,” says geoscientist Georgia Hole at the University of Oxford, UK, lead author of the research.

Hole and team came to their results by analysing tree ring patterns of the driftwood. This told them the age and type of each tree, allowing them to trace the tree back to its country – and even a specific area – of origin.

Paired with both historical and modern sea ice observations, the data shows a slow, steady northward migration of sea ice; as the world warmed and the ice melted, less driftwood washed up on the Arctic’s shores.