Science world

Astronomers Find the Slowest-Spinning Neutron Star Ever
Most neutron stars spin rapidly, completing a rotation in seconds or even a fraction of a second. But astronomers have found one that takes its time, completing a rotation in 54 minutes. What compels this odd object to spin so slowly?

When a massive supergiant star explodes as a supernova, it leaves a collapsed core behind. The extreme pressure forces protons and electrons to combine into neutrons. Since they’re made almost entirely of neutrons, we call them neutron stars. These stellar remnants are extremely small and extremely dense. Only black holes have greater density.

Due to the conservation of angular momentum, neutron stars start to spin rapidly, often rotating as fast as several hundred times per second. Astronomers have found more than 3,000 radio-emitting neutron stars, and out of all of them, only a very small number rotate slowly.

We usually detect neutron stars by their electromagnetic radiation and call them pulsars. Astrophysicists also call the ones with slow rotations long-period radio transients. There’s uncertainty around their slow rotation speeds and if they’re even neutron stars, and the most recently discovered one isn’t helping remove the uncertainty.

In new research in Nature Astronomy, a team of researchers presented the discovery of ASKAP J1935+2148, a long-period radio transient about 16,000 light-years away. The paper is “An emission-state-switching radio transient with a 54-minute period.” The lead author is Dr. Manisha Caleb from the University of Sydney in Australia.

“Long-period radio transients are an emerging class of extreme astrophysical events of which only three are known,” the paper’s authors write. “These objects emit highly polarized, coherent pulses of typically a few tens of seconds duration, and minutes to approximately hour-long periods.”

Researchers have proposed different explanations for these long-period objects, including highly-magnetic white dwarfs and highly-magnetic neutron stars called magnetars. But the research community hasn’t reached a consensus.

ASKAP J1935+2148 has an extremely long period of 53.8 minutes and three distinct emission states. Its bright pulse state lasts between 10 and 50 seconds, and its weaker pulse state, 26 times dimmer, lasts about 370 milliseconds. It also exhibits what’s called a “quenched state” with no pulses.

Astronomers discovered the puzzling object accidentally while observing an unrelated gamma-ray burst with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope in October 2022. The observations revealed ASKAP J1935+2148’s bright pulses of radio emissions. In about six hours of observations, the object emitted four bright pulses lasting from 10 to 50 seconds. Light curve inspections and follow-up observations with the MeerKAT radiotelescope revealed the object’s entire pulsing pattern.

“This discovery relied on the combination of the complementary capabilities of ASKAP and MeerKAT telescopes as well as the ability to search for these objects on timescales of minutes while studying how their emission changes from second to second! Such synergies are allowing us to shed new light on how these compact objects evolve,” said Dr. Kaustubh Rajwade, paper co-author and an Astronomer at the University of Oxford.

The three emission states, each different from the others, are puzzling. The researchers needed to verify that each signal from each state came from the same point in the sky. The fact that each signal had the same time of arrival (TOA), as determined by both ASKAP and MeerKAT observations, indicates a single source.

“What is intriguing is how this object displays three distinct emission states, each with properties entirely dissimilar from the others. The MeerKAT radio telescope in South Africa played a crucial role in distinguishing between these states. If the signals didn’t arise from the same point in the sky, we would not have believed it to be the same object producing these different signals.”

ASKAP detected the object’s strong, bright pulse mode, while MeerKAT detected its fainter, weak pulse mode. Both telescopes detected the quiescent mode.

“In the study of radio-emitting neutron stars, we are used to extremes, but this discovery of a compact star spinning so slowly and still emitting radio waves was unexpected,” said paper co-author Ben Stappers, Professor of Astrophysics at the University of Manchester. “It is demonstrating that pushing the boundaries of our search space with this new generation of radio telescopes will reveal surprises that challenge our understanding.”

The nature of the emissions and the rate of change of the spin periods strongly suggest that ASKAP J1935+2148 is a neutron star. However, the researchers say they can’t rule out a highly magnetized white dwarf. Since astrophysicists think that white dwarfs become highly magnetized as binaries, and there are no other white dwarfs nearby, the neutron star explanation is more likely.

The object’s radius also doesn’t conform to our understanding of white dwarfs. “However, the implied radius is ~0.8? solar radii, leading us to conclude that this source cannot be expected by standard white-dwarf models,” the researchers explain. White dwarfs are only slightly larger than Earth, which seems to eliminate one as the potential source.

Only follow-up observations and more dedicated studies can reveal the object’s true nature. Either way, whether it’s a white dwarf or a neutron star, the object will open another window into the extreme physics of either type of object. Our understanding of both objects is only decades old, so there’s bound to be lots left to discover.

Webb is an Amazing Supernova Hunter
The James Webb Space Telescope (JWST) has just increased the number of known distant supernovae by tenfold. This rapid expansion of astronomers’ catalog of supernovae is extremely valuable, not least because it improves the reliability of measurements for the expansion of the universe.

“Webb is a supernova discovery machine,” said Christa DeCoursey of the Steward Observatory and the University of Arizona at a press conference earlier this week. “The sheer number of detections plus the great distances to these supernovae are the two most exciting outcomes from our survey.”

JWST’s advantage over previous surveys is its specialty in infrared wavelengths. As the universe expands, the light coming from distant objects gets stretched, “redshifting” the light to longer wavelengths. Most of the light from the early universe, therefore, reaches us in infrared.

That has allowed the telescope to discover a host of new supernovae in distant galaxies, some of which are the furthest ever seen. Supernovas are transient objects – they’re exploding stars that change and fade over time – so catching them happening at such great distances is exciting.

Previously, the most distant supernova fell about the redshift 2 mark (3.3 billion years into the Universe’s life). The new record holder just discovered by JWST has a redshift of 3.6, meaning it exploded just 1.8 billion years after the Big Bang.

Of the 80 new objects discovered, several were type 1a supernovae. These are of particular interest to scientists, because they are known to explode with a standard brightness, making it possible to take accurate distance measurements for the objects.

At least, that’s true for nearby supernovae. This new survey will allow researchers to see if that pattern remains true in the distant universe too, or if they behaved differently under the conditions of the early universe. At that time, there were fewer heavy elements in the cores of stars. Finding out if this changes their behavior is essential to measuring the expansion of spacetime itself, and could help resolve the crisis in cosmology, in which measurements using type 1a supernovae don’t align with those using the Cosmic Microwave Background.

“This is really our first sample of what the high-redshift universe looks like for transient science,” said Justin Pierel, a NASA Einstein Fellow at the Space Telescope Science Institute. “We are trying to identify whether distant supernovae are fundamentally different from or very much like what we see in the nearby universe.”

Pierel carried out a preliminary examination of one of the new supernovae, found at redshift 2.9. It seems to show no difference from the expected brightness, which is good news for astronomers’ confidence in their distance measurements to date. Further analysis of other supernovae in the data will be forthcoming.

Other outcomes of this research include a better understanding of star formation and the mechanisms behind supernova explosions in the early universe.

“We’re essentially opening a new window on the transient universe,” said STScI Fellow Matthew Siebert. “Historically, whenever we’ve done that, we’ve found extremely exciting things — things that we didn’t expect.”

‘Devil comet’ is about to make its closest approach of Earth

An unusual horned comet notable for a series of outbursts, nicknamed the “devil comet,” will make its closest approach of Earth on Sunday around 3 a.m. ET.

While the comet hasn’t been visible to those in the Northern Hemisphere since the first week of May, sky-gazers in the Southern Hemisphere have a better chance of glimpsing the fuzzy object through binoculars or a telescope.

Exactly why the dynamic comet takes on a shape that has drawn comparisons to the Millennium Falcon spacecraft from the “Star Wars” films when explosively active is still an enigma to scientists. But the celestial object only completes one orbit around the sun about every 71 years, similar to Halley’s comet, which make the odds of observing it for close study a once-in-a-lifetime opportunity.

Given that the comet won’t pass by Earth again for decades, collective observations by astronomers could provide key insights into its true nature and behavior.

Officially known as Comet 12P/Pons-Brooks, the celestial object made its closest pass of the sun on April 21, coming within 74.4 million miles (119.7 million kilometers) of our star.

The comet will make its closest pass of Earth on Sunday, but it will be more than 143 million miles (230 million kilometers) away from our planet and won’t pose a risk. For reference, the sun is 93 million miles (149 million kilometers) away from Earth.

The comet peaked in brightness in late April and has been steadily fading for three to four weeks, said Dr. Dave Schleicher, astronomer at Lowell Observatory in Arizona.

“For folks down below the equator, the coming weeks and months might be their first good chance to see this thing since the 1950s,” said astronomer Dr. Teddy Kareta, a postdoctoral associate at Lowell.

Two prolific discoverers, Jean-Louis Pons and William Robert Brooks, independently observed the devil comet — Pons in 1812 and Brooks in 1883. But the comet has likely made many trips around the sun over thousands of years, long before astronomers thought of comets as anything other than “something weird in the atmosphere,” Schleicher said.

Astronomers estimate the massive comet to be between 6.2 to 12.4 miles (10 to 20 kilometers) in diameter, Kareta said.

The rare visitor has a green appearance typical of most comets because they contain diatomic carbon molecules that absorb sunlight and emit a color that appears green from our perspective, Schleicher said.

A series of cosmic outbursts
Pons-Brooks recently captured the attention of astronomers after exhibiting intriguing behavior that caused the comet to have a horned appearance and soar through our solar system.

The comet has experienced a number of outbursts during the past eight months, causing it to eject gas and dust. While such releases are not uncommon in comets and a crescent or Pac-Man shape has been observed in other ones, it’s difficult to tell what is normal for Pons-Brooks.

“I would say it’s somewhat unusual in the number of outbursts it’s been having,” Schleicher said. “On the other hand, it’s not like you have good records from the past to really let you know what is typical. And I suspect given the fairly large number of outbursts that have happened over the last eight months, that this is very clearly a usual occurrence for Pons-Brooks.”

Comets are chunks of dust, rock and ice, essentially frozen remnants from the formation of the solar system. They also contain frozen elements such as carbon dioxide and carbon monoxide.

Comets heat up and brighten as they approach the sun, and some of the frozen gases stored in comets don’t need to warm up much before they begin to turn into v***r, Schleicher said.

“We think the ultimate driver, of course, is heating from the sun,” he said. “The comet is coming in; it’s been sitting out in a deep freeze for years. The heat is going to be working its way from the surface down to wherever that carbon dioxide or carbon monoxide ice is located.”

Astronomers suspect Pons-Brooks outbursts have occurred over the course of repeated events as heat v***rizes material inside the comet, which causes pressure to build up and break through the surface. While an explosion of gas wouldn’t be visible in telescopes, the dust it kicks up would create the kind of events observed from Pons-Brooks, Schleicher said.

Scientists have traced the jets of material observed releasing from the comet during its outburst to two source regions on its surface. Astronomers are puzzled as to why “the whole surface isn’t going off like mad,” Schleicher said.

The observations imply that ice has crusted over the majority of the surface, or the ice has been v***rized away, leaving only dirt behind, but astronomers are “not quite sure which of those mechanisms runs the show,” he said.

The comet’s outbursts seem to have ceased, however, and it hasn’t shown any outburst activity since February, Kareta said.

What we can learn from comets
Astronomers have been observing Pons-Brooks in the hopes of uncovering more details about its rotation rate, or the rate at which comets spin as they move through space. Pons-Brooks has a rotation period of 57 hours, which is longer than expected, and astronomers want to know if the jets of material releasing from the comet are speeding it up or slowing it down.

An overlapping series of events likely has contributed to Pons-Brooks’ distinctive look, but it could also be due to our perspective of the comet, Kareta said.

“These are three-dimensional objects,” Kareta said. “When we take images of the night sky, we’re taking them in a limited range of colors all flattened down in two dimensions. This will make things that might make perfect sense to you, if you’re able to go up and walk around and see it in a couple of different perspectives, look much more complicated than they really are.”

Historic iceberg surges offer insights on modern climate change
by Harrison Tasoff , University of California - Santa Barbara

A great armada entered the North Atlantic, launched from the cold shores of North America. But rather than ships off to war, this force was a fleet of icebergs, and the havoc it wrought was on the ocean current itself.

This scene describes a Heinrich Event, or a period of rapid iceberg discharge from the Laurentide Ice Sheet during the last glacial maximum. These episodes greatly weakened the system of ocean currents that circulates water within the Atlantic Ocean. The Atlantic Meridional Overturning Circulation, or AMOC for short, brings warm surface water north and cold deep water south. This oceanic conveyor belt is a major component of the global climate system, influencing marine ecosystems, weather patterns and temperatures.

It's also regarded as a potential tipping element of the Earth's climate, meaning that a tiny perturbation could push the system to a point of no return.

"That's why a lot of people are worried about a potential collapse of the AMOC," said Yuxin Zhou, a postdoctoral researcher in UC Santa Barbara's Department of Earth Science. A weakened AMOC would have a global impact, dropping temperatures in the northern hemisphere and raising them in the south. We'd see dramatic cooling in western Europe and eastern North America, and changes in the tropical rain belt that impact the Amazon and central Africa.

Zhou compared the rate of icebergs coming from the Greenland Ice Sheet to ice flux during Heinrich Events, the last time the AMOC collapsed. He found that as Greenland's ice sheet retreats inland, its iceberg calving will likely not persist long enough to completely derail the Atlantic circulation. That said, increased freshwater runoff and continued global warming remain threats to the circulation's stability.

The results appear in the journal Science.

"I think that sometimes people are in such despair about the future of the climate that they just give up," Zhou said. "This study is saying that there is still hope, and we should act with that in mind."

The North Atlantic is the lynchpin of the AMOC. This is where surface water chills and sinks to the deep ocean, driving this marine conveyor belt, which is a component of the global current system. Adding cold freshwater to the North Atlantic can disrupt this process, a frightening prospect for human society.

Scientists have a number of ways to predict how the AMOC will evolve in the future, including modern observations, statistical analyses and computational models. But the ocean is vast and complex, making it difficult to capture many of its nuances in studies.

Zhou went back in history to study the most recent period when the AMOC was severely weakened—from 68,000 to 16,000 years ago, during the last glacial period. During cooler periods there is more water locked up in ice sheets, creating a reservoir for quickly flushing the ocean with freshwater in the form of icebergs or runoff. Scientists called these episodes Heinrich Events when they came from the Laurentide Ice Sheet.

"Today it does not exist. But it used to cover northern North America and was kilometers thick in New York City," Zhou said.

Comparing these Heinrich Events to current melting in Greenland enabled Zhou to predict how current trends might change the AMOC in the future. Icebergs bring larger sediment out to sea than water or wind, a signature that geologist Hartmut Heinrich noticed in seafloor cores in the North Atlantic.

To estimate how much ice each Heinrich Event released, Yuxin analyzed the amount of thorium-230 found in these sediments. This radioactive element is formed from the decay of naturally occurring uranium in seawater. Unlike uranium, thorium doesn't dissolve well in water, so it precipitates on particles in the water column. Because thorium-230 is produced at a steady rate, more sediment flux dilutes its concentration. Working in reverse: Less thorium means more sediment raining down, carried by more icebergs.

While this technique has been used before, Zhou is the first to compare the melting rate of icebergs during Heinrich Events to current trends and projections for Greenland's ice sheet. Zhou discovered that Greenland's predicted ice outflow is on par with a mid-range Heinrich Event. And what are the effects of a mid-range Heinrich Event?

"Dramatic," Zhou replied. "It can be bad."

"This is surprising, and people should be worried. But—and this is a big 'but'—during Heinrich Events, the AMOC was already moderately weakened before all the icebergs came in," he said. "In contrast, the circulation is very vigorous right now." This difference in initial state is cause for some relief.

Heinrich Events also lasted for tens to hundreds of years. In contrast, the industrial revolution only began around the late 18th century, with carbon emissions ramping up much later. "It is possible that we simply haven't screwed up badly enough for long enough for it to really mess up the AMOC," Zhou remarked.

There's another nuance to the story. Not all melting has the same effect on the Atlantic circulation. Freshwater released as icebergs has a much larger impact on the AMOC than runoff, which is released after melting on land. Icebergs can cool the surrounding seawater, causing it to freeze into sea ice. Ironically, this ice layer acts as a blanket, keeping the ocean surface warm and preventing it from plunging down to the depths and driving the Atlantic circulation. What's more, icebergs travel much farther out to sea than runoff, delivering freshwater to the regions where this deepwater formation occurs.

Scientists on the Intergovernmental Panel on Climate Change predict that the AMOC will weaken moderately over the 21st century, a trend similar to the effects of a Heinrich Event. However, Greenland's ice discharge is projected to dwindle by that time as its ice sheet melts. This will cause its glaciers to recede inland, meaning they melt on land and release freshwater runoff rather than icebergs.

"This presents a tug of war between these two factors: the more disruptive but decreasing ice discharge and the less effective but accelerating runoff," Zhou explained. "It's going to be a competition, and the interplay between the two will determine the future of the AMOC."

Zhou hopes to study the factors that caused Heinrich Events in the future. Some research suggests that each episode was preceded by ice discharge in the Pacific Ocean from the smaller Cordilleran Ice Sheet. Although this ice sheet hasn't left any remnants, Zhou believes studying these Siku Events, as the latter are known, could provide more insight into global ocean circulation.

He's also interested in the sediments around Antarctica. While Greenland's location causes it to dominate the AMOC, the southern ice sheet is much larger, meaning it could have a greater influence on global sea level and salinity. Further, the West Antarctic Ice Sheet is marine based, making it more susceptible to a feedback loop that could induce runaway melting. Zhou believes that applying the methodologies in this study to the Antarctic ice sheets could provide a better understanding of their future evolution and impacts.

"We have a lot of anxiety about how fast climate change is happening and how dramatic the changes could be," Zhou said. "But this is a piece of good climate news that hopefully will dissuade people from climate doomism, and give people hope, because we do need hope to fight the climate crisis."

A local bright spot among melting glaciers: 2,000 km of Antarctic ice-covered coastline has been stable for 85 years

By University of Copenhagen

A whaler's forgotten aerial photos from 1937 have given researchers at the University of Copenhagen the most detailed picture of the ice evolution in East Antarctica to date. The results show that the ice has remained stable and even grown slightly over almost a century, though scientists observe early signs of weakening. The research offers new insights that enhance predictions of ice changes and sea level rise.
Higher temperatures, extreme weather, melting glaciers, and rising sea levels—all indicators that the climate and the world's ice masses are in a critical state. However, a new study published in Nature Communications from the Department of Geosciences and Natural Resource Management at the University of Copenhagen offers a local bright spot.

Using hundreds of old aerial photographs dating back to 1937, combined with modern computer technology, the researchers have tracked the evolution of glaciers in East Antarctica. The area covers approximately 2,000 kilometers of coastline and contains as much ice as the entire Greenland Ice Sheet.

By comparing the historical aerial photos with modern satellite data, the researchers have been able to determine whether the glaciers have retreated or advanced and whether they have thickened or thinned. The study reveals that the ice has not only remained stable but grown slightly over the last 85 years, partly due to increasing snowfall.

"We constantly hear about climate change and new melt records, so it's refreshing to observe an area of glaciers that has remained stable for almost a century," says Ph.D. student Mads Dømgaard, the study's first author.

However, the researcher emphasizes that the study also shows the first signs of changes in the sea ice off the glacier. This could mean that the stable East Antarctic glaciers might shrink in the future.

"Our results also indicate weakening sea ice conditions, making the glaciers' floating ice tongues more vulnerable and unable to grow as large as seen in the early aerial images from 1937. We know from other parts of Antarctica that the ocean plays an extremely important role and drives the massive and increasing melt we see in, e.g., West Antarctica," says Dømgaard.

More about the study
Out of 2,200 images photographed from seaplanes in 1937, 130 were selected for the analysis.
The researchers combined the historical photos with modern satellite data to create 3D reconstructions of the glaciers.
The Norwegian aerial images were supplemented with 165 aerial images of the same glaciers from Australian surveys conducted between 1950 and 1974. This allowed the researchers to examine the evolution of the glaciers over different periods and calculate historical ice flow speeds for selected glaciers.
Compared to modern data, the ice flow speeds are unchanged. While some glaciers have thinned over shorter intermediate periods of 10–20 years, they have remained stable or grown slightly in the long term, indicating a system in balance.

Hidden from the N***s

Most of the images used in the study were captured during a 1937 expedition organized and paid for by Norwegian whaler Lars Christensen. The mission aimed to produce the first maps of this part of East Antarctica, but the maps were never published due to the German invasion of Norway. Since then, the images have been stored at the Norwegian Polar Institute in Tromsø and forgotten.

When the researchers from the University of Copenhagen read about the expedition, they realized that valuable images were likely hidden in an archive in Norway. They traveled to Tromsø and reviewed all 2,200 images taken during the expedition. They supplemented the Norwegian aerial images with images of the same glaciers from Australian surveys conducted between 1950 and 1974.

"By comparing the historical aerial photos with modern satellite data, we have gained critical knowledge about glaciers that we would not otherwise have had. I think it's fantastic that these old images can be used to generated new research results almost 100 years after they were taken," says Assistant Professor Anders Bjørk from the University of Copenhagen, who leads the group working with the historical images.

Potential for major sea level rise
The Antarctic Ice Sheet is receiving increasing attention from researchers, due to its potential for extremely large and rapid sea level rise. Unlike Greenland, very little was known about Antarctica glaciers until the 1990s, when the first good satellite observations became available.

"Early observations of glaciers are extremely valuable as they give us a unique insight into how the ice has evolved through a varying climate and whether current changes in the ice exceed the glaciers' normal cycle of advance and retreat," explains Dømgaard.

According to the researcher, solid, long-term data is crucial for producing accurate predictions of future glacier evolution and sea level rise, and this study provides new insights into a vast area in East Antarctica.

"The long time series of glaciers improves our ability to make more accurate models of future ice changes, as the models are trained on historical observations," concludes Bjørk.