A catalog of almost 3,000 white dwarfs that exploded as type Ia supernovas after overfeeding on companion stars indicates that dark energy, the mysterious force accelerating the expansion of the universe, is changing over time.

The discovery, in conjunction with data from the Dark Energy Survey (DES), backs results revealed from the Dark Energy Spectroscopic Instrument (DESI) published in 2024 that suggested dark energy's influence is weakening.

That means that the team's research doesn't just involve the most comprehensive catalog of type Ia supernovas; it presents the clearest picture yet of the evolution of the universe and the influence of dark energy.

"We've rebuilt 3 decades of astronomical observations into a single, consistent framework," team member Ryan Camilleri of the University of Queensland said in a statement."We combined our data with other cosmic measurements, including relic light from the Big Bang and maps of how galaxies are distributed through space.

"Instead of confirming the standard model of cosmology, which assumes dark energy is fixed and unchanging, we have more evidence that dark energy may change over time."

How do exploding white dwarfs tell us about dark energy?

White dwarfs are the smoldering stellar remnants that are left over when stars with around the mass of the sun exhaust the fuel for nuclear fusion in their cores. This ends the outward pressure that supports a star against its own gravity, meaning the star's core collapses as the outer layers are shed. The core becomes a white dwarf, and for single stars, that is the end. But around 50% of sun-sized stars have a binary companion, and this can lead to renewed activity and a change in the star's fate.

If the white dwarf and its companion are close enough together, the dead star begins stripping away the outer layers of its companion. As this material builds on the white dwarf, it pushes the stellar remnant's mass over the so-called Chandrasekhar limit, allowing it to go supernova.

These cosmic explosions are called type Ia supernovas, and their light output is so uniform that these events are referred to as standard candles. They are of vital importance because measuring how their light has been redshifted as it travels means type Ia supernovas can be used to measure cosmic distances.

"Over the years we've learned a lot more about how supernovae behave so we've been able to go back and apply that improved understanding to older data," Camilleri said. "Extensive work has been done to link observations from different telescopes with different capacities and take into account issues such as cosmic dust and galaxy mass which can affect the light coming from a supernova.

"We also incorporated more subtle effects such as gravitational lensing, which is the bending and magnification of light around large objects as it travels from a supernova to Earth."

Combined with the 2024 results from DESI, this research could change our idea of what dark energy actually is.

"Our supernova data from DES in 2024 first showed hints that dark energy may be time-varying, and this new compilation also sees a deviation from the standard model, although in a slightly different direction," Davis said. "Similarly, results from DESI found hints of variations in dark energy in its surveys of relic sound waves from the early universe.

"So, two completely independent measurements have found hints of time variation in dark energy, challenging the standard model that dark energy doesn't change."

Davis added that, as well as revealing what dark energy actually is, this research may also hold the clue to explaining how gravity and quantum physics fit together. While quantum physics (the best theory we have of how the universe operates at subatomic scales) and Einstein's theory of general relativity (our best picture of gravity) have been highly successful in their own rights, scientists have so far been unable to unite them. In other words, there is no theory of quantum gravity.

“We know these two theories are each immensely successful in their own realms, so if we can figure out how to put them together, that would be a huge step in theoretical physics," Davis continued.

This effort will receive a boost when data is added to the team's already comprehensive type Ia supernova catalog. This will include observations from the Dark Energy Bedrock All-Sky Supernova program (DEBASS), which is detecting hundreds more local supernovas than even the DES survey.

The team's results are available on the repository site arXiv.

Wrinkles on the surface of Mercury have revealed that the closest planet to the sun is shrinking faster than scientists thought.

New research suggests that Mercury is shrinking between 10% and 30% faster than had been previously estimated. The team behind this research calculated that the planet has lost nearly 12 miles (19 kilometers) of its total diameter since it formed.

The researchers think that the extremity of this shrinking has gone unnoticed previously because bombardment from space rocks over time has created craters that obscured the evidence of this process.

Scientists say determining the extent of the shrinking of Mercury is key to investigating the composition of the planet's interior.

"More shrinking means Mercury could have a larger metal core, less light elements like silicon mixed into the metal core, or a higher starting temperature," team leader Gaku Nishiyama, of the German Aerospace Center (DLR) Institute of Space Research said in a statement.

Mercury's rocky past

Like all rocky planets in the solar system, Mercury was formed 4.5 billion years ago during a violent and turbulent time in the solar system's history, as rocks and asteroids collided with each other and were bound together.

These impacts generated heat, which Mercury has been losing ever since. As the interior of Mercury cooled, it also shrank. This caused geological wrinkles in the form of scarps and ridges to develop in the rocky outer layers of Mercury.

This cooling should result in Mercury shrinking in a roughly uniform way, and that would make these shortening structures common across the planet. However, asteroid impacts throughout its history have not only created craters that obscure signs of its geological history, but have also spread debris across the surface of Mercury. This makes wrinkles tougher to spot among the accumulation of billions of years' worth of geological features.

The team combined previous maps of Mercury's geology with new observations of the entire planet's surface roughness. They found the roughest terrain of Mercury featured the fewest wrinkles.

"It made us think that there's a process obscuring shortening structures," said Nishiyama, who thinks that impact debris in the roughest regions of Mercury is covering shrinking wrinkles.

The team then used the ridges and scarps in regions less affected by the dispersal of debris to estimate the amount of contraction. This indicated that missing features in rough areas could amount to 10% to 30% extra shrinkage over the 4.5 billion-year lifetime of Mercury. That amounts to a total change in diameter of up to 14.5 miles (23 kilometers) rather than the currently estimated 2.5 to 10 miles (4 to 16 kilometers).

"30% is a little bit surprising, but the corrected amount of contraction actually makes sense to me," Nishiyama said.

There may be more surprises in store. Nishiyama believes that the updated figures could still be an underestimate. This estimate is based on data collected by NASA's MESSENGER probe, which ended in 2015. MESSENGER could only distinguish features larger than around 3 miles (5 kilometers) across.

In November 2026, the BepiColombo mission will start conducting scans of Mercury's surface in much higher resolution than this, and that could reveal even more shrinkage features.

The team's research was published on Thursday (Sept. 10) in the journal Geophysical Research Letters.

Though their origins may be shrouded in mystery, fast radio bursts (FRBs) could be used to probe some of the universe's biggest puzzles. This includes probing the nature of dark matter, the invisible sort of matter that somehow dominates the universe, and dark energy, the mysterious force causing the expansion of our universe to accelerate. They could even shed light on the mysteries of neutrinos, or "ghost particles." Let's dive into how.

FRBs are brief but intense blasts of radio waves currently thought to erupt from rapidly rotating dead stars with the universe's strongest magnetic fields, called magnetars. As FRBs travel billions of light-years to reach Earth, they pass through dense clouds of gas and dust in galaxies. This "cosmic fog" changes the original FRB signal. What this means is these blasts of radio waves carry the fingerprints of how matter in the universe is distributed.

Mapping the distribution and "clumpiness" of ordinary matter in galaxies can then help trace the distribution of dark matter, the effect of dark energy and the mass of neutrinos.

"We've established that FRBs are a leading probe of the distribution of matter in the universe," team leader Kritti Sharma, a graduate student working with Vikram Ravi, a professor of astronomy at the California Institute of Technology (Caltech) and also part of the team, said in a statement. "These FRB data can be used to enhance cosmology experiments that are trying to answer questions about dark matter, dark energy, and the mass of neutrinos."

For this research, Ravi and Sharma analyzed a sample of about 100 FRBs. This represents the first time scientists have used FRBs to directly measure the impact of so-called "feedback" from galaxies on the clumpiness of matter in the large-scale regions between galaxies.

Cosmic ghosts and the dark universe

Ordinary matter, composed of atoms made up of electrons, protons and neutrons, accounts for just around 5% of the universe's energy/matter budget despite comprising stars, planets, moons, our bodies, next door's cat and everything we see around us on a day-to-day basis.

Of this budget, the other 95% is composed of dark energy (68%) and dark matter (27%). It's little wonder that scientists are very keen to better understand these two aspects of the cosmos, sometimes collectively referred to as the "dark universe."

Things get even more murky when considering how, of that 5%, the second most abundant particles in the universe, aside from particles of light or photons, are neutrinos. These get their nickname of "ghost particles" because they interact with other matter particles so infrequently that approximately 100 trillion neutrinos pass through your body every second without leaving any trace. This is possible because neutrinos are virtually massless, and scientists are keen to accurately measure the mass of these cosmic ghosts.

These three mysterious elements of the cosmos have played a vital role in the evolution of large-scale cosmic structures like galaxies and galaxy clusters. That means, in turn, that measuring the clustering of matter can reveal details about the aspects of the universe that influenced that clustering.

However, to do that, scientists also have to understand how other factors smooth out cosmic clumpiness. That includes the energy pumped out from the hearts of galaxies by feeding supermassive black holes, a type of cosmic feedback that smooths out clumpy cosmic matter lying outside galaxies.

"The feedback process thins the gas around the galaxies, redistributing matter across vast distances. It smooths out clumps of matter in a way that looks astonishingly similar to what massive neutrinos do, or what dark energy or dark matter theories predict," Ravi said. "Unless scientists can independently measure this contribution from feedback, they can't tell these effects apart."

That's where FRBs come in.

The researchers found that, while galactic feedback does indeed smooth surrounding material, making it less clumpy, the effect is weaker than has previously been measured.

"Our analysis of FRBs reveals how gas ejected by astrophysical feedback suppresses cosmic structure," team member Elisabeth Krause of the University of Arizona said in the statement. "This is amazing considering we only had about 100 FRBs in our sample. It's only the beginning."

The investigation of the universe with FRBs could get a major boost in 2029 when Caltech's Deep Synoptic Array (DSA) begins operating in Nevada. This powerful radio telescope is expected to find tens of thousands of FRBs, a major boon for cosmology.

The team's research was published on Tuesday (Sept. 8) in the journal Nature Astronomy.

A "forbidden" merger between two massive black holes may not have been quite as impossible as previously thought. That's according to new research that suggests the black holes involved were smaller than expected.

On Nov. 23, 2023, the gravitational wave detector LIGO (Laser Interferometer Gravitational-Wave Observatory) detected tiny ripples in spacetime caused by the merger of two black holes. What was incredible about this signal, designated GW231123, was that it seemed to be the result of a black hole with 140 times the mass of the sun colliding with another that holds 100 solar masses.

This raised eyebrows among researchers because usual models of stellar evolution struggle to account for such massive black holes, especially ones that seemed to be spinning as fast as these two. While scientists have been attempting to explain how such an odd black hole binary could form. The team behind this new research suggests it doesn't need to be explained at all. They think that the masses of these black holes were an illusion.

The key to this illusion is a phenomenon called gravitational lensing, first predicted by Albert Einstein's 1915 theory of gravity, general relativity, which also first predicted the existence of gravitational waves. This theory says objects with mass cause the curvature of space and time, united as a four-dimensional entity called "spacetime." The more mass an object possesses, the greater the curvature, and because gravity arises from this curvature, the greater the gravitational influence.

Gravitational lensing occurs when light from a background object passes a massive foreground object. The foreground object can warp the fabric of spacetime in such a way that the light's path is curved. This means light from the same background source can reach Earth at different times, depending on how much that light was diverted.

This difference in travel time can magnify a background source, and it has been used to great effect to observe distant and ancient galaxies ordinarily too faint to be seen.

This research team thinks the effect also applies to gravitational waves, suggesting the signal GW231123 is an example of gravitationally lensed ripples in spacetime that made the black holes appear larger than they actually are.

"Like light, gravitational waves can also be deflected, magnified and split into multiple signals by massive objects," team member Miguel Zumalacárregui, group leader in the Astrophysical and Cosmological Relativity Department at the Albert Einstein Institute (AEI), said in a statement. "For gravitational waves, diffraction and interference effects give us an additional way to identify and study lensed signals."

To investigate this possibility, the team developed a mathematical model of gravitational lensing and created software powerful and fast enough to analyze it.

"If we assume that GW231123 was deflected and distorted by a compact object of about 190 to 850 solar masses — or by an extended structure such as a globular cluster — we can understand the observed high masses," said team member Srashti Goyal, who was based at the AEI when conducting the research. "Moreover, the lensing interpretation does not require unusually high spins."

When the team modeled the event with that consideration factored in, they found the merger involved a system with a mass of 140 solar masses, rather than the 240-solar-mass system initially theorized.

The team doesn't quite know what massive object is responsible for lensing the gravitational wave signal GW231123. But no matter what it is, if the team is correct, the lens could be something quite special.

"The nature of the lens remains a major mystery in our analysis, as individual compact lenses with 100 to 1,000 solar masses should be exceedingly rare," Zumalacárregui said. "Future work will need to establish whether such lenses can form, or whether an ensemble of lighter objects, including stars, can explain this event."

The team can't yet conclusively say if GW231123 is the first gravitationally lensed gravitational wave signal. Finding future signals of the sort will require upgrades to the sensitivity of detectors like LIGO.

Though even before that happens, the research does point to the utility of gravitational wave astronomy to study some of the universe's most violent events.

The team's research was published on August 25 in the Astrophysical Journal Letters.

Using the ALMA (Atacama Large Millimeter/submillimeter Array) radio telescope, astronomers have watched as two stars come together to form a massive stellar binary. The observations revealed that these stars didn't form from the same collapsing cloud of gas and dust, as most binary stars are assumed to form, but instead came together later in their infancy.

Here on Earth, we are slightly prejudiced by our single sun to view stars as somewhat solitary bodies. However, around half of sun-sized stars in the Milky Way have a companion star. This percentage of stellar partnership rises to around 90% of massive stars. Eventually, these massive stars go supernova and shape their cosmic surroundings. Thus, understanding these binary systems is vital to our understanding of stars and of galaxies in general.

The team behind this research initially observed the still-growing massive stars, or protostars, in the binary system IRAS 07299−1651, located around 5,300 light-years away in 2019. At first, the researchers didn't see anything that suggested these stars didn't form from the same disk-shaped cloud of gas and dust that later fragmented. However, one thing really stood out: the disks of material surrounding and feeding these protostars are oddly misaligned.

Over the course of eight years, the team mapped subtle shifts in the position of the stars using ALMA in addition to the Very Large Array (VLA), as well as infrared images from the James Webb Space Telescope (JWST) and the Very Large Telescope (VLT).

"For the first time, we were able to watch two massive stars move around one another while they were still being born," team leader Yichen Zhang of Shanghai Jiao Tong University, China, said in a statement.

The team was able to reconstruct the full 3-dimensional structure of IRAS 07299−1651 for the first time, obtaining details about how the stars orbit each other, the way their disks are aligned, and the angle at which they blast jets into space.

"Each telescope revealed a different piece of the puzzle," team member Rubén Fedriani, of the Instituto de Astrofísica de Andalucía (IAA) in Granada, Spain, said. "The combination of radio and infrared observations provides the most exquisite detail on the formation of this massive protobinary system."

Unexpected chaos

The team's observations took them by surprise. They were expecting these stars to orbit each other in neat, near-circular orbits. Instead, the orbits were found to be highly flattened or "eccentric," almost parabolic.

If the stars had formed from the same disk of material, then even after it fragmented, the individual disks surrounding the stars would be aligned. However, that wasn't the case; the disks are tilted at a sharp angle to each other and to the orbits of the stars.

"It felt like solving a three-dimensional puzzle," team member Yao Wang of Shanghai Jiao Tong University said. "Each new observation added another piece, and eventually the orbit, disks, and jets all came together into a single, coherent picture."

The chaotic structure of IRAS 07299−1651, as observed by the team, is difficult to explain if the two stars emerged from the same disk of material.

Instead, the researchers theorize that the two stars were born in individual clouds of gas and dust, before a chance encounter brought the two infant stars and their respective natal cocoons together.

Tracing back the orbits of the stars, the researchers found that this encounter likely occurred around 60 years ago. Considering stars live for billions of years, that is an instant on a cosmic timescale. The disk-shaped pockets of material around the stars have thus far survived the encounter, retaining their well-defined structures.

"This study demonstrates that the early lives of stars can be quite chaotic, with a chance encounter leading to this gravitational dance and stellar coupling," team member Jonathan C. Tan of the University of Technology and the University of Virginia said.

What the team can't yet establish is whether these stars are destined to stick together or if they will eventually move apart. Indeed, this fate may not have been sealed yet; interactions with the surrounding gas could determine what shape this system takes in the future.

The team hopes that further observations of IRAS 07299−1651 will help to better understand what the future holds for these stars.

In the meantime, the long-term monitoring approach adopted by the researchers could provide scientists with a powerful new way of investigating other young massive binary systems. This could reveal how common encounters like this are and if more binary systems are composed of stars brought together by chance encounters.

The team's research was published on Tuesday (Sept. 8) in the journal Nature Astronomy.