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Could dark energy be a trick played by time?

David Wiltshire, a cosmologist at New Zealand’s University of Canterbury, proposed an alternate model that gets rid of dark energy entirely. But in doing so, it sacrifices an assumption cosmologists had held sacred for decades.

Karthik Vinod

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Credit: Jon Tyson / Unsplash

In 1924, American astronomer Edwin Hubble discovered that our universe expands in all directions. Powering this expansion was a Big Bang, an event that marked the birth of our current universe some 13.7 billion years ago. Back then, the finding came as a jolt to the astronomy community and the whole world. In 1998, there was even further shake-up when observations of type 1A supernovae from distant galaxies indicated the universe was expanding – at an accelerated rate. But the source of its driving force have remained in the dark.

Dark energy was born from efforts to explain the accelerated expansion. It remains a placeholder name for an undetected energy density contribution that offers a repulsive effect counterbalancing gravity’s attractive nature at long distances. Consensus emerged in support of this dark energy model thereafter. In 2011, astronomers behind the type 1A supernovae study went on to share the Nobel Prize in Physics.

More than two decades later, we are none the wiser to uncover what dark energy is. However, cosmologists have deemed it to be a constant of nature, one that does not evolve with time. So was the surprise when preliminary findings from the Dark Energy Spectroscopic Instrument (DESI) survey indicated dark energy was not just variable, but also weakening over time. The Lambda-Cold Dark Matter, more technically known as the standard model, has never stood on shakier grounds.

Fine-tuned to a Big Crunch ending

In cosmological models, the Greek letter “Lambda” fits as a placeholder for dark energy. It depicts a major chunk – some 70% of the universe’s energy density. But this figure holds only if it is a true cosmological constant. If dark energy is variable, then inevitable we end up fine-tuning the universe’s fate. A constant dark energy would yield a universe expanding forever.

But going by DESI’s preliminary findings, if dark energy is weakening over time, the the universe is set to collapse on itself in the far future. This is the Big Crunch hypothesis. It was amidst the caucus surrounding DESI’s latest findings, the cosmology community took interest in a paper published in the December edition of the Monthly Notices of the Royal Astronomical Society.

In 2007, David Wiltshire, a cosmologist at New Zealand’s University of Canterbury, and the paper’s co-author, had proposed an alternate model called timescape cosmology, to get rid of dark energy entirely. It requires a sacrifice over an assumption cosmologists have held so sacred in their models. Known as cosmological principle, it shares much in common with Aristotle and Ptolemy’s outdated viewpoint that the earth was at the center of the solar system.

A special place in the universe

The cosmological principle assumes matter in the universe is distributed uniformly everywhere on average, and in every direction that we look around. But cosmologists propose to adopt a pragmatic approach like the Polish Prussian astronomer, Nicholas Copernicus, had proposed in the 16th century. In the Copernican model of the solar system, the earth bore no special location in it. Likewise, timescape cosmology requires earth to not occupy a special location.

Saying that, the cosmological principle has a certain appeal among cosmologists. Theoretical calculations would appear complex to manipulate discarding uniformity. At the same time, cosmologists do contend that something has to give way, in light of astronomical observations that contend the cosmological principle is indeed outright wrong.

This image has an empty alt attribute; its file name is Galaxy_superclusters_and_galaxy_voids-png.avif
An artistic illustration of all the major galaxy superclusters. Encircled regions indicate voids, barren of matter. Credit: Wikimedia

Inhabiting a time bubble

One of the hallmark phenomena in Einstein’s general theory of relativity is gravitational time dilation. Time passes slower under a gravitational field. Bizarre as though it may seem to be, experiments have proven this subtle, but measurable effect.

In 1959, two Harvard physicists Robert Pound and Glen Rebka Jr. used a pair of atomic clocks to demonstrate this effect – also known as gravitational time dilation. Two clocks were stationed in their office building – one atop the roof, and the other closer to earth. The clock stationed closer to earth, lagged in comparison to the one atop the roof. Here, time dilation occurs in response to earth’s gravity tugging weakly at the clock atop, compared to the one below.

The universe looks clumpier in certain directions at cosmic scales than others. Galaxies bind together under gravity to form strands like that of a vast, interconnected cosmic web. Voids of cosmic proportions occupy the space in between. These voids experience a faster time flow, since they’re subject to weaker gravity from the surrounding galaxies. But observers in these galaxies have a skewed perception of time, since they’re living embedded inside a bubble of strong gravity. Events outside their time bubble play out akin to a fast-forwarded YouTube video.

Not the end of dark energy

Distant galaxies appears to recede accelerated in the reference frame of our time bubble. That appearance is a mere temporal illusion; an effect David Wiltshire says we falsely assume to be dark energy. So far, timescape cosmology has only occupied a niche interest in cosmology circles. There is far too little evidence to support a claim that dark energy affects arise truly from us inhabiting a time bubble.

Cosmologists had taken to social media to critique Wiltshire’s use of type 1A supernovae datasets used in his analysis. Saying that, none of the critiques themselves are conclusive. As observations pile up in the future, there may come a definitive closure. Until then it’s a waiting game for more data and refined analysis. Meanwhile on the contrary, it is too early to abdicate dark energy as a concept altogether. Lambda-CDM model would be the first to undergo a major rehaul, should DESI’s preliminary findings hold in successive observational runs. Until then, we can only speculate the universe’s fate.

Karthik Vinod is a science writer and journalist based in the US, with bylines in Eos, Mongabay, Columbia News Service, SpaceNews and The Hindu.

Space & Physics

How Scientists Traced the Flow of Matter Around a Dead Star Using X-rays

By studying changes in X-ray signals from Centaurus X-3, researchers at Bengaluru’s Raman Research Institute have found evidence of an unusual way in which matter reaches a neutron star. The discovery could change how scientists explain the radiation coming from this distant system.

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Illustration of Centaurus X-3, an X-ray pulsar orbiting the massive companion star Krzemiński’s star in a high-mass X-ray binary system.
An artistic impression of the high-mass X-ray binary system Centaurus X-3. Not to scale.

When a massive star dies, its core can collapse into an extremely dense object called a neutron star. Despite being only about the size of a city, it can have a mass comparable to that of the Sun. Its powerful gravity can pull matter away from a nearby companion star, releasing energy in the form of X-rays as the material falls towards it.

Scientists at Bengaluru’s Raman Research Institute (RRI) have studied these X-ray signals from Centaurus X-3, a star system about 24,000 light-years from Earth. By examining changes in the signals, the researchers identified a stream of matter flowing towards the neutron star and found evidence of a rotating disk of material around it. This is an unusual finding because such disks are not commonly expected in this type of star system. The discovery could help scientists better understand how matter moves around neutron stars and how these distant objects produce X-rays.

Star That Pulls in Matter

Centaurus X-3 is in the constellation Centaurus. It belongs to a class of systems known as high-mass X-ray binaries. These systems contain a neutron star and a massive companion star held together by gravity.

A neutron star forms when the core of a massive star collapses at the end of its life. It packs roughly the Sun’s mass into a sphere only about the size of a city. Its gravity is so strong that it can pull in material from a nearby companion star. As this material falls towards the neutron star, it releases enormous amounts of energy, including X-rays. Scientists study this radiation to understand how the material behaves and how the system works.

Centaurus X-3 is also a pulsar. Its neutron star rotates and sends out radiation from regions near its magnetic poles. As the star spins, these beams sweep across space. When a beam passes an observing satellite, the satellite detects a pulse of radiation, much as a lighthouse produces a repeating flash as it turns. These regular pulses provide scientists with a way to study the neutron star and its surroundings.

What the Changing Signals Revealed

The radiation from Centaurus X-3 does not come only from the neutron star itself. Some of it interacts with nearby material, including the surface of the companion star, gas flowing away from it and matter surrounding the neutron star. This material absorbs radiation and emits it again. Scientists call this secondary radiation.

Illustration of the accretion disk and stream of matter flowing towards the neutron star in the Centaurus X-3 system, showing how the stream can block and emit X-rays as it moves around the star.
The accretion stream falling onto the neutron star along its magnetic field lines.

Changes in this radiation can help researchers work out what is happening around the neutron star. However, Centaurus X-3 is so far away that telescopes cannot clearly distinguish its surrounding structures. It appears as a single point of light. Scientists must therefore piece together the system’s structure from the signals they receive.

Earlier observations had shown that the intensity of certain secondary X-ray emission lines changed as the neutron star rotated. An emission line is a feature in a spectrum that can reveal information about the material producing or interacting with the radiation. A research team led by Kinjal Roy of RRI examined four such emission lines in detail. The researchers found that the structure producing these changes must be rotating along with the neutron star.

The pattern helped them identify the likely source which is a stream of matter moving towards the neutron star.

Following the stream of matter

This stream is part of a process called accretion, in which a compact object draws in material from its surroundings. In Centaurus X-3, the stream carries matter from an accretion disk towards the neutron star. The disk is a rotating structure of gas and other material that moves around the star before being drawn inwards. The neutron star’s magnetic field then guides the incoming matter towards its magnetic poles.

The stream also changes what an observing satellite sees. As it moves around the neutron star, it can come between the satellite and the star, partially blocking the direct radiation. When this happens, the primary X-ray signal weakens. At the same time, radiation from the stream itself becomes stronger in the observed signal.

The researchers used these changing signals to connect the observed variations to the movement of matter around the neutron star. The evidence for an accretion stream also points to an accretion disk feeding it. This matters because scientists generally expect high-mass X-ray binaries to gather material in a different way.

Why an accretion disk matters

In many high-mass X-ray binaries, a neutron star captures gas directly from the stream of material blown away by its companion star. This is known as stellar-wind accretion. An accretion disk involves a different arrangement: material gathers into a rotating structure before flowing towards the neutron star. The findings from Centaurus X-3 indicate that this disk-based process is taking place in a system where it is not generally expected.

That difference matters when scientists calculate how the system produces and releases radiation. If their models leave out the disk, they may fail to account for some of the radiation coming from the surrounding material.

“Accretion disk is not expected to occur in [HMXBs] So, if an accretion disk is forming in this system, emission models have to be modified,” Roy said in the Department of Science and Technology’s announcement. He added that future models of Centaurus X-3 would need to account for radiation from the disk.

The research does not mean that scientists have directly photographed the disk. Instead, they have used the changing X-ray signals to infer the presence and behaviour of structures that remain too distant to resolve clearly. Published in The Astrophysical Journal, the study adds to the understanding of Centaurus X-3, one of the most widely studied binary pulsars. It also shows how small changes in radiation can reveal the movement of matter around objects that are otherwise beyond the reach of direct observation.

By identifying the flow responsible for the changing signals, the researchers have provided a more detailed picture of how this neutron star draws in material. That picture will help scientists refine their models of Centaurus X-3 and examine whether similar processes occur in other high-mass X-ray binaries.

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Space & Physics

World Space Week 2026: How the Rocket Revolution Is Changing Space

World Space Week 2026 explores the Rocket Revolution, from reusable launchers and private space companies to the growing role of satellites.

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Rocket launching over the ocean at sunset: World Space Week 2026
A rocket launches over the ocean, illustrating the “Rocket Revolution” theme of World Space Week 2026 and the growing role of launch technology in space access. Representational image. Image credit: SpaceX/ Pexels

For most of the space age, rockets were built to fly once. After delivering a satellite to orbit, much of the vehicle was discarded. But that model is transforming as reusable boosters, smaller launch vehicles and shared launches are making space more accessible to companies, universities and countries beyond the traditional space powers.

This has become the focus of World Space Week 2026, observed from October 4 to 10 with the theme “Rocket Revolution.” The mission of World Space Week Association (WSWA) is to strengthen the link between space and society through public education, participation, and dialogue on the future of space activity using World Space Week as a focus.

The dates mark two milestones in space history: the launch of Sputnik 1 on October 4, 1957, and the entry into force of the Outer Space Treaty on October 10, 1967.

Rockets, Reused

SpaceX’s Falcon 9 has shown the potential of reusable rockets. Its first stage returns to Earth after launch and can fly again. The approach can reduce the need to build an entirely new rocket for every mission. Blue Origin’s New Glenn also has a reusable first stage, while Rocket Lab is developing a reusable version of its Electron launcher.

Smaller rockets and rideshare missions are opening another part of the market. A company with a small satellite no longer necessarily needs access to a large launcher or an entire rocket.

Nearly 15,000 Satellites are in Orbit

The OECD estimates that more than 14,000 operational satellites were in orbit at the end of 2025, rising to nearly 15,000 by mid-2026. Satellite observations supply more than 90% of the observations used in numerical weather prediction, according to the OECD. Earth-observation satellites also monitor crops, forests, oceans and cities, while their images can help map areas affected by floods and cyclones.

The global space economy was estimated at 550–600 billion dollars in 2025, with much of its value coming from services based on satellite communications, navigation and Earth-observation data.

India Opening Launch Sector

India is also moving towards a larger private space industry. In July 2026, Skyroot Aerospace’s Vikram-I became the first privately developed Indian rocket to conduct an orbital launch from Indian soil. It lifted off from Sriharikota on July 18 and placed two satellites, SCOPE and Grahaa, into low Earth orbit.

Interestingly, the Department of Space reported around 440 space-technology startups registered on the DPIIT Startup India portal as of August 2026. ISRO is also developing the Small Satellite Launch Vehicle (SSLV) for spacecraft weighing up to about 500 kg. A dedicated SSLV launch complex is being developed at Kulasekarapattinam in Tamil Nadu.

More spacecraft, More Orbital Risks

A busier space environment brings its own problems. About 45,860 pieces of space debris are regularly tracked, according to the OECD. Millions of smaller fragments are too difficult to monitor individually. A collision can create thousands more pieces and threaten other spacecraft.

Satellite operators therefore need to track nearby objects, avoid collisions and plan for spacecraft disposal after missions end. For World Space Week 2026, the “Rocket Revolution” theme points to a space industry that is moving beyond occasional government missions. Rockets are being reused, private companies are entering the launch business and satellites are becoming part of everyday infrastructure. The challenge that has to be tackled is the increasingly busy orbital environment usable for the next generation of missions.

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A Dead Star Feeds Off Planet Formed From Its Ashes

It adds to a known coterie of planets now found orbiting dead stars, astronomers are busy studying to spot signs of life.

Karthik Vinod

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Screenshot 2026 10 05 164626 e1791233298442
The accretion of material from an evaporating second-generation giant planet accreting on a white dwarf star | Credit: Snehalata Sahu

A planet orbiting once every 4 days around a white dwarf star HS 0209+0832  – about 270 light years in the direction of the constellation Pisces – is steadily losing its atmosphere to its host star. While many stars in solar systems beyond our own often feed on their planets, this particular star feeds on its own ashes.

The gaseous planet HS 0209+0832 b was discovered in 2024, when the Transiting Exoplanet Survey Satellite, a NASA space telescope, found it orbiting the white dwarf star over the course of four days. The new study followed through with detailed observations from TESS data, NASA’s space-based Far Ultraviolet Spectroscopic Explorer, in addition to the ESO’s mountain-based Very Large Telescope, to study the star’s atmosphere and in turn inferring some chemistry occurring in the planet.

In a study published in the journal Nature Astronomy on Monday and funded by NASA, European Research Council, Fundación Occident and the Instituto de Astrofísica de Canarias, an international team of astronomers have reported imprints of niobium, a heavy element, in the atmosphere of a white dwarf star.

Astronomers predict the transiting young planet around the dead star is supplying that niobium back to its host. The sighting is evidence of a “second generation” planet, one of many candidates identified over several years, manifesting in a myriad different ways from spent gas ejected in the wake of stellar deaths.

It adds to a known coterie of planets now found orbiting dead stars, astronomers are busy studying to spot signs of life.

What are white dwarf stars?

White dwarves are an exotic stars, and are all that’s left off giant stars shedding their large gaseous skin in violent deaths. Our sun is destined one day to transform into a white dwarf, but only after swelling in size some five billion years from now to become a red giant when it will eclipse past the earth’s orbit. It would take several million years after that for the red giant sun to shed its gaseous exterior to become a white dwarf.

Planets if any, found orbiting these dead stars may have likely migrated from the new solar system’s outer reaches. All that’s left off the progenitor star’s past are imprints of light metals and other elements on the white dwarf’s atmosphere. Such planets have previously been spotted orbiting pulsars, a kind of neutron star, back in 1992. In fact, its discovery had marked the first ever detection of any planet orbiting a star beyond our sun.

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In five billion years, our sun will evolve to become a red giant star. Credit: Svitlana Leonidivna Malchenko

Sighting niobium

Elements such as niobium don’t typically form in the core of stars like our sun. Chemical production usually limits to elements lighter than or until iron, with its 26 protons and 30 neutrons. Beyond that, slamming an extra proton or neutron will cause those to split, leaving iron to be the last element to be directly forged.

Niobium, with 41 protons and 52 neutrons, is thought to be born after absorbing slow passing neutrons when the red giant star dies to form a white dwarf star. This niobium hitches a ride along with rest of the contents of the red giant star, farther into the outer reaches of the system after the formation of the white dwarf.

These contents could create a new disc of circumstellar material with dust and gas that could condense one day to form new planets. The “second generation” planet found orbiting the white dwarf star from the new study, could have been born this way.

Alternatively, it may have been a planet in the outskirts like Neptune, migrating inwards, and enriching itself with niobium-rich star material.

Either way, the planet got too close to its host star, which is irradiating its newfound niobium-rich atmosphere, stripping it away and devouring it.

While it’s likely not a candidate planet for life as we know it to be found, it’s discovery can help ascertain how such worlds are formed in the aftermath of a star’s various phases of evolution.

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