Prof Arnab Bhattacharya, Prof Ajit Kembhavi, Chief guest Prof Ajay Kumar Sood, Prof Aniket Sule during the opening ceremony of 18th International Olymopiad on Astronomy and Astrophysics at the Jio World Convention Centre in Mumbai on August 12, 2025.
| Photo Credit: EMMANUAL YOGINI

On 27 December last year, astronomers using the ATLAS survey telescope in Chile discovered a small asteroid moving away from Earth. Follow up observations have revealed that the asteroid, 2024 YR4, is on a path that might lead to a collision with our planet on December 22 2032.

In other words, the newly-discovered space rock poses a significant impact threat to our planet.

It sounds like something from a bad Hollywood movie. But in reality, there’s no need to panic – this is just another day living on a target in a celestial shooting gallery.

So what’s the story? What do we know about 2024 YR4? And what would happen if it did collide with Earth?

A target in the celestial shooting gallery

As Earth moves around the Sun, it is continually encountering dust and debris that dates back to the birth of the Solar system. The system is littered with such debris, and the meteors and fireballs seen every night are evidence of just how polluted our local neighbourhood is.

But most of the debris is far too small to cause problems to life on Earth. There is far more tiny debris out there than larger chunks – so impacts from objects that could imperil life on Earth’s surface are much less frequent.

The most famous impact came some 66 million years ago. A giant rock from space, at least 10 kilometres in diameter, crashed into Earth – causing a mass extinction that wiped out something like 75% of all species on Earth.

Impacts that large are, fortunately, very rare events. Current estimates suggest that objects like the one which killed the dinosaurs only hit Earth every 50 million years or so. Smaller impacts, though, are more common.

On June 30 1908, there was a vast explosion in a sparsely populated part of Siberia. When explorers later reached the location of the explosion, they found an astonishing site: a forest levelled, with all the trees fallen in the same direction. As they moved around, the direction of the fallen trees changed – all pointing inwards towards the epicentre of the explosion.

In total, the Tunguska event levelled an area of almost 2,200 square kilometres – roughly equivalent to the area of greater Sydney. Fortunately, that forest was extremely remote. While plants and animals were killed in the blast zone, it is thought that, at most, only three people perished.

Estimates vary of how frequent such large collisions should be. Some argue that Earth should experience a similar impact, on average, once per century. Others suggest such collisions might only happen every 10,000 years or so. The truth is we don’t know – but that’s part of the fun of science.

More recently, a smaller impact created global excitement. On 15 February 2013, a small asteroid (likely about 18 metres in diameter) detonated near the Russian city of Chelyabinsk.

The explosion, about 30 kilometres above the Earth’s surface, generated a powerful shock-wave and extremely bright flash of light. Buildings were damaged, windows smashed, and almost 1,500 people were injured – although there were no fatalities.

It served as a reminder, however, that Earth will be hit again. It’s only a question of when.

Which brings us to our latest contender – asteroid 2024 YR4.

The 1-in-77 chance of collision to watch

2024 YR4 has been under close observation by astronomers for a little over a month. It was discovered just a few days after making a relatively close approach to our planet, and it is now receding into the dark depths of the Solar System. By April, it will be lost to even the world’s largest telescopes.

The observations carried out over the past month have allowed astronomers to extrapolate the asteroid’s motion forward over time, working out its orbit around the Sun. As a result, it has become clear that, on December 22 2032, it will pass very close to our planet – and may even collide with us.

At present, our best models of the asteroid’s motion have an uncertainty of around 100,000 kilometres in its position at the time it would be closest to Earth. At around 12,000 kilometres in diameter, our planet falls inside that region of uncertainty.

Calculations suggest there is currently around a 1-in-77 chance that the asteroid will crash into our planet at that time. Of course, that means there is still a 76-in-77 chance it will miss us.

When will we know for sure?

With every new observation of 2024 YR4, astronomers’ knowledge of its orbit improves slightly – which is why the collision likelihoods you might see quoted online keep changing. We’ll be able to follow the asteroid as it recedes from Earth for another couple of months, by which time we’ll have a better idea of exactly where it will be on that fateful day in December 2032.

But it is unlikely we’ll be able to say for sure whether we’re in the clear at that point.

Fortunately, the asteroid will make another close approach to the Earth in December 2028 – passing around 8 million kilometres from our planet. Astronomers will be ready to perform a wide raft of observations that will help us to understand the size and shape of the asteroid, as well as giving an incredibly accurate overview of where it will be in 2032.

At the end of that encounter, we will know for sure whether there will be a collision in 2032. And if there is to be a collision that year, we’ll be able to predict where on Earth that collision will be – likely to a precision of a few tens of kilometres.

How big would the impact be?

At the moment, we don’t know the exact size of 2024 YR4. Even through Earth’s largest telescopes, it is just a single tiny speck in the sky. So we have to estimate its size based on its brightness. Depending on how reflective the asteroid is, current estimates place it as being somewhere between 40 and 100 metres across.

What does that mean for a potential impact? Well, it would depend on exactly what the asteroid is made of.

The most likely scenario is that the asteroid is a rocky pile of rubble. If that turns out to be the case, then the impact would be very similar to the Tunguska event in 1908.

The asteroid would detonate in the atmosphere, with a shockwave blasting Earth’s surface as a result. The Tunguska impact was a “city killer” type event, levelling forest across a city-sized patch of land.

A less likely possibility is that the asteroid is made of metal. Based on its orbit around the Sun, this seems unlikely – but we can’t rule it out.

In that case, the asteroid would make it through the atmosphere intact, and crash into Earth’s surface. If it hit on the land, it would carve out a new impact crater, probably more than a kilometre across and a couple of hundred metres deep – something similar to Meteor Crater in Arizona.

Again, this would be quite spectacular for the region around the impact – but that would be about it.

Living in a remarkable time

This all sounds like doom and gloom. After all, we know that the Earth will be hit again – either by 2024 YR4 or something else. But there’s a real positive to take out of all this.

There has been life on Earth for more than 3 billion years. In all that time, impacts have come along and caused destruction and devastation many times.

But there has never been a species, to our knowledge, that understood the risk, could detect potential threats in advance, and even do something about the threat. Until now.

In just the past few years, we have discovered 11 asteroids before they hit our planet. In each case, we have predicted where they would hit, and watched the results.

We have also, in recent years, demonstrated a growing capacity to deflect potentially threatening asteroids. NASA’s DART mission (the Double Asteroid Redirection Test) was an astounding success.

For the first time in more than 3 billion years of life on Earth, we can do something about the risk posed by rocks from space. So don’t panic! But instead, sit back and watch the show.

Jonti Horner is a Professor of Astrophysics, University of Southern Queensland. This article is republished from The Conversation.

The Crab Nebula, the result of a bright supernova explosion seen by Chinese and other astronomers in the year 1054, 6,500 light-years from Earth, is seen in an image taken by the James Webb Telescope on June 3, 2024. At its center is a neutron star, a super-dense star produced by the supernova. This image shows the X-ray data from Chandra along with infrared data from the Webb space telescope.
| Photo Credit: Reuters

By looking at light from distant exploding stars called supernovas, in 1998 astronomers discovered the universe isn’t just expanding – its expansion is speeding up. But what’s behind this acceleration?

Enter dark energy. It’s one of the most debated and intriguing missing puzzle pieces of modern physics – a mysterious form of energy believed to uniformly permeate all of space. In the current most accepted model of modern cosmology, dark energy is what drives the accelerated expansion of the universe.

But what if there’s another explanation that doesn’t involve dark energy? A recent study using data from supernovas hints there might indeed be one, and it’s called the Timescape model.

This finding could profoundly challenge our understanding of the cosmos, so let’s dive in.

What is dark energy?

The backbone of modern cosmology is the Lambda-Cold Dark Matter (Lambda-CDM) model. It describes a universe where a dark energy – denoted with Λ, the Greek letter Lambda – is the driving mechanism behind the universe’s accelerating expansion.

Under this model, galaxies are dancing together under the effect of an invisible dark matter web made of heavy particles that don’t interact with anything. The effects of this cold dark matter can only be observed through gravity.

Dark energy accounts for nearly 70% of the universe’s total energy budget, but its exact nature remains one of the greatest mysteries in physics.

Some interpretations suggest dark energy could be linked to the energy of the vacuum, while other studies have attempted to describe it as a new, evolving energy field spread across space.

And a recent study from the international DESI collaboration that traces the universe’s expansion hinted dark energy may be weakening over time.

It’s also possible that our current theory of gravity (Einstein’s theory of general relativity) is incomplete. Perhaps it requires an extension to describe gravitational interaction at cosmological scales – distances on the order of millions to billions of light-years.

What is the Timescape model?

Matter – dark matter, gas, galaxies, star clusters and super clusters – is not uniformly spread throughout cosmos.

But for the Lambda-CDM model, we assume the universe is homogeneous and isotropic. This means that, on cosmic scales, the distribution of matter appears smooth and uniform. Any clumps and gaps we might find can be considered insignificant due to the grand scale of the entire thing.

By contrast, the Timescape model takes the uneven distribution of matter into account. It suggests our intricate cosmic web – made up of galaxies, clusters, filaments and vast cosmic voids – directly affects how we interpret the expansion of the universe.

This would mean the universe isn’t stretching out evenly.

According to the Timescape model, the universe’s expansion rate varies across different regions, depending on how dense they are.

The key parameter in the Timescape model is the “void fraction”: it quantifies the proportion of space occupied by expanding voids.

Gravity dictates that voids expand faster than denser regions – they have less matter to hold them back, allowing space to stretch more freely. This creates an average effect that can mimic the accelerated expansion attributed to dark energy in Lambda-CDM.

In short, the Timescape model suggests it might only appear to us that the universe’s expansion is speeding up. The expansion speed depends on where you are in the universe.

What did the study find?

The authors of the new study looked at one of the biggest collections of Type Ia supernovas, called the Pantheon+ dataset. These supernovas are a reliable standard used to test cosmological models.

The team compared two major models: the standard Lambda-CDM (our “vanilla” recipe of the universe), and the Timescape model.

When looking at nearby bright supernovas, the Timescape model explained things better than our standard model. This was only statistical though, with the statistical analysis showing a “very strong” preference.

Even when they examined more distant supernovas, where things should be more evenly spread out, Timescape still held up slightly better than the usual model.

The takeaway? The Timescape model, which focuses on how cosmic “clumps and gaps” change the way we see the universe growing, might be better at capturing the true nature of our universe’s expansion. This would be especially so for the nearby universe – we have a lot of voids and filaments near us, which would affect how we see the expansion.

How strong is the evidence, then?

There are important caveats. The analysis doesn’t account for peculiar velocities – small, random motions of galaxies that can affect supernova measurements. They also don’t account for Malmquist bias, when brighter supernovas are more likely to be included in the data simply because they’re easier to detect.

These potential sources of error could badly affect their results. Additionally, the study didn’t use the latest DES5yr dataset of supernovas. It’s more consistent and uniform in its data collection than Pantheon+, potentially making it more reliable for comparison.

There are other things besides supernovas currently propping up the Lambda-CDM model, most notably baryon acoustic oscillations and gravitational lensing. Future work would need to integrate those into the Timescape model.

But with this new study, the Timescape model offers an intriguing alternative to Lambda-CDM. The bottom line is that our universe’s acceleration is an illusion due to the uneven distribution of matter with large cosmic voids expanding faster than denser regions.

If confirmed, this would represent a revolutionary paradigm shift in cosmology.

This article is republished from The Conversation under a Creative Commons license. Read the original article here.

Using the largest gravitational wave detector ever made, we have confirmed earlier reports that the fabric of the universe is constantly vibrating. This background rumble is likely caused by collisions between the enormous black holes that reside in the hearts of galaxies.

The results from our detector – an array of rapidly spinning neutron stars spread across the galaxy – show this “gravitational wave background” may be louder than previously thought. We have also made the most detailed maps yet of gravitational waves across the sky, and found an intriguing “hot spot” of activity in the Southern Hemisphere.

Our research is published today in three papers in the Monthly Notices of the Royal Astronomical Society.

Ripples in space and time

Gravitational waves are ripples in the fabric of space and time. They are created when incredibly dense and massive objects orbit or collide with each other.

The densest and most massive objects in the universe are black holes, the remnants of dead stars. One of the only ways to study black holes is by searching for the gravitational waves they emit when they move near each other.

Just like light, gravitational waves are emitted in a spectrum. The most massive black holes emit the slowest and most powerful waves – but to study them, we need a detector the size of our galaxy.

The high-frequency gravitational waves created by collisions between relatively small black holes can be picked up with Earth-based detectors, and they were first observed in 2015. However, evidence for the existence of the slower, more powerful waves wasn’t found until last year.

Several groups of astronomers around the world have assembled galactic-scale gravitational wave detectors by closely observing the behaviour of groups of particular kinds of stars. Our experiment, the MeerKAT Pulsar Timing Array, is the largest of these galactic-scale detectors.

Today we have announced further evidence for low-frequency gravitational waves, but with some intriguing differences from earlier results. In just a third of the time of other experiments, we’ve found a signal that hints at a more active universe than anticipated.

We have also been able to map the cosmic architecture left behind by merging galaxies more accurately than ever before.

Black holes, galaxies and pulsars

At the centre of most galaxies, scientists believe, lives a gargantuan object known as a supermassive black hole. Despite their enormous mass – billions of times the mass of our Sun – these cosmic giants are difficult to study.

Astronomers have known about supermassive black holes for decades, but only directly observed one for the first time in 2019.

When two galaxies merge, the black holes at their centres begin to spiral towards each other. In this process they send out slow, powerful gravitational waves that give us an opportunity to study them.

We do this using another group of exotic cosmic objects: pulsars. These are extremely dense stars made mainly of neutrons, which may be around the size of a city but twice as heavy as the Sun.

Pulsars spin hundreds of times a second. As they rotate, they act like lighthouses, hitting Earth with pulses of radiation from thousands of light years away. For some pulsars, we can predict when that pulse should hit us to within nanoseconds.

Our gravitational wave detectors make use of this fact. If we observe many pulsars over the same period of time, and we’re wrong about when the pulses hit us in a very specific way, we know a gravitational wave is stretching or squeezing the space between the Earth and the pulsars.

However, instead of seeing just one wave, we expect to see a cosmic ocean full of waves criss-crossing in all directions – the echoing ripples of all the galactic mergers in the history of the universe. We call this the gravitational wave background.

A surprisingly loud signal – and an intriguing ‘hot spot’

To detect the gravitational wave background, we used the MeerKAT radio telescope in South Africa. MeerKAT is one of the most sensitive radio telescopes in the world.

As part of the MeerKAT Pulsar Timing Array, it has been observing a group of 83 pulsars for about five years, precisely measuring when their pulses arrive at Earth. This led us to find a pattern associated with a gravitational wave background, only it’s a bit different from what other experiments have found.

The pattern, which represents how space and time between Earth and the pulsars is changed by gravitational waves passing between them, is more powerful than expected.

This might mean there are more supermassive black holes orbiting each other than we thought. If so, this raises more questions – because our existing theories suggest there should be fewer supermassive black holes than we seem to be seeing.

The size of our detector, and the sensitivity of the MeerKAT telescope, means we can assess the background with extreme precision. This allowed us to create the most detailed maps of the gravitational wave background to date. Mapping the background in this way is essential for understanding the cosmic architecture of our universe.

It may even lead us to the ultimate source of the gravitational wave signals we observe. While we think it’s likely the background emerges from the interactions of these colossal black holes, it could also stem from changes in the early, energetic universe following the Big Bang – or perhaps even more exotic events.

The maps we’ve created show an intriguing “hot spot” of gravitational wave activity in the Southern Hemisphere sky. This kind of irregularity supports the idea of a background created by supermassive black holes rather than other alternatives.

However, creating a galactic-sized detector is incredibly complex, and it’s too early to say if this is genuine or a statistical anomaly.

To confirm our findings, we are working to combine our new data with results from other international collaborations under the banner of the International Pulsar Timing Array.

This article is republished from The Conversation under a Creative Commons license. Read the original article here.

Skywatchers will have the opportunity to close out the year by experiencing a rare astronomical event known as the “black moon”. The fascinating-sounding term is often used to describe the second new moon that appears in a single calendar month. It is an occurrence that is not officially recognised in astronomy but over the years, has gained popularity among amateur astronomers and stargazers.

As per the US Naval Observatory, the unique phenomenon will occur on December 30 at 5:27 pm ET (2227 GMT). For those in America, the black moon will be visible on December 30 itself while for those in Europe, Africa and Asia, it will take place on December 31, 2024. In India, the black moon phenomenon can be seen around 3:57 am on December 31.

How does a black moon happen?

A new moon happens when the sun and the moon share the same celestial longitude and the latter’s illuminated side faces away from the Earth, making it invisible to the naked eye. As the lunar cycle averages 29.5 days, sometimes a month can have two new moons, leading to the phenomenon of a black moon. It is similar to a blue moon – a phenomenon when two full moons appear in a month. Notably, the moon is not visible during this phase unless there’s a solar eclipse.

Also Read | Google Doodle Marks December’s Final Half Moon With Special Interactive Game

What to expect?

Although the black moon itself won’t be visible, its impact on the night sky is significant. The darkness allows for better visibility of stars, planets, and even distant galaxies. Binoculars or a telescope can enhance the viewing of planets like Jupiter, which will be observable all night, and Venus, which will be bright in the evening sky.

For those living in the Northern Hemisphere, the constellations Orion, Taurus, and Leo will be prominent in the night sky. Additionally, Orion’s belt will be an excellent guide, with Sirius, the brightest star in the night sky, shining to its south.

Meanwhile, in the Southern Hemisphere, the Southern Cross (Crux) will be visible, along with Canopus, a standout in the constellation Carina.

At the centre of the Milky Way is a supermassive black hole called Sagittarius A*. It is roughly 27,000 light years from Earth and 23.5 million kilometres in diameter.

In a world first, a team of astronomers led by Florian Peißker from the University of Cologne, Germany, have discovered a binary star system orbiting this black hole.

The system is known as D9. Its discovery, announced in a new paper published today in Nature Communications, sheds light on the extreme environment at the centre of our Milky Way galaxy.

It also helps explain a long-running cosmic mystery about why some stars hurtle through space much faster than others.

What Is A Binary Star System?

A binary star system is simply two stars orbiting each other.

Our Sun is not part of a binary, which is a good thing: we wouldn’t want another star wandering through our Solar System. It would disrupt the orbit of the Earth; we’d fry or freeze.

Observations show about two thirds of the stars in the Milky Way are single stars, and the remainder are part of a binary or multiple star system. Larger stars are more likely to be paired.

Binary star systems are useful to astronomers because their motion contains a wealth of information. For example, the speed and distance of the orbits tell us about the masses of the stars.

For a single star, by contrast, we usually work out its mass from how bright it is.

A Technically Challenging Discovery

Although scientists have previously predicted that binary star systems exist near supermassive black holes, they have never actually detected one.

This recent discovery was technically quite challenging. We can’t simply look at the system and see two stars, because it’s too far away. Rather, the astronomers used the European Southern Observatory’s Very Large Telescope to measure the shifting of the starlight – known as the Doppler effect. This showed that the stellar system’s light had a characteristic wobble, indicating an orbit.

But the team did much more than that.

Because binary stars contain a wealth of information, the astronomers could calculate that this particular system is approximately 2.7 million years old. That is, 2.7 million years ago, these stars first ignited.

They probably weren’t born in the black hole’s extreme surroundings, so unless they only recently wandered into this neighbourhood, they have lasted about a million years in their current environment.

This, in turn, tells us about the black hole’s ability to disrupt stars in its orbit. Black holes are mysterious beasts, but clues such as this are helping us unravel their nature.

Circling A Black Hole

The situation the astronomers discovered is quite familiar.

Think of the Moon: it orbits the Earth, and the Earth and the Moon together orbit the Sun. Because gravity is an attractive force, it can pull multiple celestial objects into complicated orbits. The complexity of this scenario inspired the recent book and Netflix series, The Three Body Problem.

If they are complicated, could the whole thing drift apart? The Moon–Earth–Sun arrangement is stable because two of the three bodies – the Earth and Moon – are much closer together than the other body, the Sun. The Moon and Earth are close enough that, so far as the Sun is concerned, it’s effectively a two-body system, which is stable.

But if all three bodies interact, the system can come apart. It is even possible for two of the bodies to eject the third body entirely.

Stars Of Unusual Speed

This mechanism probably explains a cosmic mystery: hypervelocity stars.

Most stars in the night sky are in a typical, almost-circular orbit around the centre of our galaxy. Orbital speeds are about 200 kilometres per second: very fast on Earth, but nothing special in space.

However, since 2005 we have discovered about 20 hypervelocity stars, which are hurtling through our galaxy at more than 1,000 kilometres per second. How?

Our best current idea is that hypervelocity stars were once part of a binary system orbiting our supermassive black hole. In time, the stars got too close to the black hole, and a complicated orbit resulted. In the kerfuffle, with a black hole calling the shots, one of the stars got ejected. It escaped to the outer Milky Way, where we see it as a hypervelocity star.

Finding The Hypervelocity Factory

It’s an interesting theory.

Theoretical calculations show the mechanism works and the speeds are about right. Observations show many of the known hypervelocity stars appear to be shooting away from the galactic centre, which is another plus for the theory. But how else could we test this idea?

An obvious way is to look for binary stars around our supermassive black hole.

Astronomers have been keeping a close eye on our galactic centre for decades. It’s not too difficult to find in the night sky, as you can see from the image below.

Here are two reliable methods to find Sagittarius A*. First, find Antares (bright and red), which is the centre of the back of Scorpio, and then follow the scorpion’s body to the tip of the tail, and that’s close-ish to the black hole. Alternatively, get a good night sky app on your phone; they’re amazing.

In the context of these theories, this recent discovery is very important. Astronomers found a binary star system around our supermassive black hole. An important piece of the hypervelocity puzzle falls into place.

(Author: Luke Barnes, Lecturer in Physics, Western Sydney University)

(Disclosure Statement: Luke Barnes does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment)

This article is republished from The Conversation under a Creative Commons license. Read the original article.
 

Spiral galaxy NGC 628, located 32 million light-years away from Earth, is seen in an undated image from the James Webb Space Telescope.
| Photo Credit: Reuters

Fresh corroboration of the perplexing observation that the universe is expanding more rapidly than expected has scientists pondering the cause – perhaps some unknown factor involving the mysterious cosmic components dark energy and dark matter.

Two years of data from NASA’s James Webb Space Telescope have now validated the Hubble Space Telescope’s earlier finding that the rate of the universe’s expansion is faster – by about 8% – than would be expected based on what astrophysicists know of the initial conditions in the cosmos and its evolution over billions of years. The discrepancy is called the Hubble Tension.

The observations by Webb, the most capable space telescope ever deployed, appear to rule out the notion that the data from its forerunner Hubble was somehow flawed due to instrument error.

“This is the largest sample of Webb Telescope data – its first two years in space – and it confirms the puzzling finding from the Hubble Space Telescope that we have been wrestling with for a decade – the universe is now expanding faster than our best theories can explain,” said astrophysicist Adam Riess of Johns Hopkins University in Maryland, lead author of the study published on Monday (December 9, 2024) in the Astrophysical Journal.

“Yes, it appears there is something missing in our understanding of the universe,” added Riess, a 2011 Nobel laureate in physics for the co-discovery of the universe’s accelerating expansion. “Our understanding of the universe contains a lot of ignorance about two elements – dark matter and dark energy – and these make up 96% of the universe, so this is no small matter.”

“The Webb results can be interpreted to suggest there may be a need to revise our model of the universe, although it is very difficult to pinpoint what this is at the moment,” said Siyang Li, a Johns Hopkins doctoral student in astronomy and astrophysics and a study co-author.

Dark matter, thought to comprise about 27% of the universe, is a hypothesised form of matter that is invisible but is inferred to exist based on its gravitational effects on ordinary matter – stars, planets, moons, all the stuff on Earth – which accounts for roughly 5% of the universe.

Dark energy, believed to comprise approximately 69% of the universe, is a hypothesised form of energy permeating vast swathes of space that counteracts gravity and drives the universe’s accelerating expansion.

What might explain the anomalous expansion rate?

“There are many hypotheses that involve dark matter, dark energy, dark radiation – for example, neutrinos (a type of ghostly subatomic particle) – or gravity itself having some exotic properties as possible explanations,” Riess said.

The researchers employed three different methods to measure a specific telltale metric – distances from Earth to galaxies where a type of pulsating star called Cepheids have been documented. The Webb and Hubble measurements were in harmony.

The universe’s expansion rate, a figure called the Hubble constant, is measured in kilometers per second per megaparsec, a distance equal to 3.26 million light-years. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).

Under the standard model of cosmology – basically, the conventional wisdom concerning the universe – the value of the Hubble constant should be about 67-68. The Hubble and Webb data give a value averaging about 73, with a range of about 70-76.

The Big Bang event 13-14 billion years ago initiated the universe, and it has been expanding ever since. Scientists in 1998 disclosed that this expansion was actually accelerating, with dark energy as the hypothesized reason.

The new study looked at Webb data covering about a third of Hubble’s full slate of relevant galaxies. The researchers in 2023 announced that earlier interim Webb data validated the Hubble findings.

So how might this Hubble Tension mystery be solved?

“We need more data to better characterize this clue. Exactly what size is it (the discrepancy)? Is the mismatch at the lower end – 4-5% – or the higher end – 10-12% – of what the current data allows? Over what range of cosmic time is it present? These will further inform ideas,” Riess said.

Washington:

Astronomers have spotted orbiting around a young star a newborn planet that took only 3 million years to form – quite swift in cosmic terms – in a discovery that challenges the current understanding of the speed of planetary formation.

This infant world, estimated at around 10 to 20 times the mass of Earth, is one of the youngest planets beyond our solar system – called exoplanets – ever discovered. It resides alongside the remnants of the disk of dense gas and dust circling the host star – called a protoplanetary disk – that provided the ingredients for the planet to form.

The star it orbits is expected to become a stellar type called an orange dwarf, less hot and less massive than our sun. The star’s mass is about 70% that of the sun and it is about half as luminous. It is located in our Milky Way galaxy about 520 light-years from Earth. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).

“This discovery confirms that planets can be in a cohesive form within 3 million years, which was previously unclear as Earth took 10 to 20 million years to form,” said Madyson Barber, a graduate student in the department of physics and astronomy at the University of North Carolina at Chapel Hill and lead author of the study published this week in the journal Nature.

“We don’t really know how long it takes for planets to form,” UNC astrophysicist and study co-author Andrew Mann added. “We know that giant planets must form faster than their disk dissipates because they need a lot of gas from the disk. But disks take 5 to 10 million years to dissipate. So do planets form in 1 million years? 5? 10?”

The planet, given the names IRAS 04125+2902 b and TIDYE-1b, orbits its star every 8.8 days at a distance about one-fifth that separating our solar system’s innermost planet Mercury from the sun. Its mass is in between that of Earth, the largest of our solar system’s rocky planets, and Neptune, the smallest of the gas planets. It is less dense than Earth and has a diameter about 11 times greater. Its chemical composition is not known.

The researchers suspect that the planet formed further away from its star and then migrated inward.

“Forming large planets close to the star is difficult because the protoplanetary disk dissipates away from closest to the star the fastest, meaning there’s not enough material to form a large planet that close that quickly,” Barber said.

The researchers detected it using what is called the “transit” method, observing a dip in the host star’s brightness when the planet passes in front of it, from the perspective of a viewer on Earth. It was found by NASA’s Transiting Exoplanet Survey Satellite, or TESS, space telescope.

“This is the youngest-known transiting planet. It is on par with the youngest planets known,” Barber said.

Exoplanets not detected using this method sometimes are directly imaged using telescopes. But these typically are massive ones, around 10 times greater than our solar system’s largest planet Jupiter.

Stars and planets form from clouds of interstellar gas and dust.

“To form a star-planet system, the cloud of gas and dust will collapse and spin into a flat environment, with the star at the center and the disk surrounding it. Planets will form in that disk. The disk will then dissipate starting from the inner region near the star,” Barber said.

“It was previously thought that we wouldn’t be able to find a transiting planet this young because the disk would be in the way. But for some reason that we aren’t sure of, the outer disk is warped, leaving a perfect window to the star and allowing us to detect the transit,” Barber added.
 

(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)

Washington:

The conventional wisdom among astronomers is that black holes – those exceptionally dense objects with gravity so powerful that not even light can escape – form in the violent explosion, called a supernova, of a massive dying star. But some, it turns out, may be born in a gentler fashion.

Researchers have identified a black hole that appears to have come into being through the collapse of the core of a large star in its death throes, but without the usual blast. It was observed gravitationally bound to two ordinary stars.

Black holes have previously been spotted orbiting with one other star or one other black hole in what are called binary systems. But this is the first known instance of a triple system with a black hole and two stars.

This system is located about 7,800 light-years from Earth in the constellation Cygnus. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).

This black hole, called V404 Cygni, has been extensively studied since being confirmed in 1992. It previously was believed to be orbiting with only one other star, but data from the European Space Agency’s Gaia space observatory showed it instead has two companions.

The researchers said the black hole, with an estimated mass nine times greater than our sun, is in the process of eating one of its companions, a star about seven-tenths as massive as the sun. That star orbits the black hole every 6-1/2 days at a distance only about one-seventh of that separating Earth and the sun.

The black hole appears to be siphoning material off this star, which had puffed up in what is called a red giant phase as part of its natural aging process.

The researchers detected another star about 1.2 times as massive as the sun gravitationally bound to these two but rather far away, orbiting them every 70,000 years at a distance 3,500 times greater than that separating Earth and the sun.

The reason the researchers suspect a gentle birthing process for the black hole is simple. The triple system would have broken apart, they said, if the star that became a black hole had exploded.

A black hole is thought to form when a large star exhausts the nuclear fuel at its core and collapses inward due to its own gravitational pull, triggering an immense explosion that blows off its outer layers into space. The resultant crushed core forms the black hole.

But some astronomers have proposed another path to black hole formation called “direct collapse” in which the star caves in after expending all its fuel but does not explode.

“We call these events a ‘failed supernova.’ Basically, the gravitational collapse just acts too quickly for the supernova to be able to trigger and you get an implosion instead – which sounds super dramatic and awesome but it’s ‘gentle’ in the sense that you don’t expel any matter,” said Massachusetts Institute of Technology astronomer Kevin Burdge, lead author of the study published in the journal Nature.

The researchers estimated that the members of this triple system first formed about 4 billion years ago as ordinary stars.

“The triple system could not have survived if the black hole was born with a natal kick, so this discovery tells us that at least some black holes form without a kick – implying a quiet implosion rather than an explosive supernova,” added Caltech astronomer and study co-author Kareem El-Badry.

This system will not have three members forever, considering that the black hole is consuming its closer neighbor. That suggests that some known binary systems with a black hole and an ordinary star originally may have formed as a triple system, only to have the black hole gobble up one of its partners.

“People have actually predicted that black hole binaries might form mostly through triple evolution, but there was never any direct evidence until now,” El-Badry said.
 

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Washington:

In 1995, astronomers confirmed the discovery for the first time of a brown dwarf, a body too small to be a star and too big to be a planet – sort of a celestial tweener. But it turns out that was not the full story.

Researchers now have taken a fresh look at that brown dwarf and learned that it actually is not a single brown dwarf but rather two of them orbiting astonishingly close to each other while circling a small star. This was documented in two new studies using telescopes in Chile and Hawaii.

These two brown dwarfs are gravitationally locked to each other in what is called a binary system, an arrangement commonly observed among stars. So the brown dwarf that three decades ago was named Gliese 229B is now recognized as Gliese 229Ba, with a mass 38 times greater than our solar system’s largest planet Jupiter, and Gliese 229Bb, with a mass 34 greater than Jupiter.

They are located 19 light-years from our solar system – rather close in cosmic terms – in the constellation Lepus. A light year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).

An artist’s illustration shows the nearest brown dwarf to Earth. ESO-I. Crossfield-N. Risinger/Handout via REUTERS

Binary brown dwarfs are a rarity. These two orbit each other every 12 days at a distance of only 16 times the separation between Earth and the moon. Only one other pair of brown dwarfs are known to orbit as close to each other as this twosome.

Brown dwarfs are neither a star nor a planet, but something in between. They could be considered wannabe stars that during their formative stages did not reach the mass necessary to ignite nuclear fusion at their core like a star. But they are more massive than the biggest planets.

“A brown dwarf is an object that fills the gap between a planet and a star. They are formally defined as objects that can burn a heavy form of hydrogen, called deuterium, but not the most common basic form of hydrogen,” said Sam Whitebook, a graduate student in Caltech’s division of physics, mathematics and astronomy and lead author of one of the studies, published in the Astrophysical Journal Letters.

“In practice, this means they range in mass from approximately 13 to 81 times the mass of Jupiter. Because they can’t fuse hydrogen, they can’t ignite the fusion channels that power most stars. This causes them to just glow dimly as they cool down,” Whitebook said.

The year 1995 was big for astronomers, with the discovery of the first planet beyond our solar system – an exoplanet – also being announced. Until Gliese 229B’s discovery, the existence of brown dwarfs had only been hypothesized. But there were anomalies about Gliese 229B, particularly after its mass was measured at about 71 times that of Jupiter.

“This didn’t make any sense since an object of that mass would be much brighter than Gliese 229B,” said Caltech astronomer Jerry Xuan, lead author of one of the studies, published in the journal Nature. “In fact, some models predict that objects with masses above 70 Jupiter masses fuse hydrogen and become stars, which was clearly not happening here.”

The new observations were able to discern two separate brown dwarfs. They orbit a common type of star called a red dwarf with a mass about six-tenths that of our sun. While both brown dwarfs are more massive than Jupiter, their diameter is actually smaller than the gas giant planet because they are more dense.

“We still don’t really know how different brown dwarfs form, and what the transition between a giant planet and a brown dwarf is. The boundary is fuzzy,” Xuan said. “This finding also shows us that brown dwarfs can come in weird configurations that we were not expecting. This goes to show how complex and messy the star formation process is. We should always be open to surprises.”
 

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