Betelgeuse is a star that’s never out of the news for long. It made headlines in recent years when it dimmed considerably, and since it’s a red supergiant, people wondered if it was about to explode as a supernova. That expectation died down when scientists showed that the dimming is because of dust, but now Betelgeuse is in the news again, this time because of a newly-discovered companion star.

As one of the brightest stars in the sky, ancient astronomers kept an eye on Betelgeuse. They watched as its brightness varied, and even as its colour may have changed from yellow to red. As part of the well-known Orion constellation, countless human eyes have rested their gazes on it.

Astronomers using the Gemini North Telescope are some of the most recent humans to observe Betelgeuse. Gemini North is one half of the Gemini International Observatory. Gemini North is in Hawaii, and Gemini South is in Chile. Astronomers used Gemini North and its Alopeke instrument to detect a companion star around Betelgeuse for the first time.

The discovery is presented in research titled “Radial Velocity and Astrometric Evidence for a Close Companion to Betelgeuse.” It’s published in The Astrophysical Journal and the lead author is Morgan Macleod. Macleod is from the Harvard and Smithsonian Center for Astrophysics.

“This detection was at the very extremes of what can be accomplished with Gemini in terms of high-angular resolution imaging, and it worked.” Steve Howell, NASA Ames Research Center.

Astronomers have long wondered about Betelgeuse and if it had an unseen, unresolvable companion. Researchers thought the star could be a spectroscopic binary. A spectroscopic binary is one where the pair of stars are so tight together that even our most powerful telescopes can’t see them as separate objects. Instead, their presence is revealed by the Doppler effect on their light as the stars orbit.

This new discovery is based on observational data acquired over the last century by different ground-based and space-based telescopes. Observations with Gemini North’s Alpeke instrument capped it off. “We examine a century of radial velocity, visual magnitude, and astrometric observations of the nearest red supergiant, Betelgeuse, in order to reexamine the century-old assertion that Betelgeuse might be a spectroscopic binary,” the authors write.

This is what astronomical data looked like before the computer age. They’re red and blue spectral plates number 14183 from The Carnegie Science Plate Archive, taken with the Coude spectrograph on Mt. Wilson 1961 January 22 (R. Weymann 1962). Images are provided courtesy of Carnegie Science.

Observations of Betelgeuse span a long enough time frame to detect two variable periods in its luminosity. One period is steady and lasts 5.78 years, and is called the long secondary period (LSP). The other consists of quasiperiodic pulsations that last several hundred days.

This figure from the research summarizes a century of Betelgeuse observations and reveals several trends. “Observed across the past century, Betelgeuse varies at a range of timescales from days to decades. Some of this variability appears periodic, while other portions appear uncorrelated,” the authors write. The top panel shows radial velocity measurements that span 128 years. “The LSP is visible as a 5–6 yr sine-wave cycle of RV, most obvious in periods of denser sampling like 1900–1930 and 2000–present.” Image Credit: Maclead et al. 2025. ApJ

“We show that the LSP is consistent between astrometric and radial velocity data sets, and argue that it indicates a low-mass companion to Betelgeuse, less than a solar mass, orbiting in a 2110 day period at a separation of just over twice Betelgeuse’s radius,” the researchers explain. Betelgeuse has about 16.5 solar masses, and the companion star is about 20 times less massive than thats. It’s also a million times fainter, and orbits Betelgeuse very tightly, separated by only four astronomical units. These numbers are preliminary because Betelgeuse’s distance and mass are not precisely known.

Steve Howell, a senior research scientist at NASA Ames Research Center, led the team of astrophysicists that detected the companion with the Gemini North Telescope. In a press release, Howell said “Gemini North’s ability to obtain high angular resolutions and sharp contrasts allowed the companion of Betelgeuse to be directly detected. Papers that predicted Betelgeuse’s companion believed that no one would likely ever be able to image it.”

But Gemini North and its Alopeke instrument were up to the task. Gemini North is an 8.1-metre (26.6 ft) optical/infrared telescope with several powerful instruments attached. Alopeke, which means ‘Fox’ in Hawaiian, is a speckle imager. It overcomes atmospheric distortion by taking multiple very short exposures that basically “freeze” the atmospheric distortion, allowing the telescope to work at high angular resolutions.

Betelgeuse and its companion in the context of the Orion Constellation. Image Credit: International Gemini Observatory/NOIRLab/NSF/AURA. Image Processing: M. Zamani (NSF NOIRLab)

Betelgeuse is well-known for its Great Dimming episode in 2019/20. Astronomers determined that it was likely caused by a sudden and anomalous ejection of mass, and this research suggests the companion could’ve played a role in that event. “However, if a burst of mass loss collided with a preexisting tail or shell trailing behind a companion object, shocking before cooling and forming dust, that could explain the sudden onset of the great dimming,” the researchers explain.

That idea has broad implications for our understanding of Betelgeuse and other red supergiants. “If correct, this might suggest that mass ejection episodes like the one that caused the great dimming are happening continuously in a star like Betelgeuse—this one just happened to have fortuitous alignment with the companion orbit and us as observers,” the authors write.

The researchers think that the companion likely hasn’t begun hydrogen fusion and is a pre-main sequence star. That can explain its low-mass; it’s still accreting material. That means that even though the pair likely formed from the same gas cloud, they’re an odd couple. While Betelgeuse is evolving away from the main sequence, its tiny companion hasn’t entered it yet.

There are multiple examples of other binary stars where the masses are lopsided. There are also multiple examples of other giant stars with long secondary periods, and other researchers have argued that these are caused by undetected companions. Antares could be one of them. “Indeed, Antares, another of the closest and brightest red supergiants, also hosts an LSP with photometric and RV variations that imply a companion,” the authors write.

The companion star’s fate is all tangled up with Betelgeuse’s. Betelgeuse will explode as a cataclysmic supernova, destroying everything in its vicinity. However, the small, dim companion might succumb to its fate long before that happens. Within the next 10,000 years, according to the researchers, Betelgeuse’s strong gravity will suck the companion in and it will meet its doom. Its starstuff will be expelled back into the interstellar medium when Betelgeuse explodes.

This discovery could open the door to observing more spectroscopic binaries. If it does, then astronomers may be on their way to explaining more LSPs in red supergiant stars. “This detection was at the very extremes of what can be accomplished with Gemini in terms of high-angular resolution imaging, and it worked. This now opens the door for other observational pursuits of a similar nature,” said Howell.

“While it is perhaps surprising that Betelgeuse could have such a close companion, we emphasize that a low-mass companion would essentially be hidden in plain sight—nearly a million times less luminous and of similar color to Betelgeuse itself,” the researchers write in their conclusion. They also emphasize that their conclusion is not absolute. Some other unknown mechanism could be responsible.

“However, the predictions of the binary model are now clear and offer a pathway toward a deeper understanding of our nearest red supergiant,” they conclude.

When Betelgeuse goes off, it’s going to be the show of a lifetime. But it’s not going to hurt us.

Betelgeuse is the shoulder of Orion, a red giant sitting about 500 light years away. It’s huge, weighing somewhere between 15-20 solar masses, but so extended and bloated that if you plopped it down in our own solar system, it would stretch to roughly the orbit of Mars.

And it’s not doing so great. Massive stars do not live very long lives, with their precise lifetimes depending on a host of factors like their mass, their metallicity, and spin rate. On the low side, we’re talking only a few hundred thousand years. On the high side, we’ve got a few million.

But either way, as stars go, that’s not a lot. Our own Sun will outlive multiple generations of such giants, and red dwarfs, the smallest stars in the universe, can stretch for trillions of years at a time. In fact, just a fun side note, red dwarfs live for so long that the entire universe isn’t even old enough for them to start dying yet.

No matter how you slice it, Betelgeuse is on its last legs.

It’s in what’s called the red giant phase, and it’s pretty obvious to see why astronomers picked that name for this phase in a stellar life cycle. It’s red, and it’s gigantic. And it is so close to being dead that it is in an incredibly unstable phase. In fact, we saw some very dramatic dimming episodes a few years ago where it dimmed by around 15% out of nowhere over the course of a few weeks. And then just after a few months, it popped back up to full brightness.

When a star is near the end of its life, it’s all chaos. Sometimes it’s fusing hydrogen, sometimes it’s fusing helium, sometimes it will shut down for a while, sometimes it’ll start back up. The outer edges of the atmosphere are so far away from the central core that they start getting a mind of their own. It just gets complicated.

Estimates based on the mass of Betelgeuse, its rotation rate, the group of stars it was born with, and the amount of metals we can measure in the upper layers of its atmosphere, all suggest that it’s somewhere in the neighborhood of a few hundred thousand years from now, it’s going to go supernova. But honestly it could be tomorrow. In fact, because it’s 500 light years away. It could have gone off a hundred years ago, and we won’t find out for a while. It may already be dead.

When Betelgeuse goes off as a supernova, it will be a sight to behold. Keep in mind that typical supernova can outshine entire galaxies of over a hundred billion stars. And at a distance of a few hundred light years, Betelgeuse is going to put on an impressive show.

It will be visible during the day. It will be brighter than any planet. It will be almost as bright as the full moon. You’ll be able to read a book by the light of the Betelgeuse supernova at midnight.

But it will actually be painful to look at because unlike the full moon that is this gorgeous disc in the sky, Betelgeuse is still going to be a tiny pinprick of light. So it won’t be comfortable to look at, and it will last a few months before fading away as all supernovae do. But as impressive as it is, it won’t be dangerous.

What saves us from most supernova dangers is that as bright as they are, as much radiation as they pour into the universe, stars are really stinking far apart. What helps here is something called the inverse square law. There’s a fixed amount of light that a star or a supernova or any radiating object in the universe gives off.

And so that light moves away from the star, that same amount of light has to cover more and more area. If you double the distance, the radiation in any one spot gets cut to 25%. If you go to ten times the distance, then you get a factor of a 100 drop off. It goes as the square of the distance.

If you’re trying to stay warm by a fire, you will notice if you stand really close to the fire that it’s maybe a little bit too hot, but then you take one step back, and all of a sudden, you’re cold again. That’s because of that inverse square law of the infrared radiation being emitted by the fire. But in the case of a supernova, we’re going to be grateful for the inverse square law. Because we’re talking about a giant star turning itself into an uncontrolled nuclear bomb and detonating with enough energy to overwhelm an entire galaxy’s worth of starlight.

From our perspective, Betelgeuse will go from a dot of light in the night sky to a brighter dot of light in the night sky. It’s simply not going to be a threat.

Follow space and astronomy news, and you’ll regularly hear discoveries about the red giant star Betelgeuse, and whether it’s about to explode.

You’ll read about whether Betelgeuse exploding could be a danger to life on Earth, or whether Betelgeuse exploding could be dangerous to look at.

The reason for this is because Betelgeuse – which forms the shoulder of the constellation Orion – is a red giant star nearing the end of its life.

Betelgeuse is the top-left red star in the constellation Orion. Credit: VW Pics / Getty Images’

That means it’s set to explode – go ‘supernova’ – any time soon. However, that’s ‘soon’ in the cosmic sense, which could be as much as 100,000 years!

But will Betelgeuse going supernova could be a danger to life on Earth? And have there been any such stellar explosions that have wiped out life on Earth in the past?

Artist’s impression of a supernova destroying a planet. Credit: Mark Garlick / Science Photo Library.

Past supernovae and mass extinctions

One scientific study says exploding stars could have been responsible for ravaging our planet’s atmosphere and causing two mass extinctions.

The discovery came from a survey of local stars that aimed to measure how often supernovae happen in the vicinity of Earth.

A supernova occurs when a massive star runs out of fuel at the end of its life and collapses.

It rebounds in a huge explosion that fires out radiation and stellar material in all directions.

“Supernova explosions bring heavy chemical elements into the interstellar medium, which are then used to form new stars and planets,” says Alexis Quintana, who led the study while at Keele University in the UK.

“But if a planet, including Earth, is located too close to this kind of event, this can have devastating effects.”

Could a supernova cause extinction on Earth? Studies show they may already have done in our ancient history. Credit: NASA/CXC/M. Weiss/Getty

How a supernova could destroy life on Earth

If a supernova’s radiation were to sweep over Earth at close range, it could strip our planet’s ozone layer.

This would leave life vulnerable to ultraviolet radiation from the Sun, as well as causing years of acid rain.

To see if this might have happened to our planet in the past, Quintana’s team looked at a census of massive stars within 3,260 lightyears of Earth.

They used this data to estimate how often supernovae occur close enough to have an impact on Earth’s atmosphere, out to around 65 lightyears from our planet.

This revealed there should be around 2.5 nearby supernovae every billion years

That rate tallies with the number of extinction events seen here on Earth: the Devonian extinction 372 million years ago and the Ordovician extinction 445 million years ago.

These two events have been linked to a loss of ozone, though the cause of the sudden change was unknown.

Fortunately for us, only two nearby stars look set to go supernova in the next few million years: Betelgeuse and Antares.

Both of these are more than 500 lightyears away, a safe enough distance from our planet’s fragile atmosphere.

Artist’s impression. Asteroid 2024 YR4 will skim by our planet on 22 December 2032, and has a 99% chance of passing safely by. Credit: Maciej Frolow / Getty Images

Could supernovae be good for us?

Words: Chris Lintott

Why are we so drawn to the idea of catastrophe coming from the skies?

The imminent death of Betelgeuse, the threat from asteroids like 2024YR4, and past extinctions and exploding stars undoubtedly have a morbid fascination.

But I’ll remind you that a nearby supernova may have kickstarted the formation of the Sun and its retinue of planets.

The Ordovician extinction may have created the conditions for a grand explosion in ecological diversity.

Even the asteroid that did for the dinosaurs was good news for us mammals.

Earth’s history and our own can only be properly understood once we pay attention to what’s happening in our cosmic neighbourhood, good or bad.

www.keele.ac.uk

This article appeared in the May 2025 issue of BBC Sky at Night Magazine

Waiting for the Blaze Star to go nova

Have you ever heard of the Blaze Star? It’s a star in the constellation Corona Borealis the Northern Crown that was supposed to go nova last year. Well, we’re still waiting. But when it finally does erupt, it’ll be a once-in-a-lifetime show in our night sky.

The eagerly awaited Blaze Star nova is a real opportunity for keen night sky observers to witness a “new star” in the sky … but only for a few days before it fades away again. Here’s more about why we’re still waiting on the Blaze Star. And about how you can see when it does finally erupt as a nova.

You’ll want to look east as the sky gets dark. It helps to observe from a dark-sky location. Look between the handle of the Big Dipper and the horizon to see the backward C shape that marks Corona Borealis. More on how to see it below.

Many predictions for the Blaze Star’s eruption

At first the predictions for the Blaze Star’s eruption focused on last year from about April to October. Then Jean Schneider of the Paris Observatory published some new predictions in the Research Notes of the American Astronomical Society in October 2024. He pinpointed possible dates of March 27, 2025, and November 10, 2025. The first date has come and go with no big kablooey.

Schneider came to his possible dates using a combination of the previous eruption dates and the orbital ephemeris of the binary system. While Schneider admits in his paper that no one can exactly predict the eruption, he is trying to predict eruption dates with a precision of a week or two. Will his November prediction hold up? The only way to know for sure is to wait and see.

Why hasn’t it happened yet?

Predicting eruptions of stars is not an exact science. The Blaze Star (T Coronae Borealis) underwent two known eruptions recorded by astronomers. Those events were on May 12, 1866, and on February 9, 1946. Those eruptions were 80 years apart. So scientists thought that, in another 80 years, the star would erupt again. So, 80 years from 1946 would be 2026. Which raises the question: Why did astronomers think the eruption would happen in 2024?

Well, the star brightened and dimmed before its last eruption in 1946. And it has been brightening and dimming now as well, leading some to think the nova would happen sooner rather than later. But it appears as if later is more likely. And so we wait …

In the meantime, here’s how to find Corona Borealis and be ready to see it when the nova arrives.

Why will it go nova?

The Blaze Star isn’t one star but two. It’s a binary system with a white dwarf and a red giant. White dwarfs are stellar remnants, the exposed core of a sunlike star that shed its outer layers at the end of its main-sequence life. It’s a super-dense star with the mass of our sun but only the size of Earth.

Blaze Star’s white dwarf has built up material on its surface, siphoned off from the red giant star. Periodically, it “can’t take no more” and explodes, about every 80 years.

This is our best opportunity to see a nova with some warning. Plus we have great visual context from the surrounding C-shape of stars. So cross your fingers for good weather when it happens.

Where to look to find the Blaze Star

The constellation Corona Borealis rotates around Polaris just outside of what we traditionally think of as the circumpolar constellations. This mean it’s not visible all year round for much of the Northern Hemisphere.

The easy-to-find constellation looks distinctly like a backward C at this time of year. It lies between the bright star Arcturus and the squarish four-star shape of Hercules. Look east after dark to find the constellation rising. If you can spot the Big Dipper, look between it and the horizon to find a faint backward C shape. That’s Corona Borealis.

By the summer these constellations will be high in the sky again. You always need to spend some time dark-adapting your eyes before you see the constellations properly. Plus, binoculars would be a good idea. And you need to be ready to go when we get the news, as it will only be there for a couple of days.

How bright will the Blaze Star be?

The actual explosion of the Blaze Star nova will likely dwarf any explosion you’ll ever see. But the star is far away. How bright will it get in our sky? Astronomers expect it to reach an apparent magnitude of 2. That’s a respectable brightness for a star. It’s conveniently comparable to the brightest star in the Northern Crown, the Jewel of the Crown, Alphecca. So, for a few days, the Northern Crown will have two jewels!

T Corana Borealis – the Blaze Star – also one of the most distant stars you’ll ever see. Alphecca is around 75 light-years away, while the Blaze Star is closer to 3,000 light-years away. So that gives you some perspective on the absolute magnitude (brightness) of this enormous blast. And since the light of this explosion has travelled for 3,000 years to get here, in relative terms the nova happened during the Bronze Age.

Remember that, when they are side-by-side with approximately the same brightness, the nova is 40 times farther away than Alphecca. Also, we are not seeing the two stars at the same moment in time. One we see as it was 75 years ago and the other we see as it was 3,000 years ago. It can be hard to get your head around that!

The nova will brighten the star by thousands of times, typically over just a few hours, and then take some days to fade away again. When it’s done, it will go back to its normal appearance.

Finding Corona Borealis, the Northern Crown

If you are not familiar with the Northern Crown, get out and have a look at it before this nova happens. And then, clouds willing, when it does erupt we can go out and see the C shape is harder to spot. Instead, the dominant feature will be two bright-ish stars, Alphecca (the brightest star in Corona Borealis) and the Blaze Star.

The Blaze Star is normally invisible to the unaided eye. On a regular day, it sits at around magnitude 10, making it only the 19th brightest star in the constellation. But as it undergoes a colossal outburst of energy, it will brighten.

Bottom line: We’re still waiting for the Blaze Star to go nova! Here’s how to find Corona Borealis so you’re ready when it does happen.

Source: When will the Next T CrB Eruption Occur?

The huge orange star in the night sky that could explode any day

Could Earth soon witness the most explosive event in cosmic history?

The supergiant star Betelgeuse has a vast plume of gas almost as large as our Solar System (Image: ESO/L. Calçada )

Look up to the southern sky tonight and spot the supergiant star in the constellation Orion. It’s big, bright, and orange – and could be about to explode.

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Betelgeuse is a red giant star that shines brightly in the night sky . It makes up one of the “shoulders” of Orion, one of the most famous star constellations.

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In recent years, scientists have noticed that Betelgeuse has been fluctuating in brightness. The supergiant is typically the 10th brightest star in our sky, but in 2020 it fell out of the top 20, appearing the faintest it had ever been.

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In 2023, this dimming was followed by a strange brightening, taking Betelgeuse up to seventh place on the bright star leaderboard.

Then, in March 2024, the American Association of Variable Star Observers (AAVSO) reported that Betelgeuse had dimmed by about 0.5 magnitude since late January.

The surface of the red supergiant star Betelgeuse during its unprecedented dimming in late 2019 and early 2020 (Image: ESO/M. Montargès et al. )

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This weird behaviour indicates to astronomers that something big is about to happen: Betelgeuse, the nearest red supergiant star to Earth, could soon explode as a supernova.

When Betelgeuse does eventually explode, the spectacular display could be as bright as a full Moon and visible in broad daylight.

Scientists and stargazers alike are hoping to witness the first naked-eye supernova in our galaxy since 1604 – and according to astronomers, this could happen very soon.

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When could Betelgeuse explode?

Betelgeuse is expected to reach the end of its life very soon. Its dramatic dimming in recent months could be a sign that it’s preparing to go out with a bang.

Stars in the upper portion of the constellation Orion, including the bright shoulder star Betelgeuse and Orion three-star belt (Image: NASA/JPL/Cornell )

When stars dim, this is a sign that they’re running out of fuel. Over billions of years, stars burn through fuel, mostly hydrogen, to produce energy and light. When it runs out of fuel, the core of the star collapses, and the outer layers of the star explode outward in a spectacular burst of energy called a supernova.

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Betelgeuse is only 10 million years old, whereas our Sun is nearly five billion years old. However, Betelgeuse is about 700 times larger than our Sun, according to NASA, meaning it uses much more energy.

“Think about setting a fire in your back yard,” Dr Debra Wallace, Marshall’s Deputy Branch Chief of Astrophysics told NASA. “The more fuel you throw on it, the faster and hotter it burns. It’s visually impressive – but gone in a flash.”

But when exactly is this ticking space time bomb due to blow? According to Wallace, Betelgeuse likely will burn for another 100,000 years or so.

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Betelgeuse would engulf Mercury, Venus, Earth and Mars and even the gas giant Jupiter (Image: ALMA/E. O’Gorman/P. Kervella )

However, one paper , published in 2023, found that Betelgeuse could go into supernova in “tens of years”, not thousands of years like some scientists have suggested.

“We conclude that Betelgeuse is…a good candidate for the next galactic supernova,” the authors wrote in the study.

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Given the fact that the last visible supernova happened more than 400 years ago, we’d be lucky to see any galactic supernova in our lifetimes. However, if we did, some scientists think the explosion could outshine the Moon, casting an eerie glow across the night.

During this explosion, Dr Wallace says the star will release as much energy in a split-second as our Sun generates in its entire lifetime. However, before you panic, Betelgeuse is too far away from Earth to have any effect on our solar system.

Could Betelgeuse have exploded already?

Betelgeuse is about 640 light years away from Earth, meaning it takes 640 years for its light to reach Earth.

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While it’s impossible to know for certain, there’s a statistically small chance that Betelgeuse has already exploded as a supernova, and we’re simply waiting for its light to reach Earth. However, scientists have found no definitive sign that it has already done so.

How to see Betelgeuse tonight

The fiery glow of Betelgeuse has made it a prominent feature in the night sky. Look for the bright star with a red due up and to the left of Orion’s ‘belt’ of three stars . This is Betelgeuse, which marks Orion’s right shoulder (or left as viewed from Earth)

According to Sky Tonight, Betelgeuse will be at elevation by twilight at 8.54pm on Friday (April 4), at around 34 degrees, and setting at 12.38am on Saturday morning (April 5). By April 10, Betelgeuse will have moved too close to the Sun in the sky, making it unobservable for a while.