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EarthSky | Will Betelgeuse explode in tens of years?

Betelgeuse: Orange ball of fire exploding in brilliant white, surrounded by gas and dust.
Artist’s concept of the old red supergiant star Betelgeuse as a supernova, or exploding star. Scientists have found a supernova warning sign for stars like Betelgeuse. Before exploding, these stars dim dramatically. And, in 2019, Betelgeuse did undergo a great dimming. Image via Royal Astronomical Society/ ESO/ L. Calçada/ CC BY 4.0.

Betelgeuse due to explode soon?

Betelgeuse is the nearest red supergiant star to Earth. Distance estimates vary, but it’s probably within 1,000 light-years of Earth … a hop and a skip in galactic terms. Someday, Betelgeuse will explode as a supernova. When it does, it might become as bright as a full moon. It might even be visible in broad daylight! But when will Betelgeuse explode? A decade ago, this question was interesting but academic. The answer was: Maybe today. Maybe a thousand years from now. Few imagined it would be today. But now there’s been a noticeable uptick in the brightening and dimming of Betelgeuse. And a new paper – published this week (June 1, 2023) – suggests not thousands of years but “tens of years” as Betelgeuse’s explosion timescale.

The paper focuses on the concept of stellar nucleosynthesis, the process that enables stars to shine. Inside stars, simple atoms fuse to make more complex atoms, with energy as a by-product. It’s when a star’s nuclear fuel runs out, that a supernova occurs., an open-access repository, published the new study on June 1. It’s called The evolutionary stage of Betelgeuse inferred from its pulsation periods. The scientists said:

We conclude that Betelgeuse is … a good candidate for the next galactic supernova.

The first author is Hideyuki Saio from the Astronomical Institute, Graduate School of Science, at Tohoku University in Japan. The Monthly Notices of the Royal Astronomy Society has accepted the paper for publication.

It’s got people talking

Let’s be clear. The history of observations of supernovae within our own Milky Way is sketchy. But we’d surely be lucky to see any galactic supernova, much more one as nearby as Betelgeuse, in our lifetimes.

And Betelgeuse exploding in just tens of years? That’s an amazing thought, and has people talking!

But is it realistic?

Tens of years?!

What follows are a couple of tweets that have set off a new round of chatter on Twitter. The first – from Friday, June 2 – points to the “tens of years” scenario.

An almost 50% brightness increase

A second notable tweet – from @Betelbot on Twitter, which provides daily status reports on the star – is from May 18, 2023. It points to a recent almost 50% brightness increase for the star! Note that Betelgeuse is behind the sun in summer. So, until it emerges before dawn in late summer, we won’t know what it’s doing.

The background buzz on Betelgeuse

Stars shine because they undergo thermonuclear fusion reactions in their interiors. Simply put, they fuse simple elements (like hydrogen) to create more complex elements (like helium), with energy as the by-product. As massive stars (eight or more solar masses) age, they run out of the simplest fuels, but progressively burn more complex fuels until ultimately their cores are made of iron … and then nuclear burning ceases. At that point, with no more fusion taking place, the high temperatures in a star’s interior drop. And that means the high pressures in the star’s interior drop too. The star begins to collapse on itself. It collapses … then rebounds in a terrific explosion, a supernova.

So, massive stars like Betelgeuse explode as Type II supernovae – collapsing rapidly and exploding violently – after they exhaust their fuel supply.

And so, when a star explodes depends on what’s going on inside the star, on how much fuel it has left, and on how close it is to collapse.

Star chart of constellation Orion with stars labeled.
Betelgeuse is a beloved star. It’s a highly noticeable star in the constellation Orion the Hunter, 1 of 2 very bright stars in Orion. It marks the right shoulder of the Hunter. The other bright star is Rigel, which marks the Hunter’s left foot. Notice Betelgeuse and Rigel on either side of the short, straight row of 3 medium-bright stars. But, in Northern Hemisphere summer, Betelgeuse is behind the sun. It will emerge around late July or early August.

But what’s going on inside Betelgeuse?

The new online study said:

We conclude that Betelgeuse is in the late stage of core carbon burning …

And the carbon burning phase for a massive star like Betelgeuse lasts around 1,000 years. If we are “near the end” of that stage, then Betelgeuse has neared the end of its lifetime and may be about to explode, perhaps even in “tens of years.”

But are there other possibilities? Of course there are.

UniverseToday published a great story on Betelgeuse on Friday, June 2, 2023, that explains some of the science involved with drawing any conclusion about whether Betelgeuse will explode soon. The author pointed out that:

… What hasn’t attracted as much attention is the following part of the paper.

‘In fact, it is not possible to determine the exact evolutionary stage, because surface conditions hardly change in the late stage close to the carbon exhaustion and beyond,’ the researchers write. Astronomers can only see the surface, but it’s what’s happening deep inside the star that tells the tale.

The authors of the paper are really saying that according to observations, data, and modelling, Betelgeuse could explode sooner than thought. But – and this is critical – they don’t know what stage of core carbon-burning the star’s in. Carbon burning could go on for a long time, according to some of the models that fit the data.

So, basically, we’re back to square one. Betelgeuse might explode tomorrow. It might explode in “tens of years.” Or it might explode in a thousand years.

But why did Betelgeuse dim in 2019?

In late 2019, Betelgeuse sparked excitement around the world when it began dimming noticeably. Astronomers now refer to this event as the Great Dimming of Betelgeuse. As it was happening, many believed (and hoped!) the big event – the explosion of this relatively nearby star – was close at hand.

Of course – although Betelgeuse since regained brightness, then dimmed again, now brightened again, and so on – it has not exploded yet.

So why did it dim?

Analyzing data from NASA’s Hubble Space Telescope and several other observatories, astronomers concluded that the bright red supergiant star Betelgeuse quite literally blew its top in 2019. Betelgeuse lost a substantial part of its visible surface and produced a gigantic Surface Mass Ejection (SME). This is something never before seen in a normal star’s behavior.

Our sun routinely blows off parts of its tenuous outer atmosphere, the corona, in an event known as a coronal mass ejection (CME). But the Betelgeuse SME blasted off 400 billion times as much mass as a typical CME!

Read more: Betelgeuse is recovering from blowing its top

So, the Great Dimming of Betelgeuse in 2019 was apparently caused by a cloud of hot gas, expelled by the star, that temporarily blocked some of the star’s light.

Clearly, some game is afoot at Betelgeuse!

Four panels of orange star releasing glowing gas cooling to create a dust cloud.
This artist’s concept shows how Betelgeuse belched a hot bubble of gas that then cooled into a dust cloud and temporarily blocked some of the star’s light from Earth’s point of view. Image via NASA/ ESA/ E. Wheatley (STScI).

Will its supernova destroy Earth?

Whenever Betelgeuse does blow up, our planet Earth is too far away for this explosion to harm, much less destroy, life on Earth. Studies indicate we’d have to be within 160 light-years of a supernova for it to harm us. And Betelgeuse is perhaps four times this distance.

Instead, anyone alive on Earth when Betelgeuse does finally explode will see an amazingly beautiful sight in the night sky – a very, very, very bright star.

And professional astronomers will be happy to have an exploded Betelgeuse so close. They’ll be able to study the star post-supernova.

Meanwhile, amateur astronomers and casual stargazers will enjoy the explosion, too. But the many who enjoy seeing Betelgeuse as Orion’s bright red star will dearly miss it when it’s gone!

Betelgeuse in the night sky

At mid-northern latitudes, around the first of every year, Betelgeuse rises around sunset. The star is prominent on January and February evenings.

By the beginning of March, this star is due south in early evening. By mid-May, it is briefly visible in the west after sunset. Betelgeuse is traveling behind the sun in early summer, but it returns to the east before dawn by about mid- to late July. Certainly, by early August, you can see Betelgeuse in Orion in the east before sunrise, where the constellation is known as the ghost of the summer dawn.

The star Betelgeuse has a distinctive muted orange-red color. It’s ideal for convincing non-believers that stars do, in fact, come in colors.

Stars designated as Alpha are typically brightest in their constellations. But Betelgeuse is Alpha Orionis, despite the fact that it’s fainter than Orion’s other bright star, Rigel.

Betelgeuse is the 10th-brightest star in the sky overall, and it’s the 7th-brightest star visible from most of the U.S., Canada, Europe and the majority of the Northern Hemisphere.

Starfield with bright, colorful stars of Orion with Sirius below over tropical trees.
View at EarthSky Community Photos. | Betelgeuse is the bright red-orange star in the upper left of this photo by Nikunj Rawal, who captured it at Gir National Park in India on November 21, 2020. Nikunj wrote: “Orion the Hunter in the late night.” Thanks, Nikunj!

Pop culture, history and mythology

Remember the movie Beetlejuice? This star’s name is similar to that.

The proper names of many bright stars are Arabic in origin. This fact reflects the dominance of Arabic astronomers and astrologers during Europe’s Dark Ages. The name Betelgeuse is derived from an Arabic phrase that is usually translated as The Armpit of the Giant. Of course, the Giant refers to Orion, but – rather than an armpit – some authors see Betelgeuse as representing a hand or sometimes a shoulder. While it is not entirely clear what the name means, Betelgeuse marks the right shoulder of Orion in many old star maps.

In the ancient myths, Orion is most often associated with a giant, a warrior, a hunter, a god or some other anthropomorphic or animal figure, so it is not surprising that most depictions of Betelgeuse have an anatomical connection. The Sanskrit name signified an arm, too, for example, although it likely was really the leg of a stag. In parts of Brazil, Betelgeuse was seen as the hind leg of a caiman (crocodilian) or the foreleg of a turtle. On the other hand, in ancient Japan, Betelgeuse was considered to be part of the rim of a ceremonial drum. In Peru, it was one of four vultures about to devour a criminal.

The position of Betelgeuse is RA 05h 55m 10.3053s, dec +07° 24′ 25.4″.

Betelgeuse: A fuzzy red star, surrounded by a shell and multiple thin red arcs.
This far-infrared image from 2013 shows multiple arcs around Betelgeuse, an old red star. The arcs you see here are winds from Betelgeuse crashing against the surrounding interstellar medium, creating a bow shock as the star moves through space. Image via ESA/ Herschel Space Observatory. Read more about this image.

Bottom line: Betelgeuse is due to explode as a supernova someday, although maybe not soon on a human timescale. When it does explode, it’ll be bright enough from our earthly vantage point to shine during the day. But it’s far enough away that Earth won’t be in any danger.

Source of “tens of years” paper: The evolutionary stage of Betelgeuse inferred from its pulsation periods

Read more: Colors of Betelgeuse in a star collage

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What are white dwarf stars? How do they form?

A colorful oval cloud in space, blue in the middle to orange and red on the outskirts.
View larger. | The Ring Nebula (M57) in the constellation Lyra shows the final stages of a star like our sun. The white dot in the center of this nebula is a white dwarf; it’s lighting up the receding cloud of gas that once made up the star. The colors identify various elements like hydrogen, helium, and oxygen. Image via The Hubble Heritage Team (AURA/ STScI/ NASA).

White dwarfs are the hot, dense remnants of long-dead stars. They are stellar cores, left behind when stars exhaust their fuel supplies and blow their gases into space. These objects mark the final stage of evolution for most stars, including our sun. Plus, they play a crucial role in helping us understand the evolution of the universe.

A single white dwarf contains roughly the mass of our sun, but in a volume comparable to Earth. Their small size makes white dwarfs difficult to find. No white dwarfs can be seen with the unaided eye.

The light they generate comes from the slow, steady release of incredible amounts of energy stored up during billions of years as a star’s nuclear powerhouse.

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How are white dwarf stars born?

White dwarfs are born when a star shuts down. A star spends most of its life in a balance between gravity and outward gas pressure. The weight of a couple octillion tons of gas pressing down onto the core causes hydrogen nuclei to fuse together, forming helium. This is called nuclear fusion. The steady release of thermonuclear energy from this process prevents the star from collapsing on itself.

But eventually, a star will run out of hydrogen in its center. At this point, it shifts to fusing helium into carbon and oxygen, and hydrogen fusion moves to a shell surrounding the core. The star inflates and becomes a red giant. For most stars – our sun included – this is the beginning of the end. The star expands, stellar winds blow at an increasingly ferocious rate, and its outer layers begin to escape the pull of gravity.

As the red giant star evaporates, it leaves behind its exposed core: a newly born white dwarf.

Huge brilliant blue-white star with lens flare rays coming out of it and tiny white dot next to it.
Hubble Space Telescope image of the sky’s brightest star Sirius (middle) and its faint white dwarf companion, Sirius B (lower left). Image via NASA/ ESA/ H. Bond (STScI)/ M. Barstow (University of Leicester).

What are they made of?

A newly born white dwarf consists of helium, carbon, and oxygen nuclei, swimming in a sea of highly energetic electrons. The combined pressure of the electrons holds up the white dwarf, so it doesn’t collapse into an even stranger entity like a neutron star or black hole.

The infant white dwarf is incredibly hot, so it bathes the space around it in ultraviolet light and X-rays. Some of this radiation is intercepted by the gas that the star released when it died. The gas responds by fluorescing with a rainbow of colors, creating a planetary nebula. These nebulae – like the Ring Nebula in the constellation Lyra the Harp – give us a peek into our sun’s future.

The white dwarf now has a long, quiet future ahead of it. As trapped heat trickles out, it slowly cools and dims. Eventually it will become an inert lump of carbon and oxygen floating invisibly in space: a black dwarf. However, the universe isn’t old enough for any black dwarfs to have formed. The white dwarfs born from the earliest generations of stars are still cooling off, 14-billion-years later. So the coolest white dwarfs we know of, with temperatures around 4,000 degrees Celsius (7,000 degrees Fahrenheit), may also be some of the oldest relics in the cosmos.

But not all white dwarfs go quietly

While solitary white dwarfs fade gradually, a white dwarf that orbits another star is highly explosive. It siphons gas from its companion, with hydrogen passing across a gaseous bridge and spilling onto the white dwarf’s surface. And as the hydrogen accumulates, its temperature and density eventually reaches a flash point. The entire shell of newly acquired fuel violently fuses and releases a tremendous amount of energy in a nova. The white dwarf flares briefly with the brilliance of 50,000 to 100,000 suns, and then slowly fades back into obscurity.

Two stars, with material sucked off a teardrop shaped one to form a disk around a tiny white dot.
Artist’s concept of a white dwarf siphoning gas off a binary companion into a disk of material. The stolen gas spirals through the disk and eventually crashes on to the white dwarf’s surface. Image via STScI.

Sometimes a white dwarf ends up as supernova

However, if the gas collects fast enough, it can push the white dwarf past a critical point. Then, rather than creating a thin shell of fusion, it brings the star suddenly back to life. Unregulated, the violent release of energy obliterates the stellar core in one of the most energetic events in the universe: a Type 1a supernova. The absolute luminosity of the supernova is 5-billion-times brighter than the sun. For weeks or months, it can outshine even an entire galaxy.

Very colorful ball of gas in space in dense star field.
SN 1572 is the remnant of a Type 1a supernova, 9,000 light-years from Earth, that Tycho Brahe observed 430 years ago. This composite X-ray and infrared image shows the remains of that explosion: an expanding shell of gas moving at roughly 9,000 km/second (over 20 million miles/hour)! Image via NASA/ MPIA/ Calar Alto Observatory/ Oliver Krause et al.

Such brilliance makes Type 1a supernovae visible from across the universe. Astronomers use them as standard candles to measure distances to the farthest reaches of the cosmos. Observations of detonating white dwarfs in distant galaxies led to a Nobel Prize-winning discovery: the expansion of the universe is accelerating. So dead stars have breathed life into our most fundamental assumptions about the nature of time and space.

Bottom line: A white dwarf is the incredibly dense core of a dead star, left behind when the star exhausted its fuel. Our sun will become a white dwarf one day.

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