Betelgeuse is 50% brighter than normal. What’s going on?

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The red giant Betelgeuse. Its activity can be overwhelming, and the current radiance doesn’t help. Credit: ALMA (ESO/NAOJ/NRAO)/E. O’Gorman/B. Kervilla

Whenever something happens with Betelgeuse, speculation about it explodes as a supernova spawns. It would be great if you did. We’re far enough away not to suffer any consequences, so it’s fun to imagine the sky lighting up like that for months.

Now the red giant’s star has brightened by almost 50%, and this is again intensifying speculation.

Betelgeuse will explode as a supernova. On that, there is universal agreement. But the question of when is not certain. The star’s behavior is puzzling. How could a petty mortal know that?

Betelgeuse isn’t just a red giant, it’s also a pulsating semicircular variable star. This means that there is some periodicity in their brightness changes, although amplitudes can vary. It has a cycle of approximately 400 days during which its brightness changes. It also has a shorter cycle of 125 days, another cycle of 230 days, and a mega cycle of 2,200 days, all of which are determined by impulses. All of these cycles can make a star difficult to understand clearly.

Two years ago, Betelgeuse freaked out, and people wondered what that meant. It turns out that the star’s brightness has not, in fact, changed. Instead, the star ejected material from its surface that cooled into a dust cloud and blocked out the light. The episode is called “The Great Blackout”.

This graphic shows what likely caused Betelgeuse to appear dimmer for some time in 2019. Credit: NASA, ESA, and E. Wheatley (STScI)

Now that it’s getting brighter, it’s once again attracting scientists’ attention. They want to know what developmental stage you are in and what all this activity means. New research shows it could explode as a supernova sooner than anyone expected.

The new paper is “Evolutionary stage of Betelgeuse inferred from pulse periods,” and the first author is Hideyuki Saio of the Astronomical Institute, Graduate School of Science, at Tohoku University in Japan. Monthly Notices of the Royal Astronomical Society The paper has been accepted for publication, and a copy of the paper is available at www arXiv Prepress server.

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The most confusing pieces of new research often make headlines. No sense argument against it. This is how humanity works.

We don’t pick Dr. Eldridge. She is not mistaken. It’s just that the paper says that’s just one possible outcome. It defines many others.

In their paper, the authors say that Betelgeuse could be the next supernova of the Milky Way, regardless of which their findings may be correct. “We conclude that Betelgeuse is in the late stage of primary carbon burning, and is a good candidate for the next galactic supernova,” they wrote.

As a red giant, Betelgeuse left the main sequence. Throughout its long history of 8 to 8.5 million years, it has consumed massive amounts of hydrogen by fusing it into helium and releasing the mass lost from this fusion as energy. (Thanks to Einstein.) This means that it no longer fuses hydrogen into helium like the sun does. When stars like Betelgeuse lose mass, their gravity can no longer contain their outward pressure, and they expand to form a more massive envelope. So even though they lose mass, they grow in size.

This diagram shows the scale of the red supergiant Betelgeuse and its interstellar medium compared to the Solar System. Credit: L. Calçada, European Southern Observatory (ESO)

After stars like Betelgeuse leave the main sequence and no longer fuse hydrogen into helium in their cores, things change dramatically. During the helium fusion phase that follows, carbon builds up in the nuclei. Then they start the primary carbon burning period which produces other elements. The authors of the new paper say that Betelgeuse is in the late stages of that period.

But for how long? How long do you stay? There is no exact answer to that yet.

“Despite, and in part because of, the relatively small distance from Earth, it has been difficult to obtain strict constraints on distance, luminosity, radius, current mass and zero principal sequence (ZAMS), information about the internal spin state and associated mixing and thus on The evolutionary status of Betelgeuse and when it might explode,” write the authors of a new review from Betelgeuse. ZAMS is particularly important for understanding the evolutionary stage of specific stars. It is fundamental, though not the only one responsible.

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But the study offers some strong possibilities.

The work is a mixture of notes and models, each of which fits the notes in different ways. It’s a tricky business, which is why headlines claiming it could explode in decades are a bit misleading. Small differences rarely attract attention.

This image is based on data from the Herschel mission and shows the circumferential medium (CSM) surrounding Betelgeuse as it accelerates through space. There is a prominent bow shock at 7 arc minutes, evidence of its motion. There is also another feature of the CSM at 9 arc minutes which could be evidence of a previous merger or physical expulsion of Betelgeuse. Betelgeuse is complex and difficult to understand. Credit: Dessen et al. 2012

The primary carbon burning period consists of several stages. The difficulty in determining when Betelgeuse will go supernova partly comes from determining which phases it goes through. His distance from us is also a matter of debate. Betelgeuse’s review states that “although it lies at a distance of only 200 parsecs from Earth, and can therefore be resolved spatially with appropriate instrumentation, the uncertainty that departs from it remains a critical barrier to deeper understanding”.

What caught everyone’s attention were these two sentences from the research: “According to this figure, the core will collapse within a few dozen years after the carbon is exhausted. This indicates Betelgeuse to be a very good candidate for the next galactic supernova, which occurs significantly near us.”

This is the number they are talking about.

This figure from the study shows the abundance of the various elements in Betelgeuse. The initial abundance is like a fingerprint or a snapshot of what’s going on inside the core, what stage the carbon is burning inside the star, and when it will explode. Fusion products from the core are periodically dredged from the core to the surface by convection, giving researchers a glimpse into the core. But determining when it will explode also depends on knowing the initial mass of the star, how fast it is spinning, and a host of other factors, which are difficult to determine to varying degrees. credit: Sayo et al. 2023

But what didn’t attract much attention was the next part of the paper.

“In fact, it is not possible to accurately determine the evolutionary stage, because surface conditions hardly change at the late stage near carbon depletion and beyond,” the researchers write. Astronomers can only see the surface, but it’s what’s going on deep within the star that tells the tale.

The paper’s authors really say that, according to observations, data, and modeling, Betelgeuse could explode sooner than thought. But – and this is crucial – they don’t know at what stage the star’s primary carbon is burning. Carbon combustion can continue for a long time, according to some models that fit the data.

But not everyone agrees that Betelgeuse is in the primary carbon-burning phase. The authors of the Betelgeuse review say that the star is still in the helium phase. “Because the primary helium burn is much longer than the later combustion stages, it is likely that Betelgeuse is in the helium burning core. The pulsation period is likely to constrain the radius, distance and evolutionary state of the primary helium burn,” they wrote, acknowledging the existence of “arguments to the contrary.” “.

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Another way the researchers have tried to determine the timing of the supernova’s explosion is to match its periodic pulsations to similar models.

This figure from the paper presents four models that correspond to four cycles or periods of Betelgeuse (alpha Ori). If you’re not an astrophysicist, it’s confusing. (I’m not one, and I’m so confused.) But it helps illustrate the complexity and uncertainty behind anticipating the explosion of Betelgeuse. credit: Sayo et al. 2023

When it finally explodes—and no one disagrees with its final explosion as a supernova—it’s not likely to produce a deadly gamma-ray burst as some supernovae do. And while the material will come out and produce powerful X-rays and ultraviolet rays, we’re very far from being affected. Instead, it will be a light show visible to all of humanity, and that will change the constellation of Orion forever. Scientists say it will most likely leave a neutron star, perhaps a pulsar that will be visible for millions of years. The entire event, from start to finish, will be an unprecedented opportunity to study the evolution of stars, supernovae, and stellar remnants. Scientists will be able to work backwards from exploding into all the research that has been done and all the observations and data and identifying where they were right and where they were wrong. Old Betelgeuse will teach them a lot.

The shock wave from the supernova will arrive in 100,000 years and will be easily deflected by our sun’s heliomagnetosphere. The biggest impact on Earth will be an increase in cosmic rays hitting the upper atmosphere.

Most of us will look on at this cataclysmic eruption and sit in awe of the force of nature, we hope, while others will turn to outlandish conspiracy theories or quasi-religious, pseudoscientific, cult-like reverence.

If humanity still existed when the blessed event occurred.

more information:
Hideyuki Saio et al, Developmental stage of Betelgeuse inferred from pulse intervals, arXiv (2023). doi: 10.48550/arxiv.2306.00287

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