Una estrella gigante está actuando de manera extraña, y los astrónomos están zumbando

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The constellation Orion is one of the most recognizable patterns in the night sky, visible around the world. But if you’ve looked at Orion recently and thought something seemed off, you’re not wrong: The giant red star Betelgeuse, which marks the hunter’s right shoulder, is the dimmest it’s been in almost a century.

Normally, Betelgeuse is among the 10 brightest stars in the sky. However, the red giantbegan dimming in October, and by mid-December, the star had faded so much it wasn’t even in the top 20, Villanova University’sEdward Guinanreportedin an Astronomer’s Telegram.

“Now the outline of Orion is noticeably different with Betelgeuse so faint,” he says. (See how many constellations you can identify with our interactive quiz.)

Stars 101 Countless stars dot the night sky. Learn how these celestial objects form, how they are classified by brightness and temperature, and what happens when stars die.

To be clear, dimming alone isn’t all that odd for a star like Betelgeuse. It’s what’s known as a variable star, and its shifts in brightness have been closely studied for decades. However, it is unusual for one of the sky’s most prominent points of light to fade so noticeably, prompting scientists to consider the possibility that something more exciting could be about to happen: Betelgeuse might explode and die, briefly blazingbrighter than the full moonbefore vanishing from our night sky forever.

Huge, red stars like Betelgeuse live fast and die violently, exploding in stellar events calledsupernovaethat are visible across vast distances. So, while Betelgeuse is a relatively young star—only about 8.5 million years old—astronomers know that it is nearing the end of its life.

“The biggest question now is when it will explode in a supernova,”UC Berkeley’sSarafina Nance, whostudies Betelgeuseand stellar explosions,said on Twitter. “Disclaimer: I don’t think it’s going to explode any time soon,” she added during an interview with National Geographic. “But I am excited [for] when it does.”

What do we know about Betelgeuse?

The supergiant star’s formal moniker is derivedfrom a mistranslated Arabic namemeaning “the hand of Orion” (yad al-jauza). Today, many people pronounce the name like the titular character in Tim Burton’s 1988 filmBeetlejuice. The star is also referred to as Alpha Orionis, a designation normally reserved for the brightest star in a constellation, even thoughRigel, at Orion’s left foot, is actually brighter.

Betelgeuse is huge and bloated, wielding 20 times the sun’s heft. If you swapped out the sunand replaced it with Betelgeuse, the red star would swallow Mercury, Venus, Earth, Mars, the asteroid belt, a couple of spacecraft, and maybe Jupiter; Saturn would suddenly be quite toasty.

It’s also relatively close to our solar system, in cosmic terms, estimated to bein the neighborhood of 600 light-years away. So, when this star detonates, the explosion will be bright enough to cast shadows on Earth at night and will be visible during the day for a few months, at least. Then, the star will fade from our sky.

What’ll happen to us when Betelgeuse blows?

Nothing. Even though Betelgeuse is nearby in astronomical terms, it’s nowhere near close enough for the explosion to affect life on Earth. Astronomers calculate that it’ll takeabout six million yearsfor the shock wave and any cold, diffuse debris to reach the solar system, and even then, the sun’s protective bubble will shield us from the splattered star guts.

Instead, once astronomers see that Betelgeuse is going to go supernova, you should get to a clear northern sky as quickly as possible and enjoy the show.

“It would be so incredibly cool!” Nance says. “By far and away the most incredible thing to happen in my life.”

So, is that actually about to occur?

This is the big mystery, and it’s one of the reasons why the star’s current behavior is intriguing. Scientists suspect that a precipitous drop in brightness could portend a star’s demise.

“As massive stars near the end of their lives, they experience insane and violent mass loss,” Nance says. In theory, all that ejected dust could shroud and darken the nearly dead star, causing it to dim from our perspective right before it goes supernova. In practice, though, it’s not yet certain whether stars are darkest before they blow—no one has yet been able to closely study a doomed star before, during, and after its demise.

But isn’t it normal for Betelgeuse to be dimming?

Yes. Betelgeuse is classified as a semiregular variable star, meaning that its brightness semiregularly changes. Millennia ago, Australian Aboriginesnoted the star’s fluctuating luminosity, and British astronomer John Herschel recorded the phenomenonin 1836.

More recently, theAmerican Association of Variable Star Observershas been compiling observations of Betelgeuse’s fits and starts.Decades of photometric datashow that Betelgeusebrightens and dims in cycles, with one notable cycle vacillating on a roughly six-year timescale, and another rising and falling every 425 days or so.

“The star is not strictly periodic, and the range of light variations changes from cycle to cycle,” Guinan says, noting that right now, Betelgeuse is the dimmest it has been since more precise monitoring began around a century ago; the second-duskiest observations on record date back to the mid-1920s.

The reasons for these quasiperiodic changes in variations are somewhat unclear. Guinan and others say that supergiant stars like Betelgeuse have mottled surfaces containing massive convective cells that shrink and swell, which cause such stars to darken and brighten, but that’s not the whole story.

Images of Betelgeuseshow bright and dark features on its surface, and at times it is not symmetrical,” Guinan says. “The star is bloated and unstable, with pulsations, as well.”

View Images

The star Betelgeuse, as seen from Earth by the ALMA observatory in Chile.

Guinan suspects that Betelgeuse is dramatically dimmer now because two of its cycles are overlapping at minimal brightness. In essence, the star is approaching the dimmest points in both its six-year and 425-day cycles, an intersection that makes the star’s normal fluctuations appear much more sinister. After looking through 25 years’ worth of prior data, Guinan suspects that the star will continue to fade for another couple of weeks before gradually turning back on.

But, he says, “if it keeps getting fainter, then all bets are off.”

How long do we have to wait for the fireworks?

Recent studies suggest that the star will most likely explode within the next million years, and perhaps as soon as100,000 years from now. Or … maybe Betelgeuse has already exploded and we have not yet seen it happen.

It takes light from this star about 600 years to reach us, meaning that we’re actually observing the star as it was 600 years ago. If we do see it detonate in our sky any time soon, that means the star actually blew up sometime during the European Middle Ages, and light from the blast is just reaching Earth.

Either way, scientists are excited to keep watch on Betelgeuse and see what sorts of surprises the star still has in store.

“It’s actually quite rare to study a star this well pre-explosion, whenever that happens,” Nance says. “This will inevitably yield cool and interesting ideas for what happens to stars right before they explode.”

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