Betelgeuse went dark, but didn’t go supernova. What happened?

Astrophysicist Miguel Montargès has a clear memory of the moment the stars became real places to him. He was 7 or 8 years old, looking up from the garden of his parents’ apartment in the south of France. A huge, red star winked in the night. The young space fan connected the star to a map he had studied in an astronomy magazine and realized he knew its name: Betelgeuse.

Something shifted for him. That star was no longer an anonymous speck floating in a vast uncharted sea. It was a destination, with a name.

“I thought, wow, for the first time … I can name a star,” he says. The realization was life-changing.

Since then, Montargès, now at the Paris Observatory, has written his Ph.D. thesis and about a dozen papers about Betelgeuse. He considers the star an old friend, observing it many times a year, for work and for fun. He says good-bye every May when the star slips behind the sun from the perspective of Earth, and says hello again in August when the star comes back.

So in late 2019, when the bright star suddenly dimmed for no apparent reason, Montargès was a little alarmed. Some people speculated that Betelgeuse was about to explode in a brilliant supernova that would outshine the full moon. Astronomers know the star is old and its days are numbered, but Montargès wasn’t ready to see it go.

“It’s my favorite star,” he says. “I don’t want it to die.”

Other researchers, though, were eager to watch Betelgeuse explode in real time. Supernovas mark the violent deaths of stars that are at least eight times as massive as the sun (SN: 11/7/20, p. 20). But astronomers still don’t know what would signal that one is about to blow. The outbursts sprinkle interstellar space with elements that ultimately form the bulk of planets and people — carbon, oxygen, iron (SN: 2/18/17, p. 24). So the question of how supernovas occur is a question of our own origins.

But the explosions are rare — astronomers estimate that one occurs in our galaxy just a few times a century. The last one spotted nearby, SN 1987A, was more than 33 years ago in a neighboring galaxy (SN: 2/18/17, p. 20). Betelgeuse is just one of the many aging, massive stars — called red supergiants — that could go supernova at any moment. But as one of the closest and brightest, Betelgeuse is the one that space enthusiasts know best.

So when the star started acting strangely at the end of last year, Montargès and a small band of Betelgeuse diehards aimed every telescope they could at the dimming giant. Over the following months, the star returned to its usual brightness, and the excitement over an imminent supernova faded. But the flurry of data collected in the rush

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Why we don’t know exactly what happened during a near-collision in space

Space traffic experts tracked two pieces of orbital garbage that appeared to be careening toward each other on Thursday night: a defunct Soviet satellite and a discarded Chinese rocket booster. Ultimately, the two objects narrowly missed each other, according to private space-tracking company LeoLabs.

a close up of a computer: Two pieces of orbital space debris appeared to be careening toward each other on Thursday, October 15. Ultimately, the two objects narrowly missed each other, according to a private space-tracking company, LeoLabs.

© Courtesy LeoLabs
Two pieces of orbital space debris appeared to be careening toward each other on Thursday, October 15. Ultimately, the two objects narrowly missed each other, according to a private space-tracking company, LeoLabs.

LeoLabs, which uses its own ground-based radars to track spaceborne objects, put the odds of collision at 10% or greater. That’s high, but not uncommon, LeoLabs CEO Daniel Ceperley told CNN Business on Thursday.


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But the US military, which uses data from the world’s largest network of radars and telescopes, said that its space traffic control team detected a “nearly zero percent probability of collision.”

In response, LeoLabs’s Ceperley said in a statement Friday morning: “We obviously have a great deal of respect for the [US military’s] 18th Space Control Squadron and their estimates. Nobody is disputing that these objects came close to one another.”

Meanwhile, Moriba Jah, an astrodynamicist at the University of Texas at Austin who has long been trying to raise public awareness about the abundance of junk in Earth’s orbit at constant risk of colliding, said the ordeal was only the latest piece of evidence that the world needs an internationally collaborative effort to track space traffic.

His data, an amalgamation of all publicly available real-time space traffic information, show dozens of potential collisions happening at any given moment. Jah suggested the Soviet satellite and discarded rocket booster were expected to come within 72 meters of each other. However, he couldn’t say for sure whether a collision was even “likely.”

Objects in space are tracked with telescopes and radar operated by governments and private companies. But all those organizations around the globe are hesitant to share their data with each other. So, when there is a chance that two things in space might collide, experts have an extremely difficult time hashing out exactly how high the risks are. LeoLabs does not share its data publicly.

Ceperley told CNN Business Thursday that the company decided to raise public awareness about this particular event because the two objects are both large, and because they’re in an area of orbit that’s still relatively clean compared to nearby orbits. The company is also trying to raise more general awareness about the debris problem, he said, to encourage the private sector to develop means of cleaning it up.

“Multiple times a week we’re seeing dead satellites come within 100 meters of each other, moving at tremendous speeds,” Ceperley said.

What happened Thursday

The Soviet satellite, which launched to space in 1989 and was used for navigation, weighs nearly 2,000 pounds and is 55 feet long, according to Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics. The rocket booster, part of a Chinese Long March launch vehicle that likely

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