December 9, 2023

Astronomers witness a galaxy-wide apocalypse as a planet crashes into its host star. It’s an event long thought to occur in many star systems — including our own — but this is the first time it’s been directly observed.

Earth has an expiration date: In about 5 billion years, the sun will exhaust its hydrogen fuel supply and swell into a red giant, engulfing Mercury, Venus, and possibly Earth in the process. This is a normal phase in the life cycle of many stars, and given the prevalence of planets as we now know them, this doomsday scenario is thought to play out regularly across the universe.

But it’s never been directly observed — until now. Astronomers from Caltech and MIT observed a Sun-like star called ZTF SLRN-2020, located some 12,000 light-years away, devouring a Jupiter-sized planet over the course of several months. Gas giant planet.

The first clue to the story emerged when the Zwicky Transient Facility (ZTF) observed the star brighten more than 100-fold in 10 days before dimming again. The initial hypothesis was that it was undergoing a nova, an explosion that occurs when a white dwarf sucks material from a companion star. But careful inspection with the Keck Observatory ruled that out.

“I’ve been looking for exploding stars called novae,” said Kishalay De, lead author of the study. “But the Keck data showed that the star didn’t ignite hot gas as expected for a nova. I couldn’t understand it.

So the team went on to examine infrared data collected by the NEOWISE space telescope and found that the star had been brightening in infrared light for up to nine months before ZTF detected the optical brightening. In fact, this infrared light is still visible today, the team says.

With these pieces, the researchers put together the most likely stories. The aging star has begun to swell until its surface reaches the orbit of the hapless planet. Eventually it gets close enough that the planet skims hot gas from the star’s surface, and the planet begins to disintegrate. Material from both objects was flung into space, where it cooled into dust, producing the infrared signature seen by NEOWISE. This dangerous dance continued for about nine months before the inevitable doomsday.

“The planet fell into the core of the star and was engulfed whole,” De said. “When it does, energy is transferred to the star. The star blows off its outer layers to get rid of the energy. It expands and brightens, and that brightening is what ZTF records.”

This unbelievable story is very humbling. Perhaps in the distant future, aliens will witness Earth’s own doomsday from a distance and view it with equal scientific curiosity.

The study was published in the journal nature. The revelation can be seen in the animation below.

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Astronomers watch a star devour a planet

source: Caltech