In a First, Scientists Witness a Dying Star Swallowing a Planet

Astronomers believe the doomed world was a gas giant about the size of Jupiter

Drawing of a planet skimming the surface of a star
An artist's impression of a doomed planet skimming the surface of its star. K. Miller / R. Hurt (Caltech / IPAC)

For the first time ever, astronomers have witnessed a star swallowing up an entire planet. The stellar snack appeared as a burst of light that MIT astrophysicist Kishalay De spotted in 2020 as he looked at sky scans taken by the California Institute of Technology’s Palomar Observatory.

“One night, I noticed a star that brightened by a factor of 100 over the course of a week, out of nowhere,” De says in an MIT statement. “It was unlike any stellar outburst I had seen in my life.”

De had been studying novae, or bright bursts that occur as a star snatches matter from another. But that explanation didn’t seem right for this mysterious flash. De began to hunt for clues from other observations and telescopes. Infrared data from Palomar showed that after the initial hot burst, the star was surrounded by cold gas and molecules that could only exist in frigid temperatures—which does not align with a nova, De tells Jennifer Ouellette of Ars Technica.

Alternatively, the bright light could have been an indication of two stars merging together. But after examining data from NASA’s infrared space telescope, NEOWISE, De saw that was not the case either—the energy released was just one-thousandth the magnitude of star mergers recorded in the past, per the statement. Instead, it seemed that the star had gobbled up a gaseous planet, perhaps one similar in size to Jupiter. 

“My first reaction was disbelief,” De tells the New York Times’ Becky Ferreira. “These observations give us the first glimpse into how that process plays out.”

Astronomers catch a star swallowing a planet (for the first time)

When stars begin to die, they expand and become nearly one million times larger in size. Scientists theorized that during this phase, the star likely engulfs nearby planets, emitting bursts of light in the process. But until now, evidence of these events has been purely circumstantial, as University of California, Los Angeles, astrophysicist Smadar Naoz, who was not involved with the study, tells Science News’ James R. Riordon. For decades, scientists have only been able to witness the before and after of such a planetary engulfment.

This star, called ZTF SLRN-2020, is the first to change that. It lies about 15,000 light-years away in the constellation Aquila, and it’s about ten billion years old. After ruling out other explosive explanations for the burst of light, De and his colleagues published their findings on Wednesday in the journal Nature.

Researchers can now say planetary engulfments are likely relatively common throughout the universe. In our own galaxy, this may even happen a few times a year, per the paper. Future studies of ZTF SLRN-2020 may answer further questions about the event—such as whether the planet polluted the star—and help scientists create models to discover more of these world-eating celestial bodies, writes Caitlin McDermott-Murphy for the Harvard Gazette

The research also provides a glimpse into our own planet’s eventual fate: Scientists estimate that, in about five billion years, our aging sun will also expand, swallowing the Earth, Mercury and Venus. 

“We are seeing the future of the Earth,” De says in the statement. “If some other civilization was observing us from 10,000 light-years away while the sun was engulfing the Earth, they would see the sun suddenly brighten as it ejects some material, then form dust around it, before settling back to what it was.”

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