A dramatic cosmic event just got a surprising twist, thanks to the James Webb Space Telescope (JWST). Astronomers originally believed a distant red giant star had engulfed one of its planets. But new findings reveal the real story: the planet crashed straight into the star.
It all started in 2020 when the Zwicky Transient Facility at California’s Palomar Observatory spotted a sudden brightening of a star around 12,000 light-years from Earth. Looking back at older data from NASA’s NEOWISE mission, scientists noticed that this star—named ZTF SLRN-2020—had been slowly brightening in infrared light for about a year before the optical flash was seen.
In 2023, a study suggested that ZTF SLRN-2020 was a red giant—an older star that had expanded in size—and that it had swallowed a gas giant planet orbiting around it. According to that explanation, the bright flash came from the planet being destroyed inside the red giant’s outer layers. The leftover dust, created as the planet burned up, was thought to be the source of the infrared glow picked up by NEOWISE.
But that story took a sharp turn when Ryan Lau from the National Science Foundation’s NOIRLab in Tucson, Arizona, and his team observed the star more closely using the JWST.
“Because this is such a novel event, we didn’t quite know what to expect when we decided to point this telescope in its direction,” Lau said. “With its high-resolution look in the infrared, we are learning valuable insights about the final fates of planetary systems, possibly including our own.”
To the team’s surprise, the star wasn’t big or bright enough to be a red giant. It appeared to be a regular star, with only about 70% of the mass of our sun. That changed everything. Instead of being swallowed by a growing star, the planet must have crashed into it on its own. But how does that even happen?
Astronomers have known for a while that some planets—called hot Jupiters—form far away from their stars and then move inward over time. That seems to be what happened here. This planet slowly drifted closer until the star’s gravity pulled it in for good.
“The planet eventually started to graze the star’s atmosphere. Then it was a runaway process of falling in faster from that moment,” said Morgan MacLeod of the Harvard–Smithsonian Center for Astrophysics and the Massachusetts Institute of Technology. “The planet, as it’s falling in, started to sort of smear around the star.”
As the planet fell in, the tidal forces stretched it out, eventually causing it to slam into the star’s atmosphere. When that happened, the star released a massive burst of gas into space—like a stellar burp . That gas cooled down and formed the glowing cloud seen by NEOWISE. But the surprises didn’t stop there.
Astronomers expected to find a messy cloud of gas. Instead, JWST’s Near-Infrared Spectrometer revealed something much more organized: a disk of molecular gas circling tightly around the star, much like the disks seen around young stars where new planets form.
“I could not have expected seeing what has the characteristics of a planet-forming region , even though planets are not forming here, in the aftermath of an engulfment,” said Colette Salyk, an exoplanet astronomer at Vassar College in New York.
The gas in that disk likely came from the star’s own burp—some of the ejected material fell back and began orbiting again. Scientists still aren’t sure exactly how the disk formed or how long it will last, but they hope to find out more by studying similar events.
It all started in 2020 when the Zwicky Transient Facility at California’s Palomar Observatory spotted a sudden brightening of a star around 12,000 light-years from Earth. Looking back at older data from NASA’s NEOWISE mission, scientists noticed that this star—named ZTF SLRN-2020—had been slowly brightening in infrared light for about a year before the optical flash was seen.
In 2023, a study suggested that ZTF SLRN-2020 was a red giant—an older star that had expanded in size—and that it had swallowed a gas giant planet orbiting around it. According to that explanation, the bright flash came from the planet being destroyed inside the red giant’s outer layers. The leftover dust, created as the planet burned up, was thought to be the source of the infrared glow picked up by NEOWISE.
But that story took a sharp turn when Ryan Lau from the National Science Foundation’s NOIRLab in Tucson, Arizona, and his team observed the star more closely using the JWST.
“Because this is such a novel event, we didn’t quite know what to expect when we decided to point this telescope in its direction,” Lau said. “With its high-resolution look in the infrared, we are learning valuable insights about the final fates of planetary systems, possibly including our own.”
To the team’s surprise, the star wasn’t big or bright enough to be a red giant. It appeared to be a regular star, with only about 70% of the mass of our sun. That changed everything. Instead of being swallowed by a growing star, the planet must have crashed into it on its own. But how does that even happen?
Astronomers have known for a while that some planets—called hot Jupiters—form far away from their stars and then move inward over time. That seems to be what happened here. This planet slowly drifted closer until the star’s gravity pulled it in for good.
“The planet eventually started to graze the star’s atmosphere. Then it was a runaway process of falling in faster from that moment,” said Morgan MacLeod of the Harvard–Smithsonian Center for Astrophysics and the Massachusetts Institute of Technology. “The planet, as it’s falling in, started to sort of smear around the star.”
As the planet fell in, the tidal forces stretched it out, eventually causing it to slam into the star’s atmosphere. When that happened, the star released a massive burst of gas into space—like a stellar burp . That gas cooled down and formed the glowing cloud seen by NEOWISE. But the surprises didn’t stop there.
Astronomers expected to find a messy cloud of gas. Instead, JWST’s Near-Infrared Spectrometer revealed something much more organized: a disk of molecular gas circling tightly around the star, much like the disks seen around young stars where new planets form.
“I could not have expected seeing what has the characteristics of a planet-forming region , even though planets are not forming here, in the aftermath of an engulfment,” said Colette Salyk, an exoplanet astronomer at Vassar College in New York.
The gas in that disk likely came from the star’s own burp—some of the ejected material fell back and began orbiting again. Scientists still aren’t sure exactly how the disk formed or how long it will last, but they hope to find out more by studying similar events.
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