In 2020, the Zwicky Transient Facility at Palomar Observatory detected a star—named ZTF SLRN-2020—brightening unexpectedly. Located around 12,000 light-years away, the star had been glowing in infrared for a year before the optical flash was noted.
Initial studies suggested the star was a red giant that had expanded and engulfed a nearby gas giant planet. The optical flash was interpreted as the planet being consumed, and the accompanying dust was thought to result from the planet burning up in the star's outer layers.
New observations by the James Webb Space Telescope (JWST), led by Ryan Lau of NOIRLab, indicate the star is not a red giant. Instead, it appears to be a sun-like star with only 70% of the Sun’s mass—prompting a reevaluation of the event.
With the red giant theory ruled out, astronomers concluded that the planet most likely crashed into the star. This kind of inward migration is known from "hot Jupiters"—gas giants that form at a distance but move closer over time due to gravitational forces.
The planet’s orbit brought it close enough to begin interacting with the star’s atmosphere. Gravitational tides stretched the planet, eventually causing it to plunge into the star. The resulting energy release expelled gas into space, producing the observed infrared signal.
Instead of a diffuse cloud, JWST’s Near-Infrared Spectrometer found a disk of molecular gas encircling the star. Though no new planets are forming, the structure is similar to a planet-forming disk—possibly created from material ejected during the collision.
The findings were published in The Astrophysical Journal on 10 April. With new observatories like the Vera C. Rubin Observatory and NASA’s Roman Space Telescope coming online, astronomers anticipate discovering similar planet-star collisions for further study.