In May 2020, astronomers observed a planetary engulfment for the first time that they believed was caused by a star expanding to become a red giant–swallowing an orbiting planet in the process. However, new evidence suggests that this event was the result of the planet plunging itself into its host star in what can be called an act of astrophysical suicide. The details of this development were published in The Astrophysical Journal on April 10, 2025.
At the time of the observation, scientists were not able to classify what they had witnessed, only that there was an outburst of light from a star 12,000 light-years away in our Milky Way galaxy. The star became more than 100 times brighter over ten days, quickly faded back to normal, and then followed with a colder, longer-lasting signal.
In a study published in Nature in 2023, scientists led by now Assistant Professor of Astronomy at Columbia, Kishalay De, concluded that the outburst of light was a planet being swallowed by a star. Their initial guess was an eruption in a stellar binary—systems where two stars orbit each other with one pulling mass from the other occasionally and brightening as a result.
It was at the Keck Observatory in Hawaii, whose spectroscopic telescopes allow scientists to discern a star’s chemical composition, where De discovered signs of molecules that can only exist at very cold temperatures. Stars increase in temperature as they brighten, eliminating the possibility of a binary star and leading De to the Palomar Observatory at Caltech.
Now, using an infrared camera, the team was able to see that the star was shooting out cold energy in the year following the ten-day hot flash. This led to the idea that the star could be merging with another star, but data from NASA’s infrared space telescope, NEOWISE, was used to estimate that the total amount of energy released by the star since its initial outburst was 1,000 times smaller in magnitude than any previous stellar merger.
As a result, the celestial body that merged with the star had to have been 1,000 times smaller than any star on record, the same disparity Jupiter has compared to our sun. De’s team arrived at the conclusion that a Jupiter-sized planet had been swallowed up by the star, the first time scientists had witnessed such an event.
The part of the story they were missing was discovered by astronomers working with NASA’s James Webb Space Telescope. De believed the star had entered its red giant phase–where a star that has exhausted its core hydrogen expands and brightens–and the planet was pulled in as a casualty of its ballooning atmosphere, the same fate that will befall Earth when the Sun reaches its red giant stage in five billion years. However, the star’s luminosity implies that it is too young to be in its red giant stage, according to lead author of the new study and astronomer at the National Science Foundation’s (NSF) NOIRLab, Ryan Lau.
Lau and his team surmise that the planet orbited the star at about the same distance Mercury orbits our Sun. The planet began a death spiral that lasted millions of years during which the planet’s orbit shrank and moved closer to the star until the two celestial bodies merged. This spiral began when the star’s gravitational pull deformed it, much like the Moon creates Earth’s tides. Tidal stretching generated internal friction, which sapped the planet’s orbital energy, drawing it closer to the star until it skimmed the star’s atmosphere, experiencing severe drag and disintegrating as it plunged into the star.
