The James Webb Space Telescope (JWST) has revealed an unexpected twist in what was thought to be the first observation of a star swallowing a planet, an event that has become known as ZTF SLRN-2020. Rather than the star expanding to engulf its planet as was believed, the observations from JWST shows that the planet’s orbit gradually decayed over time until it was completely consumed by the star. Lead researcher Ryan Lau from NSF NOIRLab noted that the event is providing valuable insights about the ultimate fate of planetary systems, potentially including our own Solar System.
Artist impression of the James Webb Space Telescope
The observations from JWST’s Mid-Infra Red Instrument have led to a revision in our understanding of the event that is thought to be located 12,000 light-years away in the Milky Way. It was initially detected as an optical flash by the Zwicky Transient Facility, with NASA’s NEOWISE data showing infrared brightening a year earlier.
Researchers first believed the event they were witnessing a Sun-like star expanding into a red giant and engulfing a planet. However, the superior infra-red sensitivity and spatial resolution revealed the star was not bright enough to be a red giant, contradicting the original idea that the star had swelled to consume its planet.
The team have instead proposed that a planet the size of Jupiter orbiting extremely close to its star gradually spiralled inward over millions of years until it began grazing the star’s atmosphere, triggering a runaway process of rapid infall. According to team member Morgan MacLeod, the planet “smeared” around the star during its final approach, with the violent impact blasting gas from the star’s outer layers that later expanded, cooled, and condensed into observable dust.
“The planet eventually started to graze the star’s atmosphere. Then it was a runaway process of falling in faster from that moment,” said team member Morgan MacLeod of the Harvard-Smithsonian Center for Astrophysics and the Massachusetts Institute of Technology.
The Near Infrared Spectrograph onboard the JWST revealed a hot circumstellar disk of molecular gas, including carbon monoxide, alongside the expected cooler dust cloud. Co-author Colette Salyk expressed surprise at what resembles a planet forming region after a planetary engulfment. The ability to characterise this gas raises questions about what happens when a planet is consumed by its star. Lau emphasised this observation’s significance as the only captured instance of such an event, hoping it begins a larger sample.
These observations were among JWST’s first studies for the Target of Opportunity programs for unpredictable phenomena! The team anticipate identifying similar events using the upcoming Rubin Observatory and Roman Space Telescope through repeated sky surveys.
Source : NASA Webb’s Autopsy of Planet Swallowed by Star Yields Surprise