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James Webb Space Telescope Reveals Planet Crash into Star, Challenging Red Giant Engulfment Theory
Recent observations from the James Webb Space Telescope (JWST) have unveiled a cataclysmic cosmic event: a direct planet-star collision. Astronomers initially hypothesized that a red giant star had engulfed a planet, but the JWST data reveals a contrasting scenario where the planet crashed into the star. This discovery, focusing on star ZTF SLRN-2020, sheds new light on planetary systemFinal fates and challenges previous assumptions about stellar evolution and planet destruction.
Illustration depicting a star after engulfing a planet. | Credit: NASA/ESA/CSA/Ralf Crawford (STScI)
Initial Detection of Stellar Brightening
In 2020, the Zwicky Transient Facility at Palomar Observatory in California detected a distant star, located approximately 12,000 light-years away, experiencing a sudden surge in brightness. Analysis of archival data from NASA’s NEOWISE mission revealed that this star, designated ZTF SLRN-2020, had been gradually increasing in infrared luminosity for a year prior to the optical outburst.
Previous Red Giant Theory
A study from 2023 proposed that ZTF SLRN-2020 was an evolved sun-like star, classified as a “red giant,” which had expanded, consequently engulfing a gas giant planet in its orbit. The flash of light was interpreted as the destruction of the planet as it was consumed by the expanding red giant. The preceding infrared intensification was attributed to dust generated by the planet’s disintegration within the red giant’s atmosphere, analogous to a massive meteor.
JWST Observations Challenge Red Giant Hypothesis
However, a research team, spearheaded by Ryan Lau of the National Science Foundation’s NOIRLab in Tucson, Arizona, utilized the JWST to examine ZTF SLRN-2020 more closely.
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“Given the unprecedented nature of this event, we were uncertain about what to expect when we directed the telescope towards it,” Lau stated. “The high-resolution infrared capabilities of JWST are providing invaluable insights into the ultimate fate of planetary systems, potentially including our own.”
Unexpected Stellar Characteristics
The JWST observations yielded a surprising result: the star’s luminosity was insufficient for it to be categorized as a red giant. Instead, it presented characteristics of a “normal” star, possessing roughly 70% of the mass of our sun. This finding necessitated a re-evaluation of the ZTF SLRN-2020 narrative. With the red giant scenario debunked, the only plausible explanation was that the planet had collided with the star.
Planet’s Inward Migration and Destruction
How does such a collision occur? The discovery of exoplanets has revealed a class of celestial bodies known as hot Jupiters: gas giants that originate far from their host star but subsequently migrate inwards. In this specific case, the planet must have spiraled so close to its star that gravitational tidal forces initiated an inescapable descent toward its destruction.
Morgan MacLeod of the Harvard–Smithsonian Center for Astrophysics and the Massachusetts Institute of Technology explained, “The planet eventually began interacting with the star’s outer atmosphere, initiating an accelerated inward spiral.”
“As the planet plunged into the star, it essentially smeared across the stellar surface.”
Tidal forces exerted immense pressure, stretching the planet until it finally “splashed down” into the star’s gaseous envelope. The star, in the process of consuming the planet, expelled a vast plume of gas into space. This ejected material cooled and condensed, forming a gaseous cloud that caused the infrared brightening detected by NEOWISE.
Diagrams illustrating a planet’s spiral towards collision with a star, culminating in gas ejection and disk formation. | Credit: NASA/ESA/CSA/Ralf Crawford (STScI)
Unexpected Disk Formation Post-Collision
An additional surprise emerged from the JWST data. Contrary to expectations of an amorphous gas cloud, the Near-Infrared Spectrometer revealed a disk of molecular gas closely orbiting the star. This disk exhibited characteristics strikingly similar to a miniature planet-forming disk.
Implications of Disk Discovery
Exoplanet astronomer Colette Salyk of Vassar College in New York commented, “Observing a structure resembling a planet-forming region, particularly in the aftermath of a stellar engulfment event where planet formation is not occurring, was completely unexpected.”
Future Research and Observations
The disk is believed to originate from the gas plume ejected during the collision, with some material falling back towards the star. However, detailed mechanisms remain under investigation. This observation, considered the first of potentially numerous planet-star collision events to be documented, suggests future discoveries in similar “doomsday” systems. Upcoming wide-field surveys by the Vera C. Rubin Observatory and NASA’s Nancy Grace Roman Space Telescope are anticipated to identify numerous comparable events, facilitating further JWST follow-up studies.
The research findings were published on April 10 in The Astrophysical Journal.