Rather than the star expanding and engulfing, new observations suggest that the planet may be actively crashing into its star due to a shrinking orbit.

In billions of years, our sun will be on the verge of extinction, expanding to hundreds of times its current size, and the Earth and other planets will be engulfed in a cloud of hot plasma. For a long time, astrophysicists thought this was the only scenario for a star to devour its planet. However, with NASA's JWST Space Telescope, astronomers are now revealing another possibility for planetary extinction: an active plunge headlong into their own parent star. The discovery was published this month in the Journal of Astrophysics.

"The story they tell is really fascinating," commented Adam Burgasser, an exoplanet researcher at the University of California San Diego who was not involved in the study. "The point is that it's not the stars that are expanding, it's the planets themselves falling."

The protagonist of the story is a star located within our Milky Way Galaxy, 2 light-years from Earth. It first came into the minds of researchers in 0, when it erupted in an unusual flash of light. The observations, made by the Zwicky Transient Facility at the 0.0-meter telescope at the Palomar Observatory, appear to indicate that the star has swallowed up a planet at the end of its life, the so-called red giant phase, by a sharp expansion. At the time, this was considered the first such "celestial infanticide" event directly observed by astronomers.

Therefore, when the opportunity arose to make observations with the more powerful JWST space telescope, the group of researchers did not hesitate to decide to return to this "scene of the event". "Since this is believed to be the first directly detected planetary engulfing event, what could be more in-depth than it?" Ryan Lau, lead author of the new study and astronomer at the National Science Foundation NOIRLab, said.

However, the plot unfolds like an unexpected twist in Dashiell Hammett's detective novel, and new observations completely overturn the initial seemingly clear conclusion. The data shows that the star's luminosity suggests that it is actually quite "young" and is far from being able to expand into a red giant. This means that it simply cannot expand enough to engulf the planet.

Based on new observations, Lau and his colleagues have come up with a very different explanation: the planet is about the size of Jupiter, and its orbit may be about the distance Mercury orbits the Sun. Over millions of years, the planet's orbit gradually contracted, getting closer and closer to its star, and eventually the two celestial bodies merged catastrophically. Therefore, this is not so much a "infanticide" as a planetary "astrophysical suicide". This violent impact caused the star to eject a large amount of outer gas, which then gradually cooled and condensed into dust.

The research team speculates that the planet's long, winding "death spiral" may have started like this: the star's strong gravitational pull first exerts a tidal force on the planet, causing it to deform it, just as the moon does on the Earth's oceans. This continuous stretching creates friction in the planet's interior, dissipating some of the planet's orbital energy, causing it to move closer to the star little by little. Eventually, when the planet gets close enough to begin skimming the star's atmosphere, it encounters a tremendous drag force that causes it to disintegrate and accelerate into the star's interior.

However, Lau also stressed that this new analysis is still in its preliminary stages. "We are certain that the initial hypothesis of star expansion can be ruled out, but there is currently more circumstantial evidence supporting the new theory." He noted that to date, JWST's observations have focused on a narrower band of infrared light. In the future, Lau said plans to take advantage of JWST's wider spectral range, especially longer infrared wavelengths, which will help the team gain a deeper understanding of the properties of the dust clouds around the star to test their new hypothesis.

Adam Burgasser also gives further thought about this, especially with regard to the reliability of observations. "We can't rule out the possibility that the dust that exists between the star and us obscures some of the light, making it look fainter than it actually is, like a younger star. Therefore, more measurements are needed to rule out or confirm this possibility. If follow-up observations can confirm the currently reported stellar luminosity, he added, "it will provide conclusive evidence for a new explanation of this 'planetary suicide.'" ”

At the same time, Adam Burgasser was curious about the pervasiveness of this way of planetary death. With the Vera C. Rubin Observatory in Chile expected to be operational later this year, astronomers will have access to unprecedented high-resolution images of the universe. Burgasser believes that we may be able to find more planets spiraling towards destruction in a similar way. "Perhaps, this [planetary 'suicide'] is actually a fairly common cosmic phenomenon."

This article was translated from Science and edited by sein.