A team of astronomers have achieved a milestone in stellar physics by using the James Webb Space Telescope (JWST) to peer beneath the surface activity of TRAPPIST-1, one of the most famous exoplanet host stars. Their study has revealed the hidden magnetic features on this volatile red dwarf, opening new possibilities for understanding both stellar behaviour and the habitability of nearby worlds.
Artist impression of the James Webb Space Telescope (Credit : NASA)
TRAPPIST-1 is an M8 dwarf star hosting seven known exoplanets and is currently one of the most frequently observed targets of the JWST. However, this stellar system presents a challenge; it is notoriously active, and its surface is believed to be covered by magnetic features that interfere with the planetary transmission spectra.
These magnetic features that include starspots, faculae, and other surface phenomena act like noise, interfering with attempts to analyse the atmospheres of TRAPPIST-1’s potentially habitable planets. For years, teams of researchers have needed to understand these stellar contaminants to “clean” their exoplanet observations, but the spectral signatures of these features remained elusive.
Comparison between the Sun and the ultracool dwarf star TRAPPIST-1 (Credit : ESO)
The research team led by Valeriy Vasilyev from the Max Planck Institute for Solar System Research developed an ingenious solution using time resolved observations from JWST’s NIRISS instrument. By studying four stellar flares in incredible detail, they made a remarkable discovery: a persistent feature in the spectral flux in a flare of TRAPPIST-1.
Initially, this brightening might seem like simple flare afterglow. However, the team’s analysis revealed something far more intriguing. Their analysis ruled out flare decay instead pointing to structural changes on the stellar surface induced by flares. The researchers propose that the flaring event triggers the disappearance of (part of) a dark magnetic feature, producing a net brightening. This interpretation draws on solar observations, where high resolution images have directly captured magnetic features disappearing after flares.
An X3.2-class solar flare on the Sun observed in different wavelengths (Credit : NASA/SDO)
This research represents the first measurement of the spectrum of a magnetic feature on an M8 dwarf. The analysis reveals that the disappearing magnetic feature is cooler than the TRAPPIST-1 photosphere, but by at most a few hundred kelvins.
These findings have profound implications for exoplanet research. The radiative spectra of these magnetic features are needed to clean transmission spectra, and now scientists finally have this crucial data. By understanding and accounting for stellar contamination, researchers can obtain more accurate measurements of planetary atmospheres, improving our ability to assess habitability and search for biosignatures around red dwarf stars.
This technique could revolutionise studies of the thousands of potentially habitable worlds orbiting active red dwarf stars throughout our galaxy, bringing us closer to answering whether life exists beyond Earth.
Source : Flares on TRAPPIST-1 reveal the spectrum of magnetic features on its surface