Enlargement of the region under study, where HST & JWST observations taken 20 years apart alternate. Credits: NASA/ESA/CSA/JWST/INAF – LR Bedin et al. 2024
The James Webb Space Telescope (JWST) of the NASA, ESA and CSA space agencies gives us breathtaking new images of our galactic neighborhood. A research group led by the National Institute for Astrophysics (Inaf) has exploited the enormous potential of Jwst to observe, for the first time in infrared, the entire cooling sequence of white dwarfs in a nearby globular cluster, revealing a excess infrared emission, a potential clue to destroyed ancient planetary systems. The article was recently published in the journal Astronomische Nachrichten (Astronomical Notes).
Most stars, especially those with masses similar to the Sun (from 8 to 0.07-0.08 solar masses), end their evolution as white dwarfs, which will happen to our parent star in about 5 billion years. After having exhausted the stellar “fuel” (hydrogen and helium), these objects are unable to trigger thermonuclear reactions and collapse under their own weight, cooling until they finally shut down, losing the outermost layer of their atmosphere.
The data used in the survey, extrapolated from Hubble’s twenty-year archive and from recent observations with the Webb space telescope, allowed the research group to probe the fundamental properties of white dwarfs and to look for clues to the possible existence of ancient planetary systems around they. Luigi Bedin, researcher at INAF in Padua and first author of the study, explains: «We discovered that infrared observations of white dwarfs allowed us to obtain valuable information on the properties of their dense hydrogen atmospheres. The data shows, unexpectedly, a surprising number of white dwarfs with a relative excess of infrared emission. The results will need to be confirmed, but they suggest that these white dwarfs present traces of ancient planetary systems that are now extinct.”
The research team observed, in several white dwarfs, anomalies in the spectral distribution of energy. Bedin refers to excess emissions in the infrared radiation band: «These may be due to companions of sub-stellar size or to remnants of planetary systems destroyed during the evolution of the star from dwarf to giant. What happens? During the burning of hydrogen from the core, the star’s shell swells to incorporate the innermost planets of its system.”
The observations refer to the nearby globular cluster NGC 6397 (also known as C 86), a quite bright object also visible to the naked eye in the direction of the constellation of Altar, 7200 light years from the Sun. survey led by Bedin and colleagues with the JWST involves the observation of intrinsically faint and dim stars, so proximity to the source is essential even if using the most powerful operational infrared instrument currently in orbit. “In this cluster we observed about 20% of white dwarfs with this infrared excess, while in the galactic field only a few sources show such an anomalously high infrared flux,” he adds Bedin.
The research group is planning a second observational campaign with the James Webb Miri camera/spectrograph, an instrument which – by observing in the mid-infrared – is able to characterize the energy emitted by white dwarfs with excess infrared, discriminating between the presence of sub-stellar companions, disks of extinct planetary systems, remnants of the red giant phase. «These new observations which will map the spectrum between 2 and 20 microns will allow us to solve the mystery», concludes the researcher.
To know more:
- Read the article “JWST Imaging of the Closest Globular Clusters — I. Possible Infrared Excess Among White Dwarfs in NGC 6397”by LR Bedin, D. Nardiello, M. Salaris, M. Libralato, P. Bergeron, AJ Burgasser, D. Apai, M. Griggio, M. Scalco, J. Anderson, R. Gerasimov, A. Bellini, published on magazine Astronomische Nachrichten.
