The James Webb Space Telescope detects the first young brown dwarfs outside the Milky Way
An international team of astronomers has used the James Webb Space Telescope to detect the first brown dwarf candidates outside the Milky Way in the distant and mysterious star cluster.
Imagine the outskirts of the Little Magellanic Cloud, a satellite galaxy of our Milky Way, about 200,000 light years from Earth: here is the young star cluster NGC 602. The local environment of this cluster is similar to that of the primitive Universe, with a low abundance of elements heavier than hydrogen and helium. The existence of dark clouds of dense dust and the fact that the cluster is rich in ionized gas also suggest that a star is forming. Together with its associated HII region N90, which contains clouds of ionized atomic hydrogen, this cluster provides a valuable opportunity to examine how stars can form in conditions radically different from those of the solar environment.
According to NASA in Spanish, an international team of astronomers, including Peter Zeidler, Elena Sabbi, Elena Manjavacas and Antonella Nota, used the Webb telescope to observe NGC 602 and discover candidates for the first young brown dwarfs outside our Milky Way.
"Only thanks to the incredible sensitivity and resolution in the appropriate wavelength range can we detect these objects at such great distances," shared author Peter Zeidler of AURA/STScI for the European Space Agency. "This has never been possible before and will also continue to be impossible with telescopes on the ground in the foreseeable future."
What are brown dwarfs?
Brown dwarfs are the most massive cousins of giant gas planets (they usually have between 13 and 75 masses of Jupiter, and sometimes less). They are floating, which means they are not gravitationally bound to a star like exoplanets are. However, some of them share characteristics with exoplanets, such as their atmospheric composition and storm patterns.
"Until now, we knew about 3,000 brown dwarfs, but they all live within our own galaxy," added Elena Manjavacas, a member of the AURA/STScI team for the European Space Agency.
"This discovery highlights the power of using both Hubble and Webb to study young star clusters," explained Antonella Nota, member of the team, executive director of the International Institute of Space Sciences in Switzerland and former scientist of the Webb project for ESA. "The Hubble showed that NGC 602 houses very young low-mass stars, but only with the Webb can we finally see the extent and importance of sub-mas formation in this cluster. Hubble and Webb are an incredibly powerful telescope duo!"
"Brown dwarfs seem to form in the same way as stars, only they don't capture enough mass to become a fully developed star. Our results fit well with this theory," Peter said.
The equipment's data includes a new image of NGC 602 obtained with the near-infrared camera (NIRCam) of the Webb telescope. In this image, you can see the stars of the cluster, the young star objects and the surrounding gas and dust ridges. You can also see a large number of galaxies in the background and other stars in the Little Magellanic Cloud. These observations were made in April 2023.
"These are the first analogues of giant exoplanets outside the Milky Way," Elena added. "We have to be prepared to make revolutionary discoveries in these new objects!"