First young brown dwarfs found outside the Milky Way?

Science and research

October 23, 2024
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An international team of astronomers using the NASA/ESA/CSA James Webb Space Telescope has discovered the first brown dwarf candidates outside the Milky Way in the star cluster NGC 602.

Imagine the edge of the Small Magellanic Cloud, a satellite galaxy of our Milky Way, about 200,000 light-years from Earth: this is where the young star cluster NGC 602 lies. The local environment of this cluster is similar to the environment of the early universe, with low abundances of elements, which are heavier than hydrogen and helium. The presence of dark clouds of dense dust and the fact that the cluster is rich in ionized gas also suggest that star formation is occurring. Together with the associated HII [1] In the N90 region, which contains clouds of ionized atomic hydrogen, this cluster provides a valuable opportunity to study how stars can form under completely different conditions than those in the solar environment.

An international team of astronomers, including Peter Zeidler, Elena Sabbi, Elena Manjavacas and Antonella Nota, used Webb to observe NGC 602 and discover candidates for the first young brown dwarfs outside our Milky Way.

“It is only thanks to the incredible sensitivity and resolution at the right wavelength range that we are able to detect these objects at such great distances,” said lead author Peter Zeidler from AURA/STScI for the European Space Agency. “This has never been possible before and will remain impossible for the foreseeable future, even with telescopes on the ground.”

Brown dwarfs are the more massive cousins ​​of giant gas planets (typically in the range of around 13 to 75 Jupiter masses, sometimes less). They are free-floating, which means they are not gravitationally bound to a star like exoplanets. However, some of them share similarities with exoplanets, such as their atmospheric composition and storm patterns.

“So far we knew about 3,000 brown dwarfs, but they all live in our own galaxy,” added team member Elena Manjavacas from AURA/STScI for the European Space Agency.

“This discovery highlights the power of using Hubble and Webb to study young star clusters,” said team member Antonella Nota, executive director of the International Space Science Institute in Switzerland and former Webb project scientist for ESA. “Hubble has shown that NGC602 hosts very young, low-mass stars, but it is only with Webb that we can finally appreciate the extent and importance of substellar mass formation in this cluster. “Hubble and Webb are an incredibly powerful telescope duo!”

“Brown dwarfs appear to form in the same way as stars, they just don’t capture enough mass to become a full-fledged star. Our results fit well with this theory,” noted Peter.

The team’s data includes a new image from Webb’s Near Infrared Camera (NIRCam) of NGC 602. In this image, the star clusters, the young stellar objects and the surrounding gas and dust ridges are visible. It also shows a large number of background galaxies and other stars in the Small Magellanic Cloud. These observations were made in April 2023.

“These are the first analogues of giant exoplanets outside the Milky Way,” Elena added. “We must be prepared for groundbreaking discoveries in these new objects!”

These observations were made as part of the JWST GO program #2662 (PI: P. Zeidler). The results were published in The Astrophysical Journal.

Notes
[1] Some of the most beautiful extensive objects we can see are known as HII regions, also called diffuse nebulae or emission nebulae. They consist largely of ionized hydrogen and are found throughout the interstellar medium of the Milky Way and in other galaxies.

More information
Webb is the largest and most powerful telescope ever launched into space. As part of an international cooperation agreement, ESA provided the telescope’s launch service using the Ariane 5 launch vehicle. Working with partners, ESA was responsible for the development and qualification of Ariane 5 adaptations for the Webb mission, as well as the procurement of the launch service by Arianespace. ESA also provided the powerful NIRSpec spectrograph and 50% of the MIRI mid-infrared instrument, designed and built by a consortium of nationally funded European institutes (the MIRI European Consortium) in collaboration with JPL and the University of Arizona.

Webb is an international partnership between NASA, ESA and the Canadian Space Agency (CSA).

Published on esawebb.org

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