Webb telescope finds the smallest known free-floating brown dwarf 

NASA’s James Webb Space Telescope has identified what is currently the smallest known free-floating brown dwarf. This extraordinary finding offers new insights into the mysterious world of brown dwarfs, objects that blur the line between stars and planets.

Brown dwarfs are mysterious celestial bodies that exist in a liminal space between stars and planets. They form through processes similar to stars, collapsing under their own gravity. 

However, brown dwarfs lack sufficient mass and heat for hydrogen fusion – the process that ignites stars. Some brown dwarfs are comparable to giant planets, with masses just a few times greater than Jupiter’s.

Quest for the smallest stars

In their pursuit to identify the smallest possible star-like objects, astronomers have made a significant breakthrough with the Webb telescope. 

“One basic question you’ll find in every astronomy textbook is, what are the smallest stars? That’s what we’re trying to answer,” said study lead author Kevin Luhman from Pennsylvania State University.

The team, including Luhman and Catarina Alves de Oliveira, focused on the IC 348 star cluster in the Perseus star-forming region, about 1,000 light-years away. 

This young cluster, merely five million years old, is a prime location for spotting relatively bright, newly formed brown dwarfs. The researchers utilized Webb’s NIRCam to identify potential brown dwarfs based on their brightness and color and then employed NIRSpec for detailed analysis.

Brown dwarfs are fascinating objects 

The James Webb Space Telescope’s infrared capabilities were instrumental in this discovery, allowing the detection of fainter objects than possible with ground-based telescopes. Its precision also helped distinguish between actual brown dwarfs and distant galaxies.

The research yielded three fascinating objects, ranging from three to eight Jupiter masses. The smallest of these, weighing in at just three to four times the mass of Jupiter, challenges our understanding of celestial formation. 

The relatively weak gravitational force of such a small cloud of gas makes its collapse into a brown dwarf particularly puzzling.

“It’s pretty easy for current models to make giant planets in a disk around a star,” said Catarina Alves de Oliveira of ESA, principal investigator on the observing program. “But in this cluster, it would be unlikely this object formed in a disk, instead forming like a star, and three Jupiter masses is 300 times smaller than our Sun. So we have to ask, how does the star formation process operate at such very, very small masses?”

Valuable insights 

These diminutive brown dwarfs also offer valuable insights into exoplanet characteristics. Unlike exoplanets, which are obscured by their host stars’ glare, free-floating brown dwarfs are easier to study. 

Intriguingly, two of the discovered brown dwarfs exhibit a spectral signature of an unidentified hydrocarbon, a finding that was previously made in our solar system and in the interstellar medium but never before outside of it.

“This is the first time we’ve detected this molecule in the atmosphere of an object outside our solar system,” explained Alves de Oliveira. “Models for brown dwarf atmospheres don’t predict its existence. We’re looking at objects with younger ages and lower masses than we ever have before, and we’re seeing something new and unexpected.”

Brown dwarf or rogue planet?

The mass range of these objects raises a crucial question: Are they truly brown dwarfs, or could they be rogue planets ejected from other systems? While the latter can’t be completely ruled out, the team leans towards the brown dwarf classification. The rarity of ejected giant planets and the youth of the IC 348 cluster support this view.

In summary, the discovery of more such objects will further clarify their nature. The hypothesis that rogue planets might be located on the fringes of star clusters like IC 348 could be tested by expanding the search area. Future surveys, potentially capable of detecting objects as small as one Jupiter mass, promise to unveil more secrets of these fascinating celestial bodies.

The research is published in The Astronomical Journal.

Image Credit: NASA/ESA/CSA James Webb Space Telescope

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