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NASA’s Webb Identifies Tiniest Free-Floating Brown Dwarf


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NASA’s Webb Identifies Tiniest Free-Floating Brown Dwarf

Image showing wispy pink-purple filaments and a scattering of stars.
Webb Telescope's Near-Infrared Camera shows the central portion of the star cluster IC 348.
Credits: NASA, ESA, CSA, STScI, K. Luhman (Penn State University), and C. Alves de Oliveira (ESA)

Brown dwarfs are objects that straddle the dividing line between stars and planets. They form like stars, growing dense enough to collapse under their own gravity, but they never become dense and hot enough to begin fusing hydrogen and turn into a star. At the low end of the scale, some brown dwarfs are comparable with giant planets, weighing just a few times the mass of Jupiter.

What are the smallest stars?

Astronomers are trying to determine the smallest object that can form in a star-like manner. A team using NASA’s James Webb Space Telescope has identified the new record-holder: a tiny, free-floating brown dwarf with only three to four times the mass of Jupiter.

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

Search Strategy

To locate this newfound brown dwarf, Luhman and his colleague, Catarina Alves de Oliveira, chose to study the star cluster IC 348, located about 1,000 light-years away in the Perseus star-forming region. This cluster is young, only about 5 million years old. As a result, any brown dwarfs would still be relatively bright in infrared light, glowing from the heat of their formation.

The team first imaged the center of the cluster using Webb’s NIRCam (Near-Infrared Camera) to identify brown dwarf candidates from their brightness and colors. They followed up on the most promising targets using Webb’s NIRSpec (Near-Infrared Spectrograph) microshutter array.

Image: Star Cluster IC438

Image showing wispy pink-purple filaments and a scattering of stars.
This image from the NIRCam (Near-Infrared Camera) instrument on NASA’s James Webb Space Telescope shows the central portion of the star cluster IC 348. The wispy curtains filling the image are interstellar material reflecting the light from the cluster’s stars – what is known as a reflection nebula. The material also includes carbon-containing molecules known as polycyclic aromatic hydrocarbons, or PAHs. Winds from the most massive stars in the cluster may help sculpt the large loop seen on the right side of the field of view.
NASA, ESA, CSA, STScI, K. Luhman (Penn State University), and C. Alves de Oliveira (ESA)

Webb’s infrared sensitivity was crucial, allowing the team to detect fainter objects than ground-based telescopes. In addition, Webb’s sharp vision enabled them to determine which red objects were pinpoint brown dwarfs and which were blobby background galaxies.

This winnowing process led to three intriguing targets weighing three to eight Jupiter masses, with surface temperatures ranging from 1,500 to 2,800 degrees Fahrenheit (830 to 1,500 degrees Celsius). The smallest of these weighs just three to four times Jupiter, according to computer models.

Explaining how such a small brown dwarf could form is theoretically challenging. A heavy and dense cloud of gas has plenty of gravity to collapse and form a star. However, because of its weaker gravity, it should be more difficult for a small cloud to collapse to form a brown dwarf, and that is especially true for brown dwarfs with the masses of giant planets.

“It’s pretty easy for current models to make giant planets in a disk around a star,” said Catarina Alves de Oliveira of ESA (European Space Agency), 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?”

A Mystery Molecule

In addition to giving clues about the star-formation process, tiny brown dwarfs also can help astronomers better understand exoplanets. The least massive brown dwarfs overlap with the largest exoplanets; therefore, they would be expected to have some similar properties. However, a free-floating brown dwarf is easier to study than a giant exoplanet since the latter is hidden within the glare of its host star.

Two of the brown dwarfs identified in this survey show the spectral signature of an unidentified hydrocarbon, or molecule containing both hydrogen and carbon atoms. The same infrared signature was detected by NASA’s Cassini mission in the atmospheres of Saturn and its moon Titan. It has also been seen in the interstellar medium, or gas between stars.

“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.”

Image: Three Brown Dwarfs

Image of wispy pink-purple hair-like filaments and a scattering of stars, with three image details pulled out in square boxes stacked vertically along the right.
This image from the NIRCam (Near-Infrared Camera) instrument on NASA’s James Webb Space Telescope shows the central portion of the star cluster IC 348. Astronomers combed the cluster in search of tiny, free-floating brown dwarfs: objects too small to be stars but larger than most planets. They found three brown dwarfs that are less than eight times the mass of Jupiter, which are circled in the main image and shown in the detailed pullouts at right. The smallest weighs just three to four times Jupiter, challenging theories for star formation.
NASA, ESA, CSA, STScI, K. Luhman (Penn State University), and C. Alves de Oliveira (ESA)

Brown Dwarf or Rogue Planet?

Since the objects are well within the mass range of giant planets, it raises the question of whether they are actually brown dwarfs, or if they’re really rogue planets that were ejected from planetary systems. While the team can’t rule out the latter, they argue that they are far more likely to be a brown dwarf than an ejected planet.

An ejected giant planet is unlikely for two reasons. First, such planets are uncommon in general compared to planets with smaller masses. Second, most stars are low-mass stars, and giant planets are especially rare among those stars. As a result, it’s unlikely that most of the stars in IC 348 (which are low-mass stars) are capable of producing such massive planets. In addition, since the cluster is only 5 million years old, there probably hasn’t been enough time for giant planets to form and then be ejected from their systems.

The discovery of more such objects will help clarify their status. Theories suggest that rogue planets are more likely to be found in the outskirts of a star cluster, so expanding the search area may identify them if they exist within IC 348.

Future work may also include longer surveys that can detect fainter, smaller objects. The short survey conducted by the team was expected to detect objects as small as twice the mass of Jupiter. Longer surveys could easily reach one Jupiter mass.

These observations were taken as part of Guaranteed Time Observation program 1229. The results were published in the Astronomical Journal.

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

Media Contacts

Laura Betzlaura.e.betz@nasa.gov, Rob Gutrorob.gutro@nasa.gov
NASA’s  Goddard Space Flight Center, Greenbelt, Md.

Hannah Braun hbraun@stsci.edu , Christine Pulliamcpulliam@stsci.edu
Space Telescope Science Institute, Baltimore, Md.

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Related Information

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More Webb Images – https://science.nasa.gov/mission/webb/multimedia/images/

Webb Mission Page – https://science.nasa.gov/mission/webb/

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6 Min Read

NASA’s Webb Identifies Tiniest Free-Floating Brown Dwarf

Image showing wispy pink-purple filaments and a scattering of stars.
This image from the NIRCam (Near-Infrared Camera) instrument on NASA’s James Webb Space Telescope shows the central portion of the star cluster IC 348. The wispy curtains filling the image are interstellar material reflecting the light from the cluster’s stars – what is known as a reflection nebula. The material also includes carbon-containing molecules known as polycyclic aromatic hydrocarbons, or PAHs. Winds from the most massive stars in the cluster may help sculpt the large loop seen on the right side of the field of view.
Credits: NASA, ESA, CSA, STScI, K. Luhman (Penn State University), and C. Alves de Oliveira (ESA)

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      Espinoza and co-principal investigator Natalie Allen of Johns Hopkins University are leading a team that is currently making 15 additional observations of planet e, with an innovative twist. The scientists are timing the observations so that Webb catches both planets b and e transiting the star one right after the other. After previous Webb observations of planet b, the planet orbiting closest to TRAPPIST-1, scientists are fairly confident it is a bare rock without an atmosphere. This means that signals detected during planet b’s transit can be attributed to the star only, and because planet e transits at nearly the same time, there will be less complication from the star’s variability. Scientists plan to compare the data from both planets, and any indications of chemicals that show up only in planet e’s spectrum can be attributed to its atmosphere. 
      “We are really still in the early stages of learning what kind of amazing science we can do with Webb. It’s incredible to measure the details of starlight around Earth-sized planets 40 light-years away and learn what it might be like there, if life could be possible there,” said Ana Glidden, a post-doctoral researcher at Massachusetts Institute of Technology’s Kavli Institute for Astrophysics and Space Research, who led the research on possible atmospheres for planet e. “We’re in a new age of exploration that’s very exciting to be a part of,” she said.
      The four transits of TRAPPIST-1 e analyzed in the new papers published today were collected by the JWST Telescope Scientist Team’s DREAMS (Deep Reconnaissance of Exoplanet Atmospheres using Multi-instrument Spectroscopy) collaboration.
      The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).
      To learn more about Webb, visit:
      https://science.nasa.gov/webb
      Related Information
      Webb Blog: Reconnaissance of Potentially Habitable Worlds with NASA’s Webb
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      Video: How do we learn about a planet’s Atmosphere?
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      Trappist-1 e (Artist’s Concept)
      This artist’s concept shows the volatile red dwarf star TRAPPIST-1 and its four most closely orbiting planets, all of which have been observed by NASA’s James Webb Space Telescope. Webb has found no definitive signs of an atmosphere around any of these worlds yet.


      TRAPPIST-1 e Transmission Spectrum (NIRSpec)
      This graphic compares data collected by Webb’s NIRSpec (Near-Infrared Spectrograph) with computer models of exoplanet TRAPPIST-1 e with (blue) and without (orange) an atmosphere. Narrow colored bands show the most likely locations of data points for each model.




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      Last Updated Sep 08, 2025 Editor Marty McCoy Contact Laura Betz laura.e.betz@nasa.gov Location NASA Goddard Space Flight Center Contact Media Laura Betz
      NASA’s Goddard Space Flight Center
      Greenbelt, Maryland
      laura.e.betz@nasa.gov
      Leah Ramsay
      Space Telescope Science Institute
      Baltimore, Maryland
      Hannah Braun
      Space Telescope Science Institute
      Baltimore, Maryland
      Related Terms
      James Webb Space Telescope (JWST) Exoplanets
      Related Links and Documents
      The science paper by N. Espinoza et al. The science paper by A. Glidden et al. JWST Telescope Science Team

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    • By NASA
      Explore Webb Webb News Latest News Latest Images Webb’s Blog Awards X (offsite – login reqd) Instagram (offsite – login reqd) Facebook (offsite- login reqd) Youtube (offsite) Overview About Who is James Webb? Fact Sheet Impacts+Benefits FAQ Webb Timeline Science Overview and Goals Early Universe Galaxies Over Time Star Lifecycle Other Worlds Science Explainers Observatory Overview Launch Deployment Orbit Mirrors Sunshield Instrument: NIRCam Instrument: MIRI Instrument: NIRSpec Instrument: FGS/NIRISS Optical Telescope Element Backplane Spacecraft Bus Instrument Module Multimedia About Webb Images Images Videos What is Webb Observing? 3d Webb in 3d Solar System Podcasts Webb Image Sonifications Webb’s First Images Team International Team People Of Webb More For the Media For Scientists For Educators For Fun/Learning 5 Min Read Glittering Glimpse of Star Birth From NASA’s Webb Telescope
      Webb captured this sparkling scene of star birth in Pismis 24. Full image and caption below. Credits:
      Image: NASA, ESA, CSA, STScI; Image Processing: A. Pagan (STScI) This is a sparkling scene of star birth captured by NASA’s James Webb Space Telescope. What appears to be a craggy, starlit mountaintop kissed by wispy clouds is actually a cosmic dust-scape being eaten away by the blistering winds and radiation of nearby, massive, infant stars.
      Called Pismis 24, this young star cluster resides in the core of the nearby Lobster Nebula, approximately 5,500 light-years from Earth in the constellation Scorpius. Home to a vibrant stellar nursery and one of the closest sites of massive star birth, Pismis 24 provides rare insight into large and massive stars. Its proximity makes this region one of the best places to explore the properties of hot young stars and how they evolve.
      At the heart of this glittering cluster is the brilliant Pismis 24-1. It is at the center of a clump of stars above the jagged orange peaks, and the tallest spire is pointing directly toward it. Pismis 24-1 appears as a gigantic single star, and it was once thought to be the most massive known star. Scientists have since learned that it is composed of at least two stars, though they cannot be resolved in this image. At 74 and 66 solar masses, respectively, the two known stars are still among the most massive and luminous stars ever seen.
      Image A: Pismis 24 (NIRCam Image)
      Webb captured this sparkling scene of star birth in Pismis 24, a young star cluster about 5,500 light-years from Earth in the constellation Scorpius. This region is one of the best places to explore the properties of hot young stars and how they evolve. Image: NASA, ESA, CSA, STScI; Image Processing: A. Pagan (STScI) Captured in infrared light by Webb’s NIRCam (Near-Infrared Camera), this image reveals thousands of jewel-like stars of varying sizes and colors. The largest and most brilliant ones with the six-point diffraction spikes are the most massive stars in the cluster. Hundreds to thousands of smaller members of the cluster appear as white, yellow, and red, depending on their stellar type and the amount of dust enshrouding them. Webb also shows us tens of thousands of stars behind the cluster that are part of the Milky Way galaxy.
      Super-hot, infant stars –some almost 8 times the temperature of the Sun – blast out scorching radiation and punishing winds that are sculpting a cavity into the wall of the star-forming nebula. That nebula extends far beyond NIRCam’s field of view. Only small portions of it are visible at the bottom and top right of the image. Streamers of hot, ionized gas flow off the ridges of the nebula, and wispy veils of gas and dust, illuminated by starlight, float around its towering peaks.
      Dramatic spires jut from the glowing wall of gas, resisting the relentless radiation and winds. They are like fingers pointing toward the hot, young stars that have sculpted them. The fierce forces shaping and compressing these spires cause new stars to form within them. The tallest spire spans about 5.4 light-years from its tip to the bottom of the image. More than 200 of our solar systems out to Neptune’s orbit could fit into the width its tip, which is 0.14 lightyears.
      In this image, the color cyan indicates hot or ionized hydrogen gas being heated up by the massive young stars. Dust molecules similar to smoke here on Earth are represented in orange. Red signifies cooler, denser molecular hydrogen. The darker the red, the denser the gas. Black denotes the densest gas, which is not emitting light. The wispy white features are dust and gas that are scattering starlight.
      Video A: Expedition to Star Cluster Pismis 24
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      supports HTML5 video
      This scientific visualization takes viewers on a journey to a glittering young star cluster called Pismis 24. NASA’s James Webb Space Telescope captured this fantastical scene in the heart of the Lobster Nebula, approximately 5,500 light-years from Earth. Video: NASA, ESA, CSA, STScI, Leah Hustak (STScI), Christian Nieves (STScI); Image Processing: Alyssa Pagan (STScI); Script Writer: Frank Summers (STScI); Narration: Frank Summers (STScI); Music: Christian Nieves (STScI); Audio: Danielle Kirshenblat (STScI); Producer: Greg Bacon (STScI); Acknowledgment: VISTA Video B: Zoom to Pismis 24
      This zoom-in video shows the location of the young star cluster Pismis 24 on the sky. It begins with a ground-based photo of the constellation Scorpius by the late astrophotographer Akira Fujii. The sequence closes in on the Lobster Nebula, using views from the Digitized Sky Survey. As the video homes in on a select portion, it fades to a VISTA image in infrared light. The zoom continues in to the region around Pismis 24, where it transitions to the stunning image captured by NASA’s James Webb Space Telescope in near-infrared light.
      Video: NASA, ESA, CSA, STScI, Alyssa Pagan (STScI); Narration: Frank Summers (STScI); Script Writer: Frank Summers (STScI); Music: Christian Nieves (STScI); Audio: Danielle Kirshenblat (STScI); Producer: Greg Bacon (STScI); Acknowledgment: VISTA, Akira Fujii, DSS The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).
      To learn more about Webb, visit:
      https://science.nasa.gov/webb
      Downloads
      Click any image to open a larger version.
      View/Download all image products at all resolutions for this article from the Space Telescope Science Institute.
      Media Contacts
      Laura Betz – laura.e.betz@nasa.gov
      NASA’s Goddard Space Flight Center, Greenbelt, Md.
      Ann Jenkins – jenkins@stsci.edu
      Space Telescope Science Institute, Baltimore, Md.
      Related Information
      Read more about Hubble’s view of Pismis 24
      Listen to a sonification of Hubble’s view of Pismis 24
      Animation Video: “How Dense Pillars Form in Molecular Clouds”
      Read more: Webb’s Star Formation Discoveries
      More Webb News
      More Webb Images
      Webb Science Themes
      Webb Mission Page
      Related For Kids
      What is the Webb Telescope?
      SpacePlace for Kids
      En Español
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      NASA en español 
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      Webb is the premier observatory of the next decade, serving thousands of astronomers worldwide. It studies every phase in the…


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      Last Updated Sep 04, 2025 Related Terms
      James Webb Space Telescope (JWST) View the full article
    • By European Space Agency
      The NASA/ESA/CSA James Webb Space Telescope has revealed new details in the core of the Butterfly Nebula, NGC 6302. From the dense, dusty torus that surrounds the star hidden at the centre of the nebula to its outflowing jets, the Webb observations reveal many new discoveries that paint a never-before-seen portrait of a dynamic and structured planetary nebula.
      View the full article
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