Certain cosmic entities lack the necessary attributes to evolve into stars. Specifically, they are insufficiently massive to initiate nuclear fusion at their cores. These objects are known as brown dwarfs. In the Milky Way, a few thousand brown dwarfs have been identified, yet none have been observed beyond our galaxy. Their cool temperatures make them exceptionally challenging to detect at vast distances.

Enter the James Webb Space Telescope (JWST), with its unparalleled sensitivity and clarity. Astronomers aimed the telescope at NGC 602, a nascent stellar assembly in the Small Magellanic Cloud—a neighboring galaxy situated 200,000 light-years from Earth and observable from the Southern Hemisphere. Within this region, the team uncovered objects aligning with the characteristics of brown dwarfs.

“Until now, our knowledge extended to about 3,000 brown dwarfs, all confined to our own galaxy,” noted Elena Manjavacas of AURA/STScI, representing the European Space Agency, in a press release.

Brown dwarfs are essentially heftier siblings of gas giant planets, with masses ranging between 13 and 75 times that of Jupiter. However, the classification is somewhat fluid. The boundary distinguishing gas giants from brown dwarfs is imprecise. For instance, JWST identified objects likely to be brown dwarfs but comparable in size to Jupiter. The ability to detect such minuscule entities in an entirely different galaxy is extraordinary.

“Thanks to the remarkable sensitivity and resolution across the appropriate wavelength spectrum, we can now discern these objects at immense distances,” stated lead researcher Peter Zeidler of AURA/STScI, affiliated with the European Space Agency. “This capability is unprecedented and remains beyond the reach of terrestrial telescopes for the foreseeable future.”

The findings highlighted the complementary strengths of Hubble and JWST. Hubble revealed that this stellar cluster contained numerous young, low-mass stars, while JWST provided detailed imaging that unveiled individual brown dwarf candidates.

A key distinction between brown dwarfs and planets lies in their formation. If an object originates from a collapsing clump of gas, it qualifies as a brown dwarf. Conversely, if it assembles incrementally, aggregating smaller fragments and gas, it is considered a planet. These newfound candidates appear to have formed like stars, reinforcing their classification as brown dwarfs, yet their resemblance to exoplanets could yield groundbreaking insights.

“Brown dwarfs seem to emerge in a manner akin to stars, but they fail to accumulate sufficient mass to ignite into full-fledged stars. Our findings strongly align with this hypothesis,” commented Zeidler. “These represent the first analogues to massive exoplanets identified outside the Milky Way,” added Manjavacas. “We stand on the brink of revolutionary discoveries regarding these enigmatic objects!”

The results have been published in The Astrophysical Journal.