by Using the James Webb Space Telescope (JWST), astronomers have made the surprising discovery of methane emissions coming from a brown dwarf, or “failed star.”
The discovery suggests that the brown dwarf has aurorae, and may even be orbiting an undiscovered exomoon, researchers said.
The JWST brown dwarf discovery is surprising, as these cold, remote worlds are not expected to be hot enough for methane to emit infrared light.
The findings were the result of the JWST program to investigate 12 brown dwarfs. They suggest that these failed stars can generate aurorae similar to Earth’s northern lights and southern lights, as well as those seen over Jupiter and Saturn. The lack of stars near this lonely brown dwarf could mean that the bright lights above it are being generated by an active, hidden moon.
Related: James Webb Space Telescope hints at mysterious aurora over ‘failed star’
The study team investigated the cold brown dwarf CWISEP J193518.59–154620.3 (W1935), located 47 light years from Earth. Although the mass of W1935 is poorly constrained, between 6 and 35 times that of Jupiter, its surface temperature is known to be about 400 degrees Fahrenheit (204 degrees Celsius). That is approximately the temperature at which you want to bake chocolate chip cookies (failed bronies?).
“Methane gas is expected in giant planets and brown dwarfs, but we usually see it absorbing light, not glowing,” said Jackie Faherty, team leader and senior education manager at the American Museum of Natural History, in a statement. “We were confused about what we were seeing at first, but eventually, transformed into pure excitement at the discovery.”
Why do some stars fail?
Brown dwarfs get their unfortunate nickname of “failed stars” because, despite having formed directly from a cloud of gas and dust like a collapsing star, they lack enough mass to fuel the nuclear fusion of hydrogen into helium at their cores.
This is the process that defines what a main sequence star is, so brown dwarfs – with masses greater than the largest planets but less than the smallest star – technically “fail” to achieve this status .
Faherty and his colleagues were looking at several brown dwarfs with JWST when they noticed that W1935 was similar, but with one interesting difference: It is emitting methane, something never seen before around a failed star.
The W1935 modeling also showed a so-called “temperature inversion” for this particular brown dwarf. That’s a phenomenon where a planet’s atmosphere becomes cooler at deeper levels. This is something that is usually seen on planets orbiting stars whose atmospheres pass from the top down, but was not expected for W1935 because the brown dwarf is isolated, and has no external heat source.
“We were surprised when the model clearly predicted a temperature inversion,” team member and University of Hertfordshire scientist Ben Burningham said in the statement. “But we also had to figure out where the extra heat in the upper atmosphere was coming from.”
To solve this mystery, the team looked closer to home at the solar system’s gas giants, Jupiter and Saturn. Both of these gas giants emit methane, and both have atmospheres that show a temperature inversion.
In the case of Jupiter and Saturn, aurorae are the cause of methane emissions and temperature inversions, which Faherty and team conclude were detected by the JWST around W1935. The big question is, what is driving the aurora at W1935?
This is an issue, because the solar wind — the stream of charged particles from the sun — is the main driver of aurorae for Jupiter, Saturn and Earth. These hit the planets’ magnetic fields and travel down field lines, interacting with particles in the atmosphere. This heats the upper layers of the atmosphere and causes the emission of light near the poles of the planet. With no host star to blast W1935 with large winds, however, this process cannot be the main driver of the lonely brown dwarf’s aurora.
However, the Jupiter and Saturn auroras have a minor secondary driver, in the form of charged particles streaming into the gas giants as a result of their active moons spewing material into space. For example, Jupiter’s moon Io is the largest volcanic body in the solar system, spewing lava thousands of miles into space, and Saturn’s moon Enceladus throws geysers into space containing water vapor and other material that freezes and boils when it hits space.
Thus, the aurora of W1935 with no interstellar wind or stellar winds indicates that the brown dwarf may have an active moon.
Related: Are they exomoons or not? Scientists debate the first moon seen outside our solar system
RELATED STORIES:
— James Webb Space Telescope spies record-breaking ‘failed star’ that shouldn’t exist (video)
— Volunteers observe nearly 100 cool-brown dwarfs near our sun
— A ‘failed star’ is the coolest source of radio waves ever discovered
More evidence will be needed before scientists can confirm the existence of a brown dwarf moon for the first time. Until then, these early indications give a glimpse of just how impactful the JWST has been since it began sending its observations of Earth back to Earth in the summer of 2022.
“Every time a JWST astronomer focuses on something, there’s a chance you’ll make a mind-blowing new discovery,” Faherty concluded. “Methane emissions weren’t on my radar when we started this project, but now that we know it could be there and the explanation is so enticing, I’m always on the lookout for it. That’s part of the how science proceeds.”
The team’s research was published today (April 17) in the journal Nature.
