James Webb noticed the aurora on a brown dwarf

NASA’s James Webb Space Telescope (JWST) has helped astronomers discover a brown dwarf called W1935 with signs of aurorae in its atmosphere.

The artist’s concept depicts the brown dwarf W1935, which is located 47 light-years from Earth. Photo: NASA, ESA, CSA

Aurorae usually occur as a result of the interaction of charged particles from the Sun with the Earth’s atmosphere. They are observed at high latitudes due to the influence of the magnetosphere, which directs particles to the poles. 

Other planets and their moons in the Solar System, such as Jupiter and Saturn, are also marked by aurorae, probably caused by the interaction of solar particles. However, W1935, located 47 light-years from Earth, turned out to be lonely, without stars that could supply charged particles to form the aurora.

Unexpected discovery of James Webb

Brown dwarfs are larger than gas giants and smaller than stars. They are formed from collapsing clouds of gas and dust, but they do not have enough mass to trigger the nuclear fusion of hydrogen in their hearts. That is why they are called “unborn stars”.

The potential aurora over W1935 was indicated by the infrared radiation of methane recorded by James Webb. When similar methane emissions are observed over Jupiter and Saturn, they are the result of atmospheric heating, when charged particles penetrate magnetic field lines and hit atmospheric particles, also creating aurorae. The research team believes that the same thing is happening with this isolated brown dwarf.

In the absence of an external solar wind that could cause the aurora, the team believes that an unknown internal process may be taking place inside the brown dwarf, supplying energy to its atmosphere. In addition, interstellar plasma could hit W1935, or the brown dwarf may not be completely isolated and receive an influx of particles from a nearby active moon, which remains unnoticed by James Webb instruments.

Anomaly of dwarf twins

A research team led by astronomer Jackie Faherty from the American Museum of Natural History has discovered that the brown dwarf W1935 is similar to the “twin brother” W2220. Both dwarfs have the same temperature and brightness and are almost identical in composition to water, ammonia, carbon monoxide and dioxide, and carbon dioxide. However, W1935 emits methane, which glows in the infrared range, whereas W2220 absorbs light with this substance.

Astronomers used the James Webb Space Telescope to study 12 cold brown dwarfs. Two of them — W1935 and W2220 — turned out to be close twins of each other in composition, brightness and temperature. However, W1935 demonstrated methane emissions in contrast to the expected absorption characteristic that was observed in the direction of W2220. The team suggests that the methane release may be caused by processes that cause aurorae. Illustration: NASA, ESA, CSA

Simulations of the atmospheres of brown dwarfs have shown that W2220 cools with altitude, whereas W1935 demonstrates temperature inversion – heating at high altitudes. This phenomenon has previously been observed on planets with a nearby star, but its presence in a brown dwarf without an external heat source is astounding to astronomers. 

Scientists have theorized that the temperature inversion in the atmospheres of brown dwarfs may be the result of heating by the same process that causes the aurora. This discovery, recorded by JWST, allows them to gain a new perspective on the chemistry and physics of similar objects outside our Solar System.

Earlier, we reported on how the Aurora shone over the dark spot of the Sun.

According to NASA

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