First aurora beyond the solar system

Astronomers discover aurora on a brown dwarf

This is how the Northern Lights of the Brown Dwarf LSR J1835 + 3259 could look up close © Chuck Carter and Gregg Hallinan / Caltech
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Glowing Veils: For the first time, astronomers have discovered a polar light on a celestial body beyond our solar system - on a brown dwarf 18 light-years away. These Aurors are likely to be created similar to the gas giant Jupiter. This in turn confirms that brown dwarfs are in some ways more like big planets than little stars, according to researchers in the journal Nature.

The Earth has them, Saturn, Jupiter and even our neighbor Mars: the fascinating phenomenon of the Northern Lights can be seen in our cosmic neighborhood right next to several planets. However, while the aurors in our solar system are quite well studied, it remained unclear whether there are such auroras on objects outside our solar system - and in what form.

Noticeable radio signals

This has changed now. Gregg Hallinan of the California Institute of Technology (Caltech) in Pasadena and his colleagues first detected a polar light on a celestial body outside the solar system: on a brown dwarf. These are considered failed stars because their mass is insufficient to ignite nuclear fusion inside. They therefore move in the border area between real stars and large gas planets.

When the astronomers targeted the Brown Dwarf LSR J1835 + 3259 with the radio telescopes of the Very Large Array (VLA), they registered conspicuous, pulsed radio signals. Even with optical telescopes they observed pulsating radiation emissions in time with the rotation period of the dwarf. From the location of the radiation source in the atmosphere and the spectroscopic properties, the researchers conclude that it must be a polar light.

This makes it clear that polar lights are not a feature of the solar system alone. Instead, this form of magnetic interaction may well be typical of low-mass celestial bodies such as brown dwarfs and exoplanets, the researchers said. display

Northern Lights on Jupiter NASA, J. Clarke / University of Michigan

Similar to Jupiter

However, the aurora now discovered on LSR J1835 + 3259 does not develop in the same way as on Earth. Here, these luminous phenomena occur because the field lines of the magnetic field near the poles are almost perpendicular to the earth's surface. As a result, the charged particles of the solar wind can continue to penetrate into the upper atmosphere, excite gas particles and make them glow.

But with the brown dwarf there is no solar wind from the outside. The astronomers therefore suspect that interactions within the dwarf's atmosphere trigger the aurors, similar to some polar lights of the gas giant Jupiter. "What we see on this object seems to be the same phenomenon that we observe on Jupiter - only thousands of times stronger, " explains Hallinan. On the gas giant, the aurors are formed, inter alia, by the interaction of the rotating magnetic field with plasma flows in the hydrogen atmosphere of the planet.

Astronomers suspect that this type of magnetic activity also occurs on many larger extrasolar planets. "These are good conditions for looking for similar emissions in exoplanets, " said Hallinan and his colleagues. The brown dwarf could even have another player in play: a previously undiscovered planet in orbit. He could trigger the plasma flows in his gas pocket, driving the auroras with them. "But unless we have mapped the aurora more closely, we can not say how it will come about, " says Hallinan.

Also for weather phenomena on brown dwarfs?

The brown lights of the Brown Dwarf and their magnetic causes may even explain some of the recently discovered weather phenomena on brown dwarfs. For a brown dwarf only seven light-years away from us has water clouds and striking currents in the atmosphere. "We suspect that the magnetic currents generated by the Aurors could also drive the more extreme weather phenomena of the Brown Dwarfs, " the researchers said.

According to the researchers, the newly discovered polar lights also shed new light on the nature of the brown dwarfs. "Brown dwarfs lie in the gap between stars and planets, " says co-author Stuart Littlefair of the University of Sheffield. "These results are further evidence that we should see brown dwarfs as 'inflated planets' rather than failed stars." (Nature, 2015; doi: 10.1038 / nature14619)

(National Radio Astronomy Observatory / Nature, 30.07.2015 - NPO)