BBC News Science and Environment
Aurora found around brown dwarf beyond our Solar System
By Rebecca Morelle Science Correspondent, BBC News
This artist's impression shows the brown dwarf's aurora, which is red and extremely bright
An aurora has been spotted outside our Solar System for the first time, scientists report.
An international team detected the light display around a brown dwarf about 18 light years away
in the Lyra constellation.
They say the luminous glow looks like the northern lights, but is up to a million times brighter and
more red than green in colour.
The findings are reported in the journal Nature.
Dr Stuart Littlefair, an astronomer from the University of Sheffield, said: "This is the first time that
we have confirmed we are seeing auroras on brown dwarves."
Shimmering auroras are some of the Earth's most dazzling displays. This luminous glow can also
appear around all the planets in our Solar System.
The brightness changes are consistent with what you would expect from
auroras Dr Stuart Littefair, University of Sheffield
They are caused when charged particles from the Sun interact with the atmosphere.
But the illuminated brown dwarf, an object which is too small to have become a star but too
massive to be a planet, lies further out in the galaxy.
Called LSR J1835, it was observed using the Very Large Array radio telescope and the Hale and
Keck optical telescopes.
The scientists watched the object as it rapidly rotated, and observed how the light varied.
"The brightness changes are consistent with what you would expect from auroras," said Dr
Littlefair.
On Earth, the green hue is caused when the Sun's charged particles interact with oxygen in the
atmosphere
The dwarf's aurora is mainly red in colour because the charged particles are mainly interacting
with hydrogen in its atmosphere. On Earth, the greenish glow is caused as the electrons from the
Sun hit oxygen atoms.
It is yet more reason to consider brown dwarves as scaled-up versions of
planets rather than scaled-down version of stars Dr Stuart Littlefair, University
of Sheffield
However, scientists are puzzled about how the light show is being generated.
The brown dwarf is a sort of failed star itself, and has no other star like the Sun nearby to blast it
with charged particles.
"It is possible material is being stripped off the surface of the brown dwarf to produce its own
electrons," said Dr Littlefair.
Another option is an as-yet-undetected planet or moon around the dwarf is throwing off material
to light it up.
Some of Jupiter's auroras are produced in this way, as charged particles are emitted from
volcanoes on its moon Io.
Some auroras on Jupiter are produced by material emitted from its moon Io
The discovery is also helping scientists to better understand brown dwarves.
There is some debate over whether they are more star-like in their nature, or whether they have
planetary attributes.
"If you are working in brown dwarves, it matters whether you think of them as small stars or big
planets," said Dr Littlefair.
"We already known from observations of brown dwarves that they have clouds in the
atmosphere. Now we know they also show auroras, it is yet more reason to consider brown
dwarves as scaled-up versions of planets rather than scaled-down version of stars."
Reference
BBC (2015) Aurora found around brown dwarf beyond our solar system ‘http://www.bbc.co.uk
accessed 30/07/2015