The brown dwarf is seen as a stellar failure, a dropout from the school of star formation. These gigantic objects, with their puffy, gaseous outer layers, are the universe’s students that didn’t quite make the grade. In brown dwarfs, nuclear fusion – the process that gives stars their power – has given up the ghost, leaving them relatively cold, with some no hotter than the human body. Neither planet nor star, brown dwarfs fall into the grey area between the most massive gas giant planets like Jupiter – hence why they’re known as ‘super-Jupiters’, because of their massive, gaseous nature – and the smallest stars. Their existence blurs the lines between what is a planet and what is a star, forcing us to question the differences between how planets and stars form.
Stars form when clouds of molecular gas collapse under gravity and condense until the pressure and temperature at the center of the cloud is so great that nuclear fusion reactions – which turn nuclei of the element hydrogen into heavier helium nuclei – ignite. This kind of top-down formation is one of the key differences between how stars and planets form. Meanwhile, the worlds of our Solar System and many others that astronomers have been studying over the past 25 years form through a bottom-up process, where a core gradually builds up, becoming bigger and bigger. For the most massive planets, the core has enough gravity to begin stealing gas from the proto-stellar nebula around it, and this is where gas giants such as Jupiter and Saturn got their hefty atmospheres.
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Denne historien er fra Issue 113-utgaven av All About Space.
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15 AUTUMN STARGAZING TARGETS
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MYSTERIES OF THE UNIVERSE WHY IS VENUS SO DRY?
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WHEN BLACK HOLES TURN WHITE
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THE MOON'S THIN ATMOSPHERE IS MADE BY CONSTANT METEORITE BOMBARDMENT
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Having explored much of the Solar System, attention is now turning to the stars beyond
NASA'S PERSEVERANCE ROVER FINDS POSSIBLE SIGNS OF ANCIENT RED PLANET LIFE
Further analysis is needed, but a rock contains potential evidence that life once existed on Mars in the distant past
A NASA TELESCOPE MAY HAVE FOUND ANTIMATTER ANNIHILATING IN POSSIBLY THE BIGGEST EXPLOSION SINCE THE BIG BANG
The massive explosion was captured in 2022
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Jameel Janjua made it to the bitter end in a Canadian government astronaut selection in 2009, but wasn't chosen. He found a different path to space through Virgin Galactic
BOEING NEEDS TO IMPROVE QUALITY CONTROL ON THE SLS MOON ROCKET
The NASA Inspector General's report finds serious quality-control issues affecting the upgraded version and expects cost overruns and delays
DARK ENERGY
THE MOST DOMINANT FORCE IN THE UNIVERSE IS ALSO ITS MOST MYSTERIOUS AND MOST UNANTICIPATED