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- BBC News World
They are not completely stars or completely planets, but something in between, and there may be more of them in our galaxy than previously thought.
So says a new study published in the Astrophysical Journal, which focuses on an “enigmatic” new brown dwarf, nicknamed “the accident”, because it was discovered by pure chance.
Brown dwarfs are objects too small to be stars and too large to be considered planets. They are sometimes called “failed stars”.
“This object defied all our expectations,” said Davy Kirkpatrick, co-author and astrophysicist at the California Institute of Technology (Caltech).
The study indicates that the “crash” may be between ten and thirteen billion years old, making it at least twice as old as other previously discovered brown dwarfs.
This suggests that it was formed when our galaxy was much younger and had a different chemical composition.
“If that’s the case, it’s likely that there are many more of these ancient brown dwarfs lurking in our galactic neighborhood,” Kirkpatrick adds.
A different brown dwarf
The “accident”, officially known as WISEA J153429.75-104303.3, was discovered by scientist Dan Caselden by pure luck, as it is unlike any other brown dwarf discovered in the galaxy to date, according to a NASA statement.
As they age, brown dwarfs cool, and their brightness changes at different wavelengths, similar to how hot metals change color as they cool.
The object fascinated scientists because its brightness is not typical of what is seen in other older brown dwarfs.
It emits dim light at certain key wavelengths, indicating that they are very cold, but at the same time it is brighter elsewhere, indicating that these areas are warmer.
“It’s no surprise to find such an old brown dwarf, but it’s a surprise to find one in our garden,” said Federico Marocco, a colleague of Davy Kirkpatrick and co-author of the study.
“We expected brown dwarfs at this age to exist, we also expected them to be incredibly rare,” continues the astrophysicist, who led the observations using the Keck and Hubble telescopes.
800,000 km / h more
Using ground-based telescopes at the WM Keck Observatory in Hawaii, the researchers attempted to observe the “accident” with additional infrared radiation.
But the brown dwarf was so weak that it could not be traced, confirming that it is very cold and therefore very old.
Scientists believe that the speed at which it rotates is further evidence that it has occupied the galaxy for a long time, as it pulls massive objects around that cause its gravity to accelerate.
The “accident” is about fifty light-years from Earth and rotates about 800,000 km / h faster than any other brown dwarf discovered at a similar distance from our planet, according to the study.
Another feature of the ‘crack’, the study notes, is that it contains low levels of methane compared to most other brown dwarfs found, supporting the argument that it was formed over ten billion years ago, when the galaxy was almost exclusively composed of hydrogen and helium, and lacked the carbon needed to create methane.
“The possibility of finding one so close to the solar system may be a happy coincidence, or it may mean that they are more common than we think,” Morocco concludes.