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There are many types of stars in the great and vast Universe. We have a whole system to categorize them according to temperature, size and brightness.
Still, a recently discovered object suggests that we are far from knowing everything.
It’s been nicknamed “The Accident”, and it’s a type of object called a brown dwarf, also known as failed stars. But she’s unlike any brown dwarf we’ve ever seen before, with a confusing specter – suggesting she could be almost as old as the Universe.
Considering that all of the other brown dwarfs discovered to date are considerably younger, this means that there could be a whole population of very old dwarfs that we just haven’t spotted because they don’t look like this. that we expect from them.
“This object has defied all of our expectations,” said astrophysicist Davy Kirkpatrick of Caltech.
Brown dwarfs occupy the space between the more massive planets and the smallest stars, forming from the same pattern of descending cloud collapse as stars, rather than the ascending process of accretion that the stars undergo. planets.
This is what happens when the star-forming process ends before the object gains sufficient mass to ignite the fusion of hydrogen in the nucleus.
However, unlike planets, they are massive enough to merge something, and that something is deuterium, that is, “heavy” hydrogen.
Deuterium is an isotope of hydrogen with one proton and one neutron in the nucleus instead of a single proton. Its melting temperature and pressure are lower than the melting temperature and pressure of hydrogen.
As a result, brown dwarfs tend to be smaller, cooler, and darker than most stars. Their mass range is between about 13 and 80 times the mass of Jupiter, and they cool down as they age.
So we have a pretty good understanding of what a brown dwarf should look like and we are looking for them based on that set of characteristics.
This weak and moving object in the lower left is The Accident. (NASA / JPL-Caltech / Dan Caselden)
So far, around 2,000 of these objects have been found in the Milky Way. The accident – real name WISEA J153429.75-104303.3 – was not noted in surveys of brown dwarfs because it does not match these characteristics.
Its detection by NASA’s Near-Earth Object Wide-Field Infrared Survey Explorer, and subsequent discovery, was, as the name suggests, an accident.
It really is a very special object. At certain wavelengths it is very weak, suggesting that it is also very cool – below the boiling point of water, in fact – and therefore quite old. In other wavelengths, it glows more intensely, which in turn suggests a higher temperature.
To unravel the mystery, the team turned to a different range of infrared wavelengths, as infrared wavelengths reveal thermal radiation. But observations taken using the WM Keck Earth Observatory did not reveal the crash at all, once again suggesting cooler temperatures.
The distance of the Crash from the Solar System could have been a clue – if he was far, that could explain his unease. But it turned out to be not very far at all, relatively for spatial distances, about 53 light years.
Oddly enough, it zooms around the galaxy very quickly, at speeds of around 207.4 kilometers (128.9 miles) per second. It’s over 25% faster than any other star in the genre.
Like the temperature of the Crash, this speed suggests that the star has been around for a very long time, picking up and accumulating increases in speed due to gravitational interactions with other objects in the galaxy.
The Universe is about 13.8 billion years old. Kirkpatrick’s team calculated that the accident could be between 10 and 13 billion years old, double the median age of the known population of brown dwarfs.
“It’s no surprise to find such an old brown dwarf, but it’s a surprise to find one in our backyard,” said astrophysicist Federico Marocco of Caltech.
“We expected such ancient brown dwarfs to exist, but we also expected them to be incredibly rare. The luck of finding one so close to the solar system could be a happy coincidence, or so it tells us. that they are more common than we thought. “
This venerable age suggests that The Accident’s makeup could also be very different from other brown dwarfs, which is supported by the spectrum of light it emits.
This is because, at the very beginning of the Universe, the range of the elements was much lower. Right after the Big Bang, most of the matter was hydrogen and helium, with very little else.
It took a few generations of stars for more elements to proliferate. They fused atomic nuclei into their nuclei, producing heavier elements, then died, spreading those elements throughout space. Supernova explosions produced even heavier elements through processes that can only be found in such energetic events.
If the Crash existed before these elements (including carbon) were no longer prevalent in the Universe, then its light would be stronger in specific wavelengths that would normally be absorbed by methane (made up of carbon and d ‘hydrogen) in the atmosphere of a brown dwarf. This is exactly what the researchers observed.
“This finding tells us that there is more variety in brown dwarf compositions than we’ve seen so far,” Kirkpatrick said.
“There are probably more weird ones out there, and we need to think about how to look for them.”
The research was published in Letters from the astrophysical journal.
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