There are many types of stars in the large and wide Universe. We have a whole system to classify them according to temperature, size and brightness.
However, a recently discovered object suggests that we are far from knowing everything.
It has been christened “The Accident” and is a type of object called a brown dwarf, also known as a failed star. But it doesn’t look like any brown dwarf we’ve ever seen, with a confusing spectrum, suggesting it may be almost as old as the Universe.
Since all the other brown dwarfs discovered so far are considerably younger, this means that there may be a whole population of very old people that we just haven’t seen because they don’t look like we expect.
“This object defied all our expectations,” said astrophysicist Davy Kirkpatrick of Caltech.
Brown dwarfs occupy the space between the most massive planets and the smallest stars, forming from the same top-down cloud collapse pattern as stars, rather than the bottom-up accretion process. above that the planets experience.
They are what happens when the process of star formation ends before the object gets too large enough to ignite the fusion of hydrogen in the nucleus.
However, unlike the planets, they are massive enough to fuse something, and this is deuterium, also known as “heavy” hydrogen.
Deuterium is an isotope of hydrogen with a proton and a 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 dimmer than most stars. Their mass range ranges from 13 to 80 times the mass of Jupiter and they cool as they age.
So we have a good understanding of what a brown dwarf should look like and we look for them based on this set of characteristics.
This faint object moving to the bottom left is The Accident. (NASA / JPL-Caltech / Dan Caselden)
To date, about 2,000 of these objects have been found in the Milky Way. The crash, whose real name is WISEA J153429.75-104303.3, was not collected in brown dwarf surveys because it does not match these characteristics.
Its detection by NASA’s Wide Field Infrared Explorer of objects close to Earth and its subsequent discovery were, as its name suggests, an accident.
It really is a very peculiar object. At some wavelengths, it is very weak, suggesting that it is also very cool (in fact, below the boiling point of water) and therefore quite old. At other wavelengths, it shines brighter, which in turn suggests a higher temperature.
To unravel the mystery, the team went to a different range of infrared wavelengths, as infrared wavelengths reveal thermal radiation. But observations made with the WM Keck Earth Observatory did not reveal the crash at all, once again suggesting lower temperatures.
The distance of the accident to the solar system could have been a clue: if it were far away, this could explain its weakness. But it turned out not to be very far, relatively for space distances, about 53 light-years away.
Interestingly, it zooms around the galaxy very fast, at speeds of about 207.4 kilometers (128.9 miles) per second. This is more than 25 percent faster than any other star of its kind.
Like the temperature of the crash, this speed suggests that the star has existed for a long time, catching and accumulating velocity impulses from gravitational interactions with other objects in the galaxy.
The Universe is about 13.8 billion years old. The Kirkpatrick team estimated that the crash could be between 10 and 13 billion years old, twice the average age of the known brown dwarf population.
“It’s no surprise to find such an old brown dwarf, but it’s a surprise to find her in our garden,” said astrophysicist Federico Marocco of Caltech.
“We expected brown dwarfs of this old man to exist, but we also expected them to be incredibly rare. The possibility of finding one so close to the solar system could be a coincidence, or tell us they are more common than we thought. “
This venerable age suggests that the composition of The Accident may also be very different from that of other brown dwarfs, which rests on the spectrum of light it emits.
This is because, in the very early universe, the range of elements was much lower. Right after the Big Bang, most of the issue 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, and then died, spreading them through space. Supernova explosions produced even heavier elements through processes that can only be found in such energetic events.
If the accident existed before these elements (including carbon) were more common in the Universe, their light would be stronger at specific wavelengths that would normally be absorbed by methane (made of carbon and hydrogen) in the universe. atmosphere of a brown dwarf. This is exactly what the researchers observed.
“This finding indicates to us that there is more variety of brown dwarf compositions than we have seen so far,” Kirkpatrick said.
“There are probably some weirder ones and we need to think about how to look for them.”
The research has been published in The Astrophysical Journal Letters.