The accidental discovery of a brown dwarf that moves on the border between star and planet, and which they called "The Accident", breaks the astronomers' data so far for these objects.
Dan Caselden woke up late at night, on November 3, 2018, and started playing the video game Counter-Strike, when he wrote an astronomy story. Each time he died, he flew to his laptop to check his automatic search of NASA space telescope images.
Suddenly, in the early hours of the morning, something strange happened. As Kasselden said: "It was very strange. It was moving faster than anything I have discovered. It was pale and fast, which made it very strange. "
Kasselden emailed the astronomers he worked with Backyard Worlds project: Planet 9. As soon as they ruled out that it was a work of art, they realized that they were looking at something completely unusual, an extremely dim object, 50 light-years away, running flaming in the galaxy, at 200 kilometers per second. It was given the name WISE 1534-1043, but due to its unique characteristics and accidental discovery, it soon acquired the nickname “The Accident”.
Astronomers now believe that Kasselden has found a brown dwarf, a failed star that lacks the volume needed to begin nuclear fusion in its core. "It forms like a star," she said Sarah Casewell, however, an astronomer at the University of Leicester in the United Kingdom, "However, it never gains enough mass to merge hydrogen into the sun and start burning anything."
The discovery of the "Accident" showed that we still have a lot to learn about brown dwarfs. These objects range in mass from about 13 times the mass of Jupiter to 75 times or more, but exactly where these two limits are is a constant dilemma.
"Astronomers are constantly arguing about this lower limit," she said Beth Biller, astronomer at the University of Edinburgh in the United Kingdom. While 13 times the mass of Jupiter is about the mass at which it can deuterium fusion takes place (the feature that differentiates brown dwarfs from giant gas planets), the limit can vary. "There is nothing special about the 13 masses of Jupiter," Biller said.
According to Biller, "brown dwarfs also vary greatly in temperature. The hottest have surface temperatures of about 2.000 degrees Celsius. The coldest are below 200 degrees. As they do not have their own heat source, brown dwarfs will gradually cool down, over billions of years at these lower temperatures. Dwarfs, who blur the line between planets and brown dwarfs, can be colder. An object that is called WISE 0855-0714 is below this freezing limit. It is the coldest object we know outside our solar system. "
What a brown dwarf might look like up close is also unclear. Despite their name, it was suggested by astronomer Jill Tarter in 1975, probably not coffee. They are probably more orange or red. "For better or worse, it has stuck as a name," he said Davy Kirkpatrick, astronomer at the California Institute of Technology.
They also have an atmosphere and this atmosphere can show some kind of storms, like on Jupiter. Last year, Biller and her associates used these storms to measure wind speed in a brown dwarf, about 34 light-years away. They first monitored the elements that appeared in its atmosphere as they rotated and then compared this speed by measuring the internal rotation speed of the object, which is collected by its magnetic field. Comparing the two values, the researchers calculated wind speeds of more than 2.300 kilometers per hour, five times faster than Jupiter's winds.
Because brown dwarfs bridge the gap between stars and planets, they can help us understand both. At the top of the mass scale, the boundary between the largest brown dwarfs and the smallest stars can give us information about how nuclear fusion begins.
An object must reach its core at temperatures about 3 million degrees Celsius, to start nuclear fusion, said Nolan Grieves from the University of Geneva in Switzerland. This triggers a chain reaction that converts hydrogen to helium. But no one is exactly sure how much mass it takes for this to happen and where a brown dwarf becomes a star. "There are many aspects of stellar evolution for which our knowledge is still relatively uncertain," Biller said. "Exactly where this fusion limit is is one of those questions."
Recent work led by Nolan Grieves has been identified five high-mass brown dwarfs, with masses between 77 and 98 times greater than that of Jupiter. "They are right on the border where hydrogen fusion begins," Grieves said. However, it is not clear at this time which side of the border these five objects are on. "We do not know the true nature of these objects," Grieves said, "because they are very close to that limit."
Some brown dwarfs may even be so magnetically strong that they could host their own planets. "We know of some dwarf brown systems that look like they have protoplanetary disks around them," Kirkpatrick said. "And there is every indication that there are probably brown dwarfs orbiting their own exoplanets."
At the opposite end of the mass scale of a brown dwarf is "The Accident". It is an extremely small, cold and dim object, "just at the level we could detect it," Kirkpatrick said. Astronomers are eager to find out the difference between a low-mass brown dwarf and a giant massive gas planet. This makes small and dim brown dwarfs, like Accident, useful targets.
The Accident also seems to be made of some strange things. As the universe ages, supernovae spit out heavier elements, such as carbon and oxygen, what astronomers call "metals." Because of this, old objects formed early in the history of the universe tend to have fewer metals, while new objects tend to have more.
However, despite being found in our local solar neighborhood, which hosts mostly young, metal-rich stars, Accident seems to be poor in minerals. "We think this is probably an old brown dwarf, probably created before our Galaxy," Kirkpatrick said. Casewell added that it was probably "one of the first brown dwarfs to form" in our galaxy, coming from the outer galactic halo surrounding our galaxy and then migrating inward.
As with so many other phenomena in our universe, the "Accident" finding emphasizes that these enigmatic and mysterious objects come in all sorts of forms and that placing them in strictly defined categories is not a simple matter.