A team of astrophysicists has discovered a binary pair of ultracool dwarfs so close together they look like a single star.
They are notable because they take only 20.5 hours to orbit each other, meaning their year is less than one Earth day. They are also much older than similar systems.
We can’t see ultracool dwarf stars with the naked eye, but they are the most numerous stars in the galaxy. They have such low masses that they only emit infrared light, and we need infrared telescopes to see them.
These are interesting objects because the theory shows stars this close should exist, but this system is the first time astronomers have observed this extreme closeness.
A team of astronomers presented their findings at the 241st meeting of the American Astronomical Society in Seattle. Chih-Chun “Dino” Hsu, an astrophysicist at Northwestern University, led the research. The system is named LP 413-53AB.
“It’s exciting to find such an extreme system,” said Chih-Chun “Dino” Hsu, a Northwest astrophysicist who led the study. “In principle, we knew that these systems must exist, but none of these systems had yet been identified.”
The extremes of nature play an important role in calibrating our theoretical models, and this is true for low-mass binaries. Prior to this discovery, astronomers knew of only three short-period ultracold binaries.
The research team found the pair in archival data. They were iterating through the data using an algorithm Hsu wrote to model stars based on their spectral data.
But in those earlier images, the stars were just aligned, so they appeared as a single star. The odds of that happening are high for a tight binary pair like this.
But Hsu and his colleagues thought the data was strange, so they took a closer look at the star with the Keck Observatory. Observations showed that the light curve changed so rapidly that there must have been two stars.
Eventually they realized they had found the closest binary pair they had ever found.
“When we were doing this measurement, we could see things changing within minutes of observation,” said Professor Adam Burgasser of UC San Diego. Burgasser was Hsu’s advisor while Hsu was a doctoral student.
“Most of the binaries we track have orbit periods of years. So you get a measurement every few months. Then after a while you can piece the puzzle back together. With this system we could see the spectral lines parting in real time. It’s amazing to see anything happening in the universe on the scale of human time.”
To emphasize how close the stars are to each other, Hsu compared them to our own solar system and another well-known system.
The pair are closer than Jupiter and one of its Galilean moons, Callisto. It is also closer than the red dwarf star TRAPPIST-1 to its closest planet, TRAPPIST-1b.
The stars are much older than the other three similar systems known to astronomers. While these three are relatively young, up to 40 million years old, LP 413-53AB is several billion years old, like our Sun.
Their age is a clue that the stars didn’t start out so close to each other. The researchers think they could have started in an even tighter orbit.
“It’s remarkable because when they were young, something like 1 million years old, these stars would have been on top of each other,” Burgasser said.
Or the stars may have started out as a pair in wider orbits and then come closer together over time.
Another possibility is that the stars began as a three-star system. Gravitational interactions could have simultaneously ejected one star and pulled the other two into a tighter orbit.
Further observations of the unique system might help answer this question.
Astronomers are interested in stars like these because of what they might tell us about habitable worlds. Since ultracold dwarfs are so dark and cold, their habitable zones are narrow regions.
This is the only way to warm the planets enough to keep surface water liquid. But in the case of LP 413-53AB, the distance to the habitable zone is the same as the stellar orbit, eliminating the possibility of habitable exoplanets.
“These ultracool dwarfs are neighbors to our sun,” Hsu said. “To identify potentially habitable hosts, it’s helpful to start with our near neighbors. But if near binaries are common among ultracold dwarves, there may be few habitable worlds to be found.”
Now that astronomers have found a system as accurate as this, they want to know if there are others. This is the only way to understand all these different scenarios.
It’s hard to even approach conclusions when you only have one data point.
But astronomers don’t know if they’ve only found one because they’re so rare or because they’re so hard to spot.
“These systems are rare,” said Chris Theissen, study co-author and Chancellor’s postdoctoral fellow at UC San Diego.
“But we don’t know if they’re rare because they rarely exist or because we just can’t find them. That’s an open question. We now have a data point that we can start building on. “This data has been in the archive for a long time. Dino’s tool will allow us to search for other binaries like this.”
This article was originally published by Universe Today. Read the original article.