A team of astrophysicists has discovered a binary pair of supercool dwarfs so close together that they look like a single star, they take just 20.5 hours to orbit each other, meaning their year is less than a day on Earth. It is also much older than similar systems.
We cannot see ultra-cool dwarf stars with the naked eye, but they are the most numerous stars in the galaxy. And they have such low masses that they only emit infrared light, and we need infrared telescopes to see them.
These stars are interesting objects because theory shows that stars this close should exist, but this system is the first time astronomers have observed such close proximity.
A team of astronomers presented their findings at the 241st meeting of the American Astronomical Society in Seattle. The study was led by Chih-chun “Dino” Hsu, an astrophysicist at Northwestern University. The system is called LP 413-53AB.
“It’s exciting to discover such an extreme system,” said Chih-chun “Dino” Hsu, a northwest astrophysicist who led the study. “In principle, we knew such systems should exist, but no such systems have yet been identified.”
Prior to this discovery, astronomers knew of only three short-period, ultra-cool binaries.
And the research team found the pair in archival data. They combed the data using Hsu’s algorithm that models stars based on their spectral data.
But in those earlier images, the stars just happened to be aligned, so they appeared as a single star. The chances of that happening are high for a tight binary like this.
But Hsu and his colleagues thought the data was strange, so they watched the star closely with the Keck Observatory. Observations showed that the light curve changed very quickly and there must be two stars.
Finally, they realized they had found the closest binary pair ever found.
“When we were making this measurement, we could see things change within two minutes of observation,” said Professor Adam Burgaser of the University of California, San Diego. Borgaser was Hsu’s advisor while Hsu was a PhD student… Most of the binaries we follow have orbital periods of years. So, you get measured every few months. And then, after a while, you can put the puzzle together. With this system, we can see spectral lines moving away in real time. It’s amazing to see something happen in the universe on a human time scale. “
To emphasize how close the stars are to each other, Hsu compared them to our own solar system and another known system.
Together, 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.
And the stars are much older than the other three similar systems known to astronomers. While these three are relatively young at 40 million years old, LP 413-53AB is several billion years old, like our Sun.
Their age is evidence that the stars did not start close together. The researchers believe they could have started in a narrower orbit.
“That’s cool because when they were young, almost a million years ago, these stars were outdoing each other,” Burgaser said.
Or, the stars may have started as a pair in wider orbits and only got closer over time.
Another possibility is that the stars started as a three star system. Gravitational interactions can eject one star at a time and pull the remaining two into a tighter orbit.
Further observations of the unique system may help answer this.
And astronomers are interested in stars like this because of what they might tell us about habitable worlds. Because supercooled dwarfs are so dim and cold, their habitable zones are narrow.
This is the only way they can warm the planets enough to sustain liquid surface water. But in the case of LP 413-53AB, the distance from the habitable zone is the same as the stellar orbit, eliminating the possibility of habitable exoplanets.
“These very cold dwarfs are neighbors of our sun,” said Hsu. “To identify potentially habitable hosts, it helps to start with our close neighbors. But if close binaries are common among ultracold dwarfs, there may be fewer habitable worlds to be found.”
Now that astronomers have found just one narrow system like this, they want to know if there are more out there. This is the only way to understand all these different scenarios.
And it’s hard to even come close to any conclusions when you only have one data point.
But astronomers don’t know if they’ve found one just because it’s so rare or because it’s so hard to spot.
“These systems are rare,” said Chris Thiessen, study co-author and postdoctoral fellow at the University of California, San Diego. “But we don’t know if they are rare because they rarely exist or because we don’t find them.” This is an open question. Now we have one data point that we can start building on. This data has been in the archives for a long time. The dino tool will enable us to search for more binaries like this. “
This study was originally published by Universe Today.