Using NASA’s Hubble Space Telescope, astronomers at Bucknell University have observed as astronomical anomaly that few others have encountered.
Katelyn Allers, professor of physics and astronomy at Bucknell, and postdoctoral researcher Blake Pantoja were part of an international team that discovered a binary planetary system 450 light years from Earth. That system, named Oph 98, is composed of a pair of brown dwarfs of differing masses orbiting each other from a strikingly wide distance.
The team discovered the system in the young Ophiuchus star-forming region. They said it’s a unique example of a binary system detected right after birth. The process of star creation sometimes also creates objects called brown dwarfs, which are smaller and colder than stars. Like stars, brown dwarfs often wander alone through space, but can also be seen in binary systems, where two brown dwarfs orbit one another and travel together in the galaxy.
“It’s rare that we’re able to see a binary set of objects, and especially ones at planetary masses, right at the time of their formation,” Pantoja said. “This system is only a few million years in the making and so it has not had a lot of time to form into what they are as we see right now. It really can make for a benchmark on our understanding of the formation of brown dwarfs and those in binary pairings.”
The research team, including astronomers from the Center for Space and Habitability and NCCR PlanetS at the University of Bern in Switzerland, published a study on their discovery last month in The Astrophysical Journal Letters, a leading astronomical journal. In the paper, they expressed surprise over the fact that Oph 98 A and B are orbiting each other from such a large distance — about 200 times the distance between the Earth and the Sun. In addition to its young age, Oph 98 is also distinct from other binary systems because of its low masses.
“What is really interesting about this is that it gives us some first-hand information on the formation of planetary mass objects, and because they’re so widely separated, we actually would expect these binary companions to form in a more star-like fashion,” Pantoja said.
Allers said, “Another interesting thing about this system is that the gravitational force holding these widely separated, low mass objects together is extremely weak. We expect that this system will be easily disrupted as it continues to evolve.”
Because binary systems like this are very rare, the researchers looked at 30 objects with Hubble before finding the companion to Oph 98. Confirming that the companion is associated with Oph 98 is the important next step, according to Allers.
“The complicated thing with this is that you can see an object that may be next to your target star or brown dwarf, but what’s really tricky is confirming that the companion is actually associated with it and not just some distant star that falls next to it randomly in the sky,” she said. “That’s where proper motion — where you make sure they’re moving together across the sky — is really important.”
The Bucknell researchers have been awarded time on the Gemini Observatory in Hawaii to continue their research on the Oph 98 system. They plan to gather information on both the atmospheric composition of the two planetary mass objects, as well as how they were formed.
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