Rare binary star with an oddly round orbit is one of 10 in the galaxy

The newly-discovered star system is one of only about 10 in the entire galaxy.
Chris Young
The binary star system CPD-29 2176.
The binary star system CPD-29 2176.

NOIRLab / NSF / AURA / J. da Silva / Spaceengine 

Clarissa Pavao, an undergraduate at Embry-Riddle Aeronautical University’s Prescott, Arizona, discovered a rare binary star system with very unusual features, a press release reveals.

The twin-star system is luminous with X-rays and high in mass. However, the main reason it stood out in observations is its very circular orbit, which is unusual for binary star systems.

The CPD-29 2176 system likely formed when a supernova failed to explode with the expected seismic explosion, leading to an event the researchers compared to a dud firecracker in space.

Young scientists discover an incredibly rare binary star system

Typically, once a star has consumed all of its nuclear fuel, its core collapses, and the star explodes into space as a massive supernova. In this case, however, the astronomers detected a depleted or "ultra-stripped" supernova, meaning no such explosion occurred.

In binary star systems, when one star goes supernova, the immense force of the explosion will typically kick the orbit of the two stars into an elliptical shape. However, according to Dr. Noel D. Richardson, assistant professor of Physics and Astronomy at Embry-Riddle and co-author of the Nature journal paper detailing the observation, "the star was so depleted that the explosion didn't even have enough energy to kick the orbit into the more typical elliptical shape seen in similar binaries."

Scientists estimate that there are roughly only 10 star systems similar to binary system CPD-29 2176 in our galaxy. This makes CPD-29 2176 a scarce find that could shed new light on neutron stars.

"Systems like this are likely to evolve into binary neutron stars, which eventually merge and form heavy elements that get hurled into the universe," Richardson explained. "Those heavy elements allow us to live the way that we do. For example, most gold was created by stars similar to the supernova relic or neutron star in the binary system we studied. Astronomy deepens our understanding of the world and our place in it."

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A neutron star is essentially a stellar corpse typically left over after a star has gone supernova — or not, as in this case. Neutron stars no longer burn hydrogen, helium, or any other element as fuel.

Detecting the rare binary star CPD-29 2176

Pavao discovered the binary star system while investigating data — flagged by Richardson — that was captured by the Cerro Tololo Interamerican Observatory’s 1.5-meter telescope in Chile. Pavao detected the binary system and gradually removed interference from observations to uncover the surprisingly circular orbit.

Pavao said Richardson played a key role in guiding her research and encouraging her to work hard and succeed. "He pushes his students to be on papers," she said. "That made a big difference for me."

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