Sun-Like Stars Might All Be Born In Pairs

Detail of the Perseus Molecular Cloud. NASA, ESA and J. Muzerolle, STScI

Astronomers have proposed a new model of star formation that will definitely send the astrophysical world buzzing. Their research suggests that every sun-like star in the universe almost certainly formed in pairs.

The research, accepted for publication in the Monthly Notices of the Royal Astronomical Society, focused on the Perseus molecular cloud located 600 light-years from Earth. This region is full of young stars forming in a dense cloud, so astronomers looked at how the observed population might have risen. The most likely scenario they found is that stars form in pairs.

“We ran a series of statistical models to see if we could account for the relative populations of young single stars and binaries of all separations in the Perseus molecular cloud, and the only model that could reproduce the data was one in which all stars form initially as wide binaries,” co-author Steven Stahler, from UC Berkeley, said in a statement. "These systems then either shrink or break apart within a million years."

The team define wide binaries as stars further than 75 billion kilometers (46.5 billion miles) apart. For decades, researchers have known that small regions in the gas clouds begin to collapse on themselves to form stars. These dense cores are egg-shaped and inside the cocoons, suggest the researchers, there are two stars, not one.

“The idea that many stars form with a companion has been suggested before, but the question is: how many?” added first author Sarah Sadavoy, a NASA Hubble Fellow at the Smithsonian Astrophysical Observatory. “Based on our simple model, we say that nearly all stars form with a companion. The Perseus cloud is generally considered a typical low-mass star-forming region, but our model needs to be checked in other clouds.”

The astronomers observed 55 young stars in 24 multiple-star systems (five systems had more than two stars) and 45 single-star systems. They divided them into two sets: Class 0 were stars younger than 500,000 years old and Class I were those between 500,000 and 1 million years old. All the wide binaries were Class 0 and aligned with the axis of the egg-shaped gas cocoon. Class I binary were instead closer together and did not align along the axis.

“This has not been seen before or tested, and is super interesting,” Sadavoy said. “We don’t yet know quite what it means, but it isn’t random and must say something about the way wide binaries form.”

The project is not the first one to suggest that stars form in binaries, but it does provide some new potential explanations. Their observations of the youngest stars are an indication of how stars might form. Our sun might even have a long-lost twin. 

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