Our closest neighboring star system is Alpha Centauri, located 4.37 light-years from the sun, and it has not one but three stars. Numerous other systems with two or three stars have been found in the universe, and astronomers are yet to come up with an explanation of how systems with varying numbers of stars came about.

A new study, based on radio observation of the Perseus Molecular Cloud, suggests an answer: all sun-like stars are born with a twin, and the binary system either shrinks or breaks apart — as in the case of the sun — within a million years after being born.

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The Perseus Molecular Cloud is about 600 light-years away from Earth and appears in the Perseus constellation. It contains gas and dust with mass of over 10,000 suns, and has a large number of recently formed stars. Researchers who published the study found that the only mathematical model that explained radio observations of the molecular cloud had all sun-like stars being born with a companion.

“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. These systems then either shrink or break apart within a million years,” Steven Stahler, a research astronomer at the University of California, Berkeley, who was one of the two authors of the study, said in a statement Tuesday.

The wide binaries in Stahler’s comment refer to two stars that are more than 500 astronomical units apart from each other. One AU is the distance between Earth and the sun, and equals 93 million miles. The theoretical model used in the study also suggests the sun had a sibling that “likely escaped and mixed with all the other stars in our region of the Milky Way galaxy, never to be seen again,” according to the statement.

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The sun’s former companion has been hypothesized for long, and has been nicknamed Nemesis. The name is based on the hypothesis that Nemesis caused an asteroid to crash into Earth 66 million years ago, creating the Chicxulub crater in Mexico and leading to the last mass extinction event that killed all non-bird dinosaurs, along with 75 percent of all living species at the time. Nemesis was likely at a distance of over 17 times the distance that separates the sun and the farthest planet in the solar system — Neptune. How far it is now is not known.

First author of the study Sarah Sadavoy, a NASA Hubble fellow at the Smithsonian Astrophysical Observatory, said in the statement: “The idea that many stars form with a companion has been suggested before, but the question is: how many? 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 paper, titled “Embedded Binaries and Their Dense Cores,” has been accepted for publication in the journal Monthly Notices of the Royal Astronomical Society. Observations for the study were made using the Atacama Large Millimeter/submillimeter Array in Chile.