A new analysis strengthens the hypothesis that all sunlike stars in the universe have a twin albeit not necessarily identical. Models even suggest that the solar system's sun has a twin that scientists called Nemesis, which is possibly responsible for the extinction of the dinosaurs on Earth millions of years ago.

Binary And Triple Star Systems

Many stars are known to have companions. Alpha Centauri, the closest star system to the Solar System, for instance, is a triplet system, which means it is consist of three stars. Astronomers have long wondered if binary and triple star systems are born that way or if they just fall in together after they have formed.

The "born together" hypothesis, though has been a favorite. Simulations that were recently developed showed that nearly all stars could be born as multiples that merely spin away from each other on their own. Direct evidence from observations though, has been scarce.

Now, data from the VLA nascent disk and multiplicity (VANDAM) survey, which allowed for the census of stars younger than half a million years old, equivalent to babies in stellar terms, and stars between 500,000 and 1 million years old, in the constellation Perseus, along with data on the shapes of surrounding cloud of dust hint that nearly all stars form 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," said Sarah Sadavoy, from the Smithsonian Astrophysical Observatory, adding that these systems eventually either break apart of shrink within a million years.

The data showed that all of the widely separated binary systems, or those whose stars are separated by more than 500 AU, were very young star systems. The slightly older binary stars, on the other hand, were closer together and many were separated by about 200 AU.

Dense Cores

Stars are born inside egg-shaped cocoons known as dense cores, which are scattered throughout clouds of cold, molecular hydrogen that serve as nurseries for young stars. The researchers observed that the younger star systems were often aligned with the long axis of the egg-shaped dense core while the older system showed no tendency to align along this axis.

The researchers said that the only means of explaining the observations is to assume that all stars with masses that are around the same mass as the sun's start off as wide binaries in egg-shaped dense cores and 60 percent of these split up over time. The remaining system shrink to form tight binaries.

"In the model that best explains the observations, all stars form initially as wide binaries. These binaries either break up into separate stars or else shrink into tighter orbits," the researchers wrote in their study, which has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.

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