So if the Sun has a twin, it's almost certainly not easily visible in our neighbourhood. Multistar systems such as Alpha Centauri — the sun's nearest neighbor, which harbors three stars — are common throughout the Milky Way. While their results predicted all stars were born as binaries, they amended their conclusion to take into account limitations in their model by saying most stars formed inside the dense cores of dust clouds are born with a partner. But there is an hypothesis that our Sun has a dark twin that likes to swing by every now and then, and stir things up. The new assertion is based on a radio survey of a giant molecular cloud filled with recently formed stars in the constellation Perseus, and a mathematical model that can explain the Perseus observations only if all sunlike stars are born with a companion. "We are saying, yes, there probably was a Nemesis, a long time ago," study co-author Steven Stahler, a research astronomer at the University of California, Berkeley, said in a statement. "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 UC Berkeley astronomer Steven Stahler. These systems then either shrink or break apart within a million years.” 
 
 In this study, “wide” means that the two stars are separated by more than 500 astronomical units, or AU, where one astronomical unit is the average distance between the sun and Earth (93 million miles). But the new results don't paint Nemesis as a murderer: The sibling star probably broke free of the sun and melted into the Milky Way galaxy's stellar population billions of years ago, study team members said. This research is currently on pre-print website, arXiv.org, and has been accepted for publication in an upcoming edition of Monthly Notices of the Royal Astronomical Society. Radio observations of the Perseus cloud by the Very Large Array in New Mexico and the James Clerk Maxwell Telescope in Hawaii revealed 55 young stars in 24 multistar systems (most of which were binary), as well as 45 single-star systems.. 
 
 "The key here is that no one looked before in a systematic way at the relation of real young stars to the clouds that spawn them," Stahler said. "Our work is a step forward in understanding both how binaries form and also the role that binaries play in early stellar evolution," said Stahler. I think we have the strongest evidence to date for such an assertion.” 
 
 According to Stahler, astronomers have known for several decades that stars are born inside egg-shaped cocoons called dense cores, which are sprinkled throughout immense clouds of cold, molecular hydrogen that are the nurseries for young stars. As part of the VLA nascent disk and multiplicity survey (VANDAM for short), the researchers mapped the radio waves leaking out of a dense cocoon of dust about 600 light-years away that contained a whole nursery of young stars. Called VANDAM, it was the first complete survey of all young stars in a molecular cloud, that is, stars less than about 4 million years old, including both single and mulitple stars down to separations of about 15 astronomical units. This captured all multiple stars with a separation of more than about the radius of Uranus’ orbit — 19 AU — in our solar system. The VANDAM survey allowed for a census of stars younger than half a million years old called Class 0 stars – mere babies in star terms – and stars a little older between 500,000 years and 1 million years, called Class 1. Looking closely at the distances between the stars, the researchers found all binaries separated by a gap of 500 AU or more were Class 0 and lined up with the axis of the egg-shaped cloud surrounding them. The slightly older Class I binary stars were closer together, many separated by about 200 AU, and showed no tendency to align along the egg’s axis. “We don’t yet know quite what it means, but it isn’t random and must say something about the way wide binaries form.” 
 
 Egg-shaped cores collapse into two centers 
 
 
 
 Stahler and Sadavoy mathematically modeled various scenarios to explain this distribution of stars, assuming typical formation, breakup and orbital shrinking times.
– Did the sun have an "evil twin" that wreaked havoc on Earth, perhaps obliterating the dinosaurs? Scientists think they can answer at least part of that question with near certainty: Yes, the sun had a twin, the Telegraph reports. Whether it was "evil" remains up in the air. New research out of UC Berkeley and Harvard suggests every sun in the universe is born with a fraternal twin. In fact, Earth's closest neighbor, Alpha Centauri, is a triplet system. Astronomers have long puzzled over binary and triplet solar systems and what becomes of sidekick suns, which are actually stars. And in one of space's most tantalizing mysteries, researchers have long theorized that a dwarf star dubbed Nemesis once rattled our solar system so fiercely that it unleashed killer comets toward Earth, obliterating the dinosaurs. "We are saying, yes, there probably was a Nemesis, a long time ago," says study co-author Steven Stahler. The study does not, however, address whether Nemesis had any role in the dinosaurs' fate. Researchers say the wayward sun likely broke free and ambled off into the Milky Way billions of years ago, never to be heard from again, reports Space.com. The website thinks this exonerates Nemesis in regard to dinosaurs: It would have been long gone by the time the dinosaurs arrived. But a post at Science Alert isn't so sure: It notes that one theory holds that Nemesis still swings by our solar system periodically and thus could cause trouble. In the study, scientists used data from giant telescopes in New Mexico and Hawaii, along with a mathematical model they designed, to focus on the star-studded Perseus constellation about 600 light-years away. (This space mystery was finally solved.)