Four stars swirl around each other in low orbits

Jan 11, 2008 07:53 GMT  ·  By

An unique multiple-star system located in the constellation of Aquarius, about 166 light years away, consisting of four young stars orbiting rapidly in tight formation around each other, may provide new insight in the process of star formation and evolution. Dubbed BD -22?5866, the newly discovered system represents the most densely packed accumulation of stars, directly viewed by optical methods.

Each of them having masses about half of that of the Sun and ages no more than 500 million years (compare to our Sun which is about 4.6 billion years old and half through its life cycle), the young stars orbit around each other in formations of two. Thus, two of the stars, at the time of their discovery, were orbiting each other at speeds close to 483,000 kilometers per hour, which means they are capable to make a complete rotation in less than five days, while the other binary system rotates with speeds of only 200,000 kilometers per hour, equivalent to an approximated orbital period of 55 days.

Although quadruple stellar systems are incredibly rare (according to the estimations, 1 star in 2000 could possibly take part in such a system), astronomers were mostly amazed by the orbital distances between the stars. Discovered by the Institute of Astronomy of the University of Hawaii, the first couple of stars seem to have a distance between them of only 0.06 astronomical units, whereas an astronomical unit represents the radius of the orbit of the Earth around the Sun. Naturally, the second binary system, having a smaller orbit period and speed, has a radius of about 0.26 astronomical units.

The two binaries circle around each other from a distance of 5.8 AU, close to the radius of the orbit of the planet Jupiter around the Sun. The system was detected by Evgenya Shkolnik, during a scan of the night sky which is part of a program intended to detect stars with masses smaller than that of the Sun, present in the near vicinity of our solar system.

Sklolnik argues that the stars evolved from a single cloud of dust and gas, and might have been brought together into a close configuration by the spinning disk of matter during the first 100,000 years of evolution, since it is well known, from stellar formation models, that the stars cannot usually form so close one to another. The angular momentum of the faster rotating binary system, corroborated with the gravitational interactions of the second system of stars, determined the previous to fall into a farther orbit, thus in the past the system could have been much closer than it is currently being observed.