Binary systems are normal, so much that about half of the stars in the Milky Way form one orbiting each other. So far though astronomers believed that there was a limit to the possible proximity of the stars forming a binary system. This idea was confirmed by the fact that the observations made over a few decades so far had found no pair of stars with an orbital period less than 5 hours. Astronomers concluded that if two stars were closer than this limit they would soon merge to form a bigger star.
This theory was recently disproved by the study of a team of astronomers who used the UKIRT (United Kingdom Infrared Telescope) discovering four pairs of stars orbiting each other in less than 4 hours. The nearest couple has two red dwarfs of spectral class M4 orbiting each other in only 2.5 hours.
The UKIRT is a telescope that belong to the UK Science and Technology Facilities Council built on Mauna Kea, Hawaii, between 1975 and 1978 with a relatively low budget. Over the decades, the instrumentation of this telescope has been upgraded a number of times and a few years ago a state of the art technology Wide Field Camera (WFCAM) was installed.
WFCAM is precisely the instrument that allowed to conduct a survey of binary systems consisting of red dwarfs. These stars much smaller than the Sun emit very little light so until recently it was impossible to study them extensively. The instruments produced in the last decade thanks to the latest developments in technology at last allowed to investigate these stars that are very common.
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The astronomers who conducted this research were the first to be surprised when they discovered pairs of red dwarfs very close to each other. Their existence will force scientists to rethink theories on the formation and evolution of binary systems. In fact, the main problem is that these very near stars is that at the beginning of their life they were bigger and then shrank until they reached their equilibrium. This means that their orbits must have shrunk as well over time, otherwise there couldn’t be two separate stars.
One possible explanation for the approach of these stars is that they’re more active than previously thought. In particular, it’s possible that their magnetic field generate an effect on their companion and this reciprocal influence slow down their motion leading to their progressive approach.
Now the interest in the binary systems formed by red dwarfs will certainly increase. Once again, the use of new instrument has allowed scientists to make new discoveries extending in a surprising manner our knowledge of the universe.
