In our universe, Be stars make up almost 20% of the B star population and are described as rapidly rotating stars surrounded by a disc. However, the origin of this rotation remains unclear, with the leading hypothesis provided by mass transfer within close binaries.
Stellar Classification
Hundreds of years ago, astronomers began categorizing stars according to their mass and temperature. As they learned more about these celestial objects, this classification scheme also needed to evolve.
Stars are divided into seven main categories or classes: O, B, A, F, G, K, and M. Those in the 'O' class are the most massive and hottest, while those categorized in the 'M' class are the smallest and coolest.
'B' stars are blue-white stars with temperatures that range from 10,000 - 30,000 K. They are hot stars defined by the presence of hydrogen and neutral helium in the optical spectra. Be stars are heterogeneous stars with B spectral types and emission lines. They are sometimes called non-supergiant B stars whose spectrum has one or more Balmer emission lines.
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'Be' Stars Linked to Triple Systems
In a groundbreaking discovery, scientists from the University of Leeds discovered new insights about Be stars. The study "Gaia uncovers difference in B and Be star binarity at small scales: evidence for mass transfer causing the Be phenomenon" is led by researchers Jonathan Dodd and Professor René Oudmaijer from the University's School of Physics and Astronomy.
Be stars are surrounded by a gas disk, similar to Saturn's rings. So far, the consensus among scientists has said that the rapid rotation of Be stars forms the disks and that itself can be caused by the interaction of stars in a binary system.
By analyzing the data provided by the Gaia satellite, Dodd and his colleagues claimed that they had found new evidence that massive Be stars could exist as a triple system. They observed how stars move across the night sky over long periods of 10 years and shorter periods of six months. A movement along the straight line confirms that there is only one star, but observing a slight wobble or a spiral line suggests that there could be more than one star.
The team then looked at a different data set, searching for companion stars further away. They discovered that at these larger separations, the rate of companion stars is much like those between the B and Be stars. From this information, the experts inferred that a third star comes into play in many cases, forcing the companion closer to the Be star at enough distance where mass can be transferred from one to the other.
The phenomenon is also believed to form the characteristic Be star disk. This could explain why astronomers no longer see the companions since they have become too small and faint to be observed after the "vampire" Be star has absorbed so much of their masses. This finding could significantly impact other areas of astronomy, including the recent insights on black holes, neutron stars, and gravitational wave sources.
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