Be-type stars make up almost 20% of the B star population, and are rapidly rotating stars surrounded by a disk. Although these stars have been known for about 150 years — having first been identified by the renowned Italian astronomer Angelo Secchi in 1866 — until now, no one has known how they were formed.
“The best point of reference for that is if you’ve watched Star Wars, there are planets where they have two Suns,” said University of Leeds Ph.D. student Jonathan Dodd.
“But now, by analyzing data from ESA’s Gaia satellite, we found evidence these stars actually exist in triple systems — with three bodies interacting instead of just two.”
“We observed the way the stars move across the night sky, over longer periods like 10 years, and shorter periods of around six months.”
“If a star moves in a straight line, we know there’s just one star, but if there is more than one, we will see a slight wobble or, in the best case, a spiral.”
“We applied this across the two groups of stars that we are looking at — the B stars and the Be stars — and what we found, confusingly, is that at first it looks like the Be stars have a lower rate of companions than the B stars. This is interesting because we’d expect them to have a higher rate.”
“The fact that we do not see them might be because they are now too faint to be detected,” said University of Leeds Professor René Oudmaijer.
The astronomers then looked at a different set of data, looking for companion stars that are further away, and found that at these larger separations the rate of companion stars is very similar between the B and Be stars.
From this, they were able to infer that in many cases a third star is coming into play, forcing the companion closer to the Be star — close enough that mass can be transferred from one to the other and form the characteristic Be star disk.
This could also explain why we do not see these companions anymore; they have become too small and…
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