Good Merger | by Brian Koberlein

Casey Reed, NASA

Within the constellation of Orion, there’s a sensible bluish-white star. It marks the proper foot of the starry hunter. It’s often called Rigel, and it’s the most well-known instance of a blue supergiant star. Blue supergiants are greater than 10,000 occasions brighter than the Solar, with lots 16 – 40 occasions larger. They’re unstable and short-lived, so they need to be uncommon within the galaxy. Whereas they’re uncommon, blue supergiants aren’t as uncommon as we’d count on. A brand new research could have found out why.

We aren’t completely certain how these huge stars type, although one thought is that they happen when an enormous fundamental sequence star passes by means of an interstellar cloud. By capturing gasoline and dirt from the cloud, a star can shift off the primary sequence to turn out to be a blue supergiant. One other thought is that they might type inside stellar nurseries with a mass as nice as 300 Suns. Because of this, they rapidly burn so brightly that they by no means turn out to be true main-sequence stars. Each of those fashions predict that blue supergiants are rather more uncommon than the quantity we observe.

This new research begins by noting that blue supergiants, significantly the smaller ones often called B-type supergiants, are hardly ever seen with companion stars. That is odd since most huge stars type as a part of a binary or a number of system. The authors suggest that B-type blue supergiants aren’t usually in binary programs as a result of they sometimes are the product of binary mergers.

The workforce simulated a variety of fashions the place an enormous main-sequence star has a smaller close-orbiting companion after which checked out what would end result if the 2 stars merged. They then in contrast the outcomes to observations of 59 younger blue supergiant stars within the Giant Magellanic Cloud. They discovered that not solely can these mergers produce blue supergiants within the mass vary of the Magellanic stars, however the spectra of the simulated mergers match the spectra of the 59 blue supergiants. This strongly means that many if not most B-type blue supergiants are the results of stellar mergers.

Sooner or later, the workforce want to carry this work additional to see how blue supergiants evolve into neutron stars and black holes. This might assist clarify the kind of mergers noticed by gravitational wave observatories similar to LIGO and Virgo.