Why are blue stragglers stars different from the norm

What is the News?

Indian Institute of Astrophysics, Bengaluru has conducted a study on Blue Stragglers to understand their aberrant behaviour.

For this, the researchers used the UVIT instrument (Ultra Violet Imaging Telescope) of ASTROSAT, India’s first science observatory in space.

What are Blue Stragglers?

Blue Straggler Stars are hot, blue, massive stars and seem to have a different trajectory of evolution from the norm.

Why are they called Blue Stragglers?

There are a few stars that, when they are expected to start expanding in size and cooling down, do just the opposite. They grow brighter and hotter as indicated by their blue color. Thus, standing out from the cooler red stars in their vicinity in the color-magnitude diagram.

– Since they lag their peers in evolution, they are called stragglers more specifically, blue stragglers, because of their hot, blue color.

First Discovered by: Blue stragglers were first discovered by Allan Sandage in 1953 while performing photometry of the stars.

Why are blue stragglers more massive and energetic than expected according to the study?

Blue Stragglers are more massive and energetic than expected may be due to the following reasons: 

First Possibility: They do not belong to the family of stars in the cluster and hence are not expected to have the group properties. But if they actually belong, the evasive behaviour is due to these stars gaining mass from a binary companion.

Second Possibility: The straggler draws matter from the giant companion and grows more massive, hot and blue, and the red giant ends up as a normal or smaller white dwarf.

Third possibility: The straggler draws matter from a companion star, but that there is a third star that facilitates this process.

Source: This post is based on the article “Why are blue stragglers stars different from the norm” published in The Hindu on 22nd April 2022.