Blue Straggler

Blue Straggler

Part of: Prelims and GS – III – Sci and Tech; Space 

Context Blue stragglers are a class of stars on open or globular clusters that stand out as they are bigger and bluer than the rest of the stars. 

• They have intrigued scientists who have for long probed their origin.
• Carrying out the first-ever comprehensive analysis of blue stragglers, Indian researchers recently found that half of the blue stragglers in their sample are formed through mass transfer from a close binary companion star. 

What is Blue Straggler? 

• A bunch of stars born at the same time from the same cloud form a star cluster. 
• As time passes, each star evolves differently depending on its mass. 
• The most massive and bright stars evolve and move off the main sequence creating a bend in their track, known as the turnoff. 
• Stars above this bend or brighter and hotter stars are not expected in a cluster, as they leave the main sequence to become red giants. 
• But in 1953, Allan Sandage found that some stars seem to be hotter than the turnoff of the parent cluster. 
• Initially, these blue stars, still straggling above the turnoff, were not part of these clusters.
• However, later studies confirmed that these stars are indeed cluster members, and they were termed “Blue Stragglers”.  

Recent findings of the Indian researchers

• The researchers utilised the Gaia telescope launched in 2013 by the European Space Agency with its excellent positional accuracy to select the blue stragglers in clusters 
• They found that among the clusters they scanned, 228 have a total of 868 blue stragglers.
• This is the first-ever comprehensive analysis of blue stragglers. 
• It showed that these stars are primarily present in the older and massive star clusters. 
• And due to their large mass, they are segregated towards the centre of the clusters. 
• The researchers compared the mass of the blue stragglers to the mass of the turnoff stars (which are the most massive ‘normal’ stars in the cluster) and predicted the formation mechanisms. 
• Significance of the recent findings: The study will help improve understanding of these stellar systems to uncover exciting results in studies of large stellar populations, including galaxies.