How do we see extremely short-lived stars in places that haven’t experienced star-formation in over 10 billion years?
The most fundamental truth about stars is that when they run out of fuel to burn, they die.
The least massive stars burn their fuel the most slowly, living the longest, while the most massive ones burn out the fastest.
New stars form in large clusters, creating stars of all different masses simultaneously.
As they age, the more massive stars die first, leaving only the lower-mass ones behind.
We can date star clusters by examining which stars remain when we plot out stellar color vs. temperature.
The older a cluster is, the redder, lower-mass, and less bright its surviving stars are.
Globular star clusters are the oldest; some haven’t formed stars in ~13 billion years.
Yet if we look closely inside these ancient relics from the young Universe, we’ll find a few blue stars.
These “blue stragglers” have lifetimes of 2 billion years or less: incompatible with the cluster’s age.
But there’s an explanation: many stars have companions.
By siphoning mass or merging, the net product will be a new, more massive star.
Every old cluster we know of has at least a few blue stars.
Blue stragglers exist because, in dense environments, stars can’t help but interact.
Mostly Mute Monday tells the astronomical story of an image, phenomenon, or class of objects in pictures, visuals, and no more than 200 words. Talk less; smile more.Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.