This Is How The Universe Makes Blue Stragglers: The Stars That Shouldn’t Exist
“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.”
Okay, science fans, I’ve got a mystery for you. When you look at a star cluster, you’ll find a wide variety of stars inside: from the ultra-massive, hot, blue ones down to the lower-mass, cool, red ones. The older a cluster is, the redder it is, because the more massive, hotter, bluer ones burn through their fuel faster and die first. But as a cluster gets redder, we’ll inevitably find a few blue stars that don’t belong. These “blue straggler” stars behave as though they’ve formed at a later time than the rest of the cluster, even though we know that cannot be true. Yet they’re real, they’re there, and their lifetimes are often just 10% the known age of the cluster itself.