Globular Clusters Aren't Boring

Globular clusters are collections of stars that orbit around a galactic center. Most are ancient and generally considered uneventful, remnants of a star system's early, first few billion, years. A team of researchers from the University of Surrey, however, thinks there may be more to these clusters than we can actually see.

Using advance computer modeling, researchers Miklos Peuten and Mark Gieles chose to study a globular cluster called NGC 6101 — mainly because this ancient cluster showed a less concentrated distribution of stars, unlike younger clusters.

What they discovered when mapping NGC 6101 over its lifetime of 13 billion years might change our understanding of how black holes are formed.

Riddled With Holes

It turns out, NGC 6101's less concentrated distribution of stars may be due to the large population of black holes within the cluster itself.
Black holes are not observable via telescope, because no light escape from of them. "In order to find them, we look for their gravitational effect on their surroundings. Using observations and simulations, we are able to spot the distinctive clues to their whereabouts and therefore effectively 'see' the un-seeable", explains Peuten.
Image source: University of Surrey
Originally, a black hole was thought to be expelled from its parent cluster during its supernova explosion. NGC 6101 shows that it may not entirely be the case. It seems that it's possible for black holes to stay within their parent cluster. This is the first time such a population of black holes existing within a globular cluster was detected. 

In 2013 astrophysicists discovered that some individual black holes can stay within globular clusters, a phenomena possible because a companion star donates material to the black hole. 
This study was published in the Monthly Notices of the Royal Astronomical Society.

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