Astrophysicists have uncovered a possible swarm of over 100 stellar-mass black holes hidden within a stellar cluster known as Palomar 5. Located around 80,000 light-years from Earth, this unusual star cluster spans across 30,000 light-years, sparking significant interest in its unique structure and long tidal stream of stars.

Palomar 5 is not an ordinary star cluster. Classified as a globular cluster, it contains between 100,000 and 1 million ancient stars, often referred to as "fossils" from the early Universe. These clusters play a vital role in studying the evolution of galaxies, dark matter, and cosmic history. The Milky Way hosts around 150 such clusters, including Palomar 5.

New Clues About Star Stream Formation

What makes Palomar 5 stand out is its loosely distributed stars and vast tidal stream, stretching over 20 degrees of the sky. This has led researchers to investigate how these streams form, particularly since Palomar 5 is the only known stellar system linked with such a stream. Mark Gieles, an astrophysicist at the University of Barcelona, remarked, "Palomar 5 acts as a Rosetta Stone for understanding how tidal streams emerge from star clusters."

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By conducting detailed N-body simulations, Gieles and his team tracked the movements of each star in Palomar 5. Their simulations included black holes, which may be ejecting stars into space through gravitational interactions. The findings indicate that Palomar 5 holds a much higher number of black holes than previously believed.

Palomar 5's Fate: A Black Hole Trail

The team’s study revealed that black holes likely account for over 20 percent of Palomar 5's total mass, with more than 100 black holes present. These black holes, each around 20 times the mass of the Sun, were formed from supernova explosions in the cluster’s early years. Gieles noted, "The number of black holes is roughly three times larger than expected."

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Astrophysicists predict that Palomar 5 will dissolve within the next billion years, leaving behind a trail of black holes orbiting the Milky Way. This discovery suggests other globular clusters might face a similar future. These findings emphasize the importance of clusters in detecting black hole collisions and intermediate-mass black holes.

Future Studies on Black Hole Clusters

The recent findings suggest that more black holes could be hidden in clusters across the galaxy. Fabio Antonini from Cardiff University remarked, “The number of black holes in clusters remains uncertain, but our method of analysing ejected stars brings new insights.” The study, published in Nature Astronomy, has opened new pathways for understanding black hole activity in globular clusters.

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