Hyades star cluster may contain the closest black holes to Earth

For years, the mysterious nature of black holes has intrigued scientists and the general public alike. A new study published in the journal Monthly Notices of the Royal Astronomical Society hints at the existence of multiple black holes nestled within the Hyades star cluster..

Hyades star cluster 

This discovery is particularly striking because the Hyades cluster is the nearest open cluster to our solar system. If confirmed, this would mean that these are the closest black holes to our planet ever identified.

The study was an international collaboration led by Dr. Stefano Torniamenti of the University of Padua, Italy. Key contributors to the research also included Mark Gieles, an ICREA professor affiliated with both the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and the Institute of Space Studies of Catalonia (IEEC), and Friedrich Anders from ICCUB-IEEC.

Focus of the study 

In 2015, scientists detected gravitational waves, ripples in spacetime caused by cataclysmic events like the merging of two black holes. These detections have shed light on low-mass black hole mergers, propelling the scientific community’s interest.

How the research was conducted 

To search for the presence of black holes in the Hyades cluster, the team employed intricate simulations. These digital replicas meticulously traced the trajectories and evolutionary paths of all stars within the Hyades, which is approximately 150 light-years or 45 parsecs away from our Sun.

This simulation was then compared with real-time data from the European Space Agency’s Gaia satellite, which has revolutionized our understanding of the positions and velocities of stars in open clusters.

“Our simulations can only simultaneously match the mass and size of the Hyades if some black holes are present at the centre of the cluster today (or until recently),” said Dr. Torniamenti. 

What the researchers learned 

The most plausible simulations suggest the presence of two to three black holes currently residing in the Hyades star cluster. At the same time, scenarios in which the black holes were ejected less than 150 million years ago (constituting the last quarter of the cluster’s life) cannot be completely ruled out.

What’s unequivocal is that the black holes originating from the Hyades cluster either inhabit it or reside in its close vicinity. This positioning makes them the closest known black holes to our Sun, overshadowing the prior nearest candidate, Gaia BH1, located a distant 480 parsecs away.

Study implications 

Mark Gieles highlights the broader implications of their findings: “This observation helps us understand how the presence of black holes affects the evolution of star clusters and how star clusters in turn contribute to gravitational wave sources.” 

What is a black hole?

A black hole is a region in space where the gravitational pull is so strong that nothing, not even light, can escape from it. The boundary surrounding a black hole is called the event horizon. Once something crosses the event horizon, it is inexorably drawn into the black hole and cannot escape.

How are black holes formed?

Stellar black holes are formed when massive stars undergo gravitational collapse at the end of their life cycles. The core contracts and the outer layers are expelled, and the core’s gravity increases, pulling everything into a small, infinitely dense point known as a singularity.

Supermassive black holes are found at the center of most galaxies, including our own Milky Way, have masses ranging from millions to billions of solar masses. Their formation process is still a topic of research, but they might result from the merging of several small black holes and the accretion of gas from their host galaxy.

Intermediate black holes are of a mass between stellar and supermassive black holes. Their formation is still a mystery.

Primordial black holes are theoretical entities that are thought to have formed soon after the Big Bang. They could have been created from the gravitational collapse of high-density regions in the early universe.

Key features of black holes

Singularity

At the center of a black hole, gravity crushes all matter into an infinitely small, infinitely dense point.

Event horizon

Once something crosses this threshold, it can’t escape the black hole’s gravitational pull.

Accretion disk

As matter gets drawn towards a black hole, it forms a spinning disk of gas and dust around the event horizon known as an accretion disk.

Jets

Some black holes emit streams of particles at nearly the speed of light. These are known as relativistic jets.

Image Credit: Jose Mtanous

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