“Amidst the star ball: Could Messier 4 hold the key to discovering Intermediate-mass Black Holes?”

Amidst the star ball floating in the Milky Way, there was a monster lurking.

About 6,000 light years away, the globular cluster known as Messier 4 appears to be clustered around a black hole that is 800 times the mass of our Sun.

It’s not a featherweight, but it’s far from a giant either. In fact, the body is in the rarely seen middle mass range, between the smallest black hole and super oversized chokers.

To date, our only discoveries about these black holes have not been immediate or conclusive, and this one is no exception.

Still, it’s one of the best candidates so far, and close enough that follow-up studies can be done with relative ease. This could help us finally find one of these elusive objects definitively, and solve one of the most perplexing mysteries of black holes.

“Science rarely discovers something new all at once.” said astronomer Timo Brosti European Space Agency. “It’s about being more certain of the results step by step, and that might be one step towards confirmation that intermediate-mass black holes really exist.”

We’ve identified too many black holes in the universe, and something very strange is happening their mass distribution. There are two distinct populations: stellar-mass black holes, which are about 100 times the mass of the Sun; and supermassive black holes, which are located at the cores of galaxies and bind millions to billions of suns.

Between those two mass ranges… too much, not much, really. This raises a big conundrum, which is basically, why not? Are there no intermediate-mass black holes? Or are they there, and we can’t find them for some reason?

We know how stellar-mass black holes form – the fundamental collapse of massive stars, and the fusion between these objects. But we’re not too sure about that Supermassive black hole formation. Do they grow from successive mergers of smaller black holes, or do they absorb matter and swell?

Intermediate-mass black holes may be a clue, suggesting they can start small and grow to become massive over time. This would certainly make a lot of sense, but the lack of these ideas is a very effective barrier to this idea.

One possible site Where this black hole might be hiding is in the heart of a globular cluster. It is an unusually dense and highly globular cluster of between 100,000 and a million or more stars, most of which formed at the same time from the same cloud of gas. Previous studies focusing on globular clusters have found a high concentration of mass at their center consistent with the mass range of an intermediate-mass black hole.

Messier 4 is the closest globular cluster to Earth. Led by astronomer Eduardo Vitral of the Space Telescope Science Institute, the research team used two powerful space telescopes, Hubble and Gaia, to get a closer look at the stars inside. They tracked the motions of about 6,000 stars in the cluster, to see if they could correlate this movement with orbits around the small, dense cluster.

We usually can’t see a black hole if matter isn’t actively adding to it, but an orbit will provide some reliable guidance. Their calculations revealed something, with a mass of about 800 solar masses. Although what this object may be is not clear.

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“Using the latest Gaia and Hubble data, it is impossible to distinguish the dark remnants of star clusters from a single, larger point-like source,” Vitral said. “So one possible theory is that instead of being many separate small dark bodies, this dark mass could become a medium-sized black hole.”

To try to narrow it down, the team did star modeling and displacement to see how that changed the shape of the cluster. Eliminating fast-moving stars spreads their mass over greater distances, as you might see from a swarm of small black holes and neutron stars. Further modeling shows that the clusters are not spread over a large enough area to form a herd.

On top of that, a swarm of black holes would be so close together that they would essentially create chaos. The gravitational interaction will cause the star to fly out of the cluster, smear it anarchism across the sky. We may, in fact, have seen the effect in a file The star cluster is called Palomar 5.

“We firmly believe that we have a very small area with a lot of concentrated crowd. It is about three times smaller than the denser dark masses we have found previously in other globular clusters.” Vitral said.

“While we cannot really say that it is the center of gravity, we can show that it is very small. It’s too small for us to describe it as a single black hole. Alternatively, there may be stellar mechanics that we don’t know about, at least in current physics.”

So barring new physics or invisible stars, an intermediate-mass black hole seems the most likely explanation at the moment. But the existence of a number of small black holes is still a realistic explanation. The researchers recommend further observing the cluster using the Hubble and James Webb Space Telescope to further constrain the motions of the stars within.

The results are published in Monthly Notices of the Royal Astronomical Society.