This is Scientific American 60-Second Science. I'm Christopher and Daljata.

The universe is littered with black holes, but where exactly they're all hiding? Well,

that's a little harder to say.

Our current inventory of black holes is still highly incomplete.

Yale astronomer Priya Nata Rajan says black holes present unique challenges to those

keeping count.

These are dark objects that have such peculiar properties that you can never directly

quite image them, like we image galaxies, and therefore we have to infer their presence

indirectly.

Nata Rajan inner colleagues recently predicted there might be a large population of previously

undetected supermassive black holes, just wandering around galaxies. But supermassive black

holes are, as the name implies, massively large, which makes them easier to detect compared

to their relatively tiny cousins, so-called stellar mass black holes. Those are closer

and mass to our son.

If you have a stellar mass black hole, it doesn't have the same oomph, so it's trickier

to detect them.

Now, researchers in Europe claim to have stumbled upon an unexpected trove of these stellar mass

black holes, in a puffy star cluster called Palomar 5.

In the paper, we call it the Rusepa Stone.

Marc Helis is an astrophysicist with the University of Barcelona and the Catalan Institute

for Research and Advanced Studies. He says Palomar 5 is best known

for its spectacular star trails, which are studded with stars ejected from the cluster

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