“Perfect Pairs” of black holes may dot universe

by | November 17, 2023, 6:49 AM | Galaxies & Cosmology

Image Credit: APS/Alan Stonebraker

Pairs of objects are responsible for some of the coolest phenomena in our universe, and while a lot of these pairs end up merging into a single object given enough time, there are a few… theoretically at least… that the universe carefully holds apart.

In a new paper in Physical Review Letters, researchers lead by Oscar Dias, explore the possibility that  our universe can precisely balance the desire of gravity to pull black holes together against the ability of the universe’s expansion to pull them apart.

I was a physics professor for many years, and I have to admit, if I was teaching graduate relativity, I’d have a new favorite homework assignment. 

Our reality is defined by the interaction of balanced and unbalanced forces. As I sit here, gravity pulls me into my chair cushion and the structural integrity of my chair – in the form of a normal force – pushes up. The forces are balanced, and there is nothing to accelerate me into the air or drop me to the floor. 

Anytime you have multiple forces you know it’s possible – if you work hard enough – to figure out just how to balance things.

In their models, they envisioned the simplest of systems: 2 non-spinning black holes. The physics doesn’t care about a specific size; it just cares that they are matched. They do look at the case for smaller black holes that don’t have the same physics associated with their surroundings. They find that it is possible to perfectly balance things across time and space so the two systems will stay for a time at the same separation. This isn’t a forever kind of thing; too much is constantly happening at the event horizon of black holes, and this balance just isn’t stable. But… for a time at least… two black holes can balance in space, maintaining a constant separation… and we will most likely see their lack of light and massive combined gravitational pull as coming from a single object. 

For all we know … we’ve already seen this kind of a balancing act and we just didn’t recognize it…

But probably not. As I said, their work considered non-spinning black holes that are nicely identical. It is possible to expand this work out to include non-identical systems and spinning black holes, but that is left for future work that I, for one, look forward to reading.