Scientists have long struggled to measure the expansion of the universe, but now they think colliding black holes could hold the secret to figuring it out.

As the universe expands it stretches space-time, including the gravitational waves upon it. A similar stretching of waves happens when black holes collide, so even though we might not have the capacity to actually measure it yet, scientists could believe this could be a way to make it happen.

The recent discovery that the rate of the universe’s expansion is accelerating sent shockwaves through the field, and everyone wants to know how fast its happening, how much it has changed, and how the universe has and continues to evolve.

There have been several methods tried in order to measure these things, but the results aren’t perfect or able to be accurately replicated.

Two astrophysicists, Dr. Jose Ezquiaga and Professor Daniel Holz, hope that studying black hole mergers might be the answer.

“For example, if you took a black hole and put it earlier in the universe, the signal would change and it would look like a bigger black hole than it really is.”

The extent of the changes provides a way to measure the expansion, but we also need to know the distance between the two mergers and what the black hole looked like originally.

“We measure the masses of the nearby black holes and understand their features, and then we look further away and see how much those further ones appear to have shifted.”

Since the majority of our samples are made of the union of stellar black holes, which are formed from supergiant stars, it’s reasonable to assume their growth will prove consistent as the universe evolves.

Ezquiaga and Holz have dubbed their approach the “spectral siren” method, named for the way the waves are stretched like a receding vehicle siren.

Progress is rapidly evolving, as the first gravitational wave from a black hole collision detected just six years ago–so our sample size is expected to grow quickly.

Which means there should be more knowledge to go around soon!