You’ve probably heard of gravitational waves. They get generated by the collisions of really dense objects, such as black holes or neutron stars. Scientists have speculated about gravitational waves ever since Albert Einstein first predicted their existence. But, he also suspected they would be hard to detect because those waves are quite small. Still, scientists like a challenge. So, they set out to build ultra-sensitive equipment to sort out gravitational waves from the “noise” produced by more mundane things, like earthquakes or passing dump trucks. And, six years after the first detection, we know about 90 of these events!

The first grav-wave discovery was announced in 2015. That’s when the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced the detection of waves from the collision of two black holes. One was a 29 solar-mass object and the other had 36 solar masses. The collision actually happened 1.3 billion years ago, but the waves generated by the event took that long to reach Earth (and the detectors).

Since 2015, there have been 90 detections of these gravitational waves. And, there are more than just the two LIGO installations waiting to detect them. Three facilities have banded together to form the LIGO-Virgo-KAGRA Collaboration. LIGO is located in the U.S. in Louisiana and Washington State. Virgo is located at the European Gravitational Observatory in Italy, and KAGRA (Kamioka Gravitational wave detector), is located in Japan.

Each provides data to collaborations of scientists from countries around the world, interested in studying gravitational waves. And, they have banded together in both the detection of waves and the analysis of the data provided by their instruments. The results are starting to give scientists some amazing insights about those objects and the universe itself.

Making Gravitational Waves

Recently the LIGO-Virgo-KAGRA consortium released the next edition of their gravitational wave catalog. I find it really fascinating that we’ve got enough data for not just one catalog, but three! And, the waves continue to roll in. Which tells us it’s a busy universe out there, collision-wise.

This latest edition categorizes the objects involved in collisions that produce “ripples in space”. Could the 90 known events all be black holes colliding? Or, are they neutron stars? What do the collisions tell us about the masses of the objects that did the colliding? The answers to those and other questions are all in the data.

For example, the collaboration released data on 35 new events detected since the last catalog update. A huge number of them—32—were probably the collisions of black holes. To refresh our collective memory: a black hole is a region of spacetime where gravity is incredibly strong. It’s so strong, in fact, that nothing — including light—can escape. The high gravity stems from the mass of material inside the black hole’s event horizon (its outer boundary). In short: these are incredibly massive places with strong magnetic fields.

The black holes in the latest batch of grav-wave discoveries weren’t limited to just one size or mass range. Some were about 90 times the mass of the Sun. Others were more than a hundred solar masses. That’s a lot of mass, and when you slam two of them together, it generates gravitational waves.

Neutron Stars Get into the Act, Too

A couple of collisions in the latest detections were between pairs of neutron stars. These are odd astrophysical objects made of tightly packed neutrons, with incredibly strong magnetic fields. As we used to say in the planetarium lectures, a tablespoon of neutron star “stuff” would weigh nearly a trillion kilograms.

So, try to imagine a sphere of neutrons about the size of New York or London. THAT would be massive. Now, imagine two of them colliding. Or, even better yet, a neutron star and a black hole. A lot of energy—and gravitational waves—get released. The consortium suspected that was at the root of at least one collision.

Gravitational Wave Implications

Aside from the fact that these collisions shove gravitational waves out into the universe, what else do they tell us? A lot, actually.

First, they tell us there’s a population of objects out there that can and do collide. Massive black holes and neutron stars exist throughout galaxies. They’re both the dead ends of massive stars that ended their lives in supernova explosions.

Also, there’s information to be gained about the masses of “pre-merger” objects. Those would be the massive stars that ultimately became the black holes or neutron stars that eventually collided. In addition, measurements of the gravitational waves also help scientists figure out how far away the event took place.

Data from many such distant events can also help scientists as they model the history of the universe itself. In addition, the detections of very distant mergers may give some insight into the expansion of the universe. Some scientists suggest merger data might shine some light on the nature of dark energy. That’s an unknown “thing” that influences the rate of expansion.

Those are just a few implications of the study of gravitational waves. Our takeaway here is that there are now 90 known mergers. Six years ago, there was only one. So, the universe is giving yet more clues about itself. This time, it’s in the form of dead and dying stars. Eventually, they will crash together and send out massive amounts of data hidden inside gravitational ripples.