Scientists detected a neutron star merger for the first time on Aug. 17 using two different methods of signal detection.

The neutron star merger, also known as a kilonova, sent signals that set off antennae and sensors that alerted scientists to a potential detection. This time, however, the collision was detected by two messengers: electromagnetic radiation and gravity waves.

A potential detection alert of a kilonova from the Laser Interferometer Gravitational-Wave Observatory (LIGO), whose founders won the Nobel Prize this year, piqued astronomers’ interest on Aug. 17. Unlike the black holes that LIGO previously detected, the kilonova, was expected to give off a visible explosion of light.

Seconds later, NASA’s Fermi Gamma-ray Space Telescope detected short gamma-rays coming from the same region of the sky. Then, the One-Meter Two-Hemispheres (1M2H) collaboration team based in UCSC was the first to find the source of the gravitational waves in a galaxy called NGC 4993 in the Hydra constellation and collect optical photons.

“It’s hard to understate how important this is. We’ve potentially started a new scientific field, one where we finally can look at the universe both through gravity and through light. In terms of what we’ve learned and what theories we’ve confirmed, it’s a long list,” Ryan Foley, principal investigator of the 1M2H collaboration and UCSC assistant professor of astronomy and astrophysics, said. “It’s kind of endless. There’s all sorts of things that we now know about the universe because of this one event.”

The neutron star merger is an important detection for not only astronomy, but also engineering and physics as well. The detection confirms Einstein’s general theory of relativity and provides valuable detail on kilonovas that have only been theorized about up to this point.

Once a star cannot raise its interior temperature high enough to undergo further fusion, it dies. In simple terms, every star’s death process passes through at least one of three stages: as a white dwarf, a red giant, or a neutron star.

The smallest, most dense of these stars is the neutron star. As the fusion energy of a star runs out, the star, compressed by its own large gravitational energy, begins to collapse in upon itself. However, due to the electron degeneracy pressure and the electrons in the atoms violating the Pauli exclusion principle, the outer clouds of atoms begin to push back, supporting the star against its own weight.

“[A neutron star is] material that’s so compressed that, even though it has a mass that’s one to two times the size of the sun, it’s compressed into a region of space that’s not much bigger than Manhattan Island,” UCSC professor of astronomy and astrophysics and astronomer Dr. Puragra Thakurta said. “It’s a remarkable degree of compression.”

This detection yields more than a discovery of a kilonova. While scientists gained valuable details on neutron star mergers, a new field of astronomy may also have been born.

“I do consider this to be a watershed moment,” said Dr. Thakurta. “Astronomical objects send off signals, and it’s two very different kinds of signals that were received, and that’s what’s special about this event. They’re calling it the birth of multi-messenger astronomy.”