Discoveries Enabled by Gravitational Waves

LIGO, Virgo, and KAGRA (LVK) are gravitational-wave detectors that have revolutionized our understanding of the Universe. In 2015, the first direct detection of gravitational waves was made. These waves originated from the merger of two black holes in a binary system more than a billion light-years away from Earth. This discovery confirmed predictions of General Relativity and marked the beginning of a new field in astronomy—gravitational-wave astronomy. The first detection earned the 2017 Nobel Prize in Physics. Today, LVK registers 2–3 black hole mergers per week.

Researchers from the Astronomical Observatory of the University of Warsaw participated in the first detection and subsequent observations. To date, gravitational waves have been recorded from the mergers of:

• 90 binary black hole systems,
  
• Neutron star binaries, including the famous GW170817, which was also observed electromagnetically,
  
• Neutron star–black hole mergers.
  

Key Discoveries from LIGO-Virgo-KAGRA (LVK)

1. First direct detection of gravitational waves (GW150914)
On September 14, 2015, LIGO detectors observed waves from the merger of two black holes with masses of about 36 and 29 solar masses. The merger produced a single rotating black hole of 62 solar masses, while the remaining mass—equivalent to about three solar masses (over a million times the mass of Earth)—was converted into energy and emitted as gravitational waves. This historic discovery confirmed that black holes exist in binary systems and can merge, a phenomenon previously only theorized. Remarkably, the collision displaced parts of the detector by only a tiny fraction of the width of an atom—enough to make the calculations possible.

2. Confirmation of massive black holes in binaries
Subsequent detections (e.g., GW170104, GW170814) revealed the existence of a population of massive black holes—at least 20 times the mass of the Sun—that form binary systems and merge through the emission of gravitational waves.

3. Discovery of the heaviest known merger (GW231123)
In 2023, a collision between black holes of approximately 100 and 140 solar masses produced a final black hole of about 225 solar masses. This finding is a major step in understanding the formation of very massive black holes.

4. Discovery of objects in the 3–5 solar mass range
Previously, astronomers believed objects of this mass did not exist. Gravitational-wave observations have now detected them. It remains to be determined whether they are small black holes, massive neutron stars, or something entirely new.