1. What Is a Gravitational Wave?
According to the theory of general relativity, space and time are not independent; together they form a structure called spacetime.
Massive objects bend this structure.
When these objects move very powerfully and accelerate, ripples can occur in spacetime.
These ripples are called gravitational waves.
2. What Events Produce These Waves?
The most powerful sources are mergers of compact celestial objects.
In particular:
- the merger of two black holes,
- the merger of two neutron stars,
- the merger of a black hole and a neutron star
can produce measurable gravitational waves.
For this reason, gravitational waves have become a new observational tool for investigating the most energetic events in the universe.
3. Why Don’t We See Them?
Gravitational waves are not electromagnetic radiation.
Therefore, they cannot be directly imaged with visible light telescopes.
As LIGO also emphasizes, detecting gravitational waves is a completely different method from observing light.
4. What Happens When They Reach Earth?
As a gravitational wave passes through Earth, it stretches and compresses spacetime by extremely small amounts.
While distances in one direction increase by a tiny amount, distances in the perpendicular direction can simultaneously decrease by a tiny amount.
This change then continues by switching direction.
The problem is that the effect is incredibly small.
5. The Basic Idea of Laser Interferometers
Interferometry is used to measure this extraordinarily small change.
A laser beam is split into two separate arms.
The two beams travel in different directions, are reflected back by mirrors, and then recombined.
The interference pattern created by the beams can reveal extremely small differences between the paths.
6. How Does LIGO Work?
LIGO consists of two giant L-shaped interferometers.
Each has two arms at right angles to each other, each about 4 kilometers long.
The laser light is split into two arms, reflected by mirrors, and recombined.
When a gravitational wave passes, tiny differences occur in the effective lengths of the arms, and the interference pattern of the laser light changes.
7. How Small Is the Measured Change?
The change caused by a gravitational wave is extraordinarily small.
According to LIGO’s explanation, the change in the interferometer arms can be as small as a tiny fraction of the width of a proton.
Therefore, the measuring devices must be isolated from environmental vibrations as much as possible.
8. Why Are There Two LIGO Detectors?
LIGO has two separate facilities.
They are thousands of kilometers apart.
Seeing the signal from the same cosmic event in two different detectors with the appropriate time difference helps prevent a local vibration on Earth from being mistaken for a gravitational wave.
9. Noise Is One of the Biggest Problems
The detectors are not affected only by cosmic events.
Earthquakes, wind, ocean waves, traffic, and other vibrations in the environment can create noise in the measurements.
For this reason, researchers use many sensors to monitor environmental effects and try to separate them from the data.
10. How Is the Signal Separated from Noise?
The shape of the signal produced by a gravitational wave depends on the physical properties of the source.
For example, as two black holes approach each other, their orbits speed up and the frequency and amplitude of the resulting signal change.
Researchers compare the observed data with theoretical waveforms calculated from general relativity.
This method helps distinguish real cosmic signals from noise.
11. The Signal from Merging Black Holes
As two black holes orbit each other, the system emits gravitational waves.
As energy is lost, the two black holes move closer together.
The orbital speed increases.
This process causes the frequency of the signal to increase steadily.
Eventually, the two black holes merge and a strong gravitational wave signal is produced.
12. Neutron Star Mergers
Neutron stars are also important sources of gravitational waves.
As two neutron stars approach each other, the system emits gravitational waves.
The signal produced during the merger can provide information not only about the masses of the stars but also about the properties of dense nuclear matter.
13. Gravitational Waves Are a “Cosmic Messenger”
In traditional astronomy, we mostly study celestial objects through electromagnetic radiation.
Gravitational waves, however, provide a different channel of information.
For this reason, astronomers consider them a new cosmic messenger.
If the same event produces both light and gravitational waves, the two different observation methods can be used together.
14. The Role of Virgo
The Virgo interferometer in Italy is one of the key parts of the global gravitational wave observation network along with LIGO.
Comparing data from multiple detectors helps better determine the location of the signal’s source in the sky.
15. KAGRA
KAGRA in Japan is also one of the important observatories joining the global detector network.
One of KAGRA’s notable features is that it is built underground and its mirrors are cooled cryogenically.
These features are important for reducing environmental noise and increasing sensitivity.
16. Why Are Multiple Detectors Better?
When a single detector detects a signal, it can be difficult to determine the direction of the source.
However, detectors at different locations detect the same signal at different times.
By using these time differences, the region of the sky from which the wave came can be calculated.
In the GWTC-5.0 catalog published in 2026, it was reported that the joint operation of three detectors helped determine the sky positions of some sources much more precisely.
17. The Pulsar Timing Method
Another way to study gravitational waves is through pulsar timing arrays.
Pulsars can emit radio pulses at very regular intervals.
Researchers measure the arrival times of these pulses at Earth over long periods.
When a gravitational wave passes between Earth and the pulsar, the geometry of spacetime traversed by the signal can change, causing very small deviations in arrival times.
18. What Waves Do Pulsar Arrays Search For?
Pulsar timing arrays are especially sensitive to very low-frequency gravitational waves.
At these frequencies, collective signals from merging supermassive black hole binaries are among the main targets.
This method complements the frequency range to which LIGO is sensitive.
19. Measuring Gravitational Waves from Space
Space-based detectors are being planned to measure some wave frequencies that ground-based interferometers cannot reach.
The most important example of these is ESA’s LISA mission.
LISA is planned to measure extremely small changes in spacetime by making laser distance measurements between three spacecraft.
20. What Will LISA Investigate?
LISA’s targets include white dwarf binaries, neutron star systems, and black hole systems.
It will also be able to search for signals that may arise from mergers of supermassive black holes at the centers of galaxies.
Thus, together with ground-based interferometers, a much wider frequency range can be studied.
21. Different Methods Complement Each Other
No single type of detector can study the entire universe in gravitational wave astronomy.
Ground-based interferometers are sensitive to higher-frequency signals,
pulsar timing arrays to much lower frequencies,
and space-based interferometers to another broad frequency range.
The combined use of these methods enables a more complete exploration of the gravitational wave universe.
22. The First Direct Detection
The first event in which gravitational waves were directly detected occurred in 2015.
This event was recorded when the signal from the merger of two black holes was observed in the LIGO detectors.
This discovery not only directly tested a key prediction of Einstein’s general relativity, but also marked the beginning of gravitational wave astronomy.
23. The Current Observation Network
The international network formed by LIGO, Virgo, and KAGRA is detecting more and more cosmic events.
In the GWTC-5.0 catalog published in May 2026, it was reported that the total number of confirmed events since the first detection in 2015 had reached 390.
As this number increases, scientists can go beyond studying individual events and investigate the statistical properties of black hole and neutron star populations.
24. Listening to the Universe with Gravitational Waves
Electromagnetic telescopes study the universe through light.
Gravitational wave detectors, on the other hand, measure changes in spacetime itself.
For this reason, gravitational wave astronomy has opened an observational window for exploring the universe that was previously inaccessible.
25. Conclusion and Evaluation
Detecting gravitational waves in the fabric of spacetime requires measuring some of the smallest physical changes in the universe. Interferometers like LIGO, Virgo, and KAGRA use the interference properties of laser light to measure the extremely small spacetime changes caused by gravitational waves. Filtering out sources of noise and comparing signals from different detectors are critically important for identifying real cosmic events.
In addition, while pulsar timing arrays investigate low-frequency waves, space-based interferometers like LISA will study frequency ranges that ground-based detectors cannot reach.
The discovery of gravitational waves has not only provided astronomy with a new measurement technique; it has opened a new observational window, allowing us to study the universe by measuring the vibrations of spacetime instead of seeing it with light.