Gravitational wave
Gravitational waves are ripples in the fabric of spacetime itself, produced by the accelerated movements of cosmic masses. Predicted by Albert Einstein in 1915 as part of general relativity, they were not directly detected untilin 2015, opening up a new way to observe the universe that is radically different from traditional astronomy based on light.
How Gravitational Waves Form
In principle, any accelerating mass produces gravitational waves, just as an accelerating electric charge produces electromagnetic waves. In practice, only the most extreme phenomena—black hole mergers, neutron star mergers, and asymmetric supernovae— produce waves intense enough to be detectable. The waves travel at the speed of light and stretch and then compress space in all directions perpendicular to their propagation.
The first detection: GW150914
On September 14, 2015, the LIGO detectors in the United States recorded a gravitational wave signal for the first time. This event resulted from the merger of two black holes with masses of 36 and 29 solar masses, which occurred 1.3 billion years ago. The energy released by this event—in purely gravitational form— was equivalent to 3 solar masses converted into pure energy. This detection earned the 2017 Nobel Prize in Physics.
Multimessenger astronomy
In 2017, the merger of two (GW170817) was simultaneously observed in gravitational waves and light by telescopes around the world. This first multimessenger event confirmed that neutron star mergers are a major source of heavy elements (gold, platinum, uranium) in the universe. This marks the beginning of a new era in astronomy in which multiple information channels are combined.
Current and Future Detectors
The LIGO (U.S.), Virgo (Italy), and KAGRA (Japan) detectors regularly scan the sky to detect these minute signals. The future space detector LISA, scheduled for the 2030s, will be able to detect waves at lower frequencies and observe the mergers of supermassive black holes at the centers of galaxies.
Did you know?
The gravitational wave GW150914 caused the 4-km arms of the LIGO detector to oscillate by only 10⁻¹⁸ meters— which is one-tenth of a millimeter of a proton’s diameter. This is one of the most precise measurements ever made in the history of science.
Frequently Asked Questions
Do gravitational waves travel faster than light?
No. They travel at exactly the speed of light in a vacuum, as confirmed by the simultaneous detection of GW170817 as both gravitational waves and light— the two signals arrived two seconds apart after traveling 130 million light-years.
Can gravitational waves be blocked?
Practically not. Unlike electromagnetic waves, gravitational waves pass through all matter without being significantly absorbed. It is their weak interaction with matter that makes them so difficult to detect, but also makes them ideal messengers of the most extreme events in theuniverse.
Can gravitational waves be dangerous?
No. Even the most intense waves ever detected, originating from cataclysmic cosmic mergers, were so attenuated by distance thatthey produced distortions imperceptible on any macroscopic scale.