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Glossary · Galaxies & Cosmology
Gravitational waves
Ripples in spacetime itself, detected by measuring a distance change smaller than a proton.
Accelerating masses radiate gravitational waves, stretching and squeezing space as they pass. Einstein predicted them in 1916 and doubted they would ever be measured; LIGO recorded the first in 2015, from two black holes merging 1.3 billion years ago, as a change of one part in 10^21 across a 4 km arm. A hundred-plus detections later they are a routine channel of astronomy, and the 2017 neutron star merger seen in both waves and light began multi-messenger astronomy outright.
Where it has come up lately
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Universe Today
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A Pair of White Dwarfs Locked in a Six-Minute Orbit Might One Day Be Observed By Gravitational Waves
Universe Today
Related terms
Fast radio burst
A millisecond flash of radio energy from another galaxy, cause still unsettled.
Redshift
The stretching of light from distant objects, and the universe's odometer.
Hubble tension
Two good measurements of the universe's expansion rate that stubbornly disagree.
Dark energy
The name for whatever is making the expansion of the universe speed up.
Questions
What is Gravitational waves?
Ripples in spacetime itself, detected by measuring a distance change smaller than a proton.
Why does it matter?
Einstein predicted them in 1916 and doubted they would ever be measured; LIGO recorded the first in 2015, from two black holes merging 1.3 billion years ago, as a change of one part in 10^21 across a 4 km arm. A hundred-plus detections later they are a routine channel of astronomy, and the 2017 neutron star merger seen in both waves and light began multi-messenger astronomy outright.