Gravitational waves are ripples in spacetime that travel at the speed of light, produced when massive objects accelerate asymmetrically. First predicted by Albert Einstein in 1916 within the framework of general relativity, they remained undetected for a century due to their extraordinarily small effect on matter. The first direct detection, announced in 2016 from data recorded in 2015, changed that—opening a new era in observational astronomy that does not rely on light or particles but on the geometry of spacetime itself.
\n
In practical terms, a passing gravitational wave alternately stretches and squeezes distances, an effect described by the dimensionless strain:
where ΔL is the change in separation between two test masses and L is their original separation. For astrophysical sources detected on Earth, typical strains are astonishingly small (on the order of 10−21), requiring instruments of extreme precision like the laser interferometers described in Ground-Based Detectors: LIGO, Virgo, and KAGRA.
\n
Unlike electromagnetic radiation, gravitational waves are weakly interacting; they pass through matter largely unimpeded. This property allows them to carry pristine information about dramatic phenomena otherwise hidden from view, such as the collision of black holes or the densest interiors of neutron stars. It also means that by listening for gravitational waves at multiple frequencies (from hertz to nanohertz), astronomers can survey a vast landscape of cosmic processes—from stellar remnants to supermassive black hole pairs in the hearts of galaxies. That multi-band picture is explored in Space-Based and Pulsar Timing Detectors: LISA and Nano-Hertz Background.
\n\n
How Gravitational Waves Are Generated: Sources Across the Cosmos
\n
Any time mass accelerates in an asymmetric way, it can, in principle, radiate gravitational waves. In practice, detectable signals come from systems with extreme gravity, rapid motion, and coherent dynamics. The most prominent astrophysical sources include:
\n
\n
Compact binary mergers: Pairs of black holes, neutron stars, or mixed neutron star–black hole systems lose orbital energy via gravitational radiation and spiral together. As their separation shrinks, the frequency and amplitude of the gravitational waves increase, producing a characteristic \”chirp.\” After their merger, the newly formed remnant settles (ringdown) by emitting waves that encode its mass and spin.
\n
Core-collapse supernovae: The violent implosion of a massive star’s core can generate a burst of gravitational waves. These signals are more complex and often weaker than compact-binary chirps, but they carry unique insights into the explosion mechanism, rotation, and matter at nuclear densities.
\n
Rapidly rotating neutron stars: If not perfectly symmetric—due to \”mountains\” only millimeters high or strong internal magnetic fields—spinning neutron stars can emit continuous, nearly monochromatic gravitational waves. Long-duration searches attempt to unveil such persistent signals.
\n
Supermassive black hole binaries: When galaxies merge, their central black holes can form binaries that evolve over millions of years. Their low-frequency gravitational waves, too slow for ground-based detectors, are probed by pulsar timing arrays (see Space-Based and Pulsar Timing Detectors).
\n
Stochastic backgrounds: A superposition of many unresolved sources can form a gravitational-wave background. At nanohertz frequencies, there is growing evidence for a common-spectrum background consistent with supermassive black hole binaries. There are also theoretical expectations for backgrounds from the early universe, though those remain unconfirmed in the bands where current detectors operate.
\n
\n
Each class traces different physics: compact binaries test gravity in the strong-field, dynamical regime; neutron stars probe ultra-dense matter; supernovae reveal explosion dynamics; and supermassive black hole binaries illuminate galaxy co-evolution. Together, they transform gravitational-wave astronomy into a versatile toolset for astrophysics and cosmology.
\n\n
The Physics of Waveforms: Strain, Frequency, and Polarization
\n
The detailed time series of a gravitational-wave signal—its waveform—encodes the properties of the source. Key ingredients include:
\n
\n
Frequency content: For stellar-mass compact binaries, frequencies sweep from tens to thousands of hertz as the objects spiral together and merge. Lower frequencies (millihertz to nanohertz) arise from much wider, heavier, or earlier-stage systems, such as supermassive black hole binaries and ultra-compact white dwarf binaries (targeted by future space missions).
\n
Amplitude and distance: The observed strain scales inversely with distance. Larger masses and tighter orbits yield stronger signals. The chirp mass—a specific combination of component masses—primarily controls how the frequency rises with time, which is crucial for parameter estimation (see From Signals to Science).
\n
Polarization: General relativity predicts two polarization states (often denoted “plus” and “cross”). A network of detectors with different orientations helps disentangle polarization and improve sky localization.
\n
Spin and precession: If component spins are misaligned with the orbital angular momentum, the orbital plane can wobble (precess), leaving imprints in the waveform morphology. These features help measure spin magnitudes and orientations.
\n
Eccentricity: Most observed stellar-mass binaries circularize before merging due to gravitational radiation; however, eccentric mergers can occur in dense environments (e.g., globular clusters), producing distinctive harmonics.
\n
Post-merger ringdown: The remnant black hole emits damped oscillations whose frequencies depend on its mass and spin. Measuring these “quasinormal modes” tests the “no-hair” theorems of black holes.
\n
\n
Because signal shapes are theoretically predictable to high precision for compact binaries, matched filtering—correlating data against a bank of model templates—enables detection even at low signal-to-noise ratios. Burst sources and stochastic backgrounds, by contrast, often require alternative approaches, discussed in From Signals to Science: Data Analysis and Parameter Estimation.
\n\n
Ground-Based Detectors: LIGO, Virgo, and KAGRA
\n
Ground-based interferometers exploit laser metrology to measure tiny changes in the distance between suspended mirrors many kilometers apart. Their sensitivity band (roughly 10 Hz to a few kHz) targets stellar-mass compact binaries and some transient phenomena.
\n
How laser interferometers work
\n
\n
Michelson topology: A powerful laser is split into two perpendicular arms (kilometers long). Light bounces back and forth between mirrors (test masses) before recombining. A passing gravitational wave differentially stretches and compresses the arms, changing the interference pattern at the output photodetector.
\n
Optical cavities and recycling: Power- and signal-recycling optics increase the circulating power and enhance sensitivity to phase changes, improving the signal-to-noise ratio.
\n
Seismic isolation and suspension: Multiple-stage pendulum suspensions and active isolation reduce ground motion that would otherwise swamp the tiny gravitational-wave signal.
LIGO: The Laser Interferometer Gravitational-Wave Observatory operates two sites in the United States—Hanford (Washington) and Livingston (Louisiana)—each with 4 km arms. After upgrading from initial to Advanced configurations, LIGO made the first direct detection of gravitational waves in 2015, from a binary black hole merger.
\n
Virgo: Located near Pisa, Italy, Virgo’s 3 km interferometer joined observing runs to create a network that triangulates source positions and improves parameter estimation.
\n
KAGRA: In Japan, KAGRA is built underground to reduce seismic and environmental noise and employs cryogenic mirrors to lower thermal noise. Its innovations are paving the way for future detector designs.
\n
\n
Operating as a network allows better sky localization—determining where in the sky a signal originated—by comparing arrival times and amplitudes across detectors. This is essential for coordinating follow-up observations with telescopes across the electromagnetic spectrum, discussed in Multi-Messenger Synergy.
\n
Observing runs and upgrades
\n
\n
O1–O3: Early Advanced LIGO/Virgo observing runs (2015–2020) produced numerous detections, including the first binary neutron star merger with electromagnetic counterparts.
\n
O4 and beyond: Ongoing upgrades—improved lasers, better mirror coatings, quantum squeezing—continue to enhance sensitivity. The fourth observing run began in 2023, with increased detection rates and broader reach for stellar-mass binaries.
\n
\n
Looking further ahead, concepts for third-generation detectors—such as the Einstein Telescope in Europe and Cosmic Explorer in the U.S.—aim to extend sensitivity by an order of magnitude, probe to lower frequencies, and capture vast numbers of events with exquisite detail. That future will complement space-based detectors like LISA (see this section), enabling multi-band gravitational-wave astronomy.
\n\n
Space-Based and Pulsar Timing Detectors: LISA and Nano-Hertz Background
\n
To access frequencies inaccessible on Earth, astronomers are building detectors beyond our planet and exploiting astrophysical clocks.
\n
LISA: The Laser Interferometer Space Antenna
\n\n
\n \n\n NASA illustration of the LISA mission: three spacecraft in triangular heliocentric orbits forming a laser interferometer. \n Artist: NASA\n \n
\n
\n\n
\n\n
\n
Mission concept: LISA is a planned space-based interferometer consisting of three spacecraft flying in a triangular constellation millions of kilometers apart, tracking changes in distance with laser beams. It targets millihertz frequencies.
\n
Science targets: LISA will observe mergers of massive black holes (104–107 solar masses), capture inspirals of stellar-mass objects into massive black holes (extreme mass-ratio inspirals), and detect ultra-compact binaries in the Milky Way.
\n
Status: Following the success of LISA Pathfinder in demonstrating key technologies, LISA is planned for launch in the mid-2030s through an international collaboration led by ESA with NASA participation.
\n
\n
Pulsar Timing Arrays (PTAs) and the nanohertz band
\n
\n
Technique: Millisecond pulsars act as cosmic clocks. A passing gravitational wave perturbs spacetime between Earth and the pulsar, shifting the arrival times of pulses in a correlated way across the sky. Over years, by timing dozens of pulsars, PTAs can detect very low-frequency waves (~nanohertz).
\n
Recent evidence: In 2023, collaborations including NANOGrav (North America), the European Pulsar Timing Array, the Parkes Pulsar Timing Array, and the Chinese Pulsar Timing Array reported strong evidence for a common-spectrum stochastic process with angular correlations consistent with the Hellings–Downs curve—interpreted as a gravitational-wave background likely dominated by supermassive black hole binaries.
\n
Outlook: As data sets lengthen and more pulsars are timed with higher precision, PTAs may isolate individual supermassive binaries and map how galaxies and their central black holes grow over cosmic time.
\n
\n
Taken together, ground-based interferometers, LISA, and PTAs enable coverage from kilohertz to nanohertz—spanning an astonishing nineteen orders of magnitude in wavelength. This multi-band approach mirrors multi-wavelength electromagnetic astronomy, but with the added advantage that gravitational waves carry undistorted signatures from deep gravitational wells.
\n\n
From Signals to Science: Data Analysis and Parameter Estimation
\n
Extracting astrophysical information from a noisy data stream is the core challenge of gravitational-wave astronomy. Workflows differ for well-modeled, unmodeled, and stochastic signals, but share common statistical foundations.
\n
Matched filtering for compact binaries
\n
When waveforms are known to high precision—as for compact binary inspirals—matched filtering is optimal in Gaussian noise. The idea is to correlate data with a bank of expected signals (templates) that span the parameter space of masses, spins, and orientations.
\n
# Pseudocode for matched filtering SNR in a single detector\n# d(f): strain data in frequency domain\n# h(f; θ): template waveform for parameters θ\n# S_n(f): one-sided noise power spectral density\n\n# Inner product (a|b) = 4 Re ∫_0^∞ a*(f) b(f) / S_n(f) df\n\nrho(θ) = (d|h(θ)) / sqrt(h(θ)|h(θ))\n\n# Search over template bank Θ to find max ρ above threshold\n
\n
Triggers above a threshold are followed by coincidence checks across multiple detectors, signal consistency tests, and full Bayesian parameter estimation, which yields posterior distributions for source properties. The results inform sections like Landmark Discoveries and Cosmology with Standard Sirens.
\n
Unmodeled bursts and continuous waves
\n
\n
Burst searches look for short-duration excess power without assuming a particular waveform. They can capture supernova signals or unexpected phenomena. Time–frequency methods and coherent analyses across the detector network reduce false alarms.
\n
Continuous-wave searches target nearly monochromatic emission from spinning neutron stars. These require long integration times, Doppler corrections for Earth’s motion, and strategies to handle tiny frequency drifts.
\n
\n
Stochastic backgrounds
\n
To detect a stochastic background, analysts cross-correlate data from pairs of detectors. Any correlated excess over instrumental and environmental noise points to a background. PTAs apply analogous cross-correlation techniques across pulsar timing residuals, searching for the distinctive angular pattern of the Hellings–Downs correlation.
\n
Parameter estimation and model selection
\n
\n
Bayesian inference: Methods like Markov Chain Monte Carlo and nested sampling map posterior distributions of masses, spins, distances, inclination angles, and sky positions.
\n
Waveform systematics: Different theoretical approximants (post-Newtonian, effective-one-body, numerical relativity surrogates) can affect inferences; robust analyses compare multiple models.
\n
Population studies: With many detections, hierarchical Bayesian models infer distributions of masses, spins, merger rates, and their evolution—informing how stars live and die in different environments.
\n
\n
All along, strict data-quality vetting and detector characterization ensure that instrumental artifacts do not masquerade as astrophysical signals. This discipline underlies the credibility of results discussed in Landmark Discoveries.
\n\n
Landmark Discoveries and What They Mean
\n
Gravitational-wave astronomy has already reshaped our understanding of compact objects and extremes of gravity. Highlights include:
\n
\n
GW150914: The first direct detection (observed in 2015, announced in 2016) revealed a binary black hole merger of roughly 30-solar-mass components. It confirmed that stellar-mass black-hole binaries exist and merge within the age of the universe, launching a new observational field.
\n
GW170817: The first binary neutron star merger observed in gravitational waves, accompanied by a short gamma-ray burst and a bright optical–infrared kilonova (AT2017gfo). Multimessenger observations tied heavy-element nucleosynthesis (r-process) to neutron star mergers and enabled a measurement of the Hubble constant using a “standard siren.”\n \n \n\n Illustration of the kilonova (AT2017gfo/GW170817) from two merging neutron stars. \n Artist: Albert Sneppen\n \n
\n
\n
\n
GW190521: A merger forming a black hole of about 150 solar masses, with component masses in a range that probes the predicted pair-instability mass gap. The short, massive signal opened questions about formation channels in dense stellar environments.
\n
Neutron star–black hole mergers: Events reported in 2021 (e.g., GW200105 and GW200115) provided the first definitive observations of mixed binaries, informing how such systems form and whether they produce electromagnetic counterparts.
\n
Catalog growth: With successive observing runs (GWTC catalogs), dozens of binary black hole mergers and additional neutron star events have been published. The growing sample enables population inference—mass and spin distributions, merger-rate densities, and environmental clues.
\n
\n
These milestones are remarkable not only for what they reveal individually, but also for how they validate the predictive power of general relativity in the dynamical, strong-field regime. As discussed in Cosmology with Standard Sirens and Fundamental Physics Tests, gravitational-wave observations are now a mainstream avenue for testing fundamental physics.
\n\n
Cosmology with Standard Sirens and Fundamental Physics Tests
\n
Gravitational waves allow for new cosmological measurements and precision tests of gravity, independent of many traditional assumptions.
\n
Standard sirens and the Hubble constant
\n
The amplitude of a compact-binary gravitational-wave signal provides a luminosity distance directly, without relying on a cosmic distance ladder. When paired with a source redshift obtained from an electromagnetic counterpart—like the host galaxy NGC 4993 for GW170817—astronomers can infer the Hubble constant, H0. Early results from GW170817 favored values around 70 km s−1 Mpc−1, albeit with wide uncertainties. As more events with counterparts (or statistically associated hosts) accumulate, the precision will improve, offering an independent cross-check on methods that currently disagree at the few-percent level.
\n
Speed and dispersion of gravity
\n
The near-simultaneous arrival (within seconds) of gravitational waves and gamma rays from GW170817 showed that gravitational waves travel at the speed of light to high precision—consistent with general relativity and strongly constraining alternative gravity theories. Limits on any frequency-dependent dispersion also test whether gravitons (if viewed as particles) are effectively massless.
\n
Tidal deformability and nuclear equation of state
\n
In neutron star mergers, mutual tidal distortions leave subtle imprints on the late-inspiral waveform. Measuring this tidal deformability constrains the equation of state of matter at supranuclear densities—one of the hardest problems in modern physics. Combining gravitational-wave data with electromagnetic observations of kilonova light curves and X-ray measurements of isolated neutron stars enhances these constraints.
\n
Strong-field tests of general relativity
\n
\n
Ringdown spectroscopy: Measuring multiple quasinormal modes in the post-merger phase tests whether black holes are described by the Kerr solution as predicted by general relativity.
\n
Parameterized deviations: Analysts introduce controlled deformations to general-relativistic waveforms to check for inconsistencies. So far, observations are consistent with Einstein’s theory.
\n
Parity and polarization tests: Multi-detector networks probe whether only the two tensor polarizations exist, as expected in general relativity.
Noise, Sensitivity, and How Detectors Keep Improving
\n
Achieving sensitivity to strains of 10−21 requires relentless attention to noise. Major noise sources and mitigation strategies include:
\n
\n
Seismic and Newtonian noise: Ground motion and fluctuating gravitational fields from ambient mass motions dominate at low frequencies. Multi-stage isolation, underground siting (as in KAGRA), and careful environmental monitoring help.
\n
Thermal noise: Brownian motion in mirror coatings and suspensions limits mid-band sensitivity. Advanced mirror materials and cryogenic operation reduce these effects.
\n
Quantum noise: At high frequencies, photon shot noise limits sensitivity; at low frequencies, radiation pressure noise on mirrors becomes important. Injecting squeezed light reduces quantum uncertainties in the targeted quadrature, improving performance across the band.\n \n \n\n Inside LIGO Hanford’s Pre-Stabilized Laser enclosure during squeezed-light commissioning work. \n Artist: Nkij\n \n
\n
\n
\n
Laser and control noise: Frequency and amplitude noise, as well as feedback control loops, must be engineered to avoid contaminating the science band.
\n
Environmental couplings: Magnetic fields, acoustic disturbances, and scattered light can imprint spurious signals. Comprehensive monitoring and veto procedures mitigate these couplings.
\n
\n
Each observing run is separated by commissioning periods during which upgrades are installed and characterized. The result has been a steady increase in the volume of space probed (and thus event rates), setting the stage for population-level insights outlined in From Signals to Science and Landmark Discoveries.
\n\n
Multi-Messenger Synergy: Light, Neutrinos, and Gravity
\n\n
\n \n\n Composite images of the galaxy NGC 4993 from multiple ESO instruments showing the kilonova from the neutron-star merger GW170817. \n Artist: VLT/VIMOS; VLT/MUSE; MPG/ESO 2.2-m GROND; VISTA/VIRCAM; VST/OmegaCAM\n \n
\n
\n\n
The brightest success story in multi-messenger astronomy is the binary neutron star event GW170817, which produced:
\n
\n
Gamma rays: A short burst detected seconds after the merger by space-based gamma-ray observatories.
\n
Optical/infrared kilonova: A rapidly evolving transient powered by the radioactive decay of heavy r-process elements synthesized in the ejecta. Spectral features and light-curve evolution illuminated the composition and amount of ejecta.
\n
Radio and X-rays: Afterglow emission as outflows interacted with the surrounding medium, revealing jet structure and energetics.
\n
\n
Coordinated follow-up requires rapid alerts, accurate sky localizations, and cross-disciplinary collaboration. The gravitational-wave network issues public notices that guide telescopes across wavelengths. Neutrino observatories, such as IceCube, conduct counterpart searches and set limits that complement electromagnetic data, especially for black hole mergers that may be electromagnetically quiet.
\n
The future promises even richer synergies: space missions like LISA will provide early warnings for massive black hole mergers, years in advance, allowing deep, time-resolved campaigns. As highlighted in Space-Based and Pulsar Timing Detectors, pulsar timing arrays may also guide targeted searches for low-frequency counterparts in radio and optical surveys of active galactic nuclei.
\n\n
How to Explore Gravitational Wave Data as an Enthusiast
\n
Gravitational-wave astronomy is notably open. If you want to engage directly with the data and methods, there are entry points for a range of skill levels.
\n
Access public data and tools
\n
\n
Gravitational-Wave Open Science Center (GWOSC): Provides data from LIGO and Virgo observing runs, event catalogs, tutorials, and example code notebooks.
\n
Software stacks: Community tools include PyCBC, LALSuite, Bilby, and GWpy, which support data access, filtering, and parameter estimation.
\n
GraceDB: The Gravitational-Wave Candidate Event Database lists low-latency candidates during observing runs, with alerts and updates for the community.
\n
\n
Start with simple analyses
\n
You can reproduce classic results like detecting the chirp of GW150914 by downloading a short data segment and applying a band-pass filter and whitening. Many tutorials walk through these steps. For a hands-on taste of matched filtering, adapt the pseudocode in From Signals to Science to compute a simple signal-to-noise ratio.
\n
Citizen science
\n
Occasional citizen-science projects have invited volunteers to help classify spectrograms or identify noise transients. While automated pipelines do most of the heavy lifting, human intuition remains valuable for detector characterization and education.
\n
As you progress, consider learning Bayesian inference workflows to sample posterior distributions of source parameters. Even plotting the sky localization “banana” for an event is illuminating—revealing how detector geometry shapes what we can learn from the waves themselves.
\n\n
Glossary of Key Terms in Gravitational-Wave Astronomy
\n
\n
Strain (h): Relative change in length induced by a gravitational wave, h = ΔL/L.
\n
Chirp mass: A parameter that governs the rate of frequency increase in a binary inspiral; measured precisely from the waveform.
\n
Ringdown: The damped oscillation phase of a remnant black hole after merger.
\n
Matched filtering: Optimal detection technique that correlates data with theoretically predicted waveforms.
\n
Stochastic background: A random, persistent gravitational-wave signal formed by many unresolved sources.
\n
Hellings–Downs curve: The predicted angular correlation pattern in pulsar timing residuals induced by a gravitational-wave background.
\n
Standard siren: A gravitational-wave source that provides an absolute distance measurement, analogous to a “standard candle” in astronomy.
\n
Quasinormal modes: Characteristic oscillations of perturbed black holes whose frequencies depend on mass and spin.
\n
Tidal deformability: A measure of how easily a neutron star deforms in a tidal field, impacting late-inspiral waveforms.
\n
Quantum squeezing: A technique to reduce quantum noise by manipulating uncertainties in optical fields.
\n
\n\n
Frequently Asked Questions
\n
Can gravitational waves affect life on Earth?
\n
Detections to date involve strains of roughly 10−21 at Earth, corresponding to changes in length far smaller than an atomic nucleus over kilometer scales. Such waves are harmless to people and everyday technology. Their effects are so minute that only the most sensitive instruments can detect them. Even extraordinarily energetic cosmic events have negligible direct influence on human activities through gravitational waves.
\n
How do scientists know gravitational-wave signals are real and not noise?
\n
Detections are vetted through multiple layers: coincidence across geographically separated detectors; signal-consistency tests (e.g., comparing the morphology with physical models); extensive instrumental monitoring to rule out environmental artifacts; and robust statistical analyses that estimate false-alarm rates. For some events—like the binary neutron star merger GW170817—independent electromagnetic observations confirm the astrophysical origin. The combination of rigorous internal checks and external corroboration underpins the reliability of published results.
\n\n
Final Thoughts on Exploring Gravitational Waves
\n\n
\n \n\n Fulldome view of LIGO Hanford Observatory, designed to detect gravitational waves using laser interferometry. \n Artist: NOIRLab/LIGO/NSF/AURA/T. Matsopoulos\n \n
\n
\n\n
Gravitational-wave astronomy has transformed a century-old prediction into a thriving, data-rich science. By measuring the faint ripples from cataclysmic mergers, we probe black holes and neutron stars, test general relativity under extreme conditions, and open new pathways to cosmology. The landscape is inherently multi-band—ground-based interferometers capture kilohertz chirps, pulsar timing arrays reveal nanohertz hums, and the upcoming LISA mission will chart the millihertz frontier. As sensitivity improves, detections will become routine, populations clearer, and rare events—perhaps even unexpected ones—more likely to appear.
\n
If you are curious to go further, explore public data portals, try hands-on tutorials, and follow observing-run alerts. The field is unusually open, welcoming enthusiasts and students alongside specialists. To keep up with new discoveries, methods, and deep-dive explainers, consider subscribing to our newsletter—your front-row seat to the next waves that will shake (ever so gently) our understanding of the universe.
![\"Aerial](\"https://upload.wikimedia.org/wikipedia/commons/thumb/a/a6/LIGO_Hanford_aerial_05.jpg/1280px-LIGO_Hanford_aerial_05.jpg\")
\n![\"NASA](\"https://upload.wikimedia.org/wikipedia/commons/thumb/f/f5/LISA-waves.jpg/1280px-LISA-waves.jpg\")
\n![\"Illustration](\"https://upload.wikimedia.org/wikipedia/commons/1/19/Kilonova_illustration.png\")
\n![\"Inside](\"https://upload.wikimedia.org/wikipedia/commons/thumb/c/cf/Baffled_LIGO_Scientists.jpg/1280px-Baffled_LIGO_Scientists.jpg\")
\n![\"Composite](\"https://upload.wikimedia.org/wikipedia/commons/thumb/8/87/Composite_of_images_of_NGC_4993_and_kilonova_from_many_ESO_instruments_%28eso1733c%29.tiff/lossy-page1-1280px-Composite_of_images_of_NGC_4993_and_kilonova_from_many_ESO_instruments_%28eso1733c%29.tiff.jpg\")
\n![\"Fulldome](\"https://upload.wikimedia.org/wikipedia/commons/thumb/a/a1/LIGO_at_Hanford%2C_Washington_Fulldome_%28LIGO-360-Ext_18-CC-FD%29.jpg/1280px-LIGO_at_Hanford%2C_Washington_Fulldome_%28LIGO-360-Ext_18-CC-FD%29.jpg\")
\n