Level 1 — Absolute Beginner

Far away in space, huge black holes sometimes crash into each other. When this happens, it sends tiny waves through space and time. We call these waves gravitational waves.

A black hole is a place in space where gravity is very, very strong. Nothing can escape it, not even light.

Scientists use special machines called LIGO, Virgo and KAGRA to feel these waves. LIGO is in the United States, Virgo is in Italy, and KAGRA is in Japan.

This month, the scientists shared a new list of black hole crashes. The list is called GWTC-5.0. It has 161 new crashes. Now scientists have found 390 crashes in total. That is the most ever!

black hole

a place in space with very strong gravity that pulls everything in

space

the huge area outside Earth where stars and planets are

wave

a moving ripple, like on water

gravity

the force that pulls things down or together

crash

when two things hit each other hard

machine

a tool built to do a special job

list

a group of things written one after another

catalog

a big list of many items, kept in order

Level 2 — Elementary

Gravitational waves are ripples in space and time. They happen when very heavy objects, like black holes or neutron stars, crash into each other far away in the universe. Albert Einstein predicted these waves more than a hundred years ago, but scientists did not detect one directly until 2015.

To find gravitational waves, scientists use giant detectors called LIGO, Virgo and KAGRA. LIGO has two detectors in the United States, Virgo is in Italy, and KAGRA is in Japan. Each LIGO detector is shaped like a giant L, and each arm of the L is about four kilometers long. The detectors are so sensitive that they can feel ripples much smaller than an atom.

This month, the LIGO-Virgo-KAGRA team released a new catalog called GWTC-5.0, short for Gravitational-Wave Transient Catalog, version 5.0. It is the biggest collection of gravitational-wave detections ever made. The new catalog adds 161 more black hole mergers, bringing the total number of confirmed detections to 390.

The data comes from observations made between April 2024 and the end of January 2025. Among the exciting discoveries are new signs of 'second-generation' black holes, which form when two smaller black holes merge first and then their combined black hole merges again later. One event, called GW240615, gave scientists the most precise location ever measured for a gravitational-wave source, narrowing it down to a patch of sky only about six square degrees wide.

ripple

a small wave that spreads out from a disturbance

neutron star

an extremely dense star left over after a massive star explodes

detector

a machine built to notice or measure something

sensitive

able to notice even very small changes

merger

the joining of two things into one

catalog

an organized collection or list of records

observation

the act of watching and recording something carefully

precise

very exact and accurate

Level 3 — Intermediate

Around July 1, 2026, the LIGO-Virgo-KAGRA scientific collaboration released GWTC-5.0, the fifth and largest version of its Gravitational-Wave Transient Catalog. The release adds 161 newly confirmed black hole mergers, pushing the total number of confirmed gravitational-wave detections to 390 since the field began in 2015. Gravitational waves, ripples in space and time predicted by Albert Einstein more than a century ago, are generated when extraordinarily massive objects such as black holes or neutron stars spiral into and merge with one another.

The new catalog draws on data collected jointly by the LIGO observatories in the United States, Virgo in Italy, and KAGRA in Japan during the first portion of the fourth observing run, spanning April 2024 through the end of January 2025. Each LIGO facility relies on an L-shaped instrument with arms roughly four kilometers long, sensitive enough to register distortions in space-time many times smaller than a single atomic nucleus.

Among the catalog's most notable findings is fresh evidence for so-called second-generation black holes, objects that themselves formed from an earlier merger between two smaller black holes before merging again. Researchers also achieved a first: for one merger, they measured three distinct vibrational 'ringdown' modes echoing from the newly formed black hole in the moments right after it settled into its final shape, offering an unusually detailed acoustic signature of the event.

A separate highlight involves GW240615, a merger detected on June 15, 2024 jointly by both LIGO observatories and Virgo. By combining signals from three widely separated detectors, scientists triangulated its origin to a patch of sky covering only about six square degrees, the most precise sky localization ever achieved for a gravitational-wave source. Such precision could eventually let astronomers point conventional telescopes at the same patch of sky in hopes of spotting a visible counterpart to the event.

collaboration

a joint scientific effort involving multiple institutions or teams

transient

lasting only a short time before fading

spiral

to move in a curving path that gradually closes inward

observing run

a defined period during which detectors actively collect data

ringdown

the fading vibration of a newly formed black hole settling into a stable shape

acoustic signature

a distinctive pattern of vibration or sound that identifies an event

triangulate

to determine a location by combining signals from several separated points

sky localization

the process of narrowing down where in the sky a signal originated

Level 4 — Advanced

On or around July 1, 2026, the LIGO-Virgo-KAGRA collaboration published GWTC-5.0, the fifth iteration of its Gravitational-Wave Transient Catalog and, by a wide margin, the most extensive compendium of gravitational-wave detections assembled to date. The release incorporates 161 newly confirmed compact binary mergers, raising the cumulative tally of confirmed detections since the field's inception in 2015 to 390, a milestone that underscores how rapidly the observational census of merging black holes has expanded within a single decade.

The underlying data derive from the initial segment of the fourth observing run, spanning April 2024 through the close of January 2025, gathered jointly by the twin LIGO interferometers in the United States, Virgo in Italy, and KAGRA in Japan. Each LIGO installation employs an L-shaped interferometer with arms extending roughly four kilometers, engineered to register space-time strain many orders of magnitude smaller than the diameter of an atomic nucleus, a testament to decades of refinement in laser stabilization and vibration isolation.

Scientifically, the catalog's most consequential entries concern hierarchical, or second-generation, black holes: remnants that themselves emerged from an earlier merger of two smaller black holes before participating in a subsequent coalescence. Corroborating evidence for such hierarchical formation carries implications for astrophysical formation channels, particularly dense stellar environments such as globular clusters, where repeated mergers are thought to be more plausible than in isolated binary star systems. Separately, researchers achieved an unprecedented measurement of three distinct ringdown modes, the characteristic vibrational overtones by which a newly formed black hole relaxes toward its final, stationary Kerr geometry, a result that offers a rare observational handle on black hole spectroscopy and, by extension, tests of general relativity in the strong-field regime.

A further highlight is GW240615, a merger recorded on June 15, 2024 by the coincident detection of both LIGO observatories and Virgo. The triple-detector coincidence enabled triangulation of the source to a sky region of only about six square degrees, the tightest localization ever achieved for a gravitational-wave event and a benchmark that illustrates the value of maintaining a geographically dispersed detector network. Such precision sky localization is the critical prerequisite for multimessenger follow-up, in which conventional telescopes attempt to identify an electromagnetic counterpart, though no counterpart has been reported for this particular event.

compendium

a comprehensive collection of information on a subject

compact binary

a pair of extremely dense astronomical objects, such as black holes or neutron stars, orbiting each other

interferometer

an instrument that detects tiny changes by comparing beams of light