Here in 2026, something remarkable has happened: the LIGO-Virgo-KAGRA collaboration has just released their results from the second part of their fourth observing run. All told, 161 new gravitational wave events were added to the catalog of successful direct detections, bringing the total number of events up to a staggering 390. Here in 2026, there are:

• four active gravitational wave detectors (with a fifth in the works),
• with sensors, vacuum systems, and quantum-squeezed light that have been upgraded several times,
• now capable of detecting the mergers of compact objects from over 20 billion light-years away,
• spanning mass ranges, for the post-merger remnant, from under 3 solar masses to over 200 solar masses.

It’s a remarkable feat for a field of science that, as little as 11 years ago, had not yet been born. After all, from 1915, when general relativity was first put forth in its final (correct) form until 2015, all attempts at gravitational wave direct detection had only returned null results. The first successful direct detection occurred just days after Advanced LIGO’s original two detectors, in Livingston, LA and Hanford, WA, had started collecting data: on September 14, 2015. A few months later, in early 2016, they announced the results from that detection, where a 36 solar mass and a 29 solar mass black hole had merged into a 62 solar mass object, with the other 3 solar masses worth of energy being carried away in the form of gravitational waves. A tiny amount of energy was deposited in each of LIGO’s two detectors, beginning the era of gravitational wave astronomy.

Here in mid-2026, the number of detection events has skyrocketed to 390, revealing so much about the previously-invisible Universe. Here’s how this all new field of astrophysics has matured so quickly, and what we know today that we didn’t know just a decade ago.

The story of gravitational wave astronomy has progressed rapidly: more rapidly than perhaps anyone could have anticipated. As recently as mid-2015, a full century after Einstein’s general relativity had been put forth, we had only indirect evidence for the existence of gravitational waves: largely inferred by examining the decaying orbits of binary, pulsing neutron stars. If the orbits are decaying, then they’re losing energy, and since energy is conserved for these systems, something must be carrying that energy away. Einstein’s general relativity predicted that the culprit ought to be gravitational waves, but until we observed them directly, we couldn’t be sure.

Gravitational waves are predicted to be quadrupolar in nature: when they pass through a region of space, they alternately compress/shrink and rarify/expand space in mutually perpendicular directions. By building two very long interferometer arms at right angles to one another and sending light down-and-back, very tiny changes in the path length of the two arms relative to one another could be detected by observing changes in how the light from both directions interferes when brought back together. As a gravitational wave passes through, those changes would be detectable by a sensitive enough detector. That design scheme is at the heart of all successful ground-based gravitational wave detectors.

When the two arms of an optical interferometer are of exactly equal length and there is no gravitational wave passing through, the signal is null and the interference pattern is constant. As the arm lengths change, the signal is real and oscillatory, and the interference pattern changes with time in a predictable fashion. This technique is what is used to directly reveal the presence of gravitational waves.

Beginning in the late 20th century, scientists seeking to detect these waves designed and built a prototype detector: the original LIGO. It wasn’t intended to see gravitational waves — not unless something unexpected happened, like a black hole-black hole merger in our own galaxy — but rather to demonstrate the feasibility of this technological approach for seeing gravitational waves. The success of LIGO in meeting their instrumentation and noise goals in the 2000s paved the way for Advanced LIGO: with the twin detectors in Hanford and Livingston beginning science operations in 2015.

When the first signal arrived, many assumed it was either a test being conducted, a mistake, or a prank. After all, based on the detection sensitivities and theoretical predictions, only a handful of events were expected, at most, over several months of operations. Who could have imagined that a bona fide signal would arrive just days after the machine was turned on?

Yet that’s precisely what happened, and just a few months later, the detection was announced to the world. With a signal appearing simultaneously in both detectors, LIGO’s executive director David Reitze began February 16, 2016’s address by simply stating, “Ladies and gentlemen, we have detected gravitational waves. We did it.”

GW150914 was the first ever direct detection and proof of the existence of gravitational waves. The waveform, detected by both LIGO observatories, Hanford and Livingston, matched the predictions of general relativity for a gravitational wave emanating from the inward spiral and merger of a pair of black holes of around 36 and 29 solar masses and the subsequent “ringdown” of the single resulting black hole.

Back in 1609, Galileo turned a modified spyglass skyward for the first time: heralding the era of the telescope. In 1987, neutrinos from a supernova in a nearby galaxy arrived in a particle physics detector, beginning the age of particle astrophysics for objects other than the Sun. (Solar neutrinos had been previously detected beginning in 1968.) But beginning in 2015, we could now see the Universe in an entirely new way: through the gravitational wave signals, or ripples in spacetime, that emerge from massive, compact objects accelerated in strong gravitational fields. A whole new type of astronomy had just been born.

By the end of LIGO’s first observing run in 2016, we had seen two events, later upgraded to three when LVT151012 was reanalyzed in 2018. At the end of the second observing run, after being joined by the Virgo detector in Europe, the total number of detections had increased to 11 by the close of 2018. By the end of 2020, the third observing run — ended earlier than planned due to complications from the COVID-19 pandemic — had brought us up to a total of 90 detections, with Japan’s KAGRA detector joining the LIGO-Virgo collaboration in science operations in early 2020. And the fourth observing run, broken up into three parts spanning from May 2023 to November of 2025, has now released the results from its first two portions (O4A and O4B), bringing our total number of detections up to 390.

We went from no detections to nearly 400 detections (with that number expected to pass 500 with the results from the third portion of the fourth run, O4C) in just the span of a single decade.

This view shows the source of squeezed light within LIGO’s vacuum chamber, taken when the chamber holding the technology was open for maintenance between 2020 and 2023. The frequency-dependent squeezing cavity is not in operation at the time of this photograph, but will be filled with green laser light in a room evacuated of air (and hence, inaccessible to humans) during science operations.

One of main reasons for this rapid increase is the fact that, during the time in between various data runs, upgrades to the systems are conducted. That includes improvements to:

• the vacuum system that the light travels through,
• the reflectivity of the mirrors that reflect the light back-and-forth in the interferometer arms,
• the suspension systems that maintain the stability of the detection apparatus,
• the power of the lasers that generate the light critical to the observatories,
• quieting the noise that still remains in the detector’s readouts,
• and the implementation of all-new quantum squeezing techniques to surpass the previous quantum limits of precision.

With each set of improvements, the capabilities of these gravitational wave observatories expand. Signals become clearer and more prominent, and the detection significance of each event increases. The stronger and cleaner the signal in a larger number of detectors, the better we can perform sky localization: determining where in the Universe the merger event occurred. The distance range over which the detectors are sensitive to increases, and the mass range, particularly at the edges of the detection limits, increases as well.

One of the most powerful illustrations to come out of the latest release from the LIGO-Virgo-KAGRA collaboration is shown below, which breaks down the results of the four main observing runs by color, distance (farther from the center), and time (clockwise, starting at the 12 o’clock position) from 2015 to the present.

This “petrie dish” plot of gravitational wave detections shows the results from four different runs: O1 in blue, O2 in orange, O3 in green, and O4 split up into O4A (in red) and O4B (in violet), with O4C still to come. Time goes clockwise from 2015 at the 12 o’ clock position to 2026 at present, distance to the event is coded by distance from the center, shading represents the significance of the detection, and circle size represents the mass of the merger event. All 390 detections are shown here.

As you can see, the number of detections has increased significantly with each run, as have the significances of the detections and the distances out to which detections can occur. Initially, all of the events were located within just a few billion light-years of Earth, which is important in an observable Universe 46 billion light-years in extent. Remember how volume works in our three-dimensional Universe: if you can upgrade your detector so that you’re sensitive to distances that are twice as far as they were previously, you probe eight times the initial volume, which should octuple your expected event rate. The fact that we only saw two (later, upgraded to three) events in O1 and then eight in O2 was actually great news: leading to hundreds of events at present.

In many ways, the results from gravitational wave astronomy provide our best windows into the Universe as far as understanding the population of stellar mass (as opposed to supermassive) black holes. Back in 2015, there were more than a dozen known stellar mass black holes from electromagnetic observations: because we saw either flares or signals arising from a companion orbiting a black hole within our galaxy. While the number of electromagnetic black holes has subsequently increased — to approximately 50 — the number of black holes observed from gravitational waves is well into the hundreds, even approaching 1000 if you include the pre-merger black holes rather than the post-merger ones.

Unlike the more common “Eagle plot” of gravitational wave events, this format showcases instead the population of post-merger black holes, sorted by mass, as detected in gravitational waves. On the left, in orange, neutron stars are indicated, while as we move to the right, blue colors appear, indicating black holes. The least massive post-merger remnant discovered in this fashion is under 3 solar masses, while the most massive one seen so far exceeds 200 solar masses.

Initially, physicists expected there would be a “mass gap” between about 3 and 5 solar masses, perhaps extending all the way up to 10 solar masses. It remains true that we don’t have a solid astrophysics theory for how to make black holes of that mass range directly from stars, but they clearly exist: we’ve seen them merging in two ways, in addition to the few black holes in that range detected electromagnetically.

• They arise from the merger of smaller-mass objects, like neutron stars.
• And they also arise as precursors to merging objects, where they merge with other objects to make an even heavier black hole.

From the graph above, sorted by the mass of the post-merger object, we can begin making population estimates for stellar mass black holes: how many of them form (from the pre-merger population) of a given mass as a function of the volume of the Universe over which our gravitational wave detectors are sensitive to that mass range. As you can see, there’s a large abundance of black holes between 5 and 20 solar masses, but still a significant abundance above that: going all the way up to the detection limit capabilities of LIGO, Virgo, and KAGRA.

You can also see, from the points along the curve where one of the pre-merger objects dips down to very low masses relative to the post-merger mass, that we have detected events with significantly mismatched masses, enabling us to test the predictions of Einstein’s theory for binary systems with very skewed mass ratios. (The theory passed, if you were wondering.)

This five-panel animation shows the evolution of black holes and neutron stars detected from gravitational wave events. The first, sparsest panel shows only the results from O1 and O2, the second and third panels add in the results from the first and second half of the O3 run (O3A and O3B), while the fourth and fifth panels add in the most recent results from O4A and O4B, with O4C still to come. All told, the number of confirmed detection events has now risen to 390, as of June 2026.

All in all, the newest data release, from the O4B run, adds in 161 new objects, while an additional 11 events — with the advent of reanalysis — have been mined from the earlier O4A run. The improvements that have resulted from the early days of LIGO to the modern era of LIGO-Virgo-KAGRA are even more impressive than you might expect from simply looking at the number of events and the populations of black holes and neutron stars that have been discovered. For example:

• The fourth observing run, with O4C still to come, already accounts for a full 77% of all gravitational wave events ever detected.
• The data reveals expectations for the abundance of “second generation” black holes: black holes that have arisen from the merger of objects that had already experienced mergers previously.
• The data gives us estimates for both the number of black holes and the total mass of black holes expected across the observable Universe, and it’s tremendous: around 40 quintillion black holes, representing 0.04% of the cosmic energy budget.
• The best sky localization ever has been obtained using gravitational waves alone: for event GW240615, which is localized to within just 6 square degrees: as opposed to thousands of square degrees for earlier events. (There are ~40,000 square degrees comprising the entire sky.)
• They also found the clearest, strongest, most significant gravitational wave signal ever in GW250114, enabling the most accurate test of general relativity ever, and confirming Stephen Hawking’s black hole area theorem.

These time-frequency spectrographs show how the signal evolves over time (x-axis) and frequency (y-axis) for each merger event thus far. The brightest spots represent the strongest signal strengths, while the “uptick” at the end of each merger corresponds to the chirp that gets made during the final orbits prior to the merger in question. Note how significantly the event rate grew from O2 (orange) to O3 (blue), and from O3 to O4 (in red and violet), showcasing a remarkable increase in scientific power as driven by the upgrades made to the apparatuses and the addition of new detectors.

Part of what makes this network of detectors so powerful is their complementary natures. Virgo and KAGRA are located in different positions and are oriented at different angles to the LIGO detectors in 3D space, meaning that when a gravitational wave signal passes through them:

• the incoming wave arrives at slightly different times in each location,
• and the gravitational wave alters the relative lengths of the arms in an angle-dependent fashion to the trajectory of the signal,

enabling gravitational wave astronomers to both test the predictions of Einstein’s relativity while simultaneously extracting more information about the location and nature of the event that generated the signal. The more detectors you have, the better you can do.

That’s why it’s such a big deal that in April of 2026, construction began on a fifth (relevant) gravitational wave detector here on Earth: LIGO India. Situated in a location with extremely low seismic noise and housing laser arms of identical 4-kilometer lengths to the LIGO detectors in Hanford and Livingston, it’s currently projected to begin science operations in 2030, joining the other four detectors for the anticipated fifth data run (O5) scheduled to take place between 2028 and 2031. With five detectors, three of which will have 4-kilometer arms (as opposed to Virgo’s and KAGRA’s 3-km arms), vastly superior localization of gravitational wave sources will finally be available: potentially reaching the single-square-degree level of precision for sufficiently strong signals.

This artist concept shows the layout of the LIGO India detector facility, showcasing the flat terrain, laser arms, and science complex at the center. All told, this 174-acre complex expects to begin science operations sometime in 2030, joining the other four active detectors.

What we’ve been able to accomplish, as a civilization, with the birth and growth of gravitational wave astronomy is a stunning example of how spectacularly we can advance when we invest sufficiently in high-risk, high-reward science. Without LIGO, Virgo and KAGRA never would have existed, and LIGO would not have come to fruition without major and sustained investments from the USA’s National Science Foundation. Yet, today, the USA is proposing slashing NSF funding by more than 50% while removing peer-review and science from the decision-making process of what gets funded.

Based on the merits of the underlying science — what’s already known and been established and what we can accomplish in the future — it’s an easy decision to not only continue advancing and upgrading the existing facilities, but to build a more advanced version of LIGO like Cosmic Explorer and funding a space-based gravitational wave detector like LISA. Contrary to the common narrative of competition breeding innovation, science works best when teams share knowledge and countries pool their resources to accomplish bigger things than any of them could do in isolation. The future of gravitational wave astronomy, barely imaginable a decade ago, is brighter than ever. It’s up to all of us not to squander the golden opportunity for discovery that nature has laid out before us.

This article Gravitational wave astronomy is now a fully mature science is featured on Big Think.

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