A new gravitational-wave catalogue reports 161 additional black hole mergers, bringing the total to 390 detections. Scientists at the University of Glasgow’s Institute for Gravitational Research are celebrating the release of a major new collection of gravitational wave discoveries, a milestone that highlights the rapid growth of gravitational astronomy. The latest Gravitational Wave Transient Catalogue [...]

Scientists believe an unusual LIGO detection may be evidence of a primordial black hole, potentially linking these long-theorized objects to the mystery of dark matter. Scientists at the University of Miami believe they may be closing in on evidence for one of the most elusive objects in the universe: primordial black holes. While definitive proof [...]

Editor’s Note: For the remainder of 2025, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume January 2nd.

Search for Gravitational Waves Emitted from SN 2023ixf

Published May 2025

Main takeaway:

The LIGO, Virgo, and KAGRA collaborations searched for gravitational waves from the core-collapse supernova SN 2023ixf. Though no significant gravitational wave events were detected during times when two or more gravitational wave detectors were online, the non-detection of gravitational waves from this nearby supernova places constraints on the amount of energy emitted by the explosion in the form of gravitational waves, the shape of the proto-neutron star produced in the collapse, and more.

Why it’s interesting:

When a massive star expires in a core-collapse supernova, the collapse of the stellar core into a neutron star or black hole produces gravitational waves. These gravitational waves, along with a stream of neutrinos, should arrive at Earth before the light from the explosion does; gravitational waves and neutrinos can easily escape the dense, roiling ejecta from the explosion, but photons take some time to claw their way through the debris. Gravitational waves from a supernova have never been detected, but the nearby supernova SN 2023ixf, which occurred in a galaxy about 20 million light-years away, offered the best recent opportunity to detect these waves.

What we learned from this non-detection:

Using the non-detection of SN 2023ixf, researchers placed stringent constraints on the gravitational wave energy and luminosity of a supernova explosion, but an even closer supernova is still needed to begin to rule out model predictions for these quantities. To estimate the distance out to which we can expect to detect gravitational waves from collapsing stars, the collaboration members injected synthetic supernova signals into their data. The majority of non-rotating explosions can be detected out to about 22,000 light-years — meaning events on the far side of our galaxy remain inaccessible to current detectors — while rapidly rotating explosions should be detectable out to nearly 100,000 light-years, pushing the detection horizon beyond the borders of the Milky Way.

Citation

A. G. Abac et al 2025 ApJ 985 183. doi:10.3847/1538-4357/adc681

The post Selections from 2025: A Search for Gravitational Waves from SN 2023ixf appeared first on AAS Nova.

Black holes can have messy family histories, and a recent massive merger challenged astronomers to sort out just how many generations of black holes were involved in the event. Recent research, however, may have untangled the lineages of the two progenitors.

A Massive Collision

Earlier this year, the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected the ripples in spacetime caused by the merger of two black holes somewhere in the distant universe. Though these detections have become increasingly common, this one in particular stood out among the more than 200 reported over the last decade. Named GW231123, this event must have caused more of a splash than a ripple since the two black holes that slammed together were unusually massive; both likely weighed more than 100 times the mass of the Sun. Not only that, each was also spinning unusually rapidly prior to the collision.

According to theory, black holes this large are not supposed to form on their own. When massive stars die, they can collapse into a black hole; but, when really massive stars die, the collapse is so violent that no material is left over to form the black hole. So, when researchers first measured the masses of the black holes involved in GW231123, they knew that the black holes involved couldn’t have formed directly from collapsed stars. Instead, they were likely second-generation black holes, meaning that they themselves formed from previous black hole–black hole mergers.

Merger Mystery

This result was celebrated as evidence of so-called “hierarchical formation,” in which black holes formed in dense environments swarm throughout their star clusters, merging with other black holes they encounter and growing ever larger.

However, there were a couple of complications with this picture. For one, theory predicts that it is challenging to form such rapidly spinning black holes from randomly oriented progenitors, since usually the spins wash out and leave the remnant rotating slowly. For another, the merging process tends to give the final black hole a “kick” that sends it flying rapidly away from the site of the impact, occasionally fast enough to leave the star cluster altogether, meaning second-generation black holes might not be able to merge into subsequent generations.

Born as a Pair

New research led by Jakob Stegmann, Max Planck Institute for Astrophysics, suggests a way around each of these problems. In the team’s model, the two black holes involved in the GW231123 merger didn’t form from isolated black holes in a cluster, but rather from binary stars embedded within that cluster. In this picture, two massive stars were born bound together, orbiting one another within a larger cluster of stars. Crucially for this scenario, the massive primordial stars have aligned spins — an expected outcome of massive binary star evolution.

After both stars in the binary collapsed into black holes, these black holes merged to form a rapidly spinning second-generation black hole. This second-generation black hole eventually encountered another black hole within the cluster and merged to produce the ripples in spacetime we observed as GW231123.

Since black holes born within binary systems are expected to have smaller kicks and faster spins, this scenario neatly explains the properties observed in GW231123. As LIGO keeps listening for more black hole mergers, hopefully similar events will provide more chances to untangle their complex family trees.

Citation

“Resolving Black Hole Family Issues Among the Massive Ancestors of Very High-Spin Gravitational-Wave Events like GW231123,” Jakob Stegmann et al 2025 ApJL 992 L226. doi:10.3847/2041-8213/ae0e5f

The post A Black Hole Family Tree appeared first on AAS Nova.

Meet GW241011 and GW241101, two events from the fourth observing run of the LIGO, Virgo, and KAGRA (LVK) gravitational wave detectors. With rapid spins and mismatched black hole masses, both events provide strong evidence for black hole growth through hierarchical mergers.

A Decade of Discovery

Humanity is 10 years into its study of the gravitational wave universe, and detectors across the globe are about to wrap up their fourth observing run. The recently released fourth catalog of gravitational wave transients, GWTC-4.0, more than doubles the number of recorded events.

Today, we’re taking a look at two of the fourth observing run’s gravitational wave events, both of which point to black holes born in dense environments.

Two Detections in the Spotlight

GW241011 and GW241101 are gravitational wave signals that reached Earth in late 2024. Using Bayesian parameter estimation, members of the LVK collaboration determined that each of these two signals arose from the merger of a pair of black holes.

Though the LVK detectors have by now spotted dozens of coalescing black hole pairs, these two detections stand out. GW241011 is the third-loudest gravitational wave signal ever detected, and its primary (i.e., more massive) black hole has one of the largest and most precisely measured spins among black holes detected via gravitational waves.

GW241101 flips the script: its primary black hole also spins rapidly, but it appears to do so in a direction opposite from the direction in which the black holes orbit. Though its spin isn’t measured as precisely as that of the primary black hole in GW241011, this event still provides the best evidence so far that the spins of some merging black holes are misaligned with their orbital motion.

In addition to their standout spin parameters, these events are also remarkable for the masses involved. In both cases, the larger black hole has a mass of 15–20 solar masses, and the smaller black hole is significantly smaller — about 6 solar masses for GW241011 and 8 solar masses for GW241101.

A Black Hole Genealogy Project

The rapid spins and comparatively large masses of the primary black holes of GW241011 and GW241101 don’t line up with what’s expected for black holes arising in isolated binary systems, unsubjected to outside influences. But they do match expectations for hierarchical mergers, in which one or more of the black holes involved is itself the product of a merger.

If these signals arose from hierarchical mergers, that tells us something about the environment in which the black holes lived. When two black holes merge, the product is expected to spin rapidly and receive a “kick.” For a black hole pair in a loose grouping of stars, this kick would likely boot the merger product out of the group, preventing it from encountering other black holes and merging again.

But in dense environments like compact star clusters, even a good strong kick isn’t enough to overcome the cluster’s escape velocity and launch the resulting black hole on a lonely journey through space. Instead, these black holes are retained in the dense cluster environments of their birth, where they may dance and merge with another black hole partner. While it’s not possible to entirely rule out other origins, such as an isolated pair of massive binary stars, the data strongly support the hierarchical merger scenario.

This discovery yet again demonstrates the ability of our gravitational wave detectors to reveal the lives and histories of black holes throughout our universe. Stay tuned for even more black hole news from the current observing run!

Citation

GW241011 and GW241110: Exploring Binary Formation and Fundamental Physics with Asymmetric, High-Spin Black Hole Coalescences,” A. G. Abac et al 2025 ApJL 993 L21. doi:10.3847/2041-8213/ae0d54

The post Not Their First Rodeo: Gravitational Wave Detectors Spot Merging Black Holes That Have Merged Before appeared first on AAS Nova.