Two new studies have measured the expansion of the universe in our immediate cosmic neighborhood using a novel method that analyzes the motion of two nearby galaxy groups within their surrounding cosmic flow. The results indicate that the local universe is expanding more slowly than previously estimated, bringing measurements of nearby galaxies into close agreement with observations of the early universe. The findings also suggest that less dark matter is required to explain the dynamics of galaxies within these groups than previously assumed.

The two studies were recently published in Astronomy & Astrophysics by an international team including David Benisty from the Leibniz Institute for Astrophysics Potsdam (AIP). Each paper analyzes observational data for a different nearby galaxy group—the Centaurus A group and the M81 group—to determine both their masses and the value of the Hubble constant.

The Hubble constant describes how fast the universe expands, expressed as a ratio of the recessional velocity to the distance a galaxy has toward us. The Hubble constant is measured in km/s per Megaparsec, 1 Megaparsec being 3.3 million light years.

Scientists have uncovered the first robust evidence of a black hole and neutron star crashing together but orbiting in an oval path rather than a perfect circle just before they merged. This discovery challenges long-standing assumptions about how these cosmic pairs form and evolve.

Researchers from the University of Birmingham, Universidad Autónoma de Madrid, and Max Planck Institute for Gravitational Physics published their findings today (11 Mar) in The Astrophysical Journal Letters.

Most neutron star-black hole pairs are expected to adopt circular orbits long before merging. But the analysis of the gravitational-wave event GW200105 shows that this system traveled on an oval orbit long before merging to form a black hole 13 times more massive than the sun. An oval orbit is something never seen before in this kind of collision.

A new study published in Nature Astronomy indicates that the dense, star-and dark-matter–rich environments around supermassive black hole binaries pack on the order of a million solar masses into each cubic parsec. The team used gravitational-wave data from pulsar timing arrays to probe galactic centers that are otherwise impossible to observe directly.

Pulsar timing arrays (PTAs) use precise measurements of timing residuals from millisecond pulsars to detect gravitational waves at nanohertz frequencies. These arrays revealed a stochastic gravitational-wave background, an incoherent hum from countless supermassive black hole binaries spiraling together across the universe.

However, the signal carries a twist. At the lowest frequencies, the spectrum appears to turn over, deviating from predictions for binaries evolving purely under gravitational-wave emission. That bend suggests that something in the environment, or highly eccentric orbits, is reshaping how these massive binaries lose energy and tighten over time.