Astronomers Discover Stellar Graveyard Filled With Black Hole and Neutron Star Collisions

Astronomers have discovered a "stellar graveyard" filled with mergers between extreme stellar remnants like black holes and neutron stars, created when massive stars die in supernova explosions. The newly analyzed data, collected by gravitational wave detectors LIGO, Virgo, and KAGRA, doubles the number of known "mixed mergers" between black holes and neutron stars from 1 to 2. The new research could help scientists better understand the stellar cycle of life and death that births black holes and neutron stars and shed light on the process that sees black holes increase in size by colliding and merging.

A Census of Collisions

According to the research, the detections came from the first half of LIGO-Virgo-KAGRA's fourth observing run (O4), which spanned May 2023 to January 2024. In that period the detectors heard 128 new collisions of black holes and neutron stars. Notably, two of these were the first confirmed events where a black hole merged with a neutron star, doubling the known mixed black hole–neutron star mergers to two.

The rest were mostly black hole pairs, including some record-hefty black holes. Researchers say the upgraded detectors' improved sensitivity allowed them to pick out many faint merger signals from the noise

Significance

Deeper insights into the life and death of stars and the rate of expansion of the universe are provided by new gravitational wave observations. Every detected merger offers a distance-measuring ruler, which aids in improving Hubble constant estimates.

With some of the loudest signals yet, these observations also put Einstein's theory to the test in harsh environments, allowing for accurate verifications of general relativity. In dense stellar environments, the data also suggests unusual formation pathways. New information about the evolution of stars and the universe is revealed by the dead star echoes.