Double neutron stars are pairs of ultra-dense remnants of exploded massive stars. They orbit each other and gradually spiral closer until they merge in a powerful flash — a source of gravitational waves. But where do such pairs actually form? One possibility is inside star clusters, where stars are plentiful and interact closely.
Astronomers took motion data for 11 such pairs and 167 globular clusters (dense, ancient 'balls' of stars) and 2967 open clusters (younger, looser groups). Then they 'ran the tape backward' in time, like rewinding a film.
But open clusters are far more interesting.
Especially lucky is the double pulsar J0737-3039—a pair of neutron stars that emit radio pulses like two lighthouses. Its past trajectory intersects the young open cluster Theia 58: the probability of being born there is about 14%. It's like finding an old photograph that shows where you come from.
So some of these pairs may start their lives in relatively small, young stellar families.
as written by the authors arXiv:2602.14145
We investigate the potential birthplace of Galactic binary neutron star (BNS) systems through a kinematic analysis. Using high-precision astrometry from Gaia DR3, updated pulsar distances, and Monte Carlo sampling of astrometric errors, we integrate the past trajectories of 11 Galactic BNSs and 167 globular clusters plus 2967 open clusters, to search for past encounters. Our results suggest that BNS origin in globular clusters is unlikely, with low encounter probabilities (e.g., $$\lesssim 0.5\%$$ for NGC 5139) and requiring excessive ejection velocities. Conversely, our analysis indicates that open clusters are a non-negligible formation channel. Specifically, the double pulsar J0737$$-$$3039 shows a $$13.9\%$$ ($$5.4\%$$) probability of originating from the young cluster OC 0450 (Theia 58). Based on encounter proximity and time, we argue that Theia 58 is its more plausible birthplace. Our work provides kinematic evidence consistent with an open-cluster origin for a subset of field BNSs.
The double pulsar J0737-3039 is the only known pair where both components are visible as pulsars; they orbit each other in just 2.4 hours.
In Carl Sagan's novel 'Contact', the heroine travels through a system of black holes, but neutron star mergers in reality are also 'wormholes' for gravitational waves.