In a groundbreaking study, a team of astronomers has identified 21 neutron stars in orbit around Sun-like stars, a rare pairing that sheds new light on the behavior and formation of these dense stellar remnants.
Neutron stars are the dense cores left behind after massive stars explode. Traditionally, they are difficult to detect directly due to their faintness. However, the European Space Agency’s Gaia mission enabled researchers to observe the subtle wobbles in Sun-like stars caused by the gravitational tug of orbiting neutron stars.
“Gaia is continuously scanning the sky and measuring the wobbles of more than a billion stars, so the odds are good for finding even very rare objects,” Kareem El-Badry, an assistant professor of astronomy at Caltech and an adjunct scientist at Germany’s Max Planck Institute for Astronomy, said in a Caltech statement .
The research, detailed in The Open Journal for Astrophysics , involved a global team and incorporated data from ground-based observatories, including the W. M. Keck Observatory in Hawai’i, La Silla Observatory in Chile, and the Whipple Observatory in Arizona. These observations helped determine the masses and orbits of the hidden neutron stars.
Previously detected neutron star systems around Sun-like stars were more compact, often leading to mass transfer between the stars, making the neutron star shine brightly in X-ray or radio wavelengths. In contrast, the newly discovered neutron stars are farther from their partners, between one to three times the distance from Earth to the Sun. This distance prevents them from siphoning material, leaving them dark and quiescent.
“These are the first neutron stars discovered purely due to their gravitational effects,” El-Badry explained.
The discovery challenges current models of binary star formation, as it remains unclear how a neutron star and a Sun-like star can remain gravitationally bound following a supernova explosion. “We still do not have a complete model for how these binaries form,” El-Badry admitted.
The Gaia mission’s sensitivity to wide orbits allowed the detection of these rare systems, most of which are located within 3,000 light-years of Earth. This proximity is relatively close compared to the Milky Way’s 100,000 light-year diameter.
The findings suggest such pairings are exceptionally rare, with El-Badry estimating that only about one in a million Sun-like stars has a neutron star companion in a wide orbit.
El-Badry also aims to discover dormant black holes orbiting Sun-like stars, using Gaia data. His team has already identified two such black holes, including Gaia BH1, the closest known black hole to Earth at 1,600 light-years away.
“There are clearly gaps in our models for the evolution of binary stars,” El-Badry noted. “Finding more of these dark companions and comparing their population statistics to predictions of different models will help us piece together how they form.”
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