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Looking for new neutron stars in our neighbourhood with Gaia

Unique study discovers 20 new neutron star candidates in catalogues and provides methods and tools to find more

Neutron stars are unique remnants of supernova explosions. Only a small fraction of the vast population of these compact objects in our Milky Way has been discovered so far. Now, a researcher at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute) in Hannover has for the first time developed and described new methods to identify nearby neutron stars in data from the astrometry space mission Gaia. Additionally, he provided the tools to crosscheck candidates with more than a dozen source catalogues covering the entire electromagnetic spectrum (gamma rays, X-rays, ultraviolet, broad-optical, infrared, and radio waves). The novel search unveiled more than 20 new possible neutron stars in distances between 50 and up to around 150 pc from Earth. For each candidate, the study provides information to enable further studies, for example by searching for continuous gravitational waves from them. This might allow to examine the interior structure of these still mysterious objects. With the methods described in the publication, more discoveries are possible by either using other samples from the Gaia catalogue or expanding the study to additional electromagnetic catalogues.

Paper abstract

Neutron stars are identified as pulsars, X-ray binary components, central objects of supernovae remnants, or isolated thermally emitting sources, and at distances beyond 120 pc. A population extrapolation suggests 103 objects within that boundary. Potentially, neutron stars could continuously emit gravitational wave signals at sensitivity reach of present instrumentation. As part of our Search for the Nearest Neutron Stars “Five Seasons” project, we search for nearby resolved neutron stars. Based on expected fluxes and magnitudes of thermally cooling neutron stars and pulsars, we selected sources in Gaia DR3 with G-band absolute magnitudes M_G>16 mag, parallax signal-to-noise ratios greater than two, and colours G_BP–G>0.78 and G–G_RP>0.91 mag for power-law emitters of flux F_ν ∝ ν^–ɑ_ν with spectral indices ɑ_ν< 3. The photometric region overlaps with that of white dwarfs, in confluence with most known pulsars in binaries having white dwarf companions. We looked for counterparts in gamma-ray, X-ray, ultraviolet, radio, optical, and infrared catalogues. We find about two X-ray-, 15 ultraviolet-, one radio probable counterparts, and at least four sources with power-law profiles at the ultraviolet–optical(–infrared). Because the sources have G≳20 mag, we rely on Gaia DR3 single-source parameters. We identify possible binaries based on photo- astrometric parameters, visual companions, and flux excesses. Some emission components suggest small thermal radiuses. Source types, relatedness to neutron stars, and properties require further inquiry.