A solution to the tension of burning on neutron stars and nuclear physics

Abstract

When neutron stars accrete matter from a companion star, this matter forms a disk around them and eventually falls on their surface. Here, the fuel can ignite into bright flashes called Type I bursts. Theoretical calculations based on state-of-the-art nuclear reactions are able to explain many features of the bursts. However, models predict that the bursts should cease at high accretion rates, whereas in many sources they disappear at much lower rates. Moreover, their recurrence times also show strong discrepancies with predictions. Although various solutions have been proposed, none can account for all the observational constraints. Here, we describe a new model that explains all the contradictory behaviors within a single picture. We are able to reconstruct the conditions on the star surface that determine the burst properties by comparing data to new simulations. We find strong evidence that the physical mechanism driving the burst behavior is the structure of the accretion disk in the regions closest to the star. This connection reconciles the puzzling burst phenomenology with nuclear physics and also opens a new window on the study of accretion processes around compact objects.

We thank B. de Marco, A. Marino, and R. Wijnands for useful discussions. L.R.S. and Y.C. dedicate this paper to the loving memory of T.G. Garfield. We thank B. Paxton and all MESA developers for making the code public. Y.C. acknowl- edges support from the grant RYC2021-032718-I, financed by MCIN/AEI/10.13039/501100011033 and the European Union NextGenerationEU/PRTR. M.N.C.’s work is supported by the Fonds de la Recherche Scientifique-FNRS under grant No. IISN 4.4502.19. D.P. acknowledges support from a UNAM-DGAPA grant PAPIIT-IN114424.

Postprint (published version)