The companion candidate near Fomalhaut - a background neutron star?

TL;DR

This paper explores the hypothesis that the Fomalhaut b companion candidate might actually be a background neutron star, based on photometric, astrometric, and theoretical considerations, challenging the planetary interpretation.

Contribution

It proposes a novel explanation for Fomalhaut b as a neutron star, supported by detailed analysis of observational data and theoretical modeling.

Findings

Photometric and astrometric data are consistent with a neutron star at ~11 pc.

Neutron star models fit the optical detections and infrared/X-ray upper limits.

High proper motion aligns with neutron star characteristics.

Abstract

The directly detected planetary mass companion candidate close to the young, nearby star Fomalhaut is a subject of intense discussion. While the detection of common proper motion led to the interpretation as Jovian-mass companion, later non-detections in the infrared raised doubts. Recent astrometric measurements indicate a belt crossing or highly eccentric orbit for the object, if a companion, making the planetary interpretation potentially even more problematic. In this study we discuss the possibility of Fomalhaut\,b being a background object with a high proper motion. By analysing the available photometric and astrometric data of the object, we show that they are fully consistent with a neutron star: Neutron stars are faint, hot (blue), and fast moving. Neutron stars with an effective temperature of the whole surface area being 112,000 K to 126,500 K (with small to negligible extinction) at a distance of roughly 11 pc (best fit) would be consistent with all observables, namely with the photometric detections in the optical, with the upper limits in the infrared and X-rays, as well as with the astrometry (consistent with a distances of 11 pc or more and high proper motion as typical for neutron stars) as well as with non-detection of pulsation (not beamed). We consider the probability of finding an unrelated object or even a neutron star nearby and mostly co-aligned in proper motion with Fomalhaut A and come to the conclusion that this is definitely well possible.