The companion candidate near Fomalhaut – a background neutron star?

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 nondetections 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.

Searches for Continuous Gravitational Waves from 15 Supernova Remnants and Fomalhaut b with Advanced LIGO*

“…Fomalhaut b-Considered an extrasolar planet candidate since its discovery in a visible-light image (Kalas et al 2008). Based on a lack of infrared detection, it has been proposed to be a serendipitous discovery of a nearby neutron star (Neuhäuser et al 2015). Parameters are taken from Neuhäuser et al (2015), with the maximum distance an attempt to balance the uncertainties in the scenarios discussed there.…”

“…Based on a lack of infrared detection, it has been proposed to be a serendipitous discovery of a nearby neutron star (Neuhäuser et al 2015). Parameters are taken from Neuhäuser et al (2015), with the maximum distance an attempt to balance the uncertainties in the scenarios discussed there. After this search was run, Poppenhaeger et al (2017) searched for and did not find the object with Chandra.…”

Search for continuous gravitational waves from Fomalhaut b in the second Advanced LIGO observing run with a hidden Markov model

“…However, certain peculiarities, namely its non-detection in the infrared and its potentially highly eccentric orbit, have led to specu-lation over whether or not it is in fact an exoplanet. A different hypothesis has been gaining momentum; rather than a companion object, Fomalhaut b may in fact be a background neutron star to Fomalhaut A [19]. There has also been recent evidence that Fomalhaut b may be a directly imaged catastrophic collision between two large planetesimals in an extrasolar planetary system [20].…”

A Possible Dynamical History for the Fomalhaut System

“…Unidentified conference participant: What do you think about the scenario by Neuhäuser et al (2015) in which Fom b is actually a background neutron star? V. Faramaz: It is not a possibility to exclude completely, however, this scenario fails to explain the fact that the orbit of Fom b was found to be nearly coplanar with the debris ring, as found first by Kalas et al (2013), and confirmed since by Beust et al (2014) and Pearce et al (2015).…”