# Searching for strange quark matter objects in exoplanets

## TL;DR

This paper proposes a method to detect strange quark matter objects in exoplanets by searching for extremely close-in planets around pulsars, which could indicate the presence of stable strange quark matter planets due to their unique properties.

## Contribution

It introduces a novel approach to identify strange quark matter planets by analyzing their orbital proximity and stability around pulsars, expanding the search beyond traditional neutron star models.

## Key findings

- No stable close-in planets meeting SQM criteria found around main sequence stars.
- The pulsar planet PSR J1719-1438B is a promising candidate for an SQM planet.
- The method could help distinguish strange quark matter objects from normal matter planets.

## Abstract

The true ground state of hadronic matter may be strange quark matter (SQM). Consequently, the observed pulsars may actually be strange quark stars, but not neutron stars. However, proving or disproving the SQM hypothesis still remains to be a difficult problem, due to the similarity between the macroscopical characteristics of strange quark stars and neutron stars. Here we propose a hopeful method to probe the existence of strange quark matter. In the frame work of the SQM hypothesis, strange quark dwarfs and even strange quark planets can also stably exist. Noting that SQM planets will not be tidally disrupted even when they get very close to their host stars due to their extreme compactness, we argue that we could identify SQM planets by searching for very close-in planets among extrasolar planetary systems. Especially, we should keep our eyes on possible pulsar planets with orbital radius less than $\sim 5.6 \times 10^{10}$~cm and period less than $\sim 6100$~s. A thorough search in the currently detected $\sim 2950$ exoplanets around normal main sequence stars has failed to identify any stable close-in objects that meet the SQM criteria, i.e. lying in the tidal disruption region for normal matter planets. However, the pulsar planet PSR J1719-1438B, with an orbital radius of $\sim 6 \times 10^{10}$~cm and orbital period of $7837$~s, is encouragingly found to be a good candidate.