Probing Planets in Extragalactic Galaxies Using Quasar Microlensing

TL;DR

This paper demonstrates that quasar microlensing can be used to detect and study extragalactic planets, revealing a population of unbound planets in distant galaxies through analysis of emission line shifts.

Contribution

It introduces a novel method using quasar microlensing to probe extragalactic planets and constrains their population and mass fraction in a lens galaxy.

Findings

Unbound planets between stars are needed to explain observed emission line shifts.

The planet mass fraction in the lens galaxy exceeds 0.0001 of the halo mass.

Approximately 2,000 unbound planets per star are implied by the data.

Abstract

Previously, planets have been detected only in the Milky Way galaxy. Here, we show that quasar microlensing provides a means to probe extragalactic planets in the lens galaxy, by studying the microlensing properties of emission close to the event horizon of the supermassive black hole of the background quasar, using the current generation telescopes. We show that a population of unbound planets between stars with masses ranging from Moon to Jupiter masses is needed to explain the frequent Fek line energy shifts observed in the gravitationally lensed quasar RXJ1131-1231 at a lens redshift of $z=0.295$ or 3.8 billion light-years away. We constrain the planet mass fraction to be larger than 0.0001 of the halo mass, which is equivalent to 2,000 objects ranging from Moon to Jupiter mass per main sequence star.