2,000-20,000 rogue Moon to Jupiter planets per main sequence star

Previously, planets have been detected only in the Milky Way galaxy. Researchers 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. they show that a population of unbound planets between stars with masses ranging from Moon to Jupiter masses is needed to explain the frequent Fe Kα line energy shifts observed in the gravitationally lensed quasar RXJ 1131–1231 at a lens redshift of z = 0.295 or 3.8 billion lt-yr away. They constrain the planet mass-fraction to be larger than 0.0001 of the halo mass, which is equivalent to 2000 objects ranging from Moon to Jupiter mass per main-sequence star or over ∼ 200 objects in Mars to Jupiter range including 0.08 jupiters.

The mass fraction ranges form 0.0001 to 0.001 halo mass.
2000 to 20,000 Moon to Jupiter mass per main-sequence star. Middle of the range is 10,000 Moon to Jupiter mass per main-sequence star

200 to 2000 Mars to Jupiter range including 0.08 jupiters. Middle of the range is 1000 Mars to Jupiter range including 0.08 jupiters.

(Probing Extragalactic Planets Using Quasar Microlensing, The Astrophysical Journal Letters, Xinyu Dai and Eduardo Guerras Published 2018 February 2 2018).

Arxiv – Probing Extragalactic Planets Using Quasar Microlensing (8 pages)

Over the past two decades, it has been established that planets are ubiquitous in the Milky Way galaxy (e.g., Wolszczan & Frail 1992; Mayor & Queloz 1995; Udry & Santos 2007; Lissauer et al. 2014; Winn & Fabrycky 2015). Extrapolating to the extragalactic regime, it is natural to hypothesize that planets are common in external galaxies as well. However, we lack the observational techniques to test this hypothesis, because compared to their Galactic brethren, extragalactic planets are much farther away and much more difficult to separate from the host stars/galaxies. Just as gravitational microlensing provides a unique tool to detect planets in the Galaxy (e.g., Mao & Paczynski 1991; Gould & Loeb 1992; Gaudi 2012), it can also provide the capability to detect planets in extragalactic galaxies, by combining microlensing and a galaxy scale gravitational lens.

They generated a range of magnification maps with αpl ranging from 0.0001 to 0.001, equivalent to 103 – 104 planets in the Moon to Jupiter mass range per main sequence star, where the upper boundary is selected to match the recent limit of floating jupiters in the Milky Way (Mr´oz et al. 2017). Since it is computationally expensive to calculate large magnification maps with a huge number of lenses, they constrain the size of the maps to be 400 × 400rg with each pixel 0.375 rg, and for each set of parameters, they generate 30 random maps to sample the large scale variation of the magnification pattern.

This planet to star mass ratio is equivalent to over∼ 2000 objects per main sequence star in the mass range between Moon and Jupiter, or over ∼ 200 objects in Mars to Jupiter range including 0.08 jupiters. This constraint is consistent with the upper end of the theoretical estimate of ∼ 105Planets and stars in Galaxy and Universe

The Milky Way is the second-largest galaxy in the Local Group, with its stellar disk approximately 100,000 ly (30 kpc) in diameter, and, on average, approximately 1,000 ly (0.3 kpc) thick. As a guide to the relative physical scale of the Milky Way, if the Solar System out to Neptune were the size of a US quarter (24.3 mm (0.955 in)), the Milky Way would be approximately the size of the continental United States. A ring-like filament of stars wrapping around the Milky Way may belong to the Milky Way itself, rippling above and below the relatively flat galactic plane. If so, that would mean a diameter of 150,000–180,000 light-years (46–55 kpc).

The Milky Way contains between 200 and 400 billion stars and at least 100 billion planets. If we assume 300 billion stars and 1,000 Mars to Jupiter size rogue objects.

The vast number of rogue planets suggests that there are 300 trillion Mars to Jupiter size object in the Milky Way.

If the typical galaxy had 100 billion stars, then there would be 2 x 1023 stars in the observable universe.

There should be 2 x 1026 Mars to Jupiter size rogue objects in the observable universe.