2012/01/12 by Louis E. Strigari, Matteo Barnabè, Matteo Barnabe +2 · 3 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph.EP #astro-ph.GA
paper · pdf · doi:10.1111/j.1365-2966.2012.21009.x
published as Mon.Not.Roy.Astron.Soc. 423:1856-1865, 2012 · 10 pages, 6 figures
arxiv created 2012/01/12 · openalex publication_date 2012/05/02 · arxiv updated 2015/06/03 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
We estimate that there may be up to ~105 compact objects in the mass range 10-8 -10-2 solar mass per main sequence star that are unbound to a host star in the Galaxy. We refer to these objects as nomads; in the literature a subset of these are sometimes called free-floating or rogue planets. Our estimate for the number of Galactic nomads is consistent with a smooth extrapolation of the mass function of unbound objects above the Jupiter-mass scale, the stellar mass density limit, and the metallicity of the interstellar medium. We analyze the prospects for detecting nomads via Galactic microlensing. The Wide-Field Infrared Survey Telescope (WFIRST) will measure the number of nomads per main sequence star greater than the mass of Jupiter to ~ 13%, and the corresponding number greater than the mass of Mars to ~25%. All-sky surveys such as GAIA and LSST can identify nomads greater than about the mass of Jupiter. We suggest a dedicated drift scanning telescope that covers approximately 100 square degrees in the Southern hemisphere could identify nomads as small as 10-8 solar mass via microlensing of bright stars with characteristic lightcurve timescales of a few seconds.