Journal Article

Nomads of the Galaxy

Louis E. Strigari, Matteo Barnabè, Philip J. Marshall and Roger D. Blandford

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 423, issue 2, pages 1856-1865
Published in print June 2012 | ISSN: 0035-8711
Published online June 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.21009.x
Nomads of the Galaxy

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We estimate that there may be up to ∼105 compact objects in the mass range 10−8–10−2 M 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 analyse the prospects for detecting nomads via Galactic microlensing. The Wide-Field Infrared Survey Telescope will measure the number of nomads per-main-sequence star greater than the mass of Jupiter to ∼13 per cent, and the corresponding number greater than the mass of Mars to ∼25 per cent. All-sky surveys such as Gaia and Large Synoptic Survey Telescope can identify nomads greater than about the mass of Jupiter. We suggest a dedicated drift scanning telescope that covers approximately 100 deg2 in the Southern hemisphere could identify nomads via microlensing of bright stars with characteristic time-scales of tens to hundreds of seconds.

Keywords: gravitational lensing: micro; planets and satellites: detection; planets and satellites: general

Journal Article.  8189 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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