Abstract
We show that the coolest known object that is probably formed in a star-like
mode is a free-floating planet. We discovered recently that the free-floating
planetary mass object OTS,44 (M9.5, \~12 Jupiter masses, age \~2 Myr) has
significant accretion and a substantial disk. This demonstrates that the
processes that characterize the canonical star-like mode of formation apply to
isolated objects down to a few Jupiter masses. We detected in VLT/SINFONI
spectra that OTS44 has strong, broad, and variable Paschen beta emission. This
is the first evidence for active accretion of a free-floating planet. The
object allows us to study accretion and disk physics at the extreme and can be
seen as free-floating analog of accreting planets that orbit stars. Our
analysis of OTS44 shows that the mass-accretion rate decreases continuously
from stars of several solar masses down to free-floating planets. We
determined, furthermore, the disk mass (10 Earth masses) and further disk
properties of OTS44 through modeling its SED including Herschel far-IR data. We
find that objects between 14 and 0.01 solar masses have the same ratio of the
disk-to-central-mass of about 1\%. Our results suggest that OTS44 is formed like
a star and that the increasing number of young free-floating planets and
ultra-cool T and Y field dwarfs are the low-mass extension of the stellar
population.
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