Rogue planets discovered from Microlensing

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Rogue planets discovered from Microlensing

Post by Sirius_Alpha on 18th May 2011, 9:15 pm

Unbound or Distant Planetary Mass Population Detected by Gravitational Microlensing
http://arxiv.org/abs/1105.3544

Since 1995, more than 500 exoplanets have been detected using different techniques, of which 11 were detected with gravitational microlensing. Most of these are gravitationally bound to their host stars. There is some evidence of free-floating planetary mass objects in young star-forming regions, but these objects are limited to massive objects of 3 to 15 Jupiter masses with large uncertainties in photometric mass estimates and their abundance. Here, we report the discovery of a population of unbound or distant Jupiter-mass objects, which are almost twice (1.8_{-0.8}^{+1.7}) as common as main-sequence stars, based on two years of gravitational microlensing survey observations toward the Galactic Bulge. These planetary-mass objects have no host stars that can be detected within about ten astronomical units by gravitational microlensing. However a comparison with constraints from direct imaging suggests that most of these planetary-mass objects are not bound to any host star. An abrupt change in the mass function at about a Jupiter mass favours the idea that their formation process is different from that of stars and brown dwarfs. They may have formed in proto-planetary disks and subsequently scattered into unbound or very distant orbits.

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Re: Rogue planets discovered from Microlensing

Post by atomic7732 on 18th May 2011, 11:30 pm

That's interesting...

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Re: Rogue planets discovered from Microlensing

Post by Edasich on 19th May 2011, 4:47 am

It is such an unclear paper. No clear planet mass, no rough distance estimate (since some are not considered unbound but distant), only an overload of mathematical signs and scanty parameters
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Re: Rogue planets discovered from Microlensing

Post by Lazarus on 23rd May 2011, 4:16 pm

I'm somewhat sceptical these things are actually rogue planets. One problem is that if these are objects scattered out of their planetary systems, we should probably be seeing a much larger population of massive giant planets on close orbits. These would correspond to the objects that scattered the rogue planets out of the systems in the first place.

I reckon quite a lot of these are wide-orbit planets and sub-brown dwarfs...
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Re: Rogue planets discovered from Microlensing

Post by Sirius_Alpha on 18th March 2012, 8:42 pm

You might be right.

Direct imaging constraints on planet populations detected by microlensing
http://arxiv.org/abs/1203.3647

Results from gravitational microlensing suggested the existence of a large population of free-floating planetary mass objects. The main conclusion from this work was partly based on constraints from a direct imaging survey. This survey determined upper limits for the frequency of stars that harbor giant exoplanets at large orbital separations. Aims. We want to verify to what extent upper limits from direct imaging do indeed constrain the microlensing results. We examine the current derivation of the upper limits used in the microlensing study and re-analyze the data from the corresponding imaging survey. We focus on the mass and semi-major axis ranges that are most relevant in context of the microlensing results. We also consider new results from a recent M-dwarf imaging survey as these objects are typically the host stars for planets detected by microlensing. We find that the upper limits currently applied in context of the microlensing results are probably underestimated. This means that a larger fraction of stars than assumed may harbor gas giant planets at larger orbital separations. Also, the way the upper limit is currently used to estimate the fraction of free-floating objects is not strictly correct. If the planetary surface density of giant planets around M-dwarfs is described as df_Planet ~ a^beta da, we find that beta ~ 0.5 - 0.6 is consistent with results from different observational studies probing semi-major axes between ~0.03 - 30 AU. Having a higher upper limit on the fraction of stars that may have gas giant planets at orbital separations probed by the microlensing data implies that more of the planets detected in the microlensing study are potentially bound to stars rather than free-floating. The current observational data are consistent with a rising planetary surface density for giant exoplanets around M-dwarfs out to ~30 AU.

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Re: Rogue planets discovered from Microlensing

Post by Lazarus on 10th July 2012, 2:32 pm

Interesting to see how this compares to observations of open clusters:

Substellar Objects in Nearby Young Clusters (SONYC) VI: The planetary-mass domain of NGC1333

Our results in NGC1333, as well as findings in several other clusters by ourselves and others, confirm that the star formation process extends into the planetary-mass domain, at least down to 6 MJup. However, given that planemos are 20-50 times less numerous than stars, their contribution to the object number and mass budget in young clusters is negligible. Our findings disagree strongly with the recent claim from a microlensing study that free-floating planetary-mass objects are twice as common as stars - if the microlensing result is confirmed, those isolated Jupiter-mass objects must have a different origin from brown dwarfs and planemos observed in young clusters.
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Re: Rogue planets discovered from Microlensing

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