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No large population of unbound or wide-orbit Jupiter-mass planets

Nature volume 548, pages 183–186 (2017)Cite this article

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Abstract

Planet formation theories predict that some planets may be ejected from their parent systems as result of dynamical interactions and other processes1,2,3. Unbound planets can also be formed through gravitational collapse, in a way similar to that in which stars form4. A handful of free-floating planetary-mass objects have been discovered by infrared surveys of young stellar clusters and star-forming regions5,6 as well as wide-field surveys7, but these studies are incomplete8,9,10 for objects below five Jupiter masses. Gravitational microlensing is the only method capable of exploring the entire population of free-floating planets down to Mars-mass objects, because the microlensing signal does not depend on the brightness of the lensing object. A characteristic timescale of microlensing events depends on the mass of the lens: the less massive the lens, the shorter the microlensing event. A previous analysis11 of 474 microlensing events found an excess of ten very short events (1–2 days)—more than known stellar populations would suggest—indicating the existence of a large population of unbound or wide-orbit Jupiter-mass planets (reported to be almost twice as common as main-sequence stars). These results, however, do not match predictions of planet-formation theories3,12 and surveys of young clusters8,9,10. Here we analyse a sample of microlensing events six times larger than that of ref. 11 discovered during the years 2010–15. Although our survey has very high sensitivity (detection efficiency) to short-timescale (1–2 days) microlensing events, we found no excess of events with timescales in this range, with a 95 per cent upper limit on the frequency of Jupiter-mass free-floating or wide-orbit planets of 0.25 planets per main-sequence star. We detected a few possible ultrashort-timescale events (with timescales of less than half a day), which may indicate the existence of Earth-mass and super-Earth-mass free-floating planets, as predicted by planet-formation theories3,12.

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Figure 1: Observed distribution of timescales of 2,617 high-quality microlensing events discovered by OGLE in 2010–15.
Figure 2: Distribution of event timescales corrected for the detection efficiency.
Figure 3: Light curves of ultrashort microlensing event candidates.

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References

  1. Rasio, F. A. & Ford, E. B. Dynamical instabilities and the formation of extrasolar planetary systems. Science 274, 954–956 (1996)

    Article  ADS  CAS  Google Scholar 

  2. Weidenschilling, S. J. & Marzari, F. Gravitational scattering as a possible origin for giant planets at small stellar distances. Nature 384, 619–621 (1996)

    Article  ADS  CAS  Google Scholar 

  3. Veras, D. & Raymond, S. N. Planet–planet scattering alone cannot explain the free-floating planet population. Mon. Not. R. Astron. Soc. 421, L117–L121 (2012)

    Article  ADS  Google Scholar 

  4. Luhman, K. L. The formation and early evolution of low-mass stars and brown dwarfs. Annu. Rev. Astron. Astrophys. 50, 65–106 (2012)

    Article  ADS  CAS  Google Scholar 

  5. Zapatero Osorio, M. R. et al. Discovery of young, isolated planetary mass objects in the σ Orionis star cluster. Science 290, 103–107 (2000)

    Article  ADS  CAS  Google Scholar 

  6. Liu, M. C. et al. The extremely red, young L dwarf PSO J318.5338–22.8603: a free-floating planetary-mass analog to directly imaged young gas-giant planets. Astrophys. J. 777, L20 (2013)

    Article  ADS  Google Scholar 

  7. Dupuy, T. J. & Kraus, A. L. Distances, luminosities, and temperatures of the coldest known substellar objects. Science 341, 1492–1495 (2013)

    Article  ADS  CAS  Google Scholar 

  8. Scholz, A. et al. Substellar objects in nearby young clusters (SONYC). VI. The planetary-mass domain of NGC 1333. Astrophys. J. 756, 24 (2012)

    Article  ADS  Google Scholar 

  9. Peña Ramírez, K., Béjar, V. J. S., Zapatero Osorio, M. R., Petr-Gotzens, M. G. & Martín, E. L. New isolated planetary-mass objects and the stellar and substellar mass function of the σ Orionis cluster. Astrophys. J. 754, 30 (2012)

    Article  ADS  Google Scholar 

  10. Mužić, K., Scholz, A., Geers, V. C. & Jayawardhana, R. Substellar objects in nearby young clusters (SONYC). IX: The planetary-mass domain of Chamaeleon-I and updated mass function in Lupus-3. Astrophys. J. 810, 159 (2015)

    Article  ADS  Google Scholar 

  11. Sumi, T. et al. Unbound or distant planetary mass population detected by gravitational microlensing. Nature 473, 349–352 (2011)

    Article  ADS  CAS  Google Scholar 

  12. Ma, S., Mao, S., Ida, S., Zhu, W. & Lin, D. N. C. Free-floating planets from core accretion theory: microlensing predictions. Mon. Not. R. Astron. Soc. 461, L107–L111 (2016)

    Article  ADS  Google Scholar 

  13. Udalski, A., Szymański, M. K. & Szymański, G. OGLE-IV: fourth phase of the Optical Gravitational Lensing Experiment. Acta Astron. 65, 1–38 (2015)

    ADS  Google Scholar 

  14. Woźniak, P. & Paczyzński, B. Microlensing of blended stellar images. Astrophys. J. 487, 55–60 (1997)

    Article  ADS  Google Scholar 

  15. Bennett, D. P. et al. Planetary and other short binary microlensing events from the MOA short-event analysis. Astrophys. J. 757, 119 (2012)

    Article  ADS  Google Scholar 

  16. Calchi Novati, S., de Luca, F., Jetzer, P., Mancini, L. & Scarpetta, G. Microlensing constraints on the Galactic bulge initial mass function. Astron. Astrophys. 480, 723–733 (2008)

    Article  ADS  Google Scholar 

  17. Han, C. & Gould, A. The mass spectrum of MACHOs from parallax measurements. Astrophys. J. 447, 53 (1995)

    Article  ADS  Google Scholar 

  18. Han, C. & Gould, A. Stellar contribution to the galactic bulge microlensing optical depth. Astrophys. J. 592, 172–175 (2003)

    Article  ADS  Google Scholar 

  19. Lafrenière, D. et al. The Gemini Deep Planet Survey. Astrophys. J. 670, 1367–1390 (2007)

    Article  ADS  Google Scholar 

  20. Bowler, B. P., Liu, M. C., Shkolnik, E. L. & Tamura, M. Planets around low-mass stars (PALMS). IV. The outer architecture of M dwarf planetary systems. Astrophys. J. Suppl. Ser. 216, 7 (2015)

    Article  ADS  Google Scholar 

  21. Clanton, C. & Gaudi, B. S. Constraining the frequency of free-floating planets from a synthesis of microlensing, radial velocity, and direct imaging survey results. Astrophys. J. 834, 46 (2017)

    Article  ADS  Google Scholar 

  22. Ida, S., Lin, D. N. C. & Nagasawa, M. Toward a deterministic model of planetary formation. VII. Eccentricity distribution of gas giants. Astrophys. J. 775, 42 (2013)

    Article  ADS  Google Scholar 

  23. Pfyffer, S., Alibert, Y., Benz, W. & Swoboda, D. Theoretical models of planetary system formation. II. Post-formation evolution. Astron. Astrophys. 579, A37 (2015)

    Article  ADS  Google Scholar 

  24. Barclay, T., Quintana, E. V., Raymond, S. N. & Penny, M. T. The demographics of rocky free-floating planets and their detectability by WFIRST. Astrophys. J. 841, 86 (2017)

    Article  ADS  Google Scholar 

  25. Spergel, D. et al. Wide-Field InfraRed Survey Telescope-Astrophysics Focused Telescope Assets WFIRST-AFTA 2015 report. Preprint at https://arxiv.org/abs/1503.03757 (2015)

  26. Penny, M. T. et al. ExELS: an exoplanet legacy science proposal for the ESA Euclid mission—I. Cold exoplanets. Mon. Not. R. Astron. Soc. 434, 2–22 (2013)

    Article  ADS  Google Scholar 

  27. Mao, S. & Paczynski, B. Mass determination with gravitational microlensing. Astrophys. J. 473, 57 (1996)

    Article  ADS  Google Scholar 

  28. Alard, C. & Lupton, R. H. A method for optimal image subtraction. Astrophys. J. 503, 325–331 (1998)

    Article  ADS  Google Scholar 

  29. Woźniak, P. R. Difference image analysis of the OGLE-II bulge data. I. The method. Acta Astron. 50, 421–450 (2000)

    ADS  Google Scholar 

  30. Udalski, A. The Optical Gravitational Lensing Experiment. Real time data analysis systems in the OGLE-III survey. Acta Astron. 53, 291–305 (2003)

    ADS  Google Scholar 

  31. Skowron, J. et al. Analysis of photometric uncertainties in the OGLE-IV Galactic bulge microlensing survey data. Acta Astron. 66, 1–14 (2016)

    ADS  Google Scholar 

  32. Wyrzykowski, Ł. et al. OGLE-III microlensing events and the structure of the Galactic bulge. Astrophys. J. Suppl. Ser. 216, 12 (2015)

    Article  ADS  Google Scholar 

  33. Wray, J. J., Eyer, L. & Paczyński, B. OGLE small-amplitude variables in the Galactic bar. Mon. Not. R. Astron. Soc. 349, 1059–1068 (2004)

    Article  ADS  Google Scholar 

  34. Park, B.-G. et al. MOA-2003-BLG-37: a bulge jerk-parallax microlens degeneracy. Astrophys. J. 609, 166–172 (2004)

    Article  ADS  Google Scholar 

  35. Jiang, G. et al. OGLE-2003-BLG-238: microlensing mass estimate for an isolated star. Astrophys. J. 617, 1307–1315 (2004)

    Article  ADS  Google Scholar 

  36. Smith, M. C., Woźniak, P., Mao, S. & Sumi, T. Blending in gravitational microlensing experiments: source confusion and related systematics. Mon. Not. R. Astron. Soc. 380, 805–818 (2007)

    Article  ADS  Google Scholar 

  37. Hawley, S. L. et al. Kepler flares. I. Active and inactive M dwarfs. Astrophys. J. 797, 121 (2014)

    Article  ADS  Google Scholar 

  38. Holtzman, J. A. et al. The luminosity function and initial mass function in the Galactic bulge. Astron. J. 115, 1946–1957 (1998)

    Article  ADS  Google Scholar 

  39. Gould, A. Extending the MACHO search to about 106 solar masses. Astrophys. J. 392, 442 (1992)

    Article  ADS  Google Scholar 

  40. Bennett, D. P. & Rhie, S. H. Detecting Earth-mass planets with gravitational microlensing. Astrophys. J. 472, 660–664 (1996)

    Article  ADS  Google Scholar 

  41. Kiraga, M. & Paczynski, B. Gravitational microlensing of the Galactic bulge stars. Astrophys. J. 430, L101–L104 (1994)

    Article  ADS  Google Scholar 

  42. Han, C. & Gould, A. Statistical determination of the MACHO mass spectrum. Astrophys. J. 467, 540 (1996)

    Article  ADS  Google Scholar 

  43. Bissantz, N., Debattista, V. P. & Gerhard, O. Large-scale model of the Milky Way: stellar kinematics and the microlensing event timescale distribution in the Galactic bulge. Astrophys. J. 601, L155–L158 (2004)

    Article  ADS  Google Scholar 

  44. Wood, A. & Mao, S. Optical depths and time-scale distributions in Galactic microlensing. Mon. Not. R. Astron. Soc. 362, 945–951 (2005)

    Article  ADS  Google Scholar 

  45. Dwek, E. et al. Morphology, near-infrared luminosity, and mass of the Galactic bulge from COBE DIRBE observations. Astrophys. J. 445, 716–730 (1995)

    Article  ADS  Google Scholar 

  46. Zheng, Z., Flynn, C., Gould, A., Bahcall, J. N. & Salim, S. M dwarfs from Hubble Space Telescope star counts. Astrophys. J. 555, 393–404 (2001)

    Article  ADS  Google Scholar 

  47. Gould, A. Measuring the remnant mass function of the Galactic bulge. Astrophys. J. 535, 928–931 (2000)

    Article  ADS  Google Scholar 

  48. Williams, K. A., Bolte, M. & Koester, D. Probing the lower mass limit for supernova progenitors and the high-mass end of the initial-final mass relation from white dwarfs in the open cluster M35 (NGC 2168). Astrophys. J. 693, 355–369 (2009)

    Article  ADS  CAS  Google Scholar 

  49. Kiziltan, B., Kottas, A., De Yoreo, M. & Thorsett, S. E. The neutron star mass distribution. Astrophys. J. 778, 66 (2013)

    Article  ADS  Google Scholar 

  50. Özel, F., Psaltis, D., Narayan, R. & McClintock, J. E. The black hole mass distribution in the Galaxy. Astrophys. J. 725, 1918–1927 (2010)

    Article  ADS  Google Scholar 

  51. Zoccali, M. et al. The initial mass function of the Galactic bulge down to 0.15 Msolar . Astrophys. J. 530, 418–428 (2000)

    Article  ADS  Google Scholar 

  52. Belczynski, K. et al. Compact object modeling with the StarTrack population synthesis code. Astrophys. J. Suppl. Ser. 174, 223–260 (2008)

    Article  ADS  CAS  Google Scholar 

  53. Kroupa, P. On the variation of the initial mass function. Mon. Not. R. Astron. Soc. 322, 231–246 (2001)

    Article  ADS  Google Scholar 

  54. Wegg, C., Gerhard, O. & Portail, M. MOA-II Galactic microlensing constraints: the inner Milky Way has a low dark matter fraction and a near maximal disc. Mon. Not. R. Astron. Soc. 463, 557–570 (2016)

    Article  ADS  CAS  Google Scholar 

  55. Alves de Oliveira, C. The low mass end of the IMF. Mem. Soc. Astron. Ital. 84, 905 (2013)

    ADS  Google Scholar 

  56. Allen, P. R., Koerner, D. W., Reid, I. N. & Trilling, D. E. The substellar mass function: a Bayesian approach. Astrophys. J. 625, 385–397 (2005)

    Article  ADS  Google Scholar 

  57. Quanz, S. P., Lafrenière, D., Meyer, M. R., Reggiani, M. M. & Buenzli, E. Direct imaging constraints on planet populations detected by microlensing. Astron. Astrophys. 541, A133 (2012)

    Article  ADS  Google Scholar 

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Acknowledgements

We thank M. Kubiak and G. Pietrzyński, former members of the OGLE team, for their contribution to the collection of the OGLE photometric data over the past years. The OGLE project has received funding from the National Science Center, Poland through grant MAESTRO 2014/14/A/ST9/00121 to A.U.

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Authors and Affiliations

  1. Warsaw University Observatory, Aleje Ujazdowskie 4, Warsaw, 00-478, Poland

    Przemek Mróz, Andrzej Udalski, Jan Skowron, Radosław Poleski, Szymon Kozłowski, Michał K. Szymański, Igor Soszyński, Łukasz Wyrzykowski, Paweł Pietrukowicz, Krzysztof Ulaczyk, Dorota Skowron & Michał Pawlak

  2. Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, 43210, Ohio, USA

    Radosław Poleski

  3. Department of Physics, University of Warwick, Coventry CV4 7AL, UK

    Krzysztof Ulaczyk

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Contributions

P.M. analysed and interpreted the data, and prepared the manuscript. A.U. initiated the project, reduced the data, and conducted detection efficiency simulations. All authors collected the OGLE photometric observations, reviewed, discussed and commented on the present results and on the manuscript.

Corresponding author

Correspondence to Przemek Mróz.

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Reviewer Information Nature thanks C. Clanton, S. Raymond and T. Sumi for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Figure 1 Galactic bulge luminosity function used for simulations.

a, Deep luminosity function (LF) for subfield BLG513.12, which was observed both by the OGLE-IV survey and by the Hubble Space Telescope (HST)38. Both luminosity functions overlap in the range 16 mag < I < 18 mag. This deep luminosity function was used as a template to generate artificial microlensing events in analysed fields, after shifting to match the centroid of the red clump giant stars in a given field. b, Comparison between the observed luminosity function for subfield BLG512.32 and the simulated luminosity function.

Extended Data Figure 2 Detection efficiency curves.

Detection efficiencies as a function of the Einstein timescale tE for all analysed fields (averages for all subfields in the given field). Fields BLG501, BLG505 and BLG512 were observed with a 20-min cadence, and the remaining fields with a 60-min cadence. Error bars are the 1σ Poisson uncertainties on the counts of the number of simulated events in a given tE bin.

Extended Data Figure 3 Comparison between measured Einstein timescales tE,out and ‘real’ (simulated) timescales tE,in for simulated events.

Only events passing selection criteria from Extended Data Table 3 (including the cut on the blending parameter fs > 0.1) are shown. Note that the colour scale is logarithmic. There is no systematic offset between measured and real timescales.

Extended Data Figure 4 Comparison between measured and ‘real’ (simulated) parameters.

a, Ratio between the measured Einstein timescale tE,out and ‘real’ (simulated) timescale tE,in for simulated events versus the blending parameter fs = Fs/(Fs + Fb). Timescales of faint and highly blended (fs < 0.1) events are not well measured and are biased by a strong degeneration between Einstein timescale, blending and impact parameters. Timescales of events showing a high negative blending (fs > 1.5) are systematically underestimated, but the bias is relatively small and such events comprise a negligible fraction of all events. b, Distributions of tE,out/tE,in for simulated events passing selection criteria from Extended Data Table 3 (including the cut on the blending parameter fs > 0.1). Regardless of the timescale, there is no systematic bias between measured and real timescales within 1%. For 90% of simulated events 0.63 < tE,out/tE,in < 1.65. The MAD is the median absolute deviation from the data’s median.

Extended Data Figure 5 Constraints on IMF slopes.

a, Assuming that all lenses are single; b, assuming binary fraction fbin = 0.4.

Extended Data Table 1 Best-fitting parameters for ultrashort microlensing event candidates
Full size table
Extended Data Table 2 Basic information about analysed fields
Full size table
Extended Data Table 3 Selection criteria for high-quality microlensing events
Full size table
Extended Data Table 4 Number of events detected in individual timescale bins
Full size table
Extended Data Table 5 Detection efficiencies for the analysed fields
Full size table

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Mróz, P., Udalski, A., Skowron, J. et al. No large population of unbound or wide-orbit Jupiter-mass planets. Nature 548, 183–186 (2017). https://doi.org/10.1038/nature23276

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