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Gravitational microlensing by low-mass objects in the globular cluster M22.

K C Sahu1, S Casertano, M Livio

  • 1Space Telescope Science Institute, Baltimore, MD 21218, USA. ksahu@stsci.edu

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|June 29, 2001
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Gravitational microlensing of the globular cluster M22 revealed a low-mass object of 0.13 solar masses. This study suggests a significant population of free-floating planetary-mass objects within the cluster.

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Area of Science:

  • Astronomy and Astrophysics
  • Exoplanet Research
  • Cosmic Structure Studies

Background:

  • Gravitational microlensing enables direct mass determination of celestial objects.
  • Globular clusters offer ideal conditions for microlensing due to high lensing probability and constrained stellar kinematics.
  • Studying low-mass objects in globular clusters provides insights into early universe star formation and dark baryonic matter.

Purpose of the Study:

  • To determine the mass of a lensing object within the globular cluster M22 using gravitational microlensing.
  • To investigate the abundance of low-mass objects and potential free-floating planetary-mass objects in globular clusters.
  • To assess the implications of microlensing events for understanding the composition of early star formation.

Main Methods:

  • Observation of a globular cluster (M22) against the Galactic bulge's dense stellar field.
  • Analysis of gravitational microlensing events to identify and characterize lensing objects.
  • Determination of lens mass through precise measurements of microlensing parameters.

Main Results:

  • A microlensing event associated with globular cluster M22 yielded a lens mass of 0.13 solar masses.
  • Six additional unresolved events were detected, potentially indicating microlensing.
  • These findings suggest a substantial fraction of cluster mass may comprise free-floating planetary-mass objects.

Conclusions:

  • Gravitational microlensing is effective for mass determination in dense stellar environments like globular clusters.
  • The M22 microlensing event supports the presence of low-mass stellar or sub-stellar objects.
  • The potential detection of free-floating planetary-mass objects has significant implications for models of early universe star formation and dark matter composition.