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B. S. Gaudi (IAS)
Recently Sahu et al., using the Hubble Space Telescope to monitor stars in the direction of the old globular cluster M22, detected six events in which otherwise constant stars brightened by ~50% during a time of less than one day. They tentatively interpret these unresolved events as due to microlensing of background bulge stars by a population of free-floating planets in M22. Using various simple analytic arguments, I show that if a population of planetary-mass objects is to explain the microlensing events, they cannot be associated with M22 and furthermore cannot be part of a smoothly-distributed Galactic population. Either there happens to be a massive, dark cluster of planets along our line-of-sight to M22, or the events are not due to microlensing.
This work was supported by NASA through a Hubble Fellowship grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.
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