THE MACHO PROJECT - LIMITS ON PLANETARY MASS DARK-MATTER IN THE GALACTIC HALO FROM GRAVITATIONAL MICROLENSING

The MACHO project has been monitoring about 10 million stars in the La rge Magellanic Cloud (LMC) in the search for gravitational microlensin g events caused by massive compact halo objects (MACHOs) in the halo o f the Milky Way. In our standard analysis, we have searched this data set for well-sampled, long-duration microlensing light curves, detecte d several microlensing events consistent with MACHOs in the 0.1 M. les s than or similar to m less than or similar to 1.0 M. mass range, and set limits on the abundance of objects with masses 10(-5) M. less than or similar to m less than or similar to 10(-1) M.. In this paper, we present a different type of analysis involving the search for very sho rt timescale brightenings of stars, which is used to set strong limits on the abundance of lower mass MACHOs. Our analysis of the first 2 ye ars of data toward the LMC indicates that MACHOs with masses in the ra nge 2.5 x 10(-7) M. < m < 5.2 x 10(-4) M. cannot make up the entire ma ss of a standard spherical dark halo. Combining these results with tho se from the standard analysis, we find that the halo dark matter canno t be comprised of objects with masses 2.5 x 10(-7) M. < m < 8.1 x 10(- 2) M..