Stellar Microlensing

In practice, detecting a microlensing event is rare, because the alignment required between the lensing object and the background source is so precise and the timing difficult or impossible to predict. Microlensing events are typically discovered by large surveys, which monitor potential sources for years at a time, taking observations every few days. One example of such a survey is OGLE, the Optical Gravitational Lensing Experiment, which operates out of the Las Campanas Observatory, Chile, and has been running since 1992. The background stars monitored by OGLE are in the dense regions of the Galactic Bulge of the Milky Way and two nearby galaxies: the Small Magellanic Cloud (SMC) and the Large Magellanic Cloud (LMC).

OGLE-2005-SMC-001

Below we have a sonified light curve video of a microlensing event observed in 2005 where a background star from the SMC was lensed by an intervening Milky Way star. The microlensing event is dubbed OGLE-2005-SMC-001. Typical microlensing events like this one have a very simple shape: the brightness of the background source deviates from its baseline and exhibits a smooth, gradual increase then decrease in brightness as the lensing mass (usually another, fainter star) passes in front of the source. The most important parameter that can be extracted from a typical microlensing light curve is the time scale of the event, which is related to the lens object's mass, distance, and velocity. The stellar microlensing event shown below occurs over about 200 days. At the beginning of the video, first notice the dozens of observations that display the baseline brightness of the source star. Then, after a seasonal break in observations, the microlensing event can be heard. The video scans over time (x-axis) and modulates pitch based on magnitude (y-axis). Lower pitch represents dimmer magnitudes.

The light curve data was taken from OGLE, and Wyrzykowski et al. 2011 (link to paper).