Gravitational Microlensing

Using gravitational microlensing (see Figure 1) to detect exoplanets requires the chance alignment of a distant star and a nearer exoplanet and star system.

Figure 1: Detecting the signal as a microlensing event (with both a star and planet) occurs.
Credit: Exoplanet Exploration, NASA

A detection occurs when the gravitational field of the nearer star acts like a lens, magnifying the light of a distant background star. This effect occurs only when the two stars are almost exactly aligned and is a one-off type event. Should the nearer star happen to have an orbiting exoplanet, this less massive object might also create a characteristic 'blip' in the light-curve (see Figure 2).

Figure 2: Light-curve of a microlensing event. Here, the Robonet data were taken by the Liverpool Telescope.
Credit: European Southern Observatory

These one-off lensing events generally occur over timescales of weeks to days, and to date (November 2018), just over one thousand events have been observed over the past ten years by projects such as the University of Warsaw's OGLE and the Australia-based MACHO surveys. From these, there are so far around a dozen systems that appear to have had an additional signal, indicative of an exoplanet.

These alignments mean that a large number of distant stars need to be observed to detect these rare exoplanetary microlensing candidates. This method is therefore most successfully employed by observing star-fields towards our densely populated Galactic Centre.

Go back to the main detection methods page.