Finding the phantom photobombers

By monitoring a billion stars, we are finding the fingerprints of rogue planets, stars and possibly black holes

1 Like a converging lens

When an object of mass passes in front of a distant star, it can actually make the star brighter. While some stellar radiation will be blocked, more light rays become bent towards Earth by the foreground object’s gravity.

2 Setting stars aflicker

A number of objects are capable of producing the microlensing effect. These include rogue planets, brown dwarfs, white dwarfs, neutron stars and possibly PBHs.

3 A mysterious gravitational fingerprint

One set of gravitational anomalies observed by OGLE has defied interpretation. Six ultrashort microlensing events with crossing times of 0.1 to 0.3 days have been identified by Tokyo University’s Hiroko Niikura as a possible local population of PBHs.

4 All eyes on the galactic centre

OGLE is just one of the observatories that have looked for microlensing. These include the AngloAustralian MACHO project, the French EROS collaboration and Japan’s Hawaii-based Subaru telescope. Together they monitor over a billion stars towards the galactic centre.

5 Calculating the distance

The Spitzer Space Telescope also looked for microlensing effects. However, because of its different line of sight compared to Earth telescopes, accurate timing comparisons can be used to triangulate the distance to the lensing object.