How to find a black hole with MUSE

This animation explains the method used by a team of astronomers to discover a small black hole outside of our galaxy — the first to be found using this technique. They discovered it in the star cluster NGC1850, an image of which appears at the start of the animation.

The researchers used the Multi Unit Spectroscopic Explorer (MUSE) instrument at ESO’s Very Large Telescope in Chile to analyse the spectra of thousands of stars in the cluster at the same time. Spectra (represented in the video by colourful bars) show the light emitted by the stars at different wavelengths and contain information about their chemical composition, temperature and velocity. 

The animation then focuses on one of the spectra, that of a star five times as massive as our Sun. The dark lines in its spectrum — due to different chemical elements — oscillate back and forth towards blue and red colours. This means that the star is periodically moving towards and away from us. This allowed the astronomers to infer the presence of the eleven-solar-mass black hole influencing the star’s orbit with its strong gravitational force.