Two methods of measuring the mass of a galaxy
![](https://cdn.sci.esa.int/documents/34247/35306/1567213862246-heic1812c_625.jpg)
Date: 21 June 2018
Satellite: Hubble Space Telescope
Depicts: ESO 325-G004
Copyright: ESA/Hubble, ESO, NASA
This infographic compares the two methods used to measure the mass of the galaxy ESO 325-G004. The first method used ESO's Very Large Telescope to measure the velocities of stars in ESO 325-G004. The second method used the NASA/ESA Hubble Space Telescope to observe an Einstein ring caused by light from a background galaxy being bent and distorted by ESO 325-G004. By comparing these two methods of measuring the strength of the gravity of ESO 325-G004, it was determined that Einstein's general theory of relativity works on extragalactic scales – something that had not been previously tested.
Last Update: 1 September 2019