Researched
Black Hole at the Milky Way's Centre
Tracking stars around the radio source Sagittarius A* for 16 years, teams led by Genzel and Ghez showed it is a black hole of about four million Suns (Nobel Prize 2020).
Open in the interactive tree →Bruce Balick and Robert Brown found Sagittarius A* as a bright radio source at Green Bank in 1974. Reinhard Genzel's group began tracking stars near it in 1992 with ESO telescopes; Andrea Ghez's group began detailed observations in 1995 at the Keck telescopes, where adaptive optics cancels the blur of Earth's air. The star S2 circles the centre in about 16 years, and the orbits gave a mass of 4.1 ± 0.6 million Suns in 2008, refined to 4.297 ± 0.012 million with the GRAVITY instrument in 2023. Genzel and Ghez shared half of the 2020 Nobel Prize in Physics.
Prerequisites
- Newtonian Mechanics1687Star orbits are fitted with Newtonian gravity to weigh the centre.
- Radio Astronomy1933Sagittarius A* was first found as a compact radio source in 1974.
- Black Holes (Cygnus X-1)1971-72Black holes had moved from theory to observed objects.
- Segmented-Mirror Telescopes1993Ghez's team used the 10-metre Keck telescopes with adaptive optics.
Unlocks
- First Black Hole Images (EHT)2019The 2022 image targeted an object whose mass stellar orbits had weighed.