# The Black Hole Photon Ring

- Institution: CERN
- Department: TH String Theory Seminar
- Speaker: Alex Lupsasca
- Year: 2023
- Language: English
- Source: [CERN](https://videos.cern.ch/record/3003489)
- Licence: [CERN](http://copyright.web.cern.ch)
- Who can watch: Teens profiles and older (sources give no ratings; placed by Invisible Network from the source's own words)

What does a black hole look like? The first images of the supermassive black hole M87* display a bright ring encircling the event horizon, which appears as a dark patch in its surrounding emission. But Einstein's theory of general relativity predicts that within this image there also lies a thin "photon ring" consisting of multiple mirror images of the main emission. These images arise from photons that orbited around the black hole multiple times, probing the warped space-time geometry just outside its horizon. The photon ring carries an imprint of the strong gravity in this region and encodes fundamental properties of the black hole (including, for instance, its quasinormal mode spectrum). A measurement of this predicted (but not yet observed) ring could provide a precise test of general relativity and will be the target of a NASA mission proposed to fly within the next decade. .

0:00:00 Slide 1

0:01:28 Slide 2

0:04:33 Slide 3

0:06:30 Slide 4

0:07:48 Slide 5

0:09:17 Slide 6

0:11:38 Slide 7

0:22:51 Slide 8

0:24:26 Slide 9

0:32:05 Slide 10

0:33:15 Slide 11

0:38:49 Slide 12

0:43:44 Slide 13

0:44:44 Slide 14

0:46:31 Slide 15

0:53:29 Slide 16

0:56:51 Slide 17

0:58:51 Slide 18

1:02:38 Slide 19

1:04:25 Slide 20

1:05:44 Slide 21

1:07:22 Slide 22

1:17:41 Slide 23

## Lectures

1. [The Black Hole Photon Ring](https://invisiblenetwork.ai/learn/cern/3003489/deb50eda49ca), 1 h 20 min (CERN's player)