Black hole images are not just simple "photographs", but the product of complex human choices (and can be seen at the Rijksmuseum Boerhaave)
In April 2019, the Event Horizon Telescope (EHT) collaboration released the first-ever image of a black hole. Anthropologist Rodrigo Ochigame was interested in understanding the reasons behind the choice of colours for the image. They examined the source code of the software used by the EHT and discovered many alternative options. Four of these alternatives are currently on display in the 'Towards the Black Hole' exhibition at the Rijksmuseum Boerhaave in Leiden.
The first 'picture' of the black hole
The famous image showed the supermassive black hole at the heart of the Messier 87 galaxy. The media often presented the image as a straightforward "picture" or "photograph" of a black hole. The choice of colour was important in making the image feel like a photograph. With a black background resembling the night sky and a red/orange/yellow gradient, the chosen colour scheme evocatively depicted the black hole's shadow as a "ring of fire", a description that was echoed by both scientists and the press.
Why and how were these colours chosen?
As an anthropologist, Rodrigo Ochigame became curious about the reasons behind the choice of colours in the published image. They discovered that the colour scheme used in the image was deliberately created for it. Since radio waves cannot be seen by the human eye, the images produced by the Event Horizon Telescope (EHT) were created by assigning different colours to represent different levels of estimated brightness temperature. And because many color schemes are arguably equivalent from a scientific point of view, the choice was based largely on aesthetic grounds. EHT scientists developed hundreds of custom colour schemes before settling on one. In the end, the scientists settled on colours ranging from black (representing the lowest temperature) to red, orange, yellow, and finally white (representing the highest temperature). According to Ochigame, this decision was influenced by common associations found in visual culture. "As these colours are often associated with warmth or heat, the scientists felt that they would effectively convey the high temperature of the emission surrounding a black hole".
This is the first time that the famous image has been presented to the public in different colours.
A product of many human choices
Ochigame was also interested in exploring how the image would appear in different colours. They examined the source code of the software developed or used by the Event Horizon Telescope (EHT) to find hundreds of options. They then wrote a computer program to reconstruct the image using these alternative colours. The new exhibition at the Rijksmuseum Boerhaave features a set of four images selected in consultation with the museum's curators. This is the first time that the famous image has been presented to the public in different colours. The work serves to convey that a black hole image is not a simple 'photograph', but the product of many human choices. Ochigame: "Scientists must make decisions not only about colours but also about algorithms, instruments, and much more".
Four different possibilities on show at Rijksmuseum Boerhaave
'Towards the Black Hole' is a new exhibition at the Rijksmuseum Boerhaave, the national museum of the history of science and medicine, located in Leiden. It features several works about these mysterious places in the cosmos that swallow up everything and from which nothing, not even light, can escape.
Ochigame's work consists of four images in other colours that the EHT could have used.
- In the standard colour scheme of the software used by the Event Horizon Telescope (EHT).
- In blue, which was seriously considered by the scientists because of its association with the hottest flames.
- In greyscale, which would have given a more neutral appearance.
- In the rainbow colour scheme, which is often used in scientific visualisation as it enhances the visibility of small variations.
The 'Towards the Black Hole' exhibition will be on show at the Rijksmuseum Boerhaave in Leiden from Thursday 21 March 2024 to 5 January 2025.
Picture credits:
Left side: 'M87 black hole in alternative colors, made by Rodrigo Ochigame using Event Horizon Telescope data'. Right side is a photo of the Rijksmuseum Boerhaave exhibition by Fred Ernst.