Enrique Garcia works on a supercomputer, and he wears an oxygen tank on his back. The machine stands in a building at ALMA, on the Chajnantor plateau in northern Chile. It is 5,100 metres above the sea. It is the highest supercomputer in the world. The air there is very thin, so the fans must push twice as much air to keep the machine cool. The people who work there also need help to breathe.
Nobody builds so high because it is nice. Astronomers chose this place because it is very flat and very dry. In some areas only 3 millimetres of rain falls in a year. The Atacama around it is the driest desert on Earth outside the polar regions. Some weather stations there have never measured rain.
Water in the air is a problem for these telescopes, because it blocks the signals from space. ALMA looks through very dry air.
About 250 people work at ALMA. Iván López is the safety manager. He said that about 50 of them do not always get enough oxygen. The workers go up from 2,900 metres to 5,100 metres in less than an hour, and they do this every day. So there is now an oxygen plant on site, and workers carry oxygen tanks in special backpacks. The air is very dry, so people use nasal sprays. They always work in teams of two or more. They work eight days up on the mountain and then six days down at sea level.
In 2017 ALMA joined the Event Horizon Telescope. Eight telescopes in different parts of the world worked together like one big telescope. They stood in Hawaii, Mexico, Arizona, Spain, Chile and Antarctica. Each one made about 350 terabytes of data every day. ALMA was very important, because it made the whole network much more sensitive.
On 10 April 2019 the scientists showed the picture to the world. It is a ring of hot gas with a dark centre: the black hole in the galaxy Messier 87. It is 55 million light-years from Earth.
The picture does not show the black hole. A black hole is black, so we cannot see it. We only see the hot gas around it.