New telescope to reveal the universe’s infancy

6 december 2021

The golden mirror of the James Webb telescope.

The JWST has a 25-square-metre mirror and such high resolution that an object as tiny as a coin can be discerned at a distance of 40 kilometres.

Delayed by a decade but ardently anticipated by astronomers, the James Webb Space Telescope is due to be launched just before Christmas. It will enable study of the universe's first bright objects, the history of our own solar system, and planets orbiting other stars.

“This telescope’s mirror has a diameter of 6.5 metres. It’s the biggest mirror ever to be launched into space. It’s folded to fit inside the rocket, and has to unfold according to a certain pattern after its exit,” says Erik Zackrisson.

A researcher at the Department of Physics and Astronomy in Uppsala, Zackrisson will be among the scientists who will use the James Webb Space Telescope (JWST) regularly. For him, it will be a key tool in his work on the first stars, galaxies and black holes of the early universe. Capable of capturing infrared radiation, it is built to show the oldest, very faint objects furthest away from us in the universe – the stars and galaxies that were among the first to form after the Big Bang, 13.8 billion years ago.

“This ability to locate first-generation stars for the first time is the holy grail. With the Big Bang, three elements formed: hydrogen, helium and tiny amounts of lithium. They alone composed the very first stars, which are believed to have been short-lived and enormously large. Our Sun’s life expectancy is ten billion years, but those early ‘hypergiants’ may have lived for only a few million,” Zackrisson explains.

Imploded into supermassive black holes

One hypothesis is that, at the time of their death, some of these first stars – which for the most part consisted of hydrogen and helium alone – imploded into supermassive black holes. This outcome is not seen in the stars of today. With their far more complex composition, they are not thought to be capable of growing to such a gigantic size.

“There is a supermassive black hole, as far as we know, in the middle of every galaxy, including our own Milky Way. But we don’t know where they come from. In the past few years, it’s been possible to trace them back to the first billion years after the Big Bang, but how they formed is unclear. There may have been monster stars that collapsed straight into black holes, forming the precursors to these supermassive holes.”

The fact that black holes emit neither light nor matter makes it impossible to investigate them. Nevertheless, their location and size are discernible through study of how their immense gravitational force affects their surrounding environments.

“We can detect the black holes we’re looking for because, when a black hole pulls in ambient gas that’s spinning around it in a disk, it lights up and starts to glow. If you take pictures in various wavelengths, you can use spectral information to distinguish black holes from other objects,” Zackrisson says.

First galaxies may provide the solution

The very first galaxies also interest him, because they may provide the solution to another of astronomy’s enigmas: how the universe was reionised. Ions are atoms that have more or fewer electrons than protons, which gives them a positive or negative charge.

Erik Zackrisson
Erik Zackrisson is a researcher at the Department
of Physics and Astronomy.
Photo: Mikael Wallerstedt

“The most abundant element in the universe is hydrogen. For a short time after the Big Bang, the hydrogen was ionised. But as the universe grew and cooled, roughly 380,000 years after the Big Bang, protons and electrons combined to form neutral hydrogen atoms. After that, the universe became reionised, which is thought to have been caused by energy-rich radiation. In recent years, it’s been discovered that the reionisation took place during the first billion years after the Big Bang, and astronomers think some of the first galaxies spewed out UV radiation and caused this cosmic reionisation. We want to try and understand the details of how this happened,” Zackrisson says.

If all goes to plan and barring further delays, the James Webb Space Telescope will be ready for the first observations sometime after Midsummer 2022.

Facts about the James Webb Space Telescope

Responsible for its creation: the JWST is an international collaboration between the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA) and the Canadian Space Agency (CSA).

Named after: James Webb, who headed NASA from 1961 to 1968.

Mirror diameter: 6.5 metres.

Mirror surface: 25.4 square metres.

Focal length: 131.4 metres.

Weight: 6.5 tonnes.

Distance from Earth when in place: 1,500,000 kilometres.

Temperature: 80 °C on the side facing the Sun and −233 °C on the shady side.

Planned launch date: 22 December 2021, from Europe’s Spaceport, the ESA rocket launch site in French Guiana.