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Blog: JWST: The Infrared Eye of Humankind

By PhD candidate Saugata Barat

28 November 2022

JWST (James Webb Space Telescope) is an Infrared telescope and successor to the great Hubble Space Telescope . It is expected to revolutionize our understanding of the universe by studying the atmospheres of distant worlds, exotic nebulae, the first galaxies to have formed in the universe almost 13 billion years ago. It was launched on 25th December, 2021 from Kourou, French Guiana on board an Ariane 5 rocket. It traveled for about a month from the Earth to reach its final orbit which is roughly 1.5 million km away from us.
Picture taken from outer space of the James Web Space Telescope, a shiny cubic spaceship, and the earth in the top right.
Fig 1: Humanity’s last glimpse of JWST captured by the cameras on board the rocket’s upper stage as the telescope separated from it. We can see the Earth in the background. Image: https://webb.nasa.gov/

 

Why did we put JWST in space?

Our eyes are sensitive to the world around us with optical light, however different objects emit radiation at wavelengths other than optical frequencies. For example, planets emit most of their energy in infrared and compact objects like neutron stars and black holes can emit a lot of X-rays. To study these exotic objects astronomers must turn to other parts of the electromagnetic spectrum. Most of the electromagnetic radiation is  absorbed in the upper layer of the atmosphere; our atmosphere is only transparent to optical and radio emission (See Figure 2). As a result, if astronomers want to study the universe at these electromagnetic bands, they have to use telescopes which are in space. Some examples of other space based telescopes are Chandra (X-ray), Fermi (Gamma-ray), and Hubble (UV, IR).

 

Fig 2: The upper panel shows the opaqueness of the Earth’s atmosphere for different types of electromagnetic radiation and the lower panel shows the observable windows from the Earth’s surface.
Fig 2: The upper panel shows the opaqueness of the Earth’s atmosphere for different types of electromagnetic radiation and the lower panel shows the observable windows from the Earth’s surface.

JWST observes the universe in infrared frequencies. This requires the detectors on board to be at extremely low temperatures (-267°C), which is achieved with a combination of the telescope’s location in space, ‘sunshields’ which block the sunlight from heating the telescope and cryogenic cooling of the detectors. JWST and the science instruments on board (NIRSpec, NIRCAM, NIRISS and MIRI) are marvels of engineering. Dutch astronomers from the Optical Infrared Group of the Netherlands Research School for Astronomy (NOVA) were involved in the development of the mid-infrared instrument (MIRI).

What have we seen with JWST until now?

JWST reached its final orbit in July 2022 and since then astronomers around the world have dived into the amazing data and unprecedented images from this telescope. In Figure 3 we see the deep field images taken by MIRI and NIRCam which show a rich field of astronomical objects like stars and different types of galaxies. This is one of the deepest views of the universe till date. In Fig 4 (left panel) we see the famous ‘Pillars of Creation’ which is a star forming region in the Eagle nebulae. Alongwith imaging, JWST is also capable of taking spectroscopic measurements and in Fig 4 (right panel) we see an example of a transmission spectrum of a hot Jupiter, WASP 39b observed with the NIRSPec PRISM instrument. The peak observed in this spectrum is a signature of Carbon Dioxide (CO2) within the atmosphere of this faraway world. CO2 is one of the most important molecules in the planetary atmosphere and it can help understand the formation history of the planet. This CO2 observation is the strongest ever detection in an exoplanet atmosphere.   The detection and characterization of atmospheres of exoplanets with JWST promises to address fundamental questions about our existence and future. There are more breathtaking scientific results from JWST being achieved and some of them can be found in the following website  (https://webb.nasa.gov/).

A field full of galaxies, fuzzy blobs of light with just a few stars. Some of the galaxies are deformed, a result of the bending of light by the foreground galaxies.
Fig 3: Deep field images taken with MIRI (left) and NIRCam (right) onboard JWST. Image: https://webb.nasa.gov/
The pillars of creation, a mustard coloured nebula, against a blue background. The nebula two quite distinct an one slightly less pronounced pillars of material.
Fig 4: The pillars of creation (left) captured by JWST (Credit: NASA, ESA, CSA, StSci). The pillars of creation is a region where young stars are being born.
The transmission spectrum of WASP 39b is a graph comparing wavelength on the X axis and amount of light blocked on the Y axes with a 'bump' in the middle at 4.00-4.50 microns, with as comment 'Carbon Dioxide (co2)'.
Fig 5: A transmission spectrum of the hot Jupiter WASP 39b observed with the NIRSpec instrument.