‘James Webb Space Telescope will try to look at the first stars formed 13.5 billion years ago’

Near-infrared image of the Southern Ring Nebula made by the James Webb Space Telescope. Photo: NASA, ESA, CSA, STScI

The United States National Aeronautics and Space Administration (NASA) released five images July 13, 2022 of the universe in never-seen-before detail. The first was a deep-field image teeming with galaxies. 

The rest of the photos were of region of star birth, a galaxy cluster, the atmosphere of an exoplanet and a nebula. 

All of these were captured by the James Webb Space Telescope (JWST), which sits at the L2 Lagrange point, 1.5 million kilometres from Earth. 

The telescope is primarily observing the universe through its infrared eyes, peering farther back in time. It can help us look at the first stars that emerged after the Big Bang.

Down To Earth (DTE) spoke with Jessy Jose, assistant professor, department of physics at Indian Institute of Science Education and Research, Tirupati, to understand more about the world’s most powerful telescope. 

She is a co-investigator of the accepted proposal at JWST on star formation studies near the galactic centre of the Milky Way.

Rohini Krishnamurthy: The James Webb telescope released five colourful, sharp images on July 12. But could you tell us what some of the images are telling us? 

 

Jessy Jose: The quality of the images by JWST is excellent. I am sure that science from those observations will be even more exciting. 

If you zoom into each image, a lot of features become visible. For instance, if you look at Stephan’s Quintet (290 million light-years away from Earth), where galaxies are merging, you see a lot of features. 

A lot of wild events are happening there, such as how the stars were being formed at the interacting site and how the galaxies were being disturbed.

The merging of galaxies is common. Our own Milky Way and Andromeda are moving towards each other. They are expected to merge after several billion years. During that process, the materials within the galaxies such as gases, dust and stars come together. And then, there'll be a lot of disruption in the medium in between. 

The galaxies eventually merge and there can be an active second generation of star formation during the merger. 

There is a lot of science in the images. There is science behind the colours too. It tells you something about the temperature details. 

If you look at the Southern Ring planetary nebula (2,500 light-years away) released July 12, you might see a bubble. It is coloured red on the outside and blue on the inside. So that colours tell you about the temperature distribution.

KK: How are colours produced?

JJ: There are several filters in the telescope that captures images in different wavelengths. We combine them to create a composite image. 

Individual images are in black and white. But when you make a colour composite, we assign colour based on its wavelength. 

Some filters capture longer wavelengths of light, and others look at shorter wavelengths. So, you can set colours like red, green and blue according to their wavelength.  

A longer wavelength is generally given red, while a shorter one is given blue. Green falls in between. 

We can assign more colours as well when more filters are used. Essentially, the colour of a region is a function of temperature. When you combine them, you get beautiful colouring. 

RR: The Hubble telescope took two weeks of continuous observations to capture the deep field (a part of the universe showing visible stars, distant, dimmer stars and galaxies), while JWST took 12.5 hours. What makes it so fast and sensitive?

JJ: Webb’s First Deep Field is of a known galaxy cluster SMACS 0723. It includes a lot of galaxies in that particular area. Hubble showed us that this is an attractive cluster. It has a relatively more number of galaxies when compared to others.

The speed and sensitivity are because of JWST’s large primary mirror or light collecting area, which captures more photons of light and hence takes less time to generate sensitive and high-resolution images. 

It has a diameter of 6.5 metres against Hubble’s 2.4 metres. So it's almost three times in diameter. 

And the light capturing power of a telescope is directly proportional to the diameter square. The sensitivity and the depth of the image depend on the diameter square. 

The light gathering power of JWST is seven times higher than Hubble, which makes it highly sensitive. 

KK: How does the telescope determine the distance of a cosmic object?

JJ: There are different ways of calculating the distance to a given object in the sky. For distant galaxies, we use something called the redshift method. 

The universe as we know it is expanding, which means all the galaxies around us are moving away from us. Since the universe is expanding, the wavelength of the radiation coming out of the galaxy also stretches and moves to a longer wavelength. We call it the redshift. 

When the light from a galaxy gets redshifted, it falls into another wavelength regime. So, the amount of redshift of a given spectral line (a fingerprint that can be used to identify the atoms, elements or molecules in a galaxy) is related to the velocity with which the galaxy is moving away from us. And that velocity is proportional to the distance of the galaxy.

Alternatively, astronomers use the trigonometric parallax method to measure relatively closer cosmic objects. It calculates the apparent position of two stars taken in different epochs relative to a background object. 

This gives us an apparent shift in the star’s position, which is related to its distance. The closer the object, the higher the shift.

KK: You have been given observation time with JWST. Could you please tell us a little about your project goals?

JJ: A team of 15 astronomers worldwide, including my PhD student and I, decided to submit a proposal outlining our science goals using JWST. 

We began working on the proposal in February-March 2021 and submitted it in November 2021. We are awarded time, and our observations are scheduled for April 2023. 

As part of our proposal, we'll look at a very young star-forming region towards the Galactic centre of our own Milky Way. It is about 600 light-years away from the supermassive black hole at the centre of our galaxy. 

The idea is to understand how star formation is happening in a giant molecular cloud, which is very dense and very massive.

Studying the early stages of star and planet formation can inform us about our own solar system formation and its evolution. Our solar system is about five billion years old. I'm looking at a very young phase of star formation, hardly 1 million years old. 

We are interested in understating how this region evolves and to characterize the young stars in it. 

KK: What are your expectations from JWST?

JJ: For my research area, I expect some exciting results on star and planet formation. There are other proposals by other groups, such as to capture a deeper image of the planet-forming protoplanetary disk (disk of dense gas and dust) around young stars.

Some proposals will look at distant galaxies that formed shortly after the Big Bang. The universe is about 13.8 billion years old. The first stars would have formed about 13.5 billion years ago. JWST is planning to look at them.

Galaxies formed in the early universe are predicted to be structurally different from those in the present universe. Galaxies in the present universe have different structures, but the very first galaxies might have looked different. 

JWST will study galaxy evolution. This is one of the biggest goals. The telescope will look at Mars and other planetary bodies in our solar system. 

It will observe comets and asteroids to help us learn more about our solar system. It should give us exciting results from the atmosphere of exoplanets. 

The big question: Does life exist outside Earth? We hope JWST will be able to provide some indicators to answer this. 

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