JWST And A New Era In Astronomy

The first image unveiled by the JWST shows a galaxy cluster dubbed the SMACS 0723, located some 4.6 billion light-years away from Earth. The patch of sky shown in this image amounts to a teensy-weensy fraction of the entire observable universe covered by a grain of sand held at arm's length. A grain, they say. And in this grain lies some of the oldest, if not the earliest galaxy, formed within a billion years after the Big Bang. 

After three decades of serious planning, lack of funds, technical difficulties, and squeezing the juice out of thousands of scientists, engineers, and technicians, the James Webb Space Telescope is finally up and seeing. Its predecessor, the prodigious Hubble telescope, has taken us deep into the farthest reaches of the cosmos. Looking into the constellation of Ursa Major, Hubble has detected the faintest light coming from the most distant galaxy in the known universe, located at a proper distance of 32 billion light-years. Cataloged as GN-z11, the light from this ancient galaxy has been traveling for 13.4 billion years, meaning we are seeing how it was some 400 million years after the Big Bang. Apart from this remarkable achievement, Hubble has shown what appears to be just an empty and dark patch of sky is teeming with tens of thousands of galaxies, like glowing fireflies on a summer's evening. But Hubble's successor promises more. Not only will it take us farther back in time or closer to the edge of the observable universe and trace the origins and morphologies of the oldest stars and galaxies, but the Webb is going to search for tell-tale signs of extraterrestrial life forms on planets very much similar to Earth. We can say a new era begins. 

Webb's First Deep Field shows a collection of supposedly thousands of galaxies extremely extremely far away from Earth. In this picture, we are looking at some of the very first galaxies formed to within a billion years after the big bang.  
Image Credits: NASA, ESA, CSA, STScl

Let's now perform a rough analysis of Webb's first image. The first image is also Webb's first deep field infrared view of the galaxy cluster SMACS 0723 captured across different wavelengths with an exposure time totaling 12.5 hours, looking into the southern constellation of Volans. It is a composite image obtained from observations across various bands of the infrared spectrum and later digitally colorized to give us a visual representation of what Webb can see peering into the cosmic depths. In 2017, Hubble was tasked with observing the same region in optical wavelengths. What separates Webb from Hubble is that the former operates specifically in the infrared bands of the electromagnetic spectrum. Infrared radiation encompasses a range of low-frequency, long-wavelength radiations just below the visible spectrum. As the universe expands, the light emitted from the distant galaxies lying closer to the edge of the observable universe or the earliest galaxies formed within a hundred million years after the Big Bang stretches into the infrared frequencies. This is where Webb comes into action. On top (of that) when traveling through interstellar dust and gas, the optical frequencies (visible/ultraviolet) are largely absorbed, filtering out much of the data about the very early universe. Besides, every single speck of matter in our known universe, starting from individual stars, planets, moon, galaxies, black holes, quasars, protoplanetary discs, and particularly young stars formed from the collapse of the molecular gas clouds in stellar nurseries, have their characteristic infrared signatures. Looking through the infrared band of frequencies allows us to unfurl a richer picture of the universe. And this is what Webb has shown us on its first attempt. 

The first thing that catches our eyes are those bright pointy artefacts spread throughout the image. Those are just stars, some of which are from our very own galaxy, while the rest lie along the telescope's line of sight as we are looking through the plane of the Milky Way. The pointy protrusions are the diffraction spikes, which are not real but an optical phenomenon resulting from the interaction of incoming light with the primary and secondary mirror assembly in the telescope and the struts. There are, in total, eight prominent diffraction spikes for each star and individual galaxies. The diffraction spikes serve as a good marker for Webb's light-gathering ability.  

Zoomed-in view of the SMACS 0723 galaxy cluster cropped off from the original image
Image Credits: NASA, ESA, CSA, STScl

In the above zoomed-in view, the white circular markers and the white arrows indicate some of the individual galaxies that are gravitationally bound together and form the SMACS 0723 cluster. The white haze and smudginess around the central region come from individual stars being kicked off as multiple galaxies merge into one. The combined effects of gravity originating from the aggregate of billions upon billions of stars in each of the galaxies get so strong at large distances that they are able to distort the surrounding space around themselves, acting as a gravitational lens following Einstein's general relativity. The equations of general relativity dictate that space is like a fabric that can fold and twist and warp and bend where light always follows the curvature of this space-time fabric. What is happening here is that there are innumerable galaxies obscured behind the 0723 cluster. Now, owing to the gravitational bendiness of space, light follows a curved path around the galaxy cluster, which acts as a magnifying lens, bringing the distant galaxies into our field of view. This lensing effect is so intense that the light from the distant galaxies has been stretched and elongated (shown by red arrows) as a circular arc centered about the cluster. Upon close inspection, we will also notice that some galaxies have mirror images (green arrows) while others have been stretched to the extremes (yellow arrow). 

This deep field contains at least a thousand galaxies, of which some are so distant that their light has been traveling for 13.1 billion years. 

 

The following portion reveals the sheer amount of detail picked up by Webb. Towards the right, we see a well-resolved specimen of a spiral galaxy, followed by an N-shaped galaxy that is being torn apart by some cataclysmic cosmic event. On the lower right, we have an elliptical galaxy. 

Even in this image, every luminous smudge is an island universe. And all of this amounts to just a grain of sand. Such is the extent of our observable universe. 
Image Credits: NASA, ESA, CSA, STScl

Webb's other targets have been the Southern Ring Nebula, the Carina Nebula, Stephan's Quintet and an exoplanet named WASP-96b. 

The Sothern Ring Nebula imaged at two different wavelengths of the infrared band of frequencies. The left one shows what it looks like at near-infrared (NIRCam) while the right one shows the same at mid-infrared (MIRI). 
Image Credits: NASA, ESA, CSA, STScl

The Southern Ring Nebula (NGC 3132) is a bright planetary nebula in the southern constellation of Vela located 2,500 light-years away from Earth. A planetary nebula has nothing to do with planets but refers to the expanding layers of gas and stellar material expulsed during the end stages of a mature star when it starts to shed its outer layers like a peeled onion, leaving behind its core as a white dwarf star. Technically speaking, a white dwarf is not a star but a glowing cinder of the remnant stellar core that stands as a relic of the past nuclear reactions that powered the parent star. A closer look at the second image reveals a pair of stars at the center, a bright white one and its smaller reddish companion. This reddish companion star is the one that has been periodically ejecting its outer layers. 

The left image has been taken across the near-infrared wavelengths by Webb's NIRCam, while the right has been captured by the MIRI instrument, which images across the mid-infrared frequencies. The near-infrared comprises relatively shorter wavelengths and is closer to the red end of the visible portion. Stars radiate profusely in this particular band and are seemingly bright, which explains their prominent diffraction spikes. The white dwarf companion (red star in the second image), obscured behind the diffraction spikes of the bright (still shining) star, is seen for the first time. Secondly, the near-infrared wavelengths are transparent to the clouds of gas and dust, which reveals the detailed structures of the nebula in the first image. The white dwarf's companion star is heating the gas and dust in its vicinity, observed by the blue and red luminescence in the respective images. The reddish tinge encapsulating the white dwarf is a visual manifestation of the heating of the surrounding gas. 

The Cosmic Cliffs located to the northwest corner of the Carina Nebula imaged at near-infrared wavelengths by Webb's NIRCam. 
Image Credits: NASA, ESA, CSA, STScl

The Carina Nebula (NGC 3372), also known as the Eta Carinae Nebulae or the Great Carina Nebula, is a stellar nursery, a massive and equally complex star-forming region found in the southern constellation of Carina, located 8,500 light years away from Earth in the Carina-Sagittarius arm of our Milky Way Galaxy. This region of star formations spans about 230 light-years radially. Webb did not image the entire nebula but a specific part in the northwest corner was catalogued as NGC 3324 and located roughly 7,600 light years from Earth. In the above image, what seems to be a range of mountainous offshoots is actually the edge of a giant blowout, a massive cavity carved off from NGC 3324 and blown outwards by the intense radiation pressure emanating from the newly formed stars at the center of the bubble. The blueish steam-like appearances rising above the edge of the gaseous mass are ionized hydrogen and hot dust blown apart due to the stellar winds. This picture is but a snapshot of a very dynamic situation. The younger stars found above the blueish area (not shown in this image) are radiating copious amounts of ultraviolet radiation. This outpouring of radiation pressure is collapsing the walls of cold hydrogen gas and compressing them into new stars, some of which are probably tens of times as massive as our sun. The new stars forming deep inside the nebular material are further trying to push the wall against the radiation pressure given off by the stars at the center of the bubble. Due to this constant push from both sides, at some places, a section of gaseous material rises up as a pillar into the expanding bubble (as seen below). Upon close inspection, we realize that Webb has delivered a stupefyingly detailed image, showcasing the period of very early star formation, protoplanetary discs, protostellar jets, bubbles, cavities, offshoots, and a large number of previously unseen stars, including some distant background galaxies.  

Zoomed in view of the cosmic cliffs. The protruding edge is a wall of gas and dust rising in defiance to the radiation pressure coming from the new stars forming at the heart of NGC 3324
Image Credits: NASA, ESA, CSA, STScl

Stephan's Quintet is a visual grouping of five galaxies, of which only the top four are gravitationally bound, thereby forming the Hickson Compact Group 92 (HCG 92), while the fifth one at the bottom is a separate galaxy, not interacting gravitationally with the others. The HCG 92 group, containing the NGC 7317, NGC 7318A and NGC 7318B, and NGC 7319, is located almost 290 million light-years from Earth in the northern constellation of Pegasus. In the long run, the HCG 92 group will merge into a single galaxy. The fifth galaxy, catalogued as NGC 7320, is fairly close to Earth in terms of cosmic scales sitting at a distance of 40 million light-years. 

A NIRCam/MIRI composite image of Stephan's Quintet
Image Credits: NASA, ESA, CSA, STScl

The above image is another marker for Webb's capabilities. Combining images taken across different infrared bands, Webb has been able to detect a supermassive blackhole lurking at the heart of the topmost galaxy (NGC 7319) with a mass equal to 24 million times that of our sun, with its accretion disc being as bright as 40 billion of our suns put together. In addition to that, Webb has also picked out regions of new star formation at the edge of the colliding galaxies and run way stars breaking free from the gravitational confinements of their parent galaxies in this cosmic tug-of-war.  

Transmission spectrum of WASP-96b. The image in the background depicts an artists conception of what the planet might look like.
Image Credits: NASA, ESA, CSA, STScl

Last but not least, Webb has obtained the spectra of an exoplanet named WASP-96b, located 1150 light years away from Earth in the southern constellation of Phoenix. WASP-96b is a gas giant with a mass of 0.48 times that of Jupiter and orbits a sun-like star. The planet lies extremely close to its parent star, almost 1/20th the Sun-Earth distance and completes an orbit in just 3.4 days. Unlike Jupiter, WASP-96b, because of its close proximity to its parent star, is a hot giant with an atmospheric temperature of about 725℃. Webb has obtained what astronomers call a transmission spectrum of the planet. This type of spectrum is made when the starlight has moved through the planet's atmosphere and has interacted with the atmospheric constituents and is later compared to the unfiltered starlight when the planet is not obscuring our line of sight to the star. When light travels through a planetary atmosphere, it gets absorbed by the atmosphere, leaving behind an absorption spectra. By comparing this absorption spectra with the normal spectra of the star, we can infer about the composition of the planetary atmosphere. Although spectral analysis requires sufficient time, preliminary reports hint at the presence of water vapour which is an important factor in our quest for extraterrestrial life. 

 Webb is going to operate for 20 or more years. And just like its predecessor, we can not even conceive of the things Webb is going to show us. What seems to be an empty dark patch of sky has suddenly been revealed to contain thousands, if not hundreds of thousands of galaxies, some similar to our Milky Way, while others might be astonishingly different from what we have seen so far. What is striking is that if all those galaxies contain at average a 100 billion stars, each with at least one orbiting planet, then there are a 100 billion planets in every galaxy. Even if 0.00001% of them are habitable, then that amounts to a 100 habitable planets. Across a hundred galaxies, we get 100,000 planets with the possibility of harbouring sentient living beings like us or something straight out of Hollywood. 

References: 

1. https://www.scientificamerican.com/article/how-taking-pictures-of-nothing-changed-astronomy1/
2. https://www.esa.int/ESA_Multimedia/Images/2022/07/Webb_s_first_deep_field
3. https://www.scientificamerican.com/article/behold-some-hidden-gems-from-jwst-rsquo-s-first-images/
4. https://www.nasa.gov/webbfirstimages
5. https://theconversation.com/james-webb-space-telescope-an-astronomer-explains-the-stunning-newly-released-first-images-186800
6. https://www.livescience.com/james-webb-telescope-deep-field-explained