Follow Us:

Cosmic Dawn

It is to be seen if the JWST would be able to help resolve Cosmic enigmas like dark energy the unknown 68 per cent of the universe‘s content which is responsible for its accelerating expansion and the elusive dark matter that makes up another 27 per cent of the Universe and is believed crucial to galaxy formation. There is also a recent mystery involving the so-called Fast Radio Bursts the unexplained flashes of radiation that last for milliseconds and are detectable from billions of light-years away but not attributable to any source

GOVIND BHATTACHARJEE | New Delhi |

Once upon a time, that is before time began some 13.8 billion years ago, there was nothing, neither matter nor energy, neither space nor time, neither God nor reason, neither laws of physics nor mathematics ~ only a vacuum pregnant with infinite creative potential. A fluctuation, a flicker of this vacuum had given birth to the Universe at the epoch of Genesis, creating the structure of space time and a hot matter soup or the primordial brew of creation when all matter and energy now contained in the Universe were compressed together in a superheated, superdense cosmic fireball searing at a temperature of 100 trillion trillion degrees. The hot matter soup, which had only two kinds of fundamental particles ~ quarks and leptons that would eventually constitute all matter, and photons that would make up all energy ~ had sprung into existence only 100 billion trillion trillion of a second after genesis.

The early Universe was dominated by photons, or radiation so hot that matter could then exist only in a dense state of ‘plasma’. As the Universe expanded, it cooled, but it was still too hot for electrons to combine with protons to form the simplest atoms of hydrogen. About 300,000 years after the Big Bang, the ambient temperature had dropped to about 3000 degrees and when hydrogen atoms started forming, photons were no longer energetic enough to knock electrons off the atoms which would absorb and re-emit the photons to be scattered by other atoms, slowly making the Universe transparent to light.

Photons or radiation which had embraced matter particles ever since they had met each other at the beginning of time, were now letting loose this embrace to permanently decouple from each other, and the Universe was now transparent and filled with yellowish light, the colour corresponding to matter heated to 3000 degrees. This light would subsequently fade away with progressive expansion of the Universe, its wavelength getting stretched by the expansion, and through billions of years of cooling, would lose most of its energy to lie in microwaves now at a temperature of only 2.73-degree Kelvin forming what is known as the Cosmic Microwave Background (CMB).

If we can take a picture of our 300,000-year-old Universe, we would be able to see the nascent structures in that Universe ~ the small lumps of matter that were formed from the tiny perturbations in the very early stages. These lumps would later evolve into proto-galaxies, galaxies, stars and planets shaping the large-scale structure of the Universe of today. This Universe would be open to our sight, unlike the plasma-dominated Universe before. Since plasma is opaque to radiation, the surface of the 300,000- year-old Universe would permanently block our sight and we would not be able to ‘see’ anything earlier than that, since we can see only with the help of light.

Therefore, the 300,000-yearold Universe is the earliest frame of reference for any measurement to be made, and we can call it the Cosmic Dawn. But no telescope has as yet peered that deep. At 5:50 PM IST on 25 December when the world was celebrating another muted Christmas, a majestic beast of a space telescope ~ the most powerful ever built so far-was launched into the sky on European Space Agency’s Ariane-5 rocket from Kourou in French Guiana, heralding what scientists are calling the “Apollo Moment” for astronomy.

As the 7- ton, $10 billion, James Webb Space Telescope ( JWST ), named after the NASA boss during its heydays of 1960s, began its space journey after countless delays, it will look far deeper into the early Universe than ever before and will be our premier observatory in space for the next decade. It will hopefully be able to peer into the Cosmic Dawn.

Space telescopes, also known as astronomical space observatories, are our eyes to the Universe. Space offers clearer views not obstructed by the Earth’s atmosphere, enabling a look into the farthest reaches of the Cosmos. They are like time machines since the light reaching them today from distant galaxies and stars had begun their journey millions of years ago. If today a star is discovered at a distance of say one million light-years away, as its light reaches the telescope, it carries visual information about it pertaining to the time light has left the star and we see its image as it existed one million years ago. The more distant star or the galaxy, the farther back in time are the telescopes able to gaze.

The golden era of astronomy began with the launch of Hubble space telescope in 1990, which so far been our most reliable eye into deep space. With its 2.4 metre (diameter) mirror and operating in the visible and ultraviolet and near-infrared (IR) range of the electromagnetic spectrum, Hubble has provided stunning images of countless cosmic objects, shedding light on the scale of the universe, the life cycle of stars, black holes, and formation of the first galaxies. Currently receiving its fifth and final makeover, it is expected to last at least another five years, overlapping with the JWST. Since Hubble, NASA has launched several powerful space telescopes ~ most importantly the Chandra X-ray Observatory (1999 and still working), Spitzer (2003-2020), Herschel (2009-2013) and Planck (2009- 2013).

There are now more than a dozen major observatories in space but most of these, like Hubble, are placed in orbits between 500-600 kms above the earth. But JWST dwarfs all in scale and scope. With its 6.5-metre primary mirror shielded by a five-layer, tennis court-sized sunshield that is designed to block the heat from Sun and ensure the extremely cool temperatures essential for its operation and designed to operate at the IR range of the spectrum, it will be 100 times more sensitive than Hubble. It will also be positioned far deeper into space, 1.5 million km from Earth, far away from the earth’s ‘radiation pollution’ at a point known as L2 which is one of the five points, called the Lagrange’s points, where the gravitational forces of the Sun and the Earth cancel each other out, giving it stability while requiring the minimal energy to keep it there.

Directly behind Earth in the line joining the Sun and the Earth, an object placed at L2 would be shielded by the Earth from the Sun’s rays as it goes around the Sun, in sync with the Earth, making it cold enough to reach the cryogenic temperatures its instruments have been designed to operate at. Light from the early Universe is no longer in the visible range but in the IR range and can detected only with IR cameras. Its four IR cameras can pierce through stellar dust to reveal structure that can’t otherwise be seen in the visible range.

The JWST’s primary mirror should be cooled to ~ 223 degree Celsius to enable it to pick up the faintest IR light from distant galaxies that formed in the early Universe. The other side of the shields facing the Sun would be scorching hot, at average temperatures of 93 degrees. The mirror and the sunshields are so large that no rocket could carry them unless folded ~ 18 hexagonal sections will unfold it. The mirror is made of beryllium that has tensile strength more than steel but is lighter than aluminium; it is plated with gold to reflect the IR light.

The equipment is incredibly complex ~ it has as many as 250,000 individually controlled shutters to ensure its illumination by the correct narrow slice of the sky. No scientific instrument as complex and sophisticated has ever been sent into space and should something go wrong while the telescope redeploys itself, there will be no possibility of any astronaut performing repairs on it that far away, unlike the Hubble. Apart from the IR cameras, it will be equipped with coronagraphs to block light from a star to enable observing the planets orbiting around it.

Among the most eagerly awaited images from the JWST are those of the first proto-galaxies emerging on a flat and shapeless cosmos, evolving into massive galaxies that would host the first generation of stars. It would probe the mysterious quasers that are believed to be superluminous, supermassive black holes typically located at the galactic centres, feeding on infalling matter, and unleashing fantastic torrents of radiation. It would peer into planetary origins and smaller bodies like asteroids and comets, our solar system, and yes, exoplanets ~ planets that lie in the so-called Goldilocks Zone where water exists in the liquid form ~ these are most suited for life to evolve and develop into intelligent life.

It is to be seen if the JWST would be able to help resolve the Cosmic enigmas like dark energy ~ the unknown 68 per cent of the universe’s content which is responsible for its accelerating expansion and the elusive dark matter that makes up another 27 per cent of the Universe and is believed crucial to galaxy formation, as measurements suggest that most galaxies are accumulations of dark matter with stars scattered in between.

There is also a recent mystery involving the so-called Fast Radio Bursts (FRBs) ~ the unexplained flashes of radiation that last for milliseconds and are detectable from billions of lightyears away but not attributable to any source. These mysteries today lie at the frontier of physics and resolving them would really usher in a new golden age in astronomy and astrophysics.

(The writer is a commentator, author and academic)