Veröffentlicht 7. April 2022 von Benjamin Skuse
Why the Webb Telescope Will Rewrite the Cosmic History Books
It would be little surprise if people with only a passing interest in astronomy thought NASA’s latest eye in the sky were called ‚The 10 Billion US-Dollar Space Telescope‘. So much focus is placed on the cost of the James Webb Space Telescope – ‚JWST‘ or simply ‚Webb‘ for short – so little on the return on investment we will enjoy. But assuming it suffers no major malfunction, Webb is almost guaranteed to reimburse humanity by transforming our understanding of the cosmos and our place within it.
To understand this better, we only need to look to its immediate forerunners: Hubble and Kepler. In over 30 years of service, the Hubble Space Telescope has revolutionised astronomy. For instance, its images of high-redshift supernovae were pivotal in demonstrating that remote supernovae are fainter and therefore more distant than expected. In 1998, this finding contributed to 2011 Nobel Prize in Physics recipients Adam Riess and Brian Schmidt, and Saul Perlmutter independently, concluding that the universe’s expansion was not happening at a fixed velocity or slowing down, but actually accelerating. This acceleration represents the first direct evidence of dark energy, a form of energy and pressure expanding space everywhere.
Another seminal breakthrough came in 1995 when Bob Williams – then Director of the Space Telescope Science Institute which runs Hubble operations – devoted most of his allotted time on the space telescope to staring at a seemingly dark and empty spot of space for 10 straight days. The resulting Hubble Deep Field image was far from empty. Like a core sample of the cosmos, it was spattered with thousands of galaxies at all ages and stages of development. This image proved to be the final nail in the coffin for the once popular steady-state theory of the universe, showing that the cosmos is not immutable and has in fact changed radically over time.
Reasons for Webb
Further deep-field images have been taken since, pushing Hubble to the absolute limit of its capabilities to return blurry smudges of light from primitive galaxies as far back as 500 million years after the Big Bang. But to finally understand how the universe went from a dark, gaseous fog of basic elements to the clear, transparent cosmos littered with light we see today, we need to peer even further back in time to ‚first light‘, when the earliest generation of stars formed in the universe. For that, we need Webb.
Unlike Hubble which views the universe primarily at optical and ultraviolet wavelengths, Webb sees in the infrared wavelengths of light in which the very earliest stars and galaxies are bright. Moreover, Webb’s 6.5 metre diameter main mirror dwarfs Hubble’s 2.4 metre one. Providing around 6.25 times more collecting area, Webb can peer significantly farther back into time than Hubble.
Combined, these capabilities will help astrophysicists such as JWST senior project scientist John Mather (2006 Nobel Prize in Physics) piece together how the universe developed from when the first luminous objects formed and evolved.
Because of its power to zoom deep into the universe’s past, Webb is often viewed as Hubble’s successor. Less well known is that the infrared space telescope will be taking over the reins of another venerable instrument as well: Kepler. The Kepler Space Telescope – designed to continually monitor the brightness of approximately 150,000 stars in search of dips from planets passing in front – was and continues to be a boon to scientific discovery.
Michel Mayor and Didier Queloz (2019 Nobel Prize in Physics) locating the first planet orbiting a solar-type star outside our solar system in 1995 was a seminal moment. But it wasn’t until, between 2009 and 2018, Kepler spied thousands of worlds orbiting other stars that a new era of exoplanet hunting began in earnest. At the time of writing, 2709 exoplanets have been confirmed of 4717 candidates found by Kepler. In the process of capturing all these alien worlds, the exoplanet hunter has changed our understanding of our place in the cosmos.
Among many revelations, Kepler has told us that planets outnumber stars and that exoplanets and star systems are far more diverse than the solar system would lead us to believe. It has also hinted that habitable worlds could be relatively common – over 300 exoplanets have been discovered orbiting in their stars‘ habitable zones, the region most conducive to a planet hosting life.
But up to now, the question of whether these worlds actually do harbour life has been moot. The only way to answer this is by analysing the atmospheres of these planets. And existing telescopes are only capable of doing so for the lifeless huge planets that orbit their stars very closely, known as hot Jupiters. Smaller, more distant rocky worlds that might host life pose a much more challenging problem.
Webb’s vantage point in space and infrared wavelength coverage make it particularly well suited to the task. Either analysing the parent star’s light as the planet passes in front of it, or blocking the parent star to directly image the planet, astronomers will wield Webb to search for molecules such as water, ammonia, carbon dioxide and many more in the atmospheres of promising planets.
For many, discovering just one planet with all the hallmarks of life, or witnessing the birth of just one star at the dawn of the universe will be enough to justify Webb’s cost. But it is more likely Webb will achieve much, much more. If Hubble and other space telescopes of the past are anything to go by, Webb will make discoveries revealing completely unexpected aspects of our universe that nobody could have predicted.