By having all of it’s instruments observing similar wavelengths in the InfraRed, JWST benefits by being optimised for dealing with this section of the electromagnetic spectrum. Hubble by contrast has instruments which observe the optical and ultraviolet, along with some InfraRed capability. The dedicated nature of JWST allows in-detail observations with the goal of investigating four main topics which will help to fill current gaps in understanding of our universe.
The End of the Dark Ages: First Light and Reionization
Essentially seeking to identify the first bright objects to form in the early universe, JWST will look back to a point where the universe was only around 400,000 years old, to ‘the era of recombination’ where cooling of the very young universe allowed the first proper atoms (neutral hydrogen) in the universe to form out of the individual particles (free electrons and protons) produced by the Big Bang. Due to the removal of the free electrons, light was able to travel freely for the first time without being scattered, and the universe became transparent. After this point, the first individual stars formed and lived their short and violent lives, exploding as supernovae once the universe was about a billion years old. Understanding these first sources of light in the universe is pivotal in explaining how galaxies form and offers clues about the formation of the huge black holes found in the centre of large galaxies. JWST will study this period in the history of the universe to discover exactly how and when these first stars formed, and the effects their rise and fall had on the universe after this point.
Assembly of Galaxies
The second goal of JWST will be to answer questions relating to the formation of galaxies. Since the universe was about one billion years old, galaxies have been present, but how exactly did they form? What gives them their shape? How are the chemical elements distributed through the galaxies and what effects do the central black holes in many galaxies have on the host? What happens when small and large galaxies merge together. JWST will help to answer these questions, and also perhaps help to explain how the build up of collections of visible matter (stars, galaxies etc) occurs within the framework of dark matter that accounts for almost five times as much ‘stuff’ in the universe as the visible bits.
The Birth of Stars and Protoplanetary Systems
Goal three will be to study the birth and early development of stars, along with the formation of planets. Recent discoveries of large planets close to their parent star have prompted the need for a rethink about the processes that lie behind planet formation, to help explain why these systemes are so unlike our own solar system. In our own system, the inner planets are small and rocky, whereas a large number of exoplanet systems contain gas giants orbiting very close to their parent star, rather than further away. To help uncover the early stages of planetary formation, astronomers need to look into the dusty areas of star formation, to witness the distribution of material as the star forms, and what happens within the disks of leftover debris that goes on to form planets. To peer through all this dust, which would be opaque at optical wavelengths, requires observing in the infrared, leaving JWST ideally placed to search for further answers.
Planetary Systems and the Origins of Life
Finally, goal four will home in on another big question for current astronomy, studying the physical and chemical makeup of solar systems including our own and looking to see where the building blocks of life might be present. To shed light on the origins of the Earth and life in the Universe, scientists need to study planet formation in a similar way to goal three, and the debris disks in which they form. One major question is to discover if planets such as those found in our solar system form in their eventual position, or form further out from the star and then drift inwards, eventually reaching stable orbits following potential interactions with other planets along the way. Studying the outer fringes of our own system gives a good indication of the dusty, icy conditions found more widely when the solar system was young, and enables direct comparison with other young exoplanet systems. As well as infrared images of giant planets and systems, JWST will be able to obtain spectra from the disks around other stars to see what’s present in the material that makes planets.