Imagine if scientists could use a telescope to peer back billions of years to the early days of the universe, to watch how planets, stars and galaxies formed out of the proverbial primordial soup? It might sound impossible but this is exactly what the James Webb Space Telescope – launching this month – has been designed to do.
The JWST was designed to “look” back in time, to the early universe. It performs this scientific miracle using infrared detectors, which can pick up light that has been stretched, or “redshifted” to infrared wavelengths as it travels vast interstellar distance to reach us here.
"The infrared detectors are sensitive enough to allow us to see the redshifted light of distant galaxies, and newly forming stars," says Prof Tom Ray, director of Cosmic Physics at the Dublin Institute for Advanced Studies (DIAS). Ray is co-lead investigator for the mid-infrared instrument (MIRI), one of four scientific instruments on the telescope – and an instrument he helped to build.
To work best, MIRI must be on a space telescope, out beyond the atmosphere which blocks infrared radiation reaching Earth's surface. The atmosphere glows like a furnace in the infrared, when viewed from the ground. "It is like trying to see the stars from the centre of Croke Park, while the floodlights are on," says Ray.
A space telescope such as the famous Hubble Space Telescope, would not have to deal with the problems created by the atmosphere. Hubble saw farther and clearer than any telescope in history and revolutionised scientists’ understanding of the universe. Yet, the JWST has over six times more light-gathering capacity than the Hubble had, and is far bigger too; about the size of a tennis court.
The JWST, by operating at longer wavelengths, begins to switch on where Hubble started to switch off. The mirror has been designed with a gold coating, as gold is the perfect mirror for infrared light.
Universe origins
The universe is estimated to be 13.8 billion years old. It began with a bang, a Big Bang, after which everything we see – and much that we still can’t but know is there – was formed. The universe’s first 100 million years or so are mysterious. Scientists can only guess what was going on back then, and how stuff such as planets and stars began to emerge.
Suddenly, however, after about 100,000 years, the universe goes “black” for reasons unknown, and there’s nothing producing radiation. Scientists are hoping that the JWST will shed some light on this mysterious dark age before the universe’s lights came back on.
As early as the 1920s, astronomers began to dream of putting a telescope out into space, where it would be free to clearly view the cosmos without suffering the distorting effects of the atmosphere. In 1990, scientists had their dream realised when the Hubble Space Telescope, the first optical (light) space telescope, was launched.
Hubble was placed in low-earth orbit, at an altitude of about 540 km, placing it just outside the atmosphere, which extends to a thickness of some 480km. New, earth-shaking discoveries then followed; most notably the finding that the universe was expanding, and at an ever-accelerating rate, rather than slowing as many scientists expected.
It discovered much other new knowledge, including the finding that galaxies grow by eating other galaxies until an equilibrium is reached. In this way, our own Milky Way grew bigger when it consumed a dwarf galaxy, which is now located close to its galactic centre.
Hubble was designed to last 15 years, up to 2005, but continues to send remarkable images back to Earth. It is, however, expected to decay, fall back into the atmosphere, and burn up there some time over the next decade, so a replacement space telescope is needed.
Exoplanets
JWST will study the planets beyond our own solar system, known as exoplanets. The first exoplanets were discovered in 1992, when two planets were found orbiting the pulsating pulsar star called PSR 1257+12. Since then, more than 4,000 exoplanets have been found.
Dr Neale Gibson, an astrophysicist at the school of physics in TCD, has been investigating what some of these exoplanets are made of – rocks like Earth or gases like Jupiter – and what the chemical make-up of their atmosphere is like. The instruments on board the JWST make it an ideal telescope to get answers to questions such as these.
Hubble proved a highly effective exoplanet hunter, says Gibson, though it went to space in 1990 two years before the first exoplanet was confirmed and was not designed for this. Unlike Hubble, JWST is designed, he says, specifically with exoplanet studies in mind.
“We’ll be observing hot ‘Jupiters’ to test the sensitivity of the instruments, but there are also many programmes aiming to look at the atmospheres of smaller, cooler objects,” says Gibson. “Of course, long term, we want to do this for Earth-like planets, and hung for biomarkers, like oxygen, that may indicate the presence of life.”
Dr Luca Matrà of NUI Galway's Centre for Astronomy will use the JWST to study how exoplanets interact with "debris disks" – dust and debris layers that can orbit a star. The disks can occur in belts like the Edgeworth-Kuiper belt around our Solar System, whose existence was predicted by Irish astronomer Kenneth Edgeworth.
“Belts of small icy bodies are very common in exoplanetary systems, and we can image them at a variety of wavelengths with cutting edge telescopes, including the JWST,” Matrà says. When observed at high resolution with telescopes on the ground these belts show a radial structure, he says that was thought to be the result of their gravitational interaction with, as yet unseen orbiting exoplanets.
“This is like what happened in the Edgeworth-Kuiper belt of our solar system, whose structure has been shaped by interactions with the nearby planet Neptune, just interior to the belt,” she notes.
Launch schedule
The JWST is scheduled to launch on December 22nd on board an Ariane 5 rocket from the European Space Agency's launch facility in Kourou, French Guiana. Irish company Réaltra Space Systems Engineering will play a critical role in the launch by providing video images of the separation of the fairings (equipment used to protect the spacecraft during launch), and the spacecraft from the rocket.
The telescope is huge – so big that it will be folded up inside the top of the rocket. It will reside at a so-called Lagrange point one million miles from Earth. This is a sweet spot where gravitational forces cancel out and permit the telescope to hover in line with the Earth as it orbits the sun. This position also enables the sunshield to protect the JWST from the light and heat of the sun, the Earth and moon.
The MIRI must be kept at an operating temperature of 7 Kelvin or minus 266 degrees to work most effectively. This is cooler than the temperature of space where the JWST will reside, which is 14 Kelvin, or minus 259 degrees. The instrument is cooled using helium gas.
The JWST will have a sun shield on its sunward side, which will get warmed up to 300 Kelvin, or about 27 degrees. On the other side, however, where there is no solar radiation, it will remain very cold. It is expected to have an operational life span of about 10 years.
Dr Patrick Kavanagh of DIAS school of cosmic physics will be working at the JWST Mission Operations Centre in Baltimore, Maryland, some time after the launch. Scientists will be forced to wait a few months before the MIRI instrument is operational, he says, as it will take 100 days for it to reach its operating temperature of minus 266 degrees.
Expanding universe
A big question for JWST is: what does the future hold for the universe? The Hubble found it is expanding, but scientists are unsure whether this expansion will continue to infinity, or whether it will run out of steam and collapse inwards in a so-called Big Crunch.
The JWST can shed light on this, by examining infrared light coming from the most distant galaxies and comparing them with closer, more recently formed ones, to see how the universe behaved over time.
Then there is the big question of dark matter. Scientists estimate we see just 4 per cent of the stuff that is out there, and they would dearly like to know what the other 96 per cent is made up of. They would also like to know what the mysterious force is, called dark energy, driving the expansion of universe as well as holding it all together.
"[The telescope] will be like the transformation in astronomy that occurred after Galileo turned the first telescope to the night sky and made lots of wondrous discoveries," Ray adds. "We are definitely going to find lots of things out there that we never expected."