Looking back in time!

Image credit : NASA

It is able to observe celestial bodies, such as stars, nebulae and planets that are too cool or too faint to be observed in visible light — what is visible to the human eye.

The telescope’s centrepiece is the main mirror, measuring more than 21 feet (6.5 metres) in diameter and made up of 18 smaller, hexagonal-shaped mirrors.

The Webb telescope is different than the famous Hubble telescope in that it orbits the sun, whilst Hubble orbits Earth.

One  special feature of the telescope is that its infrared capabilities are uniquely powerful, allowing to detect light from earliest starts. This will allow scientists to peer further back in time than any previous telescope, to within a few hundred million years after the Big Bang, 13.8 billion years ago. The telescope is meant to see where stars and planetary systems are being born.

Webb is designed to be an incredibly powerful tool that will see out to the edge of the cosmos, the most distant galaxies, maybe even the first stars that formed. But because it is so powerful, it has capabilities that we can apply everywhere in the cosmos.

Looking back in time might sound like a strange concept, but it’s what space researchers do every single day (1).

Our Universe is bound by the rules of physics, with one of the best-known “rules” being the speed of light. And when we talk about “light”, we’re actually referring to all the wavelengths across the electromagnetic spectrum, which travel at around a whooping 300,000 kilometres per second.

Light travels so fast that in our everyday lives it appears to be instantaneous. Even at these break-neck speeds, it still takes some time to travel anywhere across the cosmos.

When you look at the Moon, you actually see it as it was 1.3 seconds ago. It’s only a tiny peek back in time, but it’s still the past. It’s the same with sunlight, except the photons (light particles) emitted from the Sun’s surface travel just over eight minutes before they finally reach Earth.

Our galaxy, the Milky Way, spans 100,000+ light-years. And the beautiful newborn stars seen in JWST’s Carina Nebula image are 7,500 light-years away. In other words, this nebula as pictured is from a time roughly 2,000 years earlier than when the first ever writing is thought to have been invented in ancient Mesopotamia.

Anytime we look away from the Earth, we’re looking back in time to how things once were. This is a superpower for astronomers because we can use light, as observed throughout time, to try to puzzle together the mystery of our universe.

Space-based telescopes let us see certain ranges of light that are unable to pass through Earth’s dense atmosphere. The JWST was designed to use a broad range of infrared light. And this is a key reason the JWST can see further back in time than Hubble.

Galaxies emit a range of wavelengths on the electromagnetic spectrum, from gamma rays to radio waves, and everything in between. All of these give us important information about the different physics occurring in a galaxy.

When galaxies are near us, their light hasn’t changed that much since being emitted, and we can probe a vast range of these wavelengths to understand what’s happening inside them.

But when galaxies are extremely far away, we no longer have that luxury. The light from the most distant galaxies, as we see it now, has been stretched to longer and redder wavelengths due to the expansion of the universe.

This means some of the light that would have been visible to our eyes when it was first emitted has since lost energy as the universe expanded. It’s now in a completely different region of the electromagnetic spectrum. This is a phenomenon called “cosmological redshift”.

And this is where the JWST really shines. The broad range of infrared wavelengths detectable by JWST allow it to see galaxies Hubble never could. Combine this capability with the JWST’s enormous mirror and superb pixel resolution, and you have the most powerful time machine in the known universe.

Using the JWST, we will be able to capture extremely distant galaxies as they were only 100 million years after the Big Bang – which happened around 13.8 billion years ago.

So we will be able to see light from 13.7 billion years ago. What’s about to hurt your brain, however, is that those galaxies are not 13.7 billion light-years away. The actual distance to those galaxies today would be ~46 billion light-years.

This discrepancy is all thanks to the expanding universe, and makes working on a very large scale tricky.

The universe is expending due to something called “dark energy”. It’s thought to be a universal constant, acting equally in all areas of space-time (the fabric of our universe).

And the more the universe expands, the greater the effect dark energy has on its expansion. This is why even though the universe is 13.8 billion years old, it’s actually about 93 billion light-years across.

We can’t see the effect of dark energy on a galactic scale (within the Milky Way) but we can see it over much greater cosmological distances.

Footnotes:

1. https://theconversation.com/a-cosmic-time-machine-how-the-james-web...

2. https://en.wikipedia.org/wiki/James_Webb_Space_Telescope

Questions based on this topic:

Q: Does that mean that the light would have traveled for much longer than the age of the universe!

A: You are missing one crucial detail: space expands.

It works a bit like this: imagine holding a rubberband between your hands. At a certain point, someone drops an ant on it. The ant walks at 1 cm/second – no faster, no slower. But while it is walking, you are stretching the rubberband, so when the ant finally bites your thumb 13.4 seconds later, the point where the ant was placed is now 32 cm away from your thumb.

The same happens to light: the light from that galaxy took 13.4 billion years to reach us, since then, space has expanded, and the galaxy (or whatever remains of it) is now 32 billion light-years away. And since the space that light travels through expands and light still must move at the speed of light, it has to lose energy in other ways than going slower. So it becomes redshifted instead: the wavelength becomes longer, and the light is thus redder.

And that is where James Webb Space Telescope comes in: it is specialised in taking very detailed images in the red and infrared part of the spectrum. That means that when online, it can take very detailed images of galaxies even further away than GN-z11, and thus shed some light (pun intended) on the Dark Ages of the universe and the earliest stars.