What is the fate of the universe? Will it keep expanding forever? What did some of the first galaxies look like? Why are we here?
The Hubble Space Telescope was commissioned to answer just these sorts of queries – well, except for that last one, you're on your own there. Indeed, Hubble has shed clarity onto many cosmological conundrums and even delivered answers to questions we didn't know we had. However, any good scientist will admit to you that the more we know, the less we understand. Every new discovery leads to more mysteries.
Don't get me wrong, Hubble has accomplished some truly amazing feats in the last 27 years and will hopefully continue to do so. It has determined the age of the universe, spied on the most distant galaxies, even peered into the darkest depths of space. In all of its glory though, Hubble left a lot unsaid. Why do the earliest galaxies look the way that they do? Now that we've seen those first galaxies, what about the first stars? How do exactly do planets form?
The James Webb Space Telescope (JWST), scheduled to launch in October of next year, will aim to provide explanations to these questions that Hubble left behind. In order to do that, JWST must observe the universe in the realm of infrared, which means it is going to look quite a bit different than its visible-light predecessor.
Artist depictions of JWST courtesy of Flickr, Flickr
The Specs of JWST
Before we delve into the world of the infrared and exactly why it is so important, let's talk about JWST itself. What makes JWST able to see things that Hubble cannot? Well, for starters, it's a lot bigger.
The capability of a telescope is largely determined by its “light gathering power.†Most modern telescopes are reflectors, which means they use mirrors to gather and focus light. The primary mirror is the mirror that receives incident light from outer-space objects, while secondary and tertiary mirrors focus and direct the light. So the bigger the primary mirror, the more “light gathering areaâ€, and thus the more powerful the telescope. JWST will have a 6.5m primary mirror compared to Hubble's 2.4m primary. This helps JWST to be 100x more powerful than Hubble!
Spitzer, NASA's current infrared telescope, ran out of coolant almost 8 years ago and has since lost a lot of its capabilities, though not all. Although Spitzer once saw a huge portion of the infrared spectrum, it's resolution wasn't all that due to its small mirror. The Herschel Space Observatory, commissioned by the ESA, was also an infrared mission (3.5m mirror) which is now inactive.
How do you get a mirror that big into space? Logically, you fold it up like origami! The 6.5m mirror is made of 18 hexagonal gold coated components that weigh almost 50 lbs each. After being folded nicely during launch, they will expand once the telescope is settled in space. Attached mechanisms will produce slight movements on the mirror segments so that light is properly focused. The final product looks something like a very intimidating honeycomb.
If you think folding the 21ft mirror is tricky, try keeping it freezing cold at 49 degrees Kelvin above absolute zero (-370F)! Since JWST will be detecting infrared light, which is mainly transmitted as heat, any heat on the mirror could skew observations. This includes heat from the sun, earth, or even the controls on the spacecraft.
So… how do you avoid the sun when you're in space? Why, you build a sunshield, of course! This sunshield will separate the warm side (185F) of JWST, which faces the sun, from the cold side, which keeps the mirror and science instruments in a chilly shadow. The kite-shaped sunshield, boasting a size bigger than the entire Hubble spacecraft, and is made of five protective layers of Kapton, a special material that won't melt or burn. Each layer is spaced so that heat is reflected and dissipated away out of the sides efficiently. The warm side of JWST will house the ‘spacecraft bus,' which operates the telescope and communicates back to Earth.
Information from JWST will have much farther to travel back to Earth than Hubble. While Hubble is in low Earth orbit, about 340 miles above ground, JWST will orbit with the Earth rather than around the Earth. It will orbit Earth's second Lagrangian point a million miles away, almost four times the distance from Earth to the moon. Because JWST will be at “L2â€, the Earth and Sun will always be on one side of the telescope and the warm side of the sunshield will intercept all the heat.
It will take JWST about a month to reach L2 after launch. The telescope will jettison into space on an Ariane 5 rocket, the most reliable vehicle available, at European Spaceport in French Guiana near the equator (JWST is a joint effort between NASA as well as the European and Canadian Space Agencies). NASA has made all sorts of cool videos to show how the deployment of the telescope will go down, one of which you can watch here.
About 6 months after launch, plenty of time to allow for cooling and the necessary calibrations, the JWST's four science instruments will begin routine operations and the world of astronomy will never be the same. This combination of spectrographs and cameras (operating at differing portions of the infrared spectrum) will process the light gathered by the mirror and produce the deepest view of the universe that humans have ever had. But why is it so important that these instruments be sensitive to infrared light?
The Infrared World
The big questions we have now about the cosmos can only be answered by looking back in time to the farthest recesses of the universe. Hubble, a visible light telescope, can see back to when the universe was about 1 billion years old. To see back any farther, we need to look at the universe in infrared light. Let me explain why.
First off, keep in mind that light from very distant objects takes a long time to reach us. So when we look at galaxies that are say, one million light years away, we are seeing a snapshot of the galaxy as it was when the light now reaching us was first emitted one million years ago. This means that when we look at these distant objects, we are looking back in time.
The tricky thing about galaxies far, far away is that they are moving away from us. In fact, the farther something is away from us, the faster it is moving. This is because of Hubble's law , which states that the universe is expanding at an accelerating rate.
Imagine that you have a balloon, and before you inflate it, you draw some dots on it. Say you draw one dot which represents the Milky Way (where you place this is unimportant). As you begin to inflate the balloon, the dots, which represent other galaxies, begin to move away from one another. Say you place a tiny version of yourself on the mark that represents the Milky Way. Although you seem stationary, you see all the other dots moving away from you. And the further the dots are away from you, the faster they seem to move. This is akin to why we see more distant galaxies moving away from us at higher speeds. (If this made no sense to you, don't fret! Here is a great video to explain what is beyond the scope of this blog.)
Far away objects may emit visible light, but because they are moving away from us, that light is shifted to a longer wavelength. Say a star is moving away from us; we see the wavelength of the star's light as if it has been stretched. Therefore, we see visible light from such sources as having a longer wavelength than it was emitted at. Astronomers call this phenomenon “redshift,†because the visible light has been shifted to a longer, more red wavelength.
[You experience a similar phenomenon to redshift when you hear an ambulance go by. As the ambulance approaches, we hear the sirens at a higher frequency (the higher the frequency the shorter the wavelength and vice versa). After the ambulance has passed us, we hear the sirens at a lower frequency. The same sort of effect happens with light from objects in space. The difference is that the motion of the objects away from us is caused by the expansion of space rather than a set of wheels.]
This is why infrared light will give us the vision to peer back in time to when the universe was a baby – the most distant objects in space are so red shifted that their visible and ultraviolet light is actually interpreted by us as infrared light. Because JWST is such a powerful infrared telescope, it will be able to see back in time – to when the universe was only 300 million years old – by observing the most remote stars and galaxies.
What Can JWST Do For Us?
By looking so far into our beginnings, JWST will be able to tell us things that Hubble could not. There are four main areas of astronomy that JWST is designed to explore: light from the first stars, galaxy evolution, planetary studies, and stellar evolution.
Let There Be Light – What did the first stars look like?
JWST will be able to see the first visible light emitted by the universe.
No, this does not mean JWST will see the big bang occur. You see, the Universe experienced a sort of “dark ages†after the big bang. Everything at that time was so dense, that any light was scattered off of free electrons – ‘free' meaning they were not attached to any atoms. After the Universe began to cool, neutral hydrogen and helium (aka stable, equal numbers of protons and neutrons) finally formed, attracting these pesky electrons into their atoms. As this occurred, light was finally allowed to travel freely.
Now of course, it still took time – maybe a few hundred millions years – after this began for the first stars to form, and JWST is designed to look back at these youngest stars whose light marked the end of the “dark agesâ€. It may be able to show us how these first massive stars, which burned out incredibly quickly, split the neutral hydrogen back into electrons and protons again in a process called reionization. Better yet, it will be able to tell us when these first stars emerged.
How Do Galaxies Shape Up?
Hubble showed us some of the earliest galaxies, but this left us wanting to know more about them. Hubble unveiled clumpy galaxies with uneven distributions of star formation, very unlike the beautiful structures that we see today. The nearby, older galaxies that we are so familiar with show elliptical and grand spiral shapes. How did the first galaxies make such a transformation?
By looking in the back in time through the infrared to younger galaxies than Hubble and even the very first stars, JWST will study the process of galaxy formation. Infrared imaging will show us more structure of these early objects. It could also tell us how this formation is linked to black holes, which reside at the center of most massive galaxies. Dark matter is thought to help hold galaxies together, and JWST may be able to shed light onto this dark phenomenon by watching how galaxies first arranged themselves and evolved over time.
What About US?
Within our own galaxy there are still mysteries left to unravel. JWST will used infrared spectroscopy, the study of how intensely objects emit different wavelengths of light, to reveal the composition of the worlds that makes up our own solar system. Because different types of atoms and molecules emit different wavelengths of light when they are excited, JWST will be able to study this light to tell what compounds are present in solar system bodies. Although near-infrared spectroscopy like that from Hubble is useful, astronomers will use JWST to study planetary spectra at farther (longer) infrared wavelengths. This will tell us more about the atmospheric composition of other worlds since the materials we expect to see emit light at these longer wavelengths.
JWST can look at the Martian atmosphere and help us understand the extreme weather of the gas giants. This telescope will even observe the makeup of smaller rocky bodies, such as asteroids and Kuiper Belt Objects like Pluto (sorry, not a major planet, no matter how emotionally attached to it you are). This information will complement and confirm other ground-based (or rover-based, in the case of Mars) observations that have been taken.
Naturally, we will also want to apply these methods to star systems outside our own as well. Recent discoveries have revealed thousands of planets orbiting other stars (exoplanets). With its incredibly sensitive instruments, JWST will be able to directly image some exoplanets and follow up those pictures with spectroscopy. In doing this, JWST will search for atmospheres on these planets that are similar to Earth's and thus potentially habitable.
Left: a Hubble image of part of the Eagle Nebula called the “Pillars of Creationâ€. Right: Image of the same area, taken by Hubble in the near-infrared.
Another One Bites the Dust
Another important part of being an infrared telescope is that JWST can see through dust. Yes, dust sounds boring I know, but it is actually incredibly important in star and planet formation. Remember a couple of years ago when BICEP2 thought that it discovered gravitational waves remnant of the big bang? Yea… that was just galactic dust. So knowing about dust pays off! (I study dust disks around stars myself, but look, it is objectively a big deal)
Stellar nurseries, dense clouds of molecular gas and dust, are opaque to our visible light telescopes. This is because dust inside these particular types of nebula (the general term for dusty and gaseous clouds) blocks visible light from reaching us. However, looking at these areas in the near-infrared allows us to see the forming stars that are obscured by the dust. This will allow astronomers to study newborn stars and how these giant clouds condense to form them. Hubble can see through such dust to an extent; however, since JWST will be so much more powerful, it will reveal more of the structure of these star forming regions.
Studying dust (particularly at longer infrared wavelengths) can also tell us a lot about planet formation. Stars often form with a disk of gas and dust surrounding them called a protoplanetary disk. As the star matures and planets begin to form, this material is molded into planets or shifted around in the process. Collisions between objects like asteroids or forming planets can also produce large amounts of dust. By determining the properties of the dust, like its age and how large the grains of dust are, we can speculate about its source. The dust around a star therefore gives us information about what stage of planetary formation the system is in and how this takes place. That means that dust studies are also good for finding exoplanets!
So Here's the Point
With all of these potential discoveries and unprecedented capabilities, JWST will revolutionize the way we look at outer-space. It will be the largest space bound telescope ever built and an impressive feat of engineering. More importantly, it will answer our most puzzling questions about how the universe came to look as it does today.
Here on this pale blue dot (some call it Earth), hurling through the void at 67,000 mph, things get pretty hectic. We tend to forget the beautiful vastness that encompasses us. Hubble showed us quite a lot, but JWST will tell us more about how curious our cosmos really is.
About the author
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Lauren Sgro is a PhD student in the Physics department at the University of Georgia. Her research focus is in astronomy, specifically debris disks around young stars that may tell us more about planetary formation. Despite the all-consuming nature of graduate school, she enjoys doing yoga and occasionally hiking up a mountain. You can't reach her on Twitter, but you can email her at lauren.sgro25@uga.edu. More from Lauren Sgro. |
