Finding the first stars: The start of the Universe

In 2019 the most advanced space telescope and time machine ever built will be launched. That’s right, a time machine. The James Webb Space Telescope (a tribute to the second administrator of NASA), will allow us to look into the past with detail not previously observed. This means we can watch the birth of the first stars which would go on to shape the entire universe.

Looking into the past with a telescope may seem a strange concept but it is just a large-scale version of an everyday phenomenon. Warning, mind blowing moment; Everything we view is a slight delay of what has actually happened and this is due to the travel time of light. Light travels at around 186,000 miles per second, so fast that the delay is not noticeable in everyday life. However, over large distances it becomes more important. Take the sun for example. Due to the distance at which the earth orbits the sun, sunlight takes around 8 minutes to reach earth. Thus, if the sun suddenly disappeared we would still have light for ~8 mins before total darkness! If we apply this idea to the first stars in the universe, the light they emitted almost 13.6 billion years ago should still be travelling through the universe. This starlight is still visible today despite the stars having died and changed form. This phenomenon is due to the time it has taken for the light to reach us. So now we know it is possible to look into the past and see these stars, how do we do it?

Probably the most famous space telescope, Hubble, has been observing the infant universe since the 90’s and has provided a lot of spectacular photos.  One such image is ‘the pillars of creation’, beautiful right? This is a collection of interstellar gas and dust which sits ~7,000 light years away from earth, and is the birthplace for new stars (i.e. a star nursery). Hubble specialises in photos like that on the left, taken in the visible to ultraviolet part of the electromagnetic spectrum (see next picture). Whilst striking, they don’t reveal the full picture. What’s going on behind the dust?

If we take the same picture again but using Hubble’s near-infrared detection, there is a different picture (above on the right). (Side note: As you can see from the cartoon, the light we can see (i.e. visible light) is a small part of the electromagnetic spectrum. Without these telescopes we would not be able to view the light emitted from these stars or parts of galaxies. The electromagnetic spectrum is a way of categorising different types of light by their frequency and wavelength. The spectrum extends beyond the visible light we view, from x-rays all the way to radio waves).

Ok, now look at the lovely picture above on the right again. The cold dust clouds (essential for star formation) have been filtered out of the right-hand photo, uncovering a new level of detail. This method detects heat given out by the stars, transmitted as infrared light. This is an example of what we might expect to see as the first stars formed. However, at the start of the universe there wasn’t as much interstellar material (i.e. free moving stuff) free to become a star. Therefore we need to observe the first stars to find out how they came about.

So why do we need a new telescope if Hubble can already see star formation? The pillars of creation are ~7,000 light years away but in terms of the expanse that is the universe, this is a relatively short distance. When we try to look further into the past (i.e. further away) with the Hubble telescope we run into a problem. Hubble’s main detection source is in visible light. Visible light from the first stars isn’t there. When a star first emitted light it was in the visible to ultraviolet region of the spectrum. When light travels through space it is stretched (i.e. the wavelength becomes longer).  You can try this at home by drawing two dots on a deflated balloon and connecting them with a wiggly line. The dots represent two galaxies and the line is light travelling between them. The tighter the wiggles of the line, the shorter the wavelength. As you inflate the balloon, the dots (galaxies) move away from each other, and the wiggles get longer (i.e. stretching of the light, this is known as redshift – a move towards infrared wavelength in the electromagnetic spectrum). The extent of redshift observed indicates how far the light has travelled. The further it has travelled, the more it is stretched. So, the oldest stars will have the largest redshift. Therefore, there is a need for a new infrared telescope.

The James Webb telescope views this area of the spectrum and is designed to look specifically at the early universe. It also has several improvements over its predecessor. Not only is it bigger than Hubble providing a larger area to view, but it is also colder thanks to the tennis court sized sunshield! This sunshield will help detect very faint leftover heat from the first stars. This specialised star hunting machine hopes to answer some of the biggest questions in astronomy. How did these first stars influence galaxy formation, and how did they become supermassive black holes which have been observed at the centre of nearly every galaxy today?  The James Webb telescope is the next big thing in astrophysics, and I expect we shall hear a lot more about it in the future!

This post was written by my fellow PhD student Josh Horton (who wants to go by AnAverageScientist), whose background is in physics. Thank you Josh for such an insightful post!