Breakdown of the first James Webb Space Telescope image
This is a huge day for humanity. This day marks the beginning of an era. An era where our universe is much more accessible to us than it has ever been. Today, Nasa released the first image of JWST and the entire scientific community and even the world as a whole is thrilled. But what does this image show us?
What is the image of?
A galaxy field called SMACS 0723, located 4.6 billion light years away! What's more? Because of the orientation of the foreground galaxies, we get to see some really zany gravitational lensing of light from galaxies much further away in this field- about 13 billion years, to be precise! So these are all very young galaxies, all formed just a few hundred thousand years after the Big Bang.
The ones that appear to have white light are the ones creating the lensing 5-ish billion light-years away, and the reddish ones are the lensed ones. Here is Hubble's view of the same field by comparison.
Also note, JWST is an infrared telescope because its first scientific priority was to detect the earliest galaxies and by the time the light from the earliest galaxies reaches us, it has been "redshifted" to these wavelengths. So before you couldn't see these lensed galaxies with Hubble, and to see them let alone in such detail is astounding!
Pretty! Is there scientific value to it?
Yes! The thing to realize is even with these very first images because JWST is able to see in detail no telescope has had before, there's a ton of low-hanging fruit. In the case of this image, one of the big outstanding questions is a feature called the UV luminosity function, which tells you the star formation rate in those early galaxies. If you just count up the number of galaxies you see in those first JWST images, you'll already know more about the star formation rate in the early universe than we do now! Further, when you study the gravitational lensing pattern, you can learn about those foreground galaxies- things like their mass, and how the dark matter is distributed around them.
I need more JWST images in my life! What's next?
There is a press conference tomorrow at 10:30am! At the press conference, there will be several more images revealed, from the Carina Nebula to Stephan's Quintet (links go to the Hubble images to get you psyched). There will also be some data revealed, such as the first exoplanet spectrum taken by JWST- note, exoplanet spectra have been done before scientifically, but the signal to noise of JWST allows this to be done with greater accuracy than before. (No, this is not going to have a signature from life- it's a gas giant exoplanet.
Pretty pictures aside, can I access the actual science data? And when will we see the first JWST pictures?
The JWST archive will be launched with all the commissioning data for these images on Wednesday, July 13 at 11am EDT, with the first Early Release Science programs' data going up on Thursday. Specifically for the latter, there are "early release science" programs which are going to be prioritized over the first three months (list here) where those data are going to be immediately available to the public, so everyone can get a jump start on some of the science. (Also, the next cycle of JWST proposals is in January, so this is going to be really crucial for people applying for that.)
How did they decide what to observe anyway?
As is the case for all NASA telescopes, anyone in the world can apply for JWST time! You just need to write a proposal justifying why your idea is better than anyone else's, and well enough that a panel of astronomers agrees. In practice, it's really competitive, and about 4.5x more hours were requested than there are literal hours for JWST to observe (actually way better than Hubble which has been closer to 10x- Hubble can only observe on the night half of the Earth's orbit, but JWST has a sun shade so you get almost nonstop observing). The resulting proposals that won out are all a part of "Cycle 1" which begins this week, and you can read all about them here. (Cycle 1 includes the Early Release Science projects I discussed above.)
Want to know more about the JWST first image and what JWST actually is? Make sure to watch these wonderful videos:
Anyway, a toast to JWST- and if anyone who works on it is reading this, we are all so proud of you! I can't wait to see where this new adventure takes us!