Astro Bob: Webb Space Telescope takes us to brink of cosmic dawn

Formed just 300 million years after the Big Bang, GLASS-z13 may be the farthest and oldest thing we've ever set eyes on. For now.

Oldest galaxy
Just weeks into its mission, the James Webb Space Telescope found what's believed to be the oldest galaxy ever seen. Named GLASS-z13, it's located some 13.4 billion light-years away and formed when the universe was just 300 million years old.
Contributed / Naidu et al, P. Oesch, T. Treu, GLASS-JWST, NASA, CSA, ESA-STScI
We are part of The Trust Project.

NASA's James Webb Space Telescope (JWST) is barely out of the gate, yet already pushing limits with its recent discovery of GLASS-z13, possibly the oldest and most distant galaxy we've ever found. Located some 13.4 billion light-years away in the southern constellation Sculptor the sculptor , the first image jets us back to the cosmic dawn , when the first stars grew from the cooling ions and atoms left in the wake of the Big Bang.

The name comes the Grism Lens-Amplified Survey from Space (GLASS) observing program. If you've never heard of a grism, it's a combination of a grating (a piece of flat glass covered with finely etched parallel lines) and a prism. Together they spread out a galaxy's light with great precision, so astronomers can read information embedded in that light to determine particulars like a galaxy's rate of new star formation or its cosmic velocity.

The z13 part refers to the galaxy's redshift or how fast it's running away from us as the universe balloons. The letter "z" indicates the amount of redshift, 13 here. That number can be converted into the distance to that object based on the known expansion rate of the universe.

When a celestial object like a star or galaxy moves away from us (top) the color of the light it emits shifts toward the red end of the spectrum. When a star approaches us the light shifts to the blue end. Measuring the amount of that shift or "z" tells us the object's distance.
Contributed / Ales Tosovsky, CC BY-SA 3.0

The expansion literally causes light waves emitted by distant galaxies to stretch and redden, similar to the way the pitch of an ambulance siren decreases as it speeds away. Light from really far-away galaxies gets stretched so much it moves beyond red into the infrared.

If that rings a bell it should. You might remember that the JWST has been optimized (and deeply chilled!) to give us our best look yet at the infrared universe. That's the reason it found GLASS-z13 in the first place. You could say it was just doing its job.


Although astronomers are still in the process of confirming the discovery, it appears that GLASS-z13 is not only the most distant but also the oldest physical object we've ever beheld. We see it as it appeared 13.4 billion years ago, just 300 million years after the creation of the universe in the Big Bang. Its light is ancient, yet paradoxically we see the galaxy as it was almost straight out of the oven.

Red dot
That little red dot is GLASS-z13, the oldest galaxy we've ever seen — it's 97.8 percent the age of the universe.
Contributed / Naidu et al, P. Oesch, T. Treu, GLASS-JWST, NASA, CSA, ESA, STScI

Telescopes are time machines that take us back to the distant past when the universe was much younger. If we could pull up alongside GLASS-z13 13.4 billion years ago, we'd see it cranking out hot blue stars and star clusters like widgets in a factory. Since then it's aged into a different galaxy or even absorbed into a larger one for all we know.

Able to see back in time, the Webb shows us the galaxy as it once was, full of youthful zeal. But because it's now so far away thanks to universal expansion, GLASS-z13's individual stars blend into fuzzy red blobs too faint for even Hubble to detect.

Like the Milky Way, it's a self-contained system of stars, nebulae and star clusters but much smaller and less populous — 1,600 light-years across compared to 106,000 light-years for our galaxy, with only about a billion stars versus 100 to 400 billion in the Milky Way.

JWST redshift NASA ESA and L. Hustak STScl tipped with additions.jpg
With its infrared "eye", the James Webb Space Telescope can see farther back in time and space than its predecessor, the Hubble Space Telescope.
Contributed / NASA

For now, the galaxy's only competition is the previous record-holder, GN-z11 in Ursa Major, discovered with the Hubble Space Telescope in 2016. It formed 100 million years after GLASS-z13. Hubble can't observe galaxies beyond about z=12 because its optics aren't optimized for infrared light like JWST. That said, scientists don't expect the new champ to hold the top spot for long. After all, the Webb has only just opened its eyes.

For more on the discovery, you can nibble on juicy bits from the July 20 scientific paper that's still under peer review.

Read more from Astro Bob
The Red Planet is only 50.6 million miles away — almost walking distance! It won't get this close again until May 2031.

"Astro" Bob King is a freelance writer for the Duluth News Tribune.

"Astro" Bob King is a freelance writer and retired photographer for the Duluth News Tribune. You can reach him at
What to read next
Cetus emerges from the sea of night to prepare the way for Orion. How to find this enormous yet unfamiliar constellation.
When it comes to flying around in space, there's a lot happening this week.