Mini-Throughput: JWST Ready to Pierce the Veil

Looking back into the history of the Universe. The broad purple line is how far back Hubble can look. JWST will fill in the gap between that and the radiation era. (Credit: NASA).

We are very fortunate to live in the Universe that we do. I mean, sure, it’s amenable to the evolution of life and all that, which is great if you’re a living creature. But what’s really nice is that the universe acts as its own time machine, providing windows into its past. As we turn our telescopes to the distant universe, we are also seeing backward in time. The light from the most distant regions of the universe has taken billions of years to reach us and so we see the universe in those moments of the past, not in the present.

But how far back can we go? That question depends on how you look. Because the universe is also expanding, inflating like a balloon. And the further away things are, the faster they are moving away from us. This causes the light distant objects emit to change by the time it reaches us, stretching it out like an expanding slinky to longer and longer wavelengths, to redder and redder light. An ultraviolet photon that emerged from a star 10 billion light years away might be stretched out into an infrared photon by the time it reaches us. In order to see, you have to look with the right eyes.

The two effects — lookback time and cosmological redshift — that the light from the distance universe is both ancient and reddened — means that different telescopes see different things. The Hubble Space Telescope can look all the way into the near-infrared, giving it a view to when the universe was a few hundred million years old. By that time, galaxies had formed and the stars that shone are similar to those that shine now.

Radio telescopes can stretch all the way back to the very earliest stages of the Universe, when it was only 300,000 years old. At that time, the universe was just a broiling fog of hydrogen and helium that had just become transparent to light. This cosmic microwave background is the furthest back that any telescope can see. Beyond that veil, we have to use other tools.

The time between that probed by HST and by Planck — that half billion years when the universe transformed from a sea of hot hydrogen gas to familiar islands of stars — is a great unknown. We think we know what happened. We think that massive stars started forming and exploded almost overnight. That matter began to accumulate into dwarf galaxies that merged into larger galaxies. But we don’t know. We don’t know because to see that time you need a giant extremely-sensitive infrared telescope that can see those distant faint objects, something that can bridge the gap between radio/microwave telescopes and optical ones.

Enter the James Webb Space Telescope.

We are now over a month past launch. During that time, Webb has successfully completed the amazingly complex dance of deploying its sunshield and mirror. It has moved out to the LaGrange point and assumed its orbit. And now it is powering up its instruments and turning off heaters to get down to the very cold temperature it needs to thrive. Overall, we probably have another five months before the first light images come out.

But soon after that, JWST will turn its cold steady eye to the deepest reaches of the universe. It will glimpse the first stars emerging from the primordial ooze, watch the first galaxies crash into each other and unveil the building blocks of our modern universe. And, doubtless, some of what we think we know will turn out to be wrong.

Our understanding of our universe may be about to change again. And I can’t wait.