As another in my series of occasional posts showcasing science on the attack rather than under attack, this post features the James Webb Space Telescope (JWST). This state-of-the-art, massive human eyepiece was launched on Christmas Day, 2021 and is designed to probe the universe, especially the very early universe, at infrared wavelengths.

Approximately the length and weight of a school bus, the reflecting telescope has a primary mirror for light collection comprising 18 hexagonal segments made from gold-plated beryllium, which combine to form a mirror 6.5 meters (21 feet) in diameter. In comparison, the mirror of the earlier Hubble Space Telescope was only 2.4 meters (8 feet) across. Gold plating was chosen for the JWST’s mirror because it reflects up to 99% of infrared light and resists corrosion.

The size of the JWST’s mirror allows it to see celestial objects 100 times fainter than Hubble can, as well as cosmological events much closer in time to the Big Bang, the cataclysmic explosion thought to have been the birth of the universe 13.7 billion years ago. Objects and events are captured by four cleverly designed infrared cameras and spectrometers.   

Shortly after the JWST began scouring the heavens, cosmologists – who are not known for outbursts of emotion – became wildly excited by a totally unexpected finding amidst the breathtaking images streaming back from the new instrument. The telescope had detected very bright galaxies at the farthest distances it is capable of seeing, distances that correspond to light from a very young universe, only a few hundred million years after the Big Bang.

The puzzle wasn’t that the galaxies are there, but that they are much more massive than the so-called standard model of cosmology predicts. The model, based in part on Einstein’s theory of relativity, is well tested and fits a large number of astronomical observations of the universe. So this head-scratching observation had some cosmologists in a state of panic, wondering if the long-established standard model had to be thrown on the scrap heap.

There are, after all, several other predictions of the standard model for which no observational evidence exists to date – remember that empirical evidence is one of the pillars of science. Primary among these predictions are the somewhat weird concepts of dark matter and dark energy.

According to the standard model, the universe was created from pure energy in the Big Bang and now consists of only 5% ordinary matter (everything we can see, including ourselves, planets, stars and gas clouds), 27% dark matter and 68% dark energy. That’s right, 95% of the universe is invisible!

The need for dark matter, which may include black holes, is inferred from the existence of galaxies: without unseen mass to provide extra gravity, galaxies would fly apart. Dark matter is thought to reside mostly in the outer galactic reaches. Likewise, the existence of dark energy – associated with mysterious, unknown anti-gravitational forces – is postulated to explain the observed expansion of the universe, which would otherwise contract under gravity.

However, as it turns out, the excitement generated by the JWST last year about gigantic galaxies forming in an infant universe was misplaced, and the standard model of cosmology remains intact. The key was the measurement of distance to these fledgling galaxies.

Cosmic distances are determined by measuring an object’s “redshift.” Due to the Doppler effect, the light spectrum from a receding object is shifted to longer, red wavelengths. The larger the redshift, the greater the distance away. This was discovered in 1929 by astronomer Edwin Hubble, for whom the Hubble Telescope is named. The discovery later led to the modern-day concept of an expanding universe, although Hubble himself favored a static universe model.

The traditional photometric redshift, which relates the distance of an astronomical entity to its brightness, is notoriously unreliable because of effects such as dust surrounding a galaxy. That’s the method that led cosmologists to interpret the first JWST observations as overthrowing the standard model and everything we thought we understood about the universe.

But two teams of astrophysicists (see here and here) put an end to speculation in December, when they described measurements of distance to several of JWST’s early, bright galaxies, utilizing a much more reliable method of determining distance known as spectroscopic redshift.

The teams found four baby galaxies just as distant as the previously identified galaxies, but with much smaller masses. They also concluded that distances to the heavier galaxies seen with the JWST had been overestimated by the photometric redshift method, meaning that those galaxies are actually closer and formed later in the evolution of the universe.  

To resolve whether the standard cosmological model allows the smaller, baby galaxies to have existed close to the cosmic dawn, another group of researchers simulated galaxy formation and compared the simulations to the observations just mentioned. What they discovered is that the appearance of less massive galaxies in the early universe is indeed entirely compatible with the standard model. 

More unexpected and surprising observations from the JWST no doubt await us.

Next: No Evidence That Cold Extremes Are Becoming Less Frequent