Since the dawn of humanity, gazing at the night sky has been a great source of inspiration. In the past 50 years, space telescopes have transformed that gaze. Today our two keenest eyes on the universe are the Hubble Space Telescope and the James Webb Space Telescope. One tuned to the colors our eyes know, the other to the heat-glow of new beginnings, these two lenses let us look back across cosmic history.
Think of Hubble first: a steady heartbeat since 1990, circling our home planet about 330 miles (530 km) away, just above the Earth’s atmosphere. Its primary mirror is 2.4 meters and is engineered to see mostly invisible light. It is therefore great for sharp, “true to our eyes” views of the cosmos. Now think of James Webb, which like Earth orbits the Sun, roughly 1 million miles (1.5 million kilometers) away from home. It carries a 6.5 meter segmented mirror made of 18 hexagonal pieces coated in gold. Its launch on December 25, 2021, was the beginning of a new golden age of astronomy. Webb was built to listen where the universe whispers: deep infrared. It’s consequently ideal for capturing light stretched thin by cosmic expansion. Thus, with more than six times the light-collecting area that Hubble has, and being much farther from Earth, Webb is exquisitely sensitive to the faint, red-shifted glow of very distant galaxies and to the warm fingerprints of dust, molecules, and planetary atmospheres. In plain language: Hubble shows us what things look like; Webb helps us understand what things are. The partnership is by design, and, as NASA says, these observatories complement each other.
Now let’s take a closer look at what each lens sees and what they reveal. Our first stop is close by in our home galaxy, the Milky Way, at just 6500 light years away: The Pillars of Creation. These majestic columns within the Eagle Nebula, are made of cool dense gas and dust, where new stars are actively forming. Our collective imagination was first struck by these pillars in April 1995, when Hubble took its first photo of them. In Hubble’s eyes the pillars feature dark brown, opaque dust. When Webb looks at them in 2022, the pillars appear semi-transparent. Suddenly the opaque dust becomes mist, and newborn stars pierce the darkness everywhere. Below is a comparison of the Pillars of Creation as provided by the Hubble Space Telescope and the James Webb Space Telescope.
The Pillars of Creation In the photo of the Pillars of Creation taken with NASA’s Hubble Space Telescope, the pillars of gas and dust are dark and relatively impenetrable. In the image taken with NASA’s James Webb Space Telescope, scientists can peer through the dust to see more of the star-forming region. The images are composites of separate exposures. (Photos: NASA)
Another close by cosmic cloud that Webb was able to see through is the Carina Nebula, located 7500 light years away. The same structures that appeared opaque to Hubble reveal numerous newborn stars when looked at in infrared light, which can penetrate dust.
Carina Nebula The comparison of the Hubble Space Telescope images with the James Webb Space Telescope images of a star-forming region in the Carina Nebula demonstrate the latter’s ability to reveal for the first time star nurseries and individual stars. (Photos: NASA)
Our next stop is farther from us, another spiral galaxy: the Sombrero Galaxy. Located about 30 million light years away in the Virgo constellation, this galaxy is recognized by its bright bulging center resembling a Mexican hat. Webb’s mid-infrared photo of the Sombrero Galaxy pierces the dust to reveal a smooth inner disk and intricate clumps within the outer ring. Hubble’s visible light image on the other hand, shows the large and extended glow of the central bulge.
Sombrero Galaxy The James Webb Space Telescope reveals the smooth inner disk of the Sombrero Galaxy, while the Hubble Space Telescope’s visible-light image shows the large and extended glow of the central bulge of stars. (Photos: NASA)
How much farther can we go? Hubble gave us the audacity to look back at cosmos billions of light years away. In 2004, it captured the Hubble Ultra Deep Field image: nearly 10,000 galaxies framed in a sliver of sky you could cover with a grain of sand held at arm’s length. When Webb observes the field in 2022, it can reach depths comparable to Hubble’s in roughly one-tenth the observing time. Webb images also reveal more distant galaxies that were previously invisible to Hubble. As the universe expands, light from very distant objects gets stretched to longer, redder wavelengths that are beyond the visible capabilities of Hubble, but within the infrared range that Webb can see.
Ultra Deep Field In December 1995, the Hubble Space Telescope took exposures of the Hubble Ultra Deep Field over the course of 11.3 days. In October 2022, the James Webb Space Telescope took exposures for 0.83 days, or 20 hours. Several areas seen in images from the James Webb Space Telescope reveal previously invisible red galaxies, which are galaxies with little or no new star formation. (Photos: NASA).
What, then, is the lesson of Hubble and Webb? That seeing is plural. That when you look at the same thing in more than one kind of light, reality blooms into a richer geometry. Hubble gave us the courage to see the universe more clearly than before, resolving crisp visible light structures. Webb picks up where Hubble leaves off. It sees deeper into space and farther back in time. Together, they lift a curtain that has hidden much of our universe from human sight.
Zara Alavi is associate professor of physics in the LMU Frank R. Seaver College of Science and Engineering. Her areas of expertise are biophysics and biochemistry, including polymer physics, experimental biophysics, and material science.
