The Next Generation of Telescopes and Our Changing View of the Universe

For most of the history of astronomy, a better telescope meant a bigger mirror. That remains true, but the telescopes now coming into service differ from their predecessors in three further ways: where they look, how often they look, and what wavelengths they see.

Seeing in heat

The James Webb Space Telescope, operated by NASA with the European and Canadian space agencies, observes in infrared light. Light from the earliest galaxies has been stretched by the expansion of the universe into those wavelengths, which is why Webb can see objects that the Hubble Space Telescope, working mainly in visible light, could not. Its 6.5-meter segmented mirror sits behind a sunshield the size of a tennis court, cooling the instruments to the point where their own heat does not swamp the signal.

Webb's early observations produced a puzzle that is still unresolved. Some galaxies in the first several hundred million years after the Big Bang appear larger and more developed than models of galaxy formation predicted. Whether this means the models need revision or the measurements are being misread is a live debate.

Seeing everything, repeatedly

The Vera C. Rubin Observatory in Chile takes a different approach. Rather than staring at one faint object, its 8.4-meter telescope and the largest digital camera ever built photograph the entire visible southern sky every few nights for ten years. The result is a movie rather than a snapshot: anything that moves, flares or fades will be caught.

This is a new kind of astronomy. Rubin is expected to find millions of asteroids, catalog billions of galaxies and detect transient events, from supernovae to the flashes that accompany colliding neutron stars, in numbers that will require automated systems to sort.

Seeing bigger

Three ground-based telescopes with primary mirrors far larger than any now operating are in construction: the Giant Magellan Telescope and the Extremely Large Telescope, both in Chile, and the Thirty Meter Telescope, whose site remains contested. The Extremely Large Telescope's 39-meter mirror will collect more light than all existing large telescopes combined, enough to image planets around nearby stars directly.

What changes

The combined effect is that questions which were philosophical a generation ago have become observational. When did the first stars form? What are the atmospheres of rocky planets around other stars made of? How often do stars collide? The telescopes are built. The interpretation is beginning.