Transforming Astrophysics with a Mighty New Telescope

The Giant Magellan Telescope (GMT), an exciting next-generation observatory, recently got a big boost. In September, the National Science Foundation announced a grant of $17.5 million, the first major tranche of funds for GMT's continued development.

The telescope is intended to be "transformative," according to its backers, when it begins gazing at the skies circa 2029. The facility will have a spatial resolution that is ten times sharper than the Hubble Space Telescope. Resolution at that level will turn blurry, celestial sketches into detailed, crisp pictures brimming with astrophysical information.

"This resolution will yield transformative discoveries across all fields of astronomy and astrophysics, from studies of the faintest galaxies across the cosmos at the time of first light, through to the atmospheres of exoplanets around the nearest stars, and all scales and objects in between," says Michael Gladders, a professor of astronomy and astrophysics at the University of Chicago, a senior member of the Kavli Institute for Cosmological Physics (KICP), and part of the GMT science committee.

To pull off this scientific feat, though, GMT will require some significant development of its optical- and infrared-observing technologies. The telescope is slated to be built at the Las Campanas Observatory in Chile which, given the local elevation (2500 meters or 8200 feet) and ultra-low humidity, features some of the clearest skies on Earth. To take advantage of those skies and exceed the capabilities of today's instrument, designers will have to engineer GMT to exquisitely coordinate the movements of its seven, massive, 8.4 meter- (27-foot-) diameter mirrors. The mirror movement is an integral part of what is known as an adaptive optics system. Such systems compensate for the inevitable twinkling of stars—an effect caused by Earth's atmosphere—by measuring the distortion and then making tiny bends to the flexible mirrors on the fly. In GMT's case, those changes will need to happen at the astonishing, yet technically feasible rate of 1,000 times per second.

Adaptive optics systems have been added onto many of the world's largest ground-based telescopes and worked spectacularly. Yet in GMT's case, the enhancement will not be an enhancement, but built-in from the start, leveraging the considerable know-how that has accumulated regarding the technology since its first deployments about three decades ago. "The GMT will be one of the first telescope designed from the beginning to use adaptive optics," notes Gladders.

GMT will be a big deal, literally and figuratively, for the astronomical community. For Gladders, his work on galaxy formation will be newly and deeply informed by the telescope's observations, especially when paired with the natural magnifying power of so-called gravitational lenses. These phenomena are typically foreground galaxy clusters whose immense gravity warps and increase the brightness of distant, ordinarily faint, background objects. GMT plus gravitational lensing could this bring previously inaccessibly far stars into clear view.

"I am most excited to couple the sharpest images from the GMT with the power of strong gravitational lensing to study individual star clusters, and even individual stars, in distant galaxies," says Gladders. "Stars and star-clusters are the brushstrokes that paint in the picture of galaxy formation and evolution across cosmic time, and GMT will allow us to see galaxies across the universe at this key level of detail."

It's not just the ultra-distant that will be brought close, so to speak, by GMT. Many researchers are keen on how GMT will enable investigations of comparatively nearby objects, such as exoplanets. Although more than four thousand exoplanets have been found in the last quarter-century, to date, only a smidgen have been even minimally characterized. Telescopes operating at their limits of detection these days can tell us a bit about exoplanets' atmospheres and what sorts of gases they contain. Next-generation instruments will be ultimately needed to say much more, though, beyond these basics.

The most tantalizing of the sought-after atmospheric gas signatures are those that cannot have been plausibly produced by geophysical processes, and thus are deemed far more likely to be a result of—as wild as it sounds—alien biological activity. Finding such biosignatures or biomarkers would certainly qualify as "transformative."

"I am excited to see what the GMT can teach us about exoplanets, their atmospheres and potentially biomarkers," Gladders says, "as we transition from discovery to detailed study of the many exoplanets systems being discovered now."