A discoverer of worlds in Arizona's backyard

The two mirrors of the Large Binocular Telescope peer through the openings in the telescope's enclosure.

The UArizona-managed Large Binocular Telescope on Mount Graham is the only one of its kind, with two 27-foot mirrors mounted side by side.


Tucked away in the southeastern corner of Arizona, perched at nearly 11,000 feet on Mount Graham, the tallest of the state's "sky island" mountains, sits a marvel of engineering like none other in the world. The aptly named Large Binocular Telescope is the world's largest optical telescope, and the only one of its kind. It resembles a pair of binoculars, as it boasts two round mirrors, each spanning 8.4 meters, or just over 27 feet. Managed by the University of Arizona, the LBT is a discovery machine that has allowed astronomers to glimpse cosmic phenomena close to home – such as lava lakes on one of Jupiter's moons – and all the way to the farthest reaches of the universe.

The LBT surpasses even NASA's new flagship space telescope, the James Webb Space Telescope, in its resolving power – an astronomers' term to describe sharpness of vision – and serves as a test bed for the most advanced and ambitious technology that will fuel the next generation of Extremely Large Telescopes.

Joseph Shields, who recently took the helm as director of the Large Binocular Telescope Observatory, talked to University of Arizona News about the telescope's importance in past and future discoveries, and its critical role in paving the way for the future of astronomy. Before joining UArizona, Shields chaired the Department of Physics and Astronomy at Ohio University, where he also served as vice president for research and creative activity and dean of the Graduate College. During a NASA Hubble Fellowship at UArizona, Shields embarked on a career studying the physics of supermassive black holes, the makeup of the interstellar medium and the lives and deaths of stars.

Q: What makes the LBT special?

A: The LBT is arguably the most powerful optical telescope in the world at the current time. A telescope's ability to measure objects in the universe is determined by its size. The more light-collecting area a telescope has, the better it is at detecting faint cosmic sources. In the case of the LBT, the combined collecting area of its two mirrors is equivalent to a single mirror with a diameter of 11.8 meters, larger than any other single optical telescope in existence today.

A telescope's size is also important for determining its ability to distinguish fine detail and resolve objects that are close together on the sky, as in the case of a planet orbiting a distant star. For the LBT, the relevant dimension that determines this resolving power is the distance between the outer edges of its two mirrors, which is 23 meters, or 75 feet. While a few other observatories can combine the light from separate telescopes to achieve greater resolving power, the LBT is unique in achieving this with mirrors attached to the same mount.

An interesting comparison can be made with the James Webb Space Telescope. JWST has understandably wowed astronomers and the public with its images, and, like Hubble, benefits from being in space, unaffected by Earth’s atmosphere. But while producing wide-field images revealing remarkable detail of faint sources, JWST still has the resolving power of a 6-meter telescope, far less than the LBT's 23-meter baseline. Because of this, the LBT retains a unique capability for resolving fine details in bright sources, such as nearby young stars surrounded by disks of gas and dust where planets are forming.

LBTO director Joseph Shields

Joseph Shields is the director of the Large Binocular Telescope Observatory.

Q: Can you tell us about the location of the LBT and why it was selected?

A: The Large Binocular Telescope is located on Mount Graham, approximately 70 miles northeast of Tucson near the town of Safford. The site was chosen because of its dark sky and climate and atmospheric conditions favorable for producing sharp images. The observing conditions benefit from the site's altitude of 10,500 feet, which is among the highest for observatories in North America. The LBT is part of the Mount Graham International Observatory, which also hosts the Arizona Radio Observatory Submillimeter Telescope and Vatican Advanced Technology Telescope.

Q: How long has LBT been there and who uses it?

A: Construction of the telescope began in 1997, and the first observations were acquired in 2005 with one of the telescope's two 8.4-meter-diameter mirrors. Observations with both mirrors began in 2007. The LBT Observatory is funded by an international consortium of research institutions and universities in Germany, Italy and the United States, including the University of Arizona. Observations are conducted by staff and students at the partner institutions. The observatory is staffed by U of A employees, with personnel based in Tucson and Safford. We typically have at least three staff members on site, including a telescope operator who points the telescope at whatever the source of interest may be. The scientists can conduct observations either on site, from their institutions and even from home.

Lava lake on Jupiter moon Io

In this image of Jupiter's moon Io taken by the LBT, a lake of molten lava shines brightly on the left, while fainter spots indicate other active volcanic areas on the small world, which is just slightly bigger than Earth's moon.


Q: What are some of the telescope's most notable discoveries?

A: A remarkable demonstration of the LBT's unique capabilities for high-resolution studies was a study of Io, the innermost of the four moons of Jupiter discovered by famous Italian astronomer Galileo Galilei. Io is known to be volcanically active, and observations made with the LBT revealed temperature variations across a lava lake on Io, tracing the heating and flow of molten rock on the moon's surface. It's the only example where this level of volcanic detail has been directly observed on a world other than our own.

A second important finding relates to the local environments of stars like the sun, measured by combining the light from the LBT's mirrors in a manner that cancels out the light from the star, revealing surrounding disks of gas similar to the interplanetary dust in our solar system. The LBT played an important role in a large NASA-funded project, where it was tasked to find out how much dust encircles other sun-like stars and whether it would interfere with detecting planets. Fortunately, it turns out that most stars do not have disks of very bright dust that would interfere with studying exoplanets.

Another very interesting study has used the telescope to investigate the deaths of stars and the formation of black holes. A star considerably more massive than our sun will eventually exhaust the fuel in its core, which can then collapse to form a black hole. The resulting release of gravitational energy typically produces a phenomenal explosion of the outer parts of the star that we witness as a supernova. An intriguing idea suggests that the most massive stars may undergo core collapse to form a black hole without the visible fireworks. It would be a stealthy way to form black holes. A survey with the LBT has turned up candidates for such "failed supernovae" that provide clues to how often they may occur.

Q: What contributions can we expect from LBT in the future?

A: The LBT has been, and continues to be, a leader in innovation enabling astronomical discovery. Lessons learned and technologies developed at the LBT are now benefitting a new generation of Extremely Large Telescopes, or ELTs, under construction. These new facilities, with equivalent aperture diameters of 25 to 39 meters – 82 to 128 feet – will begin operation in the late 2020s. The Giant Magellan Telescope, which, like the LBT, will use 8.4-meter mirrors developed at the University of Arizona's Richard F. Caris Mirror Lab, is part of the new generation. There is a direct connection between the technical solutions embodied in this new crop of observatories and innovation pioneered at the LBT, so we say that the Large Binocular Telescope is in fact the first of the ELTs. The cost of instruments for the larger ELTs is jaw-dropping, and the LBT will remain competitive as a facility where new instrumentation and technical innovations can be piloted to drive a broad range of scientific discovery.

Q: What has you most excited about your new role as LBT director?

A: Definitely the unique capabilities of this telescope and its ability to do science that we couldn't do at any other facility. Through most of this decade, the LBT will remain singular in its combination of light collecting and resolving power. Our partner institutions are developing a new generation of instruments optimized for high angular resolution studies that will contribute across many areas of science, and in the study of extrasolar planets in particular. In my own research, I study the impact of supermassive black holes on the surroundings in their host galaxies. The LBT's exceptional angular resolution allows us to discern details at very small scales, within the clouds of gas that surround these supermassive black holes. We want to understand these extreme environments, where we know material is being swallowed and huge amounts of energy are radiated as a result, but much work is still needed to understand these processes.

Q: How can people learn more about this facility?

A: Tours of the Mount Graham International Observatory are offered in cooperation with Eastern Arizona College's Discovery Park Campus but have been on hiatus due to the pandemic. We hope to be able to restart tours within the next year.