6.6 Future of Larger Telescopes

Researchers are actively developing new technologies to explore more distant parts of the universe and achieve clearer observations.
This lesson focuses on describing the next generation of ground- and space-based observatories and the challenges involved in their construction.

James Webb Space Telescope (JWST)
- Recognized as the premier space facility for the coming decade.
- Its mission commenced with a flawless deployment in the first half of 2022.
- Specifically designed to probe the infrared universe.
- Fact: Some of its mirrors underwent cryogenic testing to accurately measure changes in their shape when exposed to extreme temperatures, as depicted in Figure 6.27.
Hubble Space Telescope
- A smaller telescope that remains functional after more than $30$ years in space.
Nancy Grace Roman Space Telescope
- An infrared instrument with a planned launch around 2027.
- Features a smaller mirror than the JWST but will offer a wider field of view.

Vera Rubin Observatory
- Features an $8.4$ -meter telescope with a significantly larger field of view compared to existing telescopes.
- Equipped with the largest digital camera ever constructed.
- Located in Chile, it will photograph the entire southern sky every three nights, effectively creating a $10$ -year "movie of the sky."
- Purpose: To identify transients, which are phenomena that change quickly, such as exploding stars and chunks of rock orbiting near Earth.
- Achieved "first light" in 2025.
Cherenkov Telescope Array (CTA)
- An international initiative planning two arrays of telescopes, one in each hemisphere.
- Purpose: To indirectly measure high-energy gamma rays from the ground.
- Will be capable of measuring gamma-ray energies a thousand times greater than those detectable by the Fermi telescope.

Challenge: Constructing ground-based telescopes with primary mirrors larger than $30$ meters across poses significant technical hurdles.
- It is technically impossible to build and transport a single astronomical mirror with a diameter of $30$ meters or larger.
Innovation: Segmented Mirrors
- The primary mirrors of these giant telescopes are designed to consist of numerous smaller mirrors.
- These smaller mirror segments are precisely aligned to function collectively as a single, very large mirror.

European Extremely Large Telescope (ELT)
- Considered the most ambitious ELT project.
- Its design incorporates a $39.3$ -meter primary mirror.
- The mirror will be composed of $798$ hexagonal segments, each $1.4$ meters in diameter.
- These segments will be held precisely in position to form a continuous surface, adopting the Keck telescope design.
- Construction commenced in 2014 in the Atacama Desert, Northern Chile.
- Operations are anticipated to begin around 2025.
Thirty-Meter Telescope (TMT)
- Developed by international consortia, with significant contributions from U.S. astronomers.
- The preferred site for its construction is Maunakea in Hawaii.
- Its design is similar to that of the European ELT.
- Will utilize $492$ hexagonal elements, each approximately $1.44$ meters ( $56.6$ inches) across its corners.
- The gaps between these segments are extremely narrow, only $2.5$ mm ( $0.1$ inch) wide.
Giant Magellan Telescope (GMT)
- The second ELT project with substantial participation from U.S. astronomers.
- Also features a segmented mirror design.
- Employs seven stiff, monolithic $8.4$ -meter mirrors as its segments.
- Construction has begun at its selected site near the Las Campanas Observatory on the southern edge of the Atacama Desert.

These advanced giant telescopes will combine immense light-gathering power with unparalleled high-resolution imaging capabilities.
They are expected to enable astronomers to address many critical astronomical problems.
Example: They will provide detailed images and spectra of planets orbiting other stars (exoplanets).
This capability potentially offers the first tangible evidence for extraterrestrial life, inferred from the chemical composition of these exoplanets’ atmospheres.