Good news and bad news for astronomers’ biggest dream

According to the National Science Board, which advises the National Science Foundation, the United States should allocate $1.6 billion to build an “extremely large telescope” that would take American astronomy into a new era.

In a Feb. 27 statement, the board gave the foundation until May to decide how to choose between two competing proposals for the telescope. The announcement came as a relief to American astronomers, who had worried about losing ground to their European counterparts in the quest to explore the sky with bigger and better telescopes.

But which of the two telescopes will be built – and the fate of the dreams and the billions of dollars of time and technology already invested – remains an open question. Many astronomers had hoped that the foundation, the traditional funder of national observatories, would find a way to invest in both projects.

The two projects are the Giant Magellan Telescope at Las Campanas in Chile and the Thirty Meter Telescope, possibly destined for Mauna Kea on the island of Hawaii, also known as the Big Island. Both would be larger and more powerful than any telescope currently on Earth or in space. Each is expected to cost around $3 billion or more, and less than half of the expected costs have so far been covered by the international partnerships that support them.

In an announcement circulating among astronomers, the board said funding even one telescope at a cost of $1.6 billion would consume most of the NSF’s typical construction budget.

“Additionally, the priorities of the astronomy and astrophysics community must be considered in the broader context of the high-priority, high-impact projects for the many disciplines that NSF supports,” the board said in its statement last week.

So far, astronomers who have a stake in the outcome have been careful to ensure that Congress, as well as the White House and the Science Foundation, will all ultimately have their say.

“This is a marathon, not a sprint,” said Robert Kirshner, director of the Thirty Meter Telescope International Observatory and former member of the Giant Magellan team. He added that he was hopeful that both telescopes could move forward.

Michael Turner, cosmologist emeritus at the University of Chicago and former assistant director for physics and astronomy at the NSF, called the recent development “excellent news for American astronomy and saw “a realistic path forward” for an extremely large telescope.

“Before you know it, the telescope will dazzle us with images of exoplanets and the early universe,” he said. “Should it have happened faster? Of course, but that’s history. Full speed ahead, eyes focused on the future!”

Wendy Freedman, a cosmologist at the University of Chicago who led the Giant Magellan project in its first decade, said in an email: “I am very pleased that the NSB has decided to fund an ELT. I think the worst outcome would have been not to fund an ELT at all; that would have been a tragedy! Realistically (and unfortunately) there is no budget for two. But an ELT is critical to the future of American astronomy.”

She added: “So I’m very relieved”

Robert Shelton, chairman of the Giant Magellan collaboration, said: “We respect the National Science Board’s recommendation to the National Science Foundation and remain committed to working closely with the NSF and the astronomical community to ensure the successful realization” of to guarantee an extremely large telescope. “Which will enable groundbreaking research and discoveries in the coming years.”

But Richard Ellis, an astrophysicist at University College London and one of the early leaders of the Thirty Meter Telescope project, told Science“It’s a tragedy considering the investments made in both telescopes.”

A telescope’s ability to see deeper and fainter objects in space is largely determined by the size of its primary mirror. The largest telescopes on Earth have a diameter of eight to ten meters. The Giant Magellan would group seven eight-meter mirrors together to make the equivalent of a 25-meter telescope; the seventh and final mirror was cast last year and workers are ready to pour concrete at the Las Campanas site.

The Thirty Meter would consist of 492 hexagonal mirror segments, scaling up the design of the twin 10-meter Keck telescopes used on Mauna Kea by the California Institute of Technology and the University of California. (The 100th segment has just been released in California, but protests from native Hawaiians and other critics have prevented any work at the TMT site on Mauna Kea; the project group has considered an alternate site in the Canary Islands.) Neither telescope will probably do. be ready until 2030.

Even as the American-led effort continues, the European Southern Observatory is building an extremely large telescope – called the Extremely Large Telescope – at the Paranal Observatory in Chile. The main mirror, consisting of 798 hexagonal segments, will be the largest and most powerful of them all: 39 meters in diameter. It will also be the first of the participants to be completed; European astronomers plan to start in 2028. If the effort is successful, it would be the first time in a century that the largest functioning telescope on Earth is not on U.S. soil.

Both the Giant Magellan and Thirty Meter telescopes are multinational partnerships headquartered a few miles apart in Pasadena, California.

NSF support has been a point of contention between the two groups since its inception two decades ago.

In 2019, the two groups agreed to join forces to establish a US ELT program, under the purview of the National Optical-Infrared Research Laboratory in Tucson, Arizona, that would allow US astronomers to use both telescopes . Astro 2020, a blue-ribbon panel of the National Academies of Science, endorsed the proposal, calling it the top priority in ground-based astronomy for the decade. The panel recommended that the science foundation raise $1.6 billion to buy part ownership of one or both telescopes.

But the cost of these telescopes has continued to rise and the $1.6 billion mark no longer goes as far as it used to. And the wheels of the scientific community and the federal government turn slowly.

“That process takes three to five years,” said Linnea Avallone, director of research facilities at the NSF. “We have been working for just over a year now. I don’t think we’re hesitating; I don’t think we’re not aggressive. She added that the foundation was “very good stewards of taxpayers’ money.”

Did she see a risk for the United States if it did not finance its own extremely large telescope?

“That’s a good question, better answered by astronomers,” said Dr. Avallone.