Size matters when it comes to telescopes. The bigger they are, the farther they can see. Prioritizing constructing large ones is therefore high on the priority list for many observational organizations. But doing so comes at a cost, and not just in terms of money. Finding a suitable site can be a challenge, and that has been particularly true for the effort to build a 30-meter telescope in the Northern hemisphere. A new paper, available in pre-print on arXiv by Francesco Coti Zelati of the Spanish Institute of Space Sciences in Barcelona and his co-authors, makes the argument for building it at the Roque de los Muchachos Observatory in La Palma in the Canary Islands.
Scientists have been planning a northern-hemisphere Thirty Meter Telescope (TMT) for decades. It was to serve as the counterpoint to observatories like the Extremely Large Telescope (39m) and the Giant Magellan Telescope (25m), both of which are located in Chile in the southern hemisphere.
That leaves the vast majority of the northern sky, including some of the most interesting galaxies like Andromeda and the Triangulum, unobserved by anything in the 30-40m range of telescopes. Such a gap is becoming more and more critical, as “multi-messenger” astronomy becomes more prevalent. In this new paradigm, one observatory could detect a pair of colliding black holes, and immediately trigger other observatories to focus on the same area in an attempt to catch the fleeting signals that result from these extraordinary events.
Fraser talks in detail about the rise of "supertelescopes"However, if a detector like the Einstein Telescope, which will be located in Europe, or the Cosmic Explorer telescope, which will be located in the US, detects one of these collisions, there will be no telescope in the entire hemisphere large enough to detect events that are far away. There’s also no guarantee that any of the large telescopes in the southern hemisphere would be able to detect it at all.
This hemispheric blind spot is the gap that the TMT was meant to fill. Originally proposed in the early 2000s, with a formal project established in 2003, the project team selected Mauna Kea, Hawai’i as its site in 2009. However, in 2014, immediately after a groundbreaking ceremony, native Hawaiian cultural practitioners protested the building of the telescope, immediately bringing construction to a halt and delaying the project by over a decade.
In 2019, astronomers, frustrated with the lack of progress at the Mauna Kea site, pivoted to a site in La Palma as an alternative. While lacking some of the advantages of Mauna Kea, such as better seeing, it had the advantage of not being tied up in litigation for decades. La Palma is also already home to some pretty large telescopes, with the appropriate infrastructure and dark sky regulations already in place. It’s also only about 4 hours ahead of Chile, so any events that do happen in a region of space telescopes in both areas can cover would result in a smooth monitoring hand-off.
Video discussing the controversy around the construction of the TMT. Credit - The Impossible Build YouTube ChannelThe new paper is the scientific justification for moving the site to La Palma, as the funding agencies for the TMT project want to ensure the site is still capable of producing the science originally expected of the project. It was submitted as a white paper to the European Southern Observatory’s (ESO’s) “Expanding Horizons: Transforming Astronomy in the 2040s” call for papers. Features of the telescope described in the white paper include ultra-fast photometers, allowing it to capture extremely fast events, and a wide bandwidth of wavelengths that it can detect.
At this point, the project community has moved on from building at the Mauna Kea site. They still hope to have this ambitious project online to start observations in time to match the gravitational wave observatories that are planned for the late 2030s. There certainly won’t be as much local resistance to building in La Palma, but the construction of such a massive project is in itself a huge undertaking. The faster the project can get started the better, but as of now there’s no final construction agreement for when that might take place. On the good news front, though, funding, other than that of the US government, which removed its support in June, is still forthcoming, and the government of Spain has stepped in to fill the gap from the US funds. As the project continues to move forward, we should eventually be able to see the northern sky in the same detail as we will the southern one.
Learn More:
F. C. Zelati et al - Why the Northern Hemisphere Needs a 30-40 m Telescope and the Science at Stake: Time-domain astronomy
UT - Rise of the Super Telescopes: The Thirty Meter Telescope