First Draft - Week 11 Seminar Blog
Seminar Title: Science with the World’s Largest Telescopes
Speaker: Dr. Katharine Johnston
Date: 10 December 2025
Our Universe contains trillions of galaxies, which each consist of billions of star systems beyond our own. Peering through our profoundly vast cosmos doesn’t just require the human eye, but also human ingenuity: the telescope.
Since Galileo, telescopes have evolved from intricate optical instruments into groundbreaking technological inventions that allow us to peer through that same cosmos across the full electromagnetic (EM) spectrum. This is because much of cosmic structure is invisible to the optical light perceived by our naked eyes, and only visible at millimetre and submillimetre wavelengths; these correspond to the radio frequencies in the EM spectrum.
The seminar initially posed the question, “Why big radio telescopes?“. The longer the wavelength, the larger the necessary diameter, D, to observe with the same resolution - as the resolution is inversely proportional to its diameter [1]:
… As a result, there is the Lovell Telescope with a 76m diameter, the Effelsberg Telescope with a 100m diameter, and even the FAST - which is a whopping 500m Aperture Spherical Telescope! Instead of 1 gigantic 100m or 500m telescope, what if there was a high-precision array of 66 smaller radio telescopes with 7m and 12m antennas, working together as a team by operating as a single interferometer capable of imaging distant protoplanetary discs, the birthplace of star systems, at those millimetre and submillimetre wavelengths from 0.32 to 3.6 mm? [2] This is the exact purpose of ALMA (Atacama Large Millimetre/Submillimetre Array), situated in the 5050m-high Chajnantor Plateau in the Atacama Desert in Chile - the driest non-polar desert on Earth. This highest, driest location has a relatively thinner atmosphere decreasing any interference from water molecules. As such, the clear skies with low humidity enable more efficient observations at those millimetre and submillimetre wavelengths.
Each mini telescope contributes specific bits and pieces of the full signal. As the Earth rotates, all those mini telescopes form an aperture. For example, ALMA’s longest baseline (longest possible Euclidean distance between 2 mini-telescopes) is 16km, which is already 16 times bigger than the Effelsberg Telescope - achieved using antennas that are 10 times smaller! What if we go further by combining ALMA and other bigger telescopes across the world so that our entire planet becomes 1 giant telescope? The EHT (Event Horizon Telescope) does exactly this, with its maximum baseline of 10700km! However, VLBI (Very Long Baseline Interferometry) signals aren’t correlated in real time due to those huge distances, so collected data is timestamped to be sent later via disks that get shipped to supercomputers at MIT and Max Planck Institute for Radio Astronomy [1].
In 2019, EHT imaged the supermassive black hole at the centre of M87 (Messier 87) [3]. At the time, I remember this became viral news (and I’m sure you do too!) as “the first black hole image”, yet I was just 15 years old - awestruck and inspired yet eager to know the science behind it at that age [4]. Fast forward to 2025, I’m not just engaging in this seminar explaining the scientific context behind the viral news, but I’m also analysing ALMA datasets of protoplanetary discs as part of my own Third Year Physics Project here at Lincoln - in my current capacity as an undergraduate Physics researcher; a beautiful full circle moment that feels surreal and positively empowering, yet it reminds us all the importance of sharing scientific knowledge to inspire the next generation of scientists.
Although ALMA may exist in a remote corner of the world, its datasets are publicly available on the ALMA Science Archive hosted by the National Radio Astronomy Observatory (NRAO) [5], involving international collaborations spanning worldwide between Europe, North America, and East Asia - enabling me and many other researchers to remotely analyse ALMA datasets for their projects, regardless of the interferometer’s physical location [2]. In this sense, the real teamwork isn’t just in the EHT/ALMA telescopes, but also in the worldwide scientific community of researchers and astronomers teaming up together to contribute new knowledge. ALMA doesn’t just illuminate the interferometer by shining cosmic light into it, it illuminates new astrophysical insights by shining light into novel datasets. Whether or not the 66 antennas may choose to work together as 1 aperture, it is certain that thousands of researchers and students worldwide will always work together as 1 scientific community - bringing humanity 1 step closer to better understanding our Universe.
References:
[1] K. Johnston, “Science with the world’s largest telescopes,” in School of Engineering and Physical Sciences, University of Lincoln, 2025.
[2] ALMA Observatory, “About alma, at first glance,” [Online]. Available: https://www.almaobservatory.org/en/about-alma/. [Accessed 28 December 2025].
[3] The Event Horizon Telescope Collaboration, “First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole,” The Astrophysical Journal Letters, vol. 875, 2019.
[4] P. Ghosh, “First ever black hole image released,” BBC News, 10 April 2019. [Online]. Available: https://www.bbc.co.uk/news/science-environment-47873592. [Accessed 28 December 2025].
[5] National Radio Astronomy Observatory (NRAO), “ALMA Science Archive,” [Online]. Available: https://almascience.nrao.edu/aq/. [Accessed 28 December 2025]
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