HERA telescope to unravel Epoch of Reionisation mysteries

The Hydrogen Epoch of Reionisation Array (HERA), a US$25 million radio telescope in South Africa dedicated to observing large-scale structures during and prior to the period of reionisation, has opened research opportunities weeks ahead of its completion.

Construction of the facility – an array of 350 antennas, each with a 14m-diameter dish – started in 2015, and 332 dishes have been installed.

The COVID-19 pandemic slowed construction but work continued, with most of the array now completed, courtesy of a reduced team completing the last antennas and signal paths, said Dr David DeBoer, HERA project manager, and a research astronomer at the University of California, Berkeley.

“We do expect to complete it early next year,” DeBoer, told University World News.

HERA, a collaborative project of the US National Science Foundation, the Gordon and Betty Moore Foundation, and several international member institutions from the US, South Africa, the United Kingdom, Canada, and Italy, will cost approximately US$25 million, including construction and operation.

Construction of the array is phased in such a way that, as antennas are completed, they are hooked into the telescope data correlation system, said Kathryn Rosie, HERA project engineer, in an article published in Engineering News on 16 September 2021. “This enables observations and early science to be carried out while construction continues,” Rosie said.

Phase I observations were carried out throughout the southern summer in 2017-18 using about 50 dishes after the initial construction, giving a glimpse of what the universe looked like about 13 billion years ago.

Probing the Epoch of Reionisation

Based in South Africa, HERA includes the dishes, receivers and the signal chain that relays the received signal into the correlator, a big ‘computer’, all set in the small Karoo town of Carnarvon in the Northern Cape province.

When the first stars and galaxies formed, the radiation they emitted ionised all the hydrogen atoms that were spread across the universe. The hydrogen between galaxies is the most abundant element in the universe, said Professor Mario Santos, the South African Radio Astronomy Observatory (SARAO) representative on the HERA board and South African Research Chair in Cosmology with Multi-Wavelength Data at the University of the Western Cape, South Africa.

“We call this process the Epoch of Reionisation which happened about 13 billion years ago when the universe was still very young. Unfortunately, we only have indirect information about this process,” he told University World News.

DeBoer said: “The data taken to date with the first antennas is allowing us to place some limits, but not actually detect our elusive signal. When done, and when we’ve sufficiently understood the complex details, we expect to detect the signal over many time spans and many different spatial scales.”

But Santos added: “HERA will allow probing this epoch directly, thus telling us something about the first galaxies and black holes in the universe.

“HERA is considered the current instrument with the best sensitivity in the world to measure the tiny radiation emitted from the hydrogen atoms that we use to observe this epoch. We will have to wait for the full SKA [Square Kilometre Array precursor telescope] to improve on that sensitivity,” Santos said.

When completed, HERA will also be able to probe the universe even further back in time before the stars started to ionise. “We call that era the Cosmic Dawn instead of the Epoch of Reionisation,” he added.

“It will tell us something fundamental about the initial processes of star formation and about cosmology in the early universe, just a mere hundreds of millions of years after the Big Bang (the universe is now almost 14 billion years old),” he said, adding that such detection will require sophisticated signal processing and analysis techniques, and high computing power that are developed hand in hand with the construction of the telescope.

Only after the data has been acquired and goes through various stages of processing in a computer room next to the telescope, the data is sent to the US using fibre optics for further analysis.

“Although we also keep the data in South Africa for analysis and Inter-University Institute for Data Intensive Astronomy (IDIA) has been helping with that,” Santos said.

IDIA is a partnership between the Universities of Cape Town, of the Western Cape and of Pretoria as well as the South African Radio Astronomy Observatory. South Africa has been putting in a lot of effort with the constructs, and several research groups in the country are working on the data and its theoretical interpretation.

The first results from HERA Phase I present the most sensitive upper limits to date on the strength of the signal that can be detected from the universe at around 66 million years after the Big Bang.

High-tech instruments develop knowledge

First, it helped to ‘cement’ South Africa as a major hub for radio astronomy, Santos said.

“With MeerKAT and HERA, we have two of the most powerful radio telescopes in the world. Such high-tech instruments also help to develop know-how and local companies in South Africa,” he said. Moreover, it gives an opportunity to South African universities to join such big international projects and attract students to the important subject of science and technology.

“Besides the pure joy of understanding the universe through a telescope in South Africa, our students learn several techniques in the field of signal processing and machine learning, skills in high demand in today’s industries,” Santos added.

Global collaboration

Pushing the limits of human knowledge is one of the most rewarding endeavours of human society in the long term.

“Who knows what new theories might be developed with the findings of these telescopes and what such theories will imply, not only for the common knowledge of the world we live in but also what practical implications they might have,” Santos said.

The high-end technology used in the telescope is being developed at universities across the world, he said, adding that pushing the limits of current technologies helps develop hardware that can later be used in various industries, also in consumer applications.

“But I think the biggest impact is really to develop this large international collaboration of scientists working together to learn about the mysteries of the universe; coming together to test new theories, new hardware, develop new data processing methods, pushing the limits of high-performance computing and attracting students to this field where they will learn all these state-of-the-art skills,” he said. Such know-how will ‘trickle down’ to the economy.

“Of course, we shouldn’t forget that detection of this primordial signal by HERA would be Nobel Prize material. But even if we don’t get there exactly, what we learn from observing with HERA and the techniques developed in its construction are a crucial step towards developing even more powerful telescopes that can shed light on what is going on in the universe.”