Building a Radio Telescope on the Far Side of the Moon

Assistant Professor of Physics Jonathan Pober is working with NASA to build a radio telescope array to unlock the secrets of the Cosmic Dark Ages.

The proposed radio telescope array will be located on the far side of the moon, where it will be shielded from radio interference from Earth. (Photo credit: Conan/Wikimedia)

By Pete Bilderback

PROVIDENCE, R.I. [Brown University] —The secrets of the Cosmic Dark Ages, a period following the Big Bang, may be found on the far side of the moon, and Assistant Professor of Physics Jonathan Pober will be helping NASA to unlock them. Pober has been awarded a prestigious Nancy Grace Roman Technology Fellowship (RTF) in Astrophysics for early researchers, the aim of which is to help young researchers develop innovative technologies that have the potential to enable major scientific breakthroughs in the future. 

The award will support Pober in advancing the ambitious agenda of building a giant radio telescope array on the far side of the moon. Pober explained, “Generally, we can do radio astronomy from the ground, the Earth’s atmosphere is pretty forgiving to radio waves. Neutral hydrogen has a 21-centimeter wavelength, and wavelengths of that size can go straight through the Earth’s atmosphere with no issues.” 

But there’s a catch that has to do with the fact that the universe has been expanding ever since the Big Bang. “We’re looking for signals from back when the universe was one-tenth its current size,” said Pober. And critically, wavelengths expand along with the universe, a phenomenon known as redshifting. “And so, as the universe expanded to its current size, a 21-centimeter wave stretched into a two-meter wave,” he noted. “And at two meters, the Earth’s atmosphere starts to become a bit of a nuisance.”

“But we want to look way back in cosmic history to a time when the universe was one hundredth its current size – the Cosmic Dark Ages when there were no galaxies, no stars, no planets.” Pober explained, “and the wavelengths stretched along with the universe as they’ve traveled to us. So now we’re talking about a 20-meter wavelength, and that absolutely can’t make it through the Earth’s atmosphere. And so the idea that we’ve been steadily trying to build the case for is building a very, very large radio telescope on the far side of the moon.”

An ultra-long-wavelength radio telescope on the far side of the moon would have tremendous advantages over Earth-based telescopes beyond being able to observe longer wavelengths. “The Earth will be obscured,” Pober explained, and “the moon will block radio and television signals.” It will also block noise from Earth-orbiting satellites, the ionosphere, and the sun’s noise during the solar night. “If you can get an experiment there, it’s a fantastic place to do ultra-low frequency or ultra-long wavelength radio astronomy,” said Pober.

While there is not yet a formal NASA mission, NASA is exploring the concept of building a large antenna array on the far side of the moon. Such a mission is incredibly ambitious because, in addition to being located on the far side of the moon, in order to be sensitive to long radio wavelengths, the telescope will need to be gigantic. The plan is to build an array of thousands of radio telescopes on the far side of the moon, where it will be shielded from all of the radio noise produced on Earth. One such NASA-funded mission concept being developed by Pober and collaborators is FarView, with a primary objective “focused upon investigation in exquisite detail the unexplored Cosmic Dark Ages using the highly redshifted hydrogen 21-cm line and identifying the conditions and processes under which the first stars, galaxies, and accreting black holes formed.” 

The Cosmic Dark Ages began approximately 400,000 years following the Big Bang when the universe cooled enough to form neutral hydrogen and helium atoms. During this period, which ended when protogalaxies produced enough light to ionize the universe about a billion years after the Big Bang, the universe was enveloped by a fog of neutral hydrogen that trapped all light. 

Any light from this period cannot reach the Earth, so the only way for humans to peer back into this period is using radio telescopes. Cosmologists currently know very little about this period, but it could hold the answers to some of science’s biggest mysteries. NASA claims FarView “could give extraordinarily precise measurements of the early structure of the universe because the sea of neutral hydrogen from which protogalaxies formed can be directly imaged using radio waves.”

No equivalent observatory exists today. According to NASA, “This radio telescope will be the first of its kind at this scale and sensitivity and will open a new window (low-frequency radio) into the early universe, analogous to the detection of gravitational waves by LIGO [Laser Interferometer Gravitational-Wave Observatory] and the details of the CMB [cosmic microwave background] by Planck.”

 Murchison Widefield Array
Part of the Murchison Widefield Array in Western Australia. The proposed FarView Array would be much larger and located on the far side of the moon. (Photo credit: Natasha Hurley-Walker/Wikimedia)

Pober does not have any immediate plans to visit the far side of the moon. He estimates that if everything goes perfectly, the earliest the project could be completed would be in thirty years’ time. “It’s an ambitious project,” he said, “this grant is just for simulation and design of a future experiment that could be on the far side of the moon.” “The first couple of radio antennas will be landing on the moon in the next couple of years as pathfinders,” Pober noted. “Those are just to show that radio astronomy can be done from the moon, but to actually do the science we want, we’ll need to have hundreds of thousands of radio antennas on the far side of the moon.”

There will be enormous logistical challenges involved in building such a large array in a difficult-to-reach location. “You have to change the antenna design to make them deployable,” Pober said. “Because people aren’t going to go to the far side of the moon to set them up. The deployment will need to be automated, so a lot of this grant will involve figuring out how that will work.”

While the timescale for the project is long, the RTF grant will allow Pober to make important contributions to advancing the design of the array. “A successful mission design will require a team with expertise in radio antenna design, space systems engineering, astrophysical cosmology, and data science,” Pober said. “The RTF will provide funding to assemble key personnel with expertise spanning these areas, delivering key technological advances to make this concept a reality.”

Scientists inch closer than ever to signal from cosmic dawn

The Murchison Widefield Array radio telescope, a portion of which is pictured here, is searching for a signal emitted during the formation of the first stars in the universe. Goldsmith/MWA Collaboration/Curtin University

Researchers using the Murchison Widefield Array radio telescope have taken a new and significant step toward detecting a signal from the period in cosmic history when the first stars lit up the universe.

PROVIDENCE, R.I. [Brown University] — Around 12 billion years ago, the universe emerged from a great cosmic dark age as the first stars and galaxies lit up. With a new analysis of data collected by the Murchison Widefield Array (MWA) radio telescope, scientists are now closer than ever to detecting the ultra-faint signature of this turning point in cosmic history.

In a paper on the preprint site ArXiv and soon to be published in The Astrophysical Journal, researchers present the first analysis of data from a new configuration of the MWA designed specifically to look for the signal of neutral hydrogen, the gas that dominated the universe during the cosmic dark age. The analysis sets a new limit — the lowest limit yet — for the strength of the neutral hydrogen signal.

“We can say with confidence that if the neutral hydrogen signal was any stronger than the limit we set in the paper, then the telescope would have detected it,” said Jonathan Pober, an assistant professor of physics at Brown University and corresponding author on the new paper. “These findings can help us to further constrain the timing of when the cosmic dark ages ended and the first stars emerged.”

The research was led by Wenyang Li, who performed the work as a Ph.D. student at Brown. Li and Pober collaborated with an international group of researchers working with the MWA.

Despite its importance in cosmic history, little is known about the period when the first stars formed, which is known as the Epoch of Reionization (EoR). The first atoms that formed after the Big Bang were positively charged hydrogen ions — atoms whose electrons were stripped away by the energy of the infant universe. As the universe cooled and expanded, hydrogen atoms reunited with their electrons to form neutral hydrogen. And that’s just about all there was in the universe until about 12 billion years ago, when atoms started clumping together to form stars and galaxies. Light from those objects re-ionized the neutral hydrogen, causing it to largely disappear from interstellar space.

The goal of projects like the one happening at MWA is to locate the signal of neutral hydrogen from the dark ages and measure how it changed as the EoR unfolded.  Doing so could reveal new and critical information about the first stars — the building blocks of the universe we see today. But catching any glimpse of that 12-billion-year-old signal is a difficult task that requires instruments with exquisite sensitivity.

When it began operating in 2013, the MWA was an array of 2,048 radio antennas arranged across the remote countryside of Western Australia. The antennas are bundled together into 128 “tiles,” whose signals are combined by a supercomputer called the Correlator. In 2016, the number of tiles was doubled to 256, and their configuration across the landscape was altered to improve their sensitivity to the neutral hydrogen signal. This new paper is the first analysis of data from the expanded array.

Neutral hydrogen emits radiation at a wavelength of 21 centimeters. As the universe has expanded over the past 12 billion years, the signal from the EoR is now stretched to about 2 meters, and that’s what MWA astronomers are looking for. The problem is there are myriad other sources that emit at the same wavelength — human-made sources like digital television as well as natural sources from within the Milky Way and from millions of other galaxies.

“All of these other sources are many orders of magnitude stronger than the signal we’re trying to detect,” Pober said. “Even an FM radio signal that’s reflected off an airplane that happens to be passing above the telescope is enough to contaminate the data.”

To home in on the signal, the researchers use a myriad of processing techniques to weed out those contaminants. At the same time, they account for the unique frequency responses of the telescope itself.

“If we look at different radio frequencies or wavelengths, the telescope behaves a little differently,” Pober said. “Correcting for the telescope response is absolutely critical for then doing the separation of astrophysical contaminants and the signal of interest.”

Those data analysis techniques combined with the expanded capacity of the telescope itself resulted in a new upper bound of the EoR signal strength. It’s the second consecutive best-limit-to-date analysis to be released by MWA and raises hope that the experiment will one day detect the elusive EoR signal.

“This analysis demonstrates that the phase two upgrade had a lot of its desired effects and that the new analysis techniques will improve future analyses,” Pober said. “The fact that MWA has now published back-to-back the two best limits on the signal gives momentum to the idea that this experiment and its approach has a lot of promise.”

The research was supported in part by the U.S. National Science Foundation (grant #1613040). The MWA receives support from the Australian government and acknowledges Wajarri Yamatji people as the traditional owners of the observatory site.

Original article:

And then there was light: looking for the first stars in the Universe

Researchers hunt for a 12-billion-year-old signal that marks the end of the post Big Bang “dark age”.

Astronomers are closing in on a signal that has been travelling across the Universe for 12 billion years, bringing them nearer to understanding the life and death of the very earliest stars.

In a paper on the preprint site arXiv and soon to be published in the Astrophysical Journal, a team led by Dr Nichole Barry from Australia’s University of Melbourne and the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) reports a 10-fold improvement on data gathered by the Murchison Widefield Array (MWA) – a collection of 4096 dipole antennas set in the remote hinterland of Western Australia.

The results published in this paper were the culmination of over five years of work.  The data used in the study were collected in 2013 and were first analyzed in a paper published in 2016.  The years since saw a concerted effort to develop new techniques for improving the precision of the analysis and better identifying (and excluding) data contaminated by human-generated radio signals.

Brown University researcher Jonathan Pober was a part of this process from the beginning and played a substantial role in vetting the new techniques. Of particular importance was to ensure they would return an accurate and unbiased measurement of any signal present in the data, since techniques to remove contamination from the data can also remove the signal of interest unless the utmost care is taken. Prof. Pober designed a suite of high-precision simulations to validate the entire analysis, while Brown Physics PhD student Wenyang Li conducted a parallel analysis, applying the same techniques to an independent data set to ensure their broader applicability.

This paper is therefore important for two key reasons: it presents the most constraining limit on the EoR signal strength in the literature, but it also represents the highest level of internal validation and scrutiny applied to an analysis in this field and will serve as an exemplar for future such work.

In this simulation of the Epoch of Reionisation, neutral hydrogen, in red, is gradually ionised by the first stars, shown in white. The video was made by the University of Melbourne’s Dark-ages Reionisation And Galaxy Observables from Numerical Simulations (DRAGONS) programme. Credit: Paul Geil and Simon Mutch 

Original Press Release Here

More about the MWA

The Murchison Widefield Array (MWA) is a low-frequency radio telescope, located at the CSIRO Murchison Radio-astronomy Observatory (MRO) in Western Australia. The telescope is operated by Curtin University on behalf of an international collaboration of 21 research organisations spanning  Australia, New Zealand, Japan, China, Canada and the United States. More details are available at

Original article: