NASA’s Lunar Crater Radio Telescope could help us study the cosmic dark ages

STORY BY The Cosmic Companion, Exploring the wonders of the Cosmos, one mystery at a time.

Following the Big Bang, our budding Universe slowly cooled, and the first atoms took shape. Gravity gradually pulled on clumps of hydrogen and helium gas, forming the earliest stars. This era, lasting a few hundred million years prior to the large-scale formation of stars, is called the cosmic dark ages.

The Lunar Crater Radio Telescope (LCRT), an ambitious concept to place a massive radio telescope on the far side of the Moon, would study the Universe during this ancient era in detail for the very first time.

“While there were no stars, there was ample hydrogen during the universe’s Dark Ages — hydrogen that would eventually serve as the raw material for the first stars. With a sufficiently large radio telescope off Earth, we could track the processes that would lead to the formation of the first stars, maybe even find clues to the nature of dark matter,” explained Joseph Lazio, radio astronomer at NASA’s Jet Propulsion Laboratory and a member of the LCRT team.

How low can you go (in frequency)?

The same ionosphere that allows this Boy Scout to use shortwave radio in 1937 prevents Earth-bound astronomers from seeing light from the first stars in the Cosmos. Image credit: Public domain/Harris and Ewing, photographers.

In 1930, a young radio engineer working at Bell Telephone Laboratories named Karl Jansky was tasked with a project to find natural sources of interference that might play havoc with communication systems of the day. A pesky signal in their readings that would not go away turned out to be radiation from the core of the Milky Way galaxy, (eventually, slowly) heralding the era of radio astronomy. Today, the intensity of radio signals from space is measured in a unit called a Jansky, in his honor.

Early work on radios focused on communications over extremely long wave transmissions. As technology progressed, the frequencies used in systems grew shorter. Today, astronomers often look at bodies over wavelengths of a centimeter or shorter. We might not think of 10 meters as being “shortwave” today, but this was the case in the time Jansky did his work, and the name stuck.

As the Universe expands, the wavelength of electromagnetic signals (like light) coming from ancient targets stretches, becoming longer. Radio signals from the cosmic dark ages are — not surprisingly — very long.

Once operational, the Lunar Crater Radio Telescope would allow astronomers to conduct extensive studies of the ancient Universe at wavelengths greater than 10 meters in great detail for the first time. These frequencies are used on Earth in VHF television broadcasts and shortwave radio.

Radio telescopes on Earth are unable to see this long-wavelength (low-frequency) radiation, as these signals are reflected back to space by the ionosphere, a layer of ions and electrons in the upper layers of our atmosphere. (This reflection also allows shortwave radios, including ham radios, to broadcast over great distances).

Human-made radio interference can also wreak havoc with sensitive astronomical equipment. Visitors to observatories with radio telescopes are asked to turn their phones to airplane mode to prevent interference with these instruments. Ultra-sensitive instruments studying radiation from the oldest stars in the Universe would need to be shielded from stray electromagnetic radiation.

“Invisible airwaves crackle with life
Bright antennae bristle with the energy
Emotional feedback on a timeless wavelength
Bearing a gift beyond price — almost free” — Rush, ‘The Spirit of Radio’

The LCRT would provide unprecedented looks at the early Universe. Image credit: Saptarshi Bandyopadhyay / NASA
The LCRT would provide unprecedented looks at the early Universe. Image credit: Saptarshi Bandyopadhyay / NASA