Researchers at the University of Cambridge have proposed CosmoCube, a suitcase-sized satellite designed to orbit the Moon and detect ancient 21-centimeter radio signals from the cosmic dark ages, operating from the lunar far side to shield its instruments from terrestrial interference before a potential launch within five years.
A satellite no bigger than a small carry-on suitcase could help investigate a period of cosmic history that has never been directly observed. Developed in the UK, CosmoCube is designed to search for evidence of what happened during roughly 150 million years of cosmic dark ages before the universe’s first stars began to shine.
Led by the University of Cambridge, an international group of scientists plans to send CosmoCube around the Moon and use its far side as a natural shield from radio interference generated on Earth. From there, the satellite will listen for an exceptionally faint signal left by the early universe.
Known as the 21-centimeter line, the signal comes from hydrogen atoms during the period between the afterglow of the Big Bang and Cosmic Dawn, when nuclear fusion ignited the first stars. Astronomers have yet to observe this era directly.
Following the Big Bang, the universe went through a period known as the cosmic dark ages. It lasted roughly 150 million years before the first stars began to form. Although there were no stars yet, the universe contained large amounts of hydrogen. These atoms produced a faint radio signal known as the 21-centimeter line.
This Suitcase-Sized Spacecraft Could Detect a Signal From Before
Searching for a signal more than 13.5 billion years old from Earth is extremely difficult. The ionosphere blocks the relevant radio frequencies, while FM radio, satellites, and telecommunications create additional interference that can overwhelm the faint cosmic signal. Earth’s ionosphere blocks the relevant low-frequency radio waves, while FM radio, telecommunications systems, satellites and other human-made sources can overwhelm the much weaker signal from ancient hydrogen.
The Moon offers a way around both problems. During each two-hour orbit, CosmoCube would spend about 40 minutes behind the Moon, protected from radio noise coming from Earth. When the spacecraft moves behind the Moon, the lunar body would block radio signals coming from Earth. This would create a much quieter environment for the spacecraft’s instruments to listen for the faint 21-centimeter signal. Over a planned two-year mission, researchers expect the satellite to accumulate around 1000 hours of observations from one of the least explored periods in cosmic history, providing clues to how the universe evolved from a dark, relatively empty state into the complex cosmos seen today.
The mission has received funding from the UK Space Agency, and researchers hope to launch CosmoCube within five years. Details of the project were published in Nature Astronomy.
CosmoCube is also intended to investigate dark matter, the invisible matter whose gravity plays a major role in forming and holding galaxies together, by examining conditions before the first stars appeared. The observations could also help scientists investigate dark matter, the mysterious form of matter that does not emit or reflect light but whose gravitational effects influence visible matter.
This emission from hydrogen after the Big Bang, but before the first stars, will hopefully allow us to understand the role of dark matter in the early universe, how it worked to pull together hydrogen into the first stars and galaxies,
said lead author Professor Eloy de Lera Acedo from Cambridge’s Cavendish Laboratory.
How a Suitcase-Sized Spacecraft Could Rev
The satellite will observe extremely low radio frequencies between 10 and 50 MHz, a range that is largely inaccessible to ground-based telescopes. That limitation is what makes the Moon’s far side so valuable as CosmoCube’s fortress of solitude.
There’s no other place where you can get the sort of shielding you need to detect such a faint signal, while at the same time looking at the whole of space,
said de Lera Acedo, who is also affiliated with the Kavli Institute for Cosmology. De Lera Acedo said the far side of the Moon is really the only option
because it can solve several observation problems simultaneously and provide a clearer window into the early universe.
Once CosmoCube reaches lunar orbit, it will deploy a long, lightweight radio antenna designed to detect the 21-centimeter hydrogen signal while the spacecraft passes behind the Moon. As the universe expanded, the wavelengths of signals traveling across space were stretched. This allows astronomers to use the signal to investigate different stages of cosmic history.
Because the desired signal is so weak, CosmoCube must also carefully track noise produced by its own electronics. A ‘Dicke switched’ calibrator will repeatedly alternate between observations of the sky and several built-in reference sources, allowing researchers to identify and correct small instrumental drifts that might otherwise imitate a cosmic signal.
After the observations return to Earth, researchers will apply advanced Bayesian statistical techniques to separate the desired signal from foreground emission, particularly radio waves produced within the Milky Way.
