A few years ago, astronomers were surprised to detect a very loud radio signal with no determined origin, a space roar that remains unexplained.
In space, no one can hear you scream, said the poster for the first movie in the Alien series. The reason is well known: in the vacuum of space there is no air and therefore no sound. However, in 2006, NASA discovered what they called a “space roar”, a signal six times stronger than expected.
This signal is not a sound, but a radio signal. Space roar was first discovered by ARCADE, the Absolute Radiometer for Cosmology, Astrophysics and Diffuse Emission. It is a detector that NASA attached to a stratospheric balloon, which rose to 36,000 meters in the air with the aim of searching for radio signals from distant galaxies.
Radio waves are electromagnetic radiation, just like visible light or infrared light that allows the Webb telescope to capture incredible images. The radio waves that a star like our sun emits are not very different from the light we receive. That’s why we have huge radio telescopes, like the ill-fated Arecibo. Due to the expansion of the universe, distant light decreases in energy as it travels, and high-energy light ends up being converted into radio waves.
This was ARCADE’s mission, to detect these faint radio signals from distant stars unimpeded by Earth’s atmosphere. Instead, he was given the radio equivalent of turning the television on to full volume. The researchers described it as a “boom”, six times stronger than anyone had predicted.
After some investigation, scientists dismissed the idea that they were simply very noisy early stars. They also ruled out that it somehow came from the dust of our own galaxy. It was just a radio blast, dubbed the “space roar”, which seemed to be part of the background noise for no reason.
The roar, or radio synchrotron background emission, is a diffuse signal coming from all directions, so a single object is dropped. The signal also has a frequency spectrum, or “color”, which is similar to the radio emission from our Milky Way.
It has been known since the late 1960s that the combined radio emission from distant galaxies must form a diffuse radio background coming from all directions. What was not expected is its magnitude, which cannot be explained because there don’t seem to be six times as many galaxies as there are already known. This raises many unknowns about its origin.
Although the space roar has piqued the interest of many, there is still no explanation for it. There is still controversy over whether it comes from our galaxy, the Milky Way, or from outside it, although the latter is more likely, according to experts. It is also speculated that it is residual radiation extended across many parallel universes, or that it comes from the annihilation of dark matter, or that it is produced by interstellar dust and gas.
Either way, space roar is a real problem that makes it difficult to capture radio waves from the first stars after the universe formed. Another mystery that science must solve.