What is "space roar"?

In space, no one can hear you scream. Probably because space itself can scream louder than you can. In 2006, NASA found something called "space roar" — it's a sound that is six times louder than anything that anyone was expecting, and it's clearly covering something up.

Okay, invoking Alien was a bit sneaky of me. In space, no one can hear you scream because there is no medium through which sound can move. And space roar isn't really a sound, it's radio waves. Otherwise it parallels the Alien plot pretty well — a space voyage, an unknown transmission, scientists getting more than they bargained for, and no suitable explanation in sequels (zing!).

Space roar was first discovered by ARCADE, the Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission. It's a very fancy name for some very fancy equipment that NASA attached to a big balloon and sent about 120,000 feet up into space. ARCADE was meant to be looking for radio signals from distant galaxies. Because radio is so commonly used, and used to create auditory signals, it's easy to forget that it's just another form of light. It's much less energetic than visible light, and our eyes aren't tuned for it, but it behaves the same way. A star emitting radio waves isn't much different from a our sun emitting visible light. In fact, to someone far away or far in the future, our sun probably is emitting primarily radio waves.

Because of the expanding universe, distant light gets ratcheted down in energy as it travels, and high energy light eventually shifts down to radio waves. Light takes time to travel, and so when we look at the radio emissions of distant stars, we are looking at stars as they were at the beginning of their lives. We are even looking at the universe as it was in its early life.

What is "space roar"?

Or at least we're trying to. This is what ARCADE was sent to do, unhindered by Earth's atmosphere. It was meant to pick up the faint radio signals of distant stars. Instead it got a strong blare of radio. The input, described as a "boom" by those studying it, was about six times stronger than anything that anyone predicted. After some research, scientists ruled out the idea that it was just very loud early stars. They also ruled out that it was somehow coming from the dust of our own galaxy. It was just a blast of radio, dubbed "space roar," that seemed to be part of the background noise for no understood reason.

Although space roar piqued the interests of many, there is still no explanation for it. ARCADE only took a look at a specific circle of area that makes up 7% of the sky, but even this limited area makes the roar fairly widespread. It's just out there, covering up our view of the early stars. And being emitted by something we can't yet imagine.

Top Image: X-ray (NASA/CXC/Virginia/A.Reines et al); Radio (NRAO/AUI/NSF); Optical (NASA/STScI)

Via NASA, arXiv, and Sciverse Direct.