Last year, on March 16, I wrote an article on one of the newest problems from the list of the greatest unsolved problems in physics — the space roar. Well, believe it or not, since then, that post turned out to be one the most popular articles from the series on unsolved problems in physics. And, when you think about it, it’s not surprising. After all, how can you not be interested in a mystery with such a catchy name worthy of being a title for a great sci-fi horror flick. So let’s have another look at this mystery and see whether we moved any closer to solving it.
For those, who are not aware of what space roar is all about, check out this great video by SciShow.
Long story short, it’s an unexplained radio signal detected by the ARCADE radiometer. Although various radio signals from galaxies have been observed many times, the space roar is 6 times stronger than any predicted signal.
So, as you might imagine, scientists have spent a lot of time trying to figure out what this mysterious signal is, but so far, they only found out what it is not. After additional analysis, primordial stars, neutron stars, supernovae, gas in the outermost halo of our galaxy and any known radio source has been ruled out. The strangest thing is the strength of the signal — there just aren’t enough radio galaxies to account for it .”You’d have to pack them into the universe like sardines,” said a team member of the original study Dale Fixsen of the University of Maryland. “There wouldn’t be any space left between one galaxy and the next.”
In 2011 the team of ARCADE 2 has also observed the mysterious signal, which, by then, has also been independently detected by FIRAS (Far-InfraRed Absolute Spectrophotometer). The findings of ARCADE 2 are summarized in this paper. Basically, they confirm that they have observed an unusual signal and discuss the possible sources of it. These include a population of faint unaccounted radio sources or an error in modelling the foreground emission.
A more recent paper from arXiv examines the problem of the space roar more closely and comes to similar conclusions. Here’s an excerpt from the abstract:
Analyses of measurements of the distribution of absolute brightness temperature over the radio sky have led recently to suggestions that there exists a substantial un-explained extragalactic radio background. Consequently, there have been numerous attempts to place constraints on plausible origins for the `excess’. We suggest here this expectation of a large extragalactic background, over and above that contributed by the sources observed in the surveys, is based on an extremely simple geometry adopted to model the Galactic emission and the procedure adopted in the estimation of the extragalactic contribution.
Then they work out what a more realistic model of galactic emission could be and whether it might explain the anomaly. Finally, the paper is concluded as follows:
Therefore, the models we have derived might well be local minima and indicative of a plausible decomposition. For this reason, the analysis presented herein may be interpreted as demonstrating that an `excess’ uniform background is not an imperative of the data but depends on the model components chosen for the Galactic emission… We conclude that there is no compelling evidence for an unexplained `excess’ uniform back-ground…
So it seems that another plausible explanation of the strange phenomena could simply be that we do not have an accurate model of calculating the background radiation. However, to confirm this further investigation will be needed. So, hopefully, next time I write about space roar we will have more answers.