One of the most interesting things in science is finding something unexpected in your data, and this is exactly what happened to a group of astronomers when they looked at the objects present in their large radio sky survey.
Before I get to what they found though, we’re going to need a little bit of background (don’t worry, there’s not much). These days when astronomers look at a large patch of sky with a particular telescope they tend to chose a bit that other people have looked at before at a different wavelength. Objects in the Universe emit light at many wavelengths, from gamma-ray through optical to radio, so combining observations from several complementary surveys gives a more complete picture of what’s going on up there. A consequence of this approach is that once you have one set of data for a particular source you can predict how it will look in another, assuming your guess as to what kind of source it is is correct.
So, to get back to the astronomers and their radio survey, the unexpected things they found were infrared-faint radio sources. These are objects which, as their name suggests, are bright at radio wavelengths but very, very faint when they looked for them in the infrared. Normally, radio sources like this are active galactic nuclei (AGN), but the lack of an infrared detection is weird.
What are they then? Well, in the words of this post’s referenced paper, “Are the infrared-faint radio sources pulsars?”. A pulsar is the rapidly rotating remains of an exploded star in our own galaxy, from which we see regular radio pulses of the right sort of brightness to be candidates for these mystery objects; Niall gives a longer description of them here. Unfortunately when the astronomers looked into this hypothesis they found that their odd infrared-faint radio sources weren’t pulsing, and the answer to their title question is no.
This paper is a great example of how a non-detection in science can also be useful. The paper authors may not have pinned down just what infrared-faint radio sources are, but they’ve managed to rule out something they aren’t.
A. D. Cameron M. J. Keith, G. Hobbs, R. P. Norris, M. Y. Mao, & E. Middelberg (2011). Are the infrared-faint radio sources pulsars? accepted by MNRAS arXiv: 1103.6062v1