Measure the beam from a pulsar for an hour or so and you’ll see all kinds of interference fringes in amongst the noise. This intereference is caused by light scattered from the interstellar medium, probably in the form of whisps of gas and dust although nobody knows for sure.
There’s all kinds of infromation locked in this data. In fact, this interference pattern can be thought of as a kind of hologram of the interstellar medium. But to unlock it, to reconstrcut the image from the interference data, you’ve gotta know the structure of the light field before it was distorted and this depends on thousands of unknown parameters.
A few astrophysicists have tried to reconstruct these holograms by guessing what these parameters should be but their results have been predictably poor.
Now Mark Walker at the University of Sydney and a few cobbers have made a dramatic improvement by developing an algorithm that can simultaneously optimise the eight thousand coefficients that describe the electric field.
This has allowed them to reconstruct the field and create an image of the interstellar medium. It’s impressive work.
Having done that, Walker and co say the information can be used to correct other observations of the such as timing measurements on the pulsar beams. And it might also give an idea what’s doing all this scattering and how it changes over very short time scales.
Ref: arxiv.org/abs/0801.4183: Interstellar Holography