Engineering student cracks major riddle of the universe

An engineering undergraduate in Australia has made a major step forward in solving one of the greatest riddles of the universe: that is, where most of it is.

Boffins know from observing the universe that it must have a certain amount of mass, otherwise it would have failed to hold itself together as well as it has. Argument continues as to just how well it has or is doing so, but in general astrophysicists are agreed that all the mass we can see – observed galaxies of stars, dust, gas etc – is not enough to account for what's going on. There must be a whole lot more mass out there in some form or another.

It is this "missing mass" – or anyway a good chunk of it – that 22-year-old undergraduate student Amelia Fraser-McKelvie, studying Aerospace Engineering at Melbourne's Monash uni, has tracked down.

"It was thought from a theoretical viewpoint that there should be about double the amount of matter in the local Universe compared to what was observed," says Dr Kevin Pimbblet, a Monash astrophysicist.

Over the decades, various theories have been offered to account for the mass that must be there but which we can't see: brown dwarfs, cosmic strings, wandering sunless interstellar planets, various kinds of hard-to-spot particles including neutrinos, wimps, winos etc. But the theory that Pimbblet and his colleagues decided to look into was that of "filaments", enormous cosmic structures extending from galaxies which would account for a lot of mass – even though there would be very little to them.

Theory indicated that the filaments ought to exist at extremely high temperatures if they were there, which offered the prospect that they would emit X-rays and thus that they could be detected. Ms Fraser-McKelvie joined the X-ray filament hunting team on a summer scholarship.

At first the X-ray data appeared to show no sign of any filaments, but then X-ray expert Dr Jasmina Lazendic-Galloway uncovered traces of the "missing mass".

"Using her expert knowledge in the X-ray astronomy field, Jasmina reanalysed our results to find that we had in fact detected the filaments in our data, where previously we believed we had not," says Fraser-McKelvie.

The young intern's contributions to the project were nonetheless deemed so valuable that she was named lead author on the study paper, whose importance to the missing-matter debate is such that it has been accepted for publication in prestigious astroboffinry journal Monthly Notices of the Royal Astronomical Society. Having a paper published in such a hefty periodical so early in her academic career is a major score for Fraser-McKelvie.

"She has managed to get a refereed publication accepted by one of the highest ranking astronomy journals in the world as a result of her endeavours. I cannot underscore enough what a terrific achievement this is," enthuses Pimbblet.

It's "very exciting for me", adds Fraser-McKelvie, taking care to add her thanks to co-authors Pimbblet and Lazendic-Galloway.

The paper An estimate of the electron density in filaments of galaxies at z~0.1 can be read in advance of publication here, and there's a Monash uni statement here. ®