Three researchers at the University of Waterloo in Canada and a colleague from the Institute d’Astrophysique de Paris in France have created the most comprehensive three-dimensional map of the cosmic neighbourhood to date.
The spherical map, published online in the peer-reviewed journal Monthly Notices of the Royal Astronomical Society, spans nearly two billion light years across and is likely to be of much use in determining the distribution of both “regular” and “dark” matter in the Universe.
One of the researchers behind the map – Professor Michael Hudson – claims we are closing in on the peculiar motions of both the Universe and dark matter, and the link between them.
“The galaxy distribution isn’t uniform and has no pattern. It has peaks and valleys much like a mountain range. This is what we expect if the large-scale structure originates from quantum fluctuations in the early universe,” noted Hudson.
The team spent more than three years compiling telescope images, gathered over an entire decade, into a complex map that approximates the actual direction of the Universe’s many clusters of galaxies, the speed of their expansion and distance from Earth.
“It’s been a huge effort. Different groups have spent years looking at different parts of the sky, and we collected that data,” said Hudson, who is also an affiliate member of the Perimeter Institute for Theoretical Physics.
“All these other groups were like explorers who went off in different directions and brought back their pieces of data. We assembled it into one coherent map.”
Since the Universe is expanding unevenly – for example, our own Milky Way and the neighbouring Andromeda are moving at the speed of around 600 kilometres per second – such detailed inter-galactic 3D renderings may prove indispensable in mapping its “lumpiness” and seeking out the precise location and concentrations of dark matter.
“It’s believed that dark matter slows down the expansion of the universe in some areas, acting as a beacon,” said Hudson. “It’s a way to measure something that can’t otherwise be measured.”
The next step will involve getting more detailed samples of peculiar velocities (galaxies moving at unusual speeds) to enhance and expand the map up to three or four billion light years across – a feat to be accomplished in collaboration with researchers from Australia.
“By doing this map, we’ve explained most of that motion but not all of it yet. We have to go deeper still,” explained Hudson. “We want to see if we can understand all of it. There may be other galaxies out there that we haven’t mapped yet that are accounting for this extra pull.”