Spiral galaxies

MYSTERIES OF THE UNIVERSE

There are far fewer spiral galaxies than elliptical ones in the Supergalactic Plane, and scientists are keen to discover why

Reported by David Crookes

The Milky Way is a spiral galaxy located in the Supergalactic Plane, and while we already T know it’s special because it contains Earth, it’s remarkable in other ways, too. Look across our cosmic backyard, for instance, and you’ll find the Milky Way is something of a rarity. In the Supergalatic Plane, measuring about a billion light years across, there’s a super-high concentration of galaxies, but the vast majority of them are elliptical. Spiral galaxies like the Milky Way are far less common, and astronomers have long wanted to know why.

“Among the brightest galaxies, there are around twice as many ellipticals as spirals close to the Supergalactic Plane – it is not an enormous excess, but it is statistically significant,” explains Dr Till Sawala, a postdoctoral researcher at Durham University and the University of Helsinki. Keen to get to the bottom of this mystery, which has been known about for more than 40 years, he wondered whether it pointed to a flaw in the standard model of cosmology. With that in mind, he turned to a computer simulation for answers, and it points to an explanation.

“I first became interested in this question when I read a review by the Nobel Prize winner Jim Peebles where he pointed it out as an anomaly,” Sawala says. “I then saw him raise the same question at a cosmology symposium. He argued that such a large-scale difference in galaxy distribution, extending over hundreds of megaparsecs, was not expected in the standard cosmological model.” In other words, the distribution of galaxies should be more even within the several massive clusters and thousands of individual galaxies that make up the Supergalactic Plane. At large scales, the spatial distribution of matter in the universe is close to homogeneous, but that’s not what is being observed here.

Spiral galaxies have a supermassive black hole at the centre, but ellipticals have black holes that are far larger

© NASA/JPL; Adobe Stock