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Dark matter bridge in cosmic neighborhood

Astronomers see a bridge of dark matter stretching from our Local Group to the Virgo galaxy cluster. It’s bound on each side by vast bubbles devoid of galaxies.

View larger. | The figure shows the current stream of galaxies - the flow along in the cosmic super-highway and on the bridge to Virgo, in the region around the Milky Way, Andromeda and Centaurus A.

View larger. | The flow along in the cosmic super-highway and on the bridge to Virgo, in the region around the Milky Way, Andromeda and Centaurus A.

Astronomers led by Noam Libeskind at the Leibniz Institute for Astrophysics Potsdam this week (July 14, 2015) announced they’ve built a detailed map of how nearby galaxies move. In it, they say, they’ve discovered a bridge of dark matter stretching from our Local Group all the way to the Virgo cluster – a huge cluster of some 2,000 galaxies roughly 50 million light-years away. The astronomers say the dark matter bridge is bound on either side by vast bubbles completely devoid of galaxies. They say this bridge and these voids will help them understand a 40-year-old problem regarding the curious distribution of dwarf galaxies.

Dwarf galaxies are often found swarming around larger galaxies like our own Milky Way. Since they are dim, they are hard to detect, and are thus we know dwarf galaxies almost exclusively in our cosmic neighborhood.

One of their most fascinating aspects is that, near the Milky Way and at least two of our closest neighboring galxies – the Andromeda and Centaurus A galaxies – these satellites don’t just fly around randomly. Instead, they’re compressed on to vast, flat, possibly spinning, planes.

Current stream of galaxies

Current stream of galaxies

Most modern cosmologists rely on a theory known as the Cold Dark Matter model to understand the universe forms galaxies. But this model does not explain this feature of dwarf galaxies, which are thus an unexplained challenge to the theory.

The dark matter bridge might help explain them. The dwarf galaxies “echo the geometry of structure on much greater scales,” the astronomer said in a July 14 statement. Libeskind added:

This is the first time we have had observational verification that large filamentary super highways are channeling dwarf galaxies across the cosmos along magnificent bridges of dark matter.

This cosmic “super highway” gives the speeding satellites an off ramp along which they can be beamed towards the Milky Way, Andromeda and Centaurus A. Libeskind said:

The fact that this galactic bridge can affect the dwarf galaxies around us is impressive, given the difference in scale between the two: the planes of dwarfs are around one percent of the size of the galactic bridge to Virgo.

Known Milky Way galaxy satellite candidates.  Some may not be true satellites, but may simply be passing near us in space.

These dwarf galaxies are among the known Milky Way galaxy satellite candidates. Some may not be true satellites, but may simply be passing near us in space.

Bottom line: Astronomers at the Leibniz Institute for Astrophysics Potsdam have discovered a bridge of dark matter stretching from our Local Group to the Virgo galaxy cluster. It’s bound on each side by vast bubbles devoid of galaxies. The presence of this dark matter bridge helps explain a mysterious aspect of neighboring dwarf galaxies.

Via the Leibniz Institute for Astrophysics Potsdam

Deborah Byrd

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