Posts by: Brent Tully

In this 2D slice of the supergalactic equatorial plane, the boundary of Laniakea is the closed orange curve. The white lines are velocity-flow curves where red denotes areas of high density and blue shows low density. The Milky Way is the black dot on the right-hand side of Laniakea. (Courtesy: Brent Tully et al./Nature)

By Brent Tully at the International Astronomical Union General Assembly in Honolulu, Hawaii

We know that we live on a planet in a solar system in a galaxy in a group of galaxies. But what do we know about our location in the universe beyond that? Some astronomers would answer that we live in the “Local” or “Virgo” supercluster of galaxies. However, the concept has been vague. In the interconnected “cosmic web” it has not been clear where one dense region of galaxies ends and another begins.

Rather than just looking at the distribution of galaxies, it is instructive to consider the motions of galaxies with respect to each other. On the grand scale, galaxies are flying apart from each other with the expansion of the universe. We have to cancel out that motion to see the residual “peculiar” velocities of galaxies that arise from local gravitational attractors.

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