Large-Scale Structure: the Organization of the Universe.Galaxies are not distributed randomly across the universe. They are often found ingroups and clusters… and clusters cluster in superclusters!

Hercules galaxy cluster (from APOD).

Superclusters:-are filamentary or planar structures connecting several large clusters. Theyusually surround bubble-like voids.

- are probably the largest scale of structure in the universe, though there are somevery large ones.

Hercules galaxy cluster (from APOD).

- One of the largest known structures: “The Great Wall” 170x60x5 Mpc3.

- More “locally,” we have the “Great Attractor”…

Tully et al. 1992, Astrophys. J. 388, 9.

Explanation: Our universe is filled with galaxies. Galaxies -- huge conglomerations of stars,gas, dust -- and mysterious dark matter are the basic building blocks of the large-scaleuniverse. Although distant galaxies move away from each other as the universe expands, gravityattracts neighboring galaxies to each other, forming galaxy groups, clusters of galaxies, andeven larger expansive filaments. Some of these structures are visible on one of the mostcomprehensive maps of the sky ever made in galaxies: the APM galaxy survey map completed inthe early 1990s. Over 2 million galaxies are depicted above in a region 100 degrees acrosscentered toward our Milky Way Galaxy's south pole. Bright regions indicate more galaxies, whilebluer colors denote larger average galaxies.

Simulating the UniverseCredit: G. L. Bryan, M. L. Norman, UIUC, NCSA, GC3

2 Difficult questions:

-How to make the bubble structure in the early phases of the universe?

- How to make galaxies simultaneously?