Active galaxies pour out lots of energy, due to their central supermassive black holes gobbling down matter. Galaxies tend not to be loners but instead exist in smaller groups and larger clusters. Our Milky Way is part of the Local Group, and will one day collide with the Andromeda galaxy. Clusters of galaxies also clump together to form superclusters, the largest structures in the Universe. In total, there are hundreds of billions of galaxies in the Universe.

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Introduction: Active Galaxies 00:00
Active Galaxy Structure: Central Black Hole 2:26
Active Galaxy Structure: Accretion Disks 3:42
The Milky Way’s Supermassive Black Hole 5:38
The Local Group 6:45
Miklomeda: Andromeda and the Milky Way Collide! 7:29
Galaxy Clusters 9:47
Superclusters 11:19
How Many Galaxies Are There? 12:32
Review 14:25

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Galactic Wreckage in Stephan’s Quintet [credit: NASA, ESA, and the Hubble SM4 ERO Team]
Best image of bright quasar 3C 273 [credit: ESA/Hubble & NASA]
Nearby Quasar 3C 273 [credit: NASA, M. Clampin (STScI), H. Ford (JHU), G. Illingworth (UCO/Lick Observatory), J. Krist (STScI), D. Ardila (JHU), D. Golimowski (JHU), the ACS Science Team, J. Bahcall (IAS) and ESA]
Gamma Rays [credit: X-ray: NASA/CXC/SAO, Optical: NASA/STScI, Radio: NSF/NRAO/VLA]
Black hole (artist’s impression) [credit: ESA/Hubble (M. Kornmesser & L. L. Christensen)]
Matter accreting around a supermassive black hole (artist’s impression) [credit: ESA/Hubble (M. Kornmesser)]
Artist’s animation of galaxy with jets from a supermassive black hole [credit: ESA/Hubble, L. Calçada (ESO)]
NASA’s Swift Finds ‘Missing’ Active Galaxies [credit: NASA/Goddard Space Flight Center]
Sagittarius A*: NASA’s Chandra Detects Record-Breaking Outburst from Milky Way’s Black Hole [credit: NASA/CXC/Amherst College/D.Haggard et al]
NASA Hubble Sees Sparring Antennae Galaxies [credit: Hubble/European Space Agency]
A New Dawn [credit: NASA, ESA, G. Besla (Columbia University) and R. van der Marel (STScI)]
Galaxy Sky [credit: NASA, ESA, Z. Levay and R. van der Marel (STScI) T. Hallas, and A. Mellinger]
Virgo Cluster [credit: Rogelio Bernal Andreo]
Cosmic Clumps [credit: NASA’s Scientific Visualization Studio]
Laniakea: Our Home Supercluster of Galaxies [credit: R. Brent Tully (U. Hawaii) et al., SDvision, DP, CEA/Saclay]
Webb Science Simulations [credit: NASA/Goddard Space Flight Center and the Advanced Visualization Laboratoy at the National Center for Supercomputing Applications]
Hubble Deep Field [credit: R. Williams (STScI), the Hubble Deep Field Team and NASA]
Hubble Ultra Deep Field 2014 [credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)]