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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Chapters:
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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PHOTOS/VIDEOS
Galactic Wreckage in Stephan's Quintet http://hubblesite.org/newscenter/arch... [credit: NASA, ESA, and the Hubble SM4 ERO Team]
Best image of bright quasar 3C 273 http://www.spacetelescope.org/images/... [credit: ESA/Hubble & NASA]
Nearby Quasar 3C 273 http://hubblesite.org/newscenter/arch... [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 http://chandra.harvard.edu/photo/2014... [credit: Xray: NASA/CXC/SAO, Optical: NASA/STScI, Radio: NSF/NRAO/VLA]
Black hole (artist's impression) http://www.spacetelescope.org/videos/... [credit: ESA/Hubble (M. Kornmesser & L. L. Christensen)]
Matter accreting around a supermassive black hole (artist's impression) http://www.spacetelescope.org/videos/... [credit: ESA/Hubble (M. Kornmesser)]
Artist’s animation of galaxy with jets from a supermassive black hole http://www.spacetelescope.org/videos/... [credit: ESA/Hubble, L. Calçada (ESO)]
NASA's Swift Finds 'Missing' Active Galaxies https://svs.gsfc.nasa.gov/cgibin/det... [credit: NASA/Goddard Space Flight Center]
Sagittarius A*: NASA's Chandra Detects RecordBreaking Outburst from Milky Way's Black Hole http://chandra.harvard.edu/photo/2015... [credit: NASA/CXC/Amherst College/D.Haggard et al]
NASA Hubble Sees Sparring Antennae Galaxies https://www.nasa.gov/content/goddard/... [credit: Hubble/European Space Agency]
A New Dawn http://svs.gsfc.nasa.gov/cgibin/deta... [credit: NASA, ESA, G. Besla (Columbia University) and R. van der Marel (STScI)]
Galaxy Sky http://svs.gsfc.nasa.gov/vis/a010000/... [credit: NASA, ESA, Z. Levay and R. van der Marel (STScI) T. Hallas, and A. Mellinger]
Virgo Cluster http://deepskycolors.com/astro/2015/0... [credit: Rogelio Bernal Andreo]
Cosmic Clumps http://svs.gsfc.nasa.gov/cgibin/deta... [credit: NASA's Scientific Visualization Studio]
Laniakea: Our Home Supercluster of Galaxies http://apod.nasa.gov/apod/ap140910.html [credit: R. Brent Tully (U. Hawaii) et al., SDvision, DP, CEA/Saclay]
Webb Science Simulations http://svs.gsfc.nasa.gov/vis/a010000/... [credit: NASA/Goddard Space Flight Center and the Advanced Visualization Laboratoy at the National Center for Supercomputing Applications]
Hubble Deep Field https://upload.wikimedia.org/wikipedi... [credit: R. Williams (STScI), the Hubble Deep Field Team and NASA]
Hubble Ultra Deep Field 2014 http://hubblesite.org/newscenter/arch... [credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)]