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Home , Seyfert galaxy

Chapter 21 Preview: Evolution of Structure in the Universe Evolution

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Our best models for Denser regions galaxy formation contracted, forming assume: protogalactic clouds

• Matter originally filled all of space H and He gases in almost uniformly these clouds formed the first • Gravity of denser regions pulled in surrounding matter

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Supernova Models: Evolution of Galaxy Interactions explosions from first stars kept much of the gas from forming stars

Leftover gas settled into spinning disk

Conservation of angular momentum https://www.youtube.com/watch?v=Xu3-0Ubhiwo

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1 NGC 4414 M87 Conditions in Protogalactic Cloud?

Spin: Initial angular momentum of protogalactic cloud could determine size of resulting disk But why do some end up looking so different?

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Conditions in Protogalactic Cloud?

Density: Elliptical galaxies could come from dense protogalactic clouds that were able to cool and form stars before gas settled into a disk Collisions were more common in early smaller Universe. Many of the galaxies we see at great distances (and early times) indeed look violently disturbed.

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Modeling such collisions on a computer shows that two spiral galaxies can merge to make an elliptical: – Andromeda collision in the future https://www.youtube.com/watch?v=mzgGhpAu2_I Stars miss but gas collides triggering bursts of formation

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2 Shells of stars Collisions observed may explain around some why elliptical elliptical galaxies tend galaxies are to be found probably the where remains of past galaxies are collisions closer together

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Giant elliptical Collisions galaxies at the may induce centers of Starburst clusters seem Galaxies; to have form stars so consumed a quickly they number of would use up smaller all their gas galaxies in less than a billion years

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X-ray image

Intensity of explosions in starburst galaxies Intensity of supernova explosions in starburst galaxies can drive galactic winds can drive galactic winds

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3 If the center of a Next Time: Active galactic nuclei galaxy is unusually bright we call it an

Quasars are the most luminous examples; large redshifts (Hubble’s Law) Active Nucleus in M87

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Characteristics of Active Galaxies

12 • can be enormous (>10 LSun) • Luminosity can rapidly vary (comes from a space smaller than solar system) • Emit energy over a wide range of wavelengths (contain matter with wide temperature range) • Some drive jets of plasma at near speed

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Radio galaxies contain active nuclei shooting out vast jets of plasma that emits radio waves coming from electrons moving at near light speed

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4 Radio galaxies or don’t appear Seyfert Galaxy as because Radio dusty gas Galaxy clouds block our view of

What we see depends on orientation

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Orbital speed and distance of gas orbiting center of M87 Accretion of gas onto a produces indicate a black hole with mass of 6 billion MSun friction, heat, radiation, jets (10-40% of mass-energy can be converted to radiation on approach to event horizon). 27 28

Event Horizon Telescope Thought Question

• Array of radio telescopes What can you conclude from the fact that quasars usually around the world have very large redshifts? • Gathered data on distant giant galaxy M87 A. They are generally very distant • Final image reveals the B. They were more common early in time central black hole shadow: C. Galaxy collisions might turn them on first picture of a black hole D. Nearby galaxies might hold dead quasars • https://www.youtube.com/ watch?v=oLeKFDfCrTg E. All of the above

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5 Black Holes in Galaxies

• Many nearby galaxies – perhaps all of them – have supermassive black holes at their centers • These black holes seem to be dormant active galactic nuclei • All galaxies may have passed through a quasar- Gas clouds between a quasar and Earth absorb some of a like stage earlier in time quasar’s light • Even found in very distant galaxies at times when Universe was less than one billion years old We can learn about protogalactic clouds by studying the absorption lines they produce in quasar spectra

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Galaxies and Black Holes Galaxies and Black Holes • Mass of a • Development galaxy’s of central central black black hole hole is must be closely somehow related to related to mass of its galaxy bulge evolution

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How did supermassive black holes form? • Collisions of galaxies and gas infall • Explosions of clusters of massive stars • Concentrating stars in the centers of star clusters • Very dense locations https://rh.gatech.edu/news/616736/birth- massive-black-holes-early-universe-revealed

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