ASTR 1120 REVIEW Active Galactic Nuclei (AGNs): General Astronomy: Another Type of Galactic Fireworks Stars & Galaxies • Galaxies with strange stuff going on in their � NNOUNCEMENTS NNOUNCEMENTS centers • Some galaxies at high redshift (large • Homework #8 due next Tue, Nov. 17, by 5pm lookback times) have extremely active centers • Midterm #3 on Thu, Nov.19 – More than 1000 times the light of the entire Milky Way combined from a point source at the center!! • EXTRA OBSERVING NIGHT - TONIGHT, from 8:30pm (20 students every 1/2 hr) REVIEW “Central Engine” -- artist’s conception REVIEW AGNs Central Engines • Accretion disk around super- How do AGNs emit so massive black much light in so little hole space? • Disk itself may or • They are powered by may not be obscured accretion disks around JET by dust supermassive black holes • If bright nucleus is visible, looks like a • In some AGNs, huge DISK quasar, if not, then jets of material are shot its a radio galaxy out at the poles. These jets are strong radio sources.
Cygnus A radio jets REVIEW REVIEW Another example of “central beaming engine” 400,000 ly Jet as fine thread, radio active nucleus - HST big lobes at end, central hot spot • 400 light year wide disk of material in core of elliptical galaxy with radio jets – looks like a supermassive black hole at work! VLA REVIEW Somehow, the rest of the galaxy knows Do ALL galaxies have supermassive about the SMBH during formation!! black holes in their centers? • likely YES! • Linked to the process of galaxy formation • More quasars seen in the distant (early) universe than now • Black holes gradually grow, but can run out of available fuel and become nearly invisible (like in our Milky Way)
Clicker Question Resurrected by galaxy collisions? Supermassive black holes at the center of galaxy are believed to be produced • Many galaxies with bright nuclei show signs of being disturbed A. by the death of supermassive stars • Collisions funnel material down into the black hole lurking at the B. by mergers of many solar mass black core holes • Expect more such collisions in denser early universe C. during the process of galaxy formation – This may help explain why fewer quasars today D. soon after the creation of the universe E. by a magician :-) Clicker Question Next…. more on the.. Supermassive black holes at the center of galaxy are believed to be produced PAST of the Universe: A. by the death of supermassive stars structure formation B. by mergers of many solar mass black holes FUTURE of the Universe: C. during the process of galaxy formation D. soon after the creation of the universe what is its fate? E. by a magician :-)
Both our past and our future Formation of Structure depend on amount of matter in Universe • In the beginning: • Past: Birth of galaxies and clusters – Density distribution mostly smooth but very – Matter provided the first tugs to assemble small “ripples” exist in density galaxies and clusters out of protogalactic clouds. Most of the mass is in dark matter. – Gravity pulls together dark matter in slightly denser regions to form dark halos • Future: Fate of the universe – Is there enough total matter in the universe – “Light” matter radiates energy and sinks to to reverse the expansion and pull the the middle to form galaxies universe back together again? Numerical simulations of structure formation • Simulations show that gravity of dark matter pulls mass into denser regions – universe grows lumpier with time – Those “lumps” are galaxy clusters
Computer Real data vs simulations Structures in galaxy observations look very similar to the •Agreement is generally pretty good! ones found in models in which dark matter is WIMPs •Despite the fact that we don’t know what the DM is ! Lessons from Imaginary Universes • Cold (Slow) dark matter works better than hot (fast) dark matter • Neutrinos are too fast– structure would be smeared out • What is slow and dark enough? We don’t know yet! – Particle experiments under way…..
Clicker Question Clicker Question What do we mean by “large-scale What do we mean by “large-scale structures?” structures?” A. Massive central dominant elliptical galaxies. A. Massive central dominant elliptical galaxies. B. Massive spiral galaxies with star birth rates B. Massive spiral galaxies with star birth rates more than 100x that in the Milky Way more than 100x that in the Milky Way C. Supermassive black holes that reside at the C. Supermassive black holes that reside at the centers of galaxies centers of galaxies D. Huge walls of galaxies and clusters of galaxies D. Huge walls of galaxies and clusters of galaxies E. The giant architectural structure that is the E. The giant architectural structure that is the engineering building on CU’s campus engineering building on CU’s campus Some say the world will end in fire The Fate of the Universe Some say with ice From what I’ve tasted of desire • Expansion begins with the Big Bang (we’ll talk about I hold with those who favor fire this next week) But if I had to perish twice I think I know enough of hate • At that point, everything in the universe is flung To say that for destruction ice apart at outrageous speeds! Is also great And would suffice • Several different models for Past and Future depending upon the amount of dark matter -- Robert Frost (1874-1963) National Poet Laureate
Predictions of General Relativity Theory (GTR ) Very important diagram • Einstein in 1917 realized GTR predicted universes in motion, but preferred `steady state’ – added `cosmological constant’ “Average distance SIZE (CC) as repulsive force in space-time to counteract attractive between force of gravity (A fudge factor!) galaxies” • Willem de Sitter (A, Dutch, 1917) solves GTR equations with no CC and low density of matter: showed universe must measure of expand “expansion factor • Alexander Friedmann (M, Russian, 1920) solves GTR with no of Universe” CC but any density of matter: universe can expand forever, or collapse again, depending on mean matter density NOW • Georges Lemaitre (P, Belgian, 1927) rediscovers Friedmann solutions, told Hubble (observing redshifts since 1924) that Hubble constant NOW TIME cosmic expansion suggests more distant galaxies should have sets how fast greater redshifts (Hubble publishes V = H o d in 1929) universe is • Einstein visited Hubble in 1932, said CC was “the greatest expanding NOW blunder” of his career Big Bang = when distance zero The expansion rate of the universe is Since gravity is what pulls everything not necessarily constant for all time back in, there must be a magic number • GRAVITY should SLOW • Just the right amount of mass (in our current universe) to expansion rate � pull everything back together in an infinite amount of time deceleration • Just like the exact escape velocity for a rocket fired up • Different models for different amounts of dark matter • We call this exact amount of matter, the CRITICAL – Let’s ignore accelerating for DENSITY now ~10 -29 grams/cm 3 = a few atoms in a closet
Critical Universe Recollapsing Universe Flat Universe Closed Universe • Dark matter density is • Density of greater than matter = “critical density” “critical density” • Expansion will stop in the • Will expand future, will forever, but collapse back more and in more slowly – Big Crunch with time – Oscillations? Coasting Universe Three models for fates of universe Open Universe • The universe has always expanded at the same rate (no deceleration due to gravity!) • The age of the Universe = 1/H o CLOSED FLAT OPEN
Clicker Question Which model predicts the largest • C. Coasting age for the universe today? • Age of universe A. Recollapsing is how far to left curves hit (closed) horizontal axis B. Critical (distance (flat) between galaxies = 0) C. Coasting (open) Which is it? What is the fate of the Universe? Is there enough dark matter • Recollapse to gnaB giB: to recollapse the universe? – Crushing heat Baryonic matter: only a few % of critical density – Destruction of all matter – Rebirth? Dark matter: only about 25% of what is needed • Eternal expansion: • Universe should be in between the “coasting” and “critical” models – Cold, galaxies dimming – Star formation slowing The Universe will expand forever – Everything winds up as a brown dwarf, black dwarf, neutron star or black hole … and with an unexpected twist…
A New Twist for the 21 st Using supernovae to determine Century the fate of the Universe • Redshifts of the supernovae gives • Scientists using white their vertical position dwarf supernovae to – Space has measure distances stretched since discovered something they gave off their light quite strange • Apparent brightness gives their horizontal position – Dimmer=more distant = high lookback Supernovae are not consistent even with How can the universe be the expectations of a coasting universe!!! accelerating??????? A force that counteracts gravity? “Dark energy”– outweighs every other form of mass/energy! Truly an unknown force in all of physics The Cosmological Constant actually exists! Universe is accelerating?!?! (Check out “Einstein’s Greatest Blunder” p 679)
Four models for fates of universe CLOSED FLAT OPEN ACCELERATING
Recommend
More recommend
