Final Exam. 12:30 2:30 pm, Friday, May 6th, in this room. Written Questions covering all the material from this semester.

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1 Final Exam 12:30 2:30 pm, Friday, May 6th, in this room. Written Questions covering all the material from this semester.

3 Dark Matter Black Holes Dark matter is noninteracting, so it has no way of losing angular momentum as it comes near a black hole. Unless a dark matter particle actually hits the hole s event horizon directly, it passes right by.

4 A Twist Turn the problem around... if there is too much dark matter in the inner vicinity of a SMBH, it would grow too quickly, and swallow its galaxy! We don t see such gigantic black holes, so Dark Matter is not super-concentrated at the centers of galaxies.

5 A Twist Turn the problem around... if there is too much dark matter in the inner vicinity of a SMBH, it would grow too quickly, and swallow its galaxy! We don t see such gigantic black holes, so Dark Matter is not super-concentrated at the centers of galaxies.

6 arxiv: v1 [astro-ph.co] 2 Feb 2010 An upper limit to the central density of dark matter haloes from consistency with the presence of massive central black holes X. Hernandez and William H. Lee Instituto de Astronomía, Universidad Nacional Autónoma de México, Apartado Postal C.P México D.F. México. Released 2007 Xxxxx XX ABSTRACT We study the growth rates of massive black holes in the centres of galaxies from accretion of dark matter from their surrounding haloes. By considering only the accretion due to dark matter particles on orbits unbound to the central black hole, we obtain a firm lower limit to the resulting accretion rate. We find that arunaway accretion regime occurs on a timescale which depends on the three characteristic parameters of the problem: the initial mass of the black hole, and the volume density and velocity dispersion of the dark matter particles in its vicinity. An analytical treatment of the accretion rate yields results implying that for the largest black hole masses inferred from QSO studies (> 10 9 M ), the runaway regime would be reached on time scales which are shorter than the lifetimes of the haloes in question for central dark matter densities in excess of 250M pc 3. Since reaching runaway accretion would strongly distort the host dark matter halo, the inferences of QSO black holes in this mass range lead to an upper limit on the central dark matter densities of their host haloes of ρ 0 < 250M pc 3. This limit scales inversely with the assumed central black hole mass. However, thinking of dark matter profiles as universal across galactic populations, as cosmological studies imply, we obtain a firm upper limit for the central density of dark matter in such structures. Key words: galaxies: haloes galaxies: evolution dark matter gravitation accretion 1 INTRODUCTION The question of what is the central density profile of galactic dark matter haloes has been much debated in the literature over many years. Since the work of Navarro et. al (1997), cosmological N-body simulations have consistently agreed in onic component, a function of the assumed mass to light ratio, the relevance of observational uncertainties such as beam smearing, and the importance of non circular motions and non centrifugal support of asymmetric drift and hydrodynamic pressure terms (e.g. Valenzuela et al. 2007).

arxiv:1002.0553v1 [astro-ph.co] 2 Feb 2010 An upper limit to the central density of dark matter haloes from consistency with the presence of massive central black holes X. Hernandez and William H.

7 arxiv: v1 [astro-ph.co] 2 Feb 2010 An upper limit to the central density of dark matter haloes from consistency with the presence of massive central black holes X. Hernandez and William H. Lee Instituto de Astronomía, Universidad Nacional Autónoma de México, Apartado Postal C.P México D.F. México. Given Released 2007 Xxxxx XX the existence of event horizons associated ABSTRACT to black holes, and the We study the growth rates of massive black holes in the centres of galaxies from accretion of dark matter from their surrounding haloes. By considering only the accretion due to dark matter particles on orbits unbound to the central black hole, we obtain a firm lower limit to the resulting accretion rate. We find that arunaway accretion regime occurs on a timescale which depends on the three characteristic parameters of the problem: the initial mass of the black hole, and the volume density and velocity dispersion of the dark matter particles in its vicinity. An analytical treatment of the accretion rate yields results implying that for the largest black hole masses inferred from QSO studies (> 10 9 M ), the runaway regime would be reached on time scales which are shorter than the lifetimes of the haloes in question for central dark matter densities in excess of 250M pc 3. Since reaching runaway accretion would strongly distort the host dark matter halo, the inferences of QSO black holes in this mass range lead to an upper limit on the central dark matter densities of their host haloes matter of ρ 0 < 250M pc 3 particles.. This limit scales inversely with the assumed central black hole mass. However, thinking of dark matter profiles as universal across galactic populations, as cosmological studies imply, we obtain a firm upper limit for the central density of dark matter in such structures. assumption of standard cold dark matter subject only to gravitational interactions, it follows that central black holes have grown over the history of galactic dark haloes, through the capture of dark Key words: galaxies: haloes galaxies: evolution dark matter gravitation accretion 1 INTRODUCTION The question of what is the central density profile of galactic dark matter haloes has been much debated in the literature over many years. Since the work of Navarro et. al (1997), cosmological N-body simulations have consistently agreed in onic component, a function of the assumed mass to light ratio, the relevance of observational uncertainties such as beam smearing, and the importance of non circular motions and non centrifugal support of asymmetric drift and hydrodynamic pressure terms (e.g. Valenzuela et al. 2007).

9 Are We Alone? The Search for Intelligent Life

10 Look and See Searches for signs of intelligence using electromagnetic radiation: Radio waves (continuous signals, information encoded). Optical light flashes. X-rays or gamma rays.? Search for Extra- Terrestrial Intelligence = SETI

11 Optical SETI Looking for pules arriving within a billionth of a second. Aimed at known star systems and clusters. Nothing yet!

12 SETI Institute/ Project Phoenix 1,000 3,000 MHz search band, 1 Mhz at a time! 28 million channel Phoenix receiver can accumulate radio energy for minutes Sensitive targeted searches, aimed at nearby stars

13 ATA The Allen Telescope Array, funded by Microsoft Exec s Paul Allen and Nathan Myhrvold. Was to have 350 telescopes in a large array.

15 Of all the Frequencies

16 Types of Signals Deliberate: Sent on purpose, like a message in a bottle. Accidental: Used for other purposed by a civilization, leaking signals in to space.

17 Wow! Signal Strong signal at the Big Ear Radio Telescope (Ohio State) at 1420MHz: the exact frequency of atomic Hydrogen! In the constellation sagittarius, it lasted the full 72s it could be observed. Not detected again.

18 SETI/SERENDIP Piggy back on existing telescopes, like Arecibo on Puerto Rico. Most recent probes 128 million different frequencies at once

SETI@Home SETI Produces 100GBytes/Day: too much to analyze without help.

19 SETI Produces 100GBytes/Day: too much to analyze without help. Solution: Break it into small pieces and hand them out to volunteers running a custom piece of software at home. Released in 1999; over 5 million participants. 2 million years of computing time logged!

20 Outgoing Call What would a message look like? We have only (deliberately) sent a single message. In 1974 a digital signal composed of 73 lines x dots per line was beamed at the star cluster M13. It will take 25,000 years to get there.

21 Outgoing Call What would a message look like? We have only (deliberately) sent a single message. In 1974 a digital signal composed of 73 lines x dots per line was beamed at the star cluster M13. It will take 25,000 years to get there.

What about TV + Radio? Since about 1940.

23 What about TV + Radio? Since about Problem: even with our best technology, we d have difficult detecting Earth s radio broadcasts past 1 light year! Also: Tending away from easilydiscernible over-theair broadcasting

24 Drake Equation How can we estimate the number of intelligent, detectable civilizations there are in the Galaxy? Frank Drake, who undertook the first attempt to find extraterrestrial civilizations in 1960, decided to find out... By multiplying together all the parameters of our ignorance!

26 Examples Original numbers proposed by Drake: R = 10 new stars/year are born in the Galaxy fp = 1/2 of which form planets ne = 2.0 habitable planets per star fl = 100% of habitable planets have life emerge fi = 1% of such planets evolve intelligence fc = 1% of those are capable of interstellar communication L = 10,000 years such a civilization remains detectable Answer: N=10 broadcasting civilizations in the galaxy at a given time!

27 Distances N=10 THIS IS US N=50 THIS IS US

28 The Drake Equation

29 CLosing in on an estimate We know fairly well R, fp: about 4 planetary systems come into existence each year in our Galaxy. Closing in on ne: probably not too close to 0.0! The rest of the parameters are pure guesswork!

30 Parameter Optimistic Pessimistic Compromise R (per yr) fp ne fl fi fc Rate/yr Time between 2.8 months! 50 million years! 29.6 L (yrs) 10 billion ,000 Total 43 billion ,375 Nearest (LY) million 561

31 Where we ve looked

32 Fermi s paradox If extraterrestrial life is common, where is everyone? If even a single life form developed space travel and began colonizing, or sending self-replicating probes out at reasonable speeds (say 0.1c). Within a few to 100 million years or so, the entire Galaxy is colonized!

33 silentium universi

35 Evidence The median earth-like planet is probably around 2 billion years older than earth... there as been plenty of time for them to get here. There has been no convincing evidence of extra-terrestrial visitation. No alien spacecraft, no probes, no artifacts of any kind!

Explanations There are no, and have never been any space-faring civilizations in the galaxy. Thought experiment: Lemmings multiply fast: 3 litters of 8 offspring per year. In 6.

36 Explanations There are no, and have never been any space-faring civilizations in the galaxy. Thought experiment: Lemmings multiply fast: 3 litters of 8 offspring per year. In 6.3 years (18 generations), a single lemming couple could parent offspring. They would cover the entire Earth s surface. You ve never seen a lemming, therefore they do not exist.

37 Rare Intelligent Life Many reasons possible: Life forms very rarely from unusual combinations that almost never occur. Intelligence rarely develops. Intelligent species may never have the need or interest in developing technology substantially. They may communicate using entirely different methods! Language could be unique to humans.

38 Better Explanations They are here. but are hiding. Problem: No reason for them (or us) to hide the evidence! They are us. We descend from ancient alien civilizations. Problem: What about all the other ancient alien civilizations? Gamma-Ray Bursts sterilize a large swath of the Galaxy on regular intervals. They re trying to contact us, but we don t know how to answer. Problem: at least some civilization should be using normal EM methods. They are not interested in colonizing or communicating.

39 The worst Explanation They are all dead: Civilizations like our own, and even far more advanced, develop frequently... but the lifetime of these advanced civilizations is characteristically short.

40 The worst Explanation They are all dead: Civilizations like our own, and even far more advanced, develop frequently... but the lifetime of these advanced civilizations is characteristically short.

41 A Final Note Every year, we learn more about the universe, how it was assembled, its ultimate fate, and the meager part played by Earth and Human Kind Whether or not we are alone in the universe, this yearning for knowledge about our origins is the true hallmark of an intelligent species! It was wonderful having you in class! Good Luck!

42 Assignment Watch The Eerie Silence: Are We Alone in the Universe? Royal Society

Lecture 40: SETI. Astronomy Winter This lecture is about SETI, the Search for Extra- Terrestrial Intelligence.

Lecture 40: SETI. Astronomy Winter This lecture is about SETI, the Search for Extra- Terrestrial Intelligence. Lecture 40 SETI: The Search for Extraterrestrial Intelligence Astronomy 141 Winter 2012 This lecture is about SETI, the Search for Extra- Terrestrial Intelligence. Searching for artificial radio signals