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Exoplanets (1st session) Sohrab Rahvar physics Department, Sharif University of Technology International School for Young Astronomers Content of this lecture • • • • • • Habitable Universe. Story of Life on Earth Formation of Planets Observation of exo-planets. Intelligent Life. Light Curve (time series analysis): folding and chi-square method Fundamental Questions: - Milky Galaxy has hundred billions of stars and we have billions of galaxies in the observable Universe. - Taking into account that each star has its own planet, are there possibility for the formation of life in other parts of Universe. - Are we alone ? And are there any other intelligent life at other parts of Universe ? - Is the formation of life the fix point of chemical, physical processes in the habitable conditions ? This field (Astro-biology) is an interdisciplinary area • • • • • • Physics Astronomy Biology Organic Chemistry Advanced Technology Philosophy A Brief History of elements in the Universe 75% is Hydrogen and 25% Helium and light elements that have been synthesized in nuclear fission process during the early phases of Universe. Are we living in a fine-tuned Universe Initial condition of Universe: (1) What is the initial condition for the pre-inflationary area to have a suitable condition for a Habitable Universe (formation of planets and … life) (2) There is a Asymmetry between the matter and antimatter ( i.e. Baryons and Anti-Baryons, leptons and Anti-leptons). How big this asymmetry should be to allow the formation of planets and eventually the life ? Cosmic Initial condition for Habitable Universe, S.Rahvar (arXiv:1608.00967) Initial domains for the formation of Universes in chaotic inflationary model Evolution of Ω as a function of scale factor The essential condition to have at least formation of structures in baby phase (linear regime) • For a closed Universe e-folding > 57 (Universe should has opportunity for the formation of structures, stars … ) • For an open Universe e-folding>53 (Universe dilutes in a short time scale and prevent formation of structures. Ref: 1608.00967 (S. Rahvar) Asymmetry between matter and Antimatter Interaction between the matter and antimatter The amount of Asymmetry depends on the chemical potential of particles. Formation of Baryonic structures in the gravitational potential of dark halo Gravitational potential of dark matter heat and condense baryonic matter. Baryonic matter start cooling by radiating and if the radiation becomes efficient, matter cools and condense at the center gravitational potential. Here are the cooling condition Having asymmetry less than four orders of magnitude compare to the present value, no star, planet is formed. Having higher asymmetry turns all matter to continue the nuclear reaction to Iron and no hydrogen will be left for the stars. Metal synthesis inside stars Proton-proton chain reaction In the heaver stars CNO reaction 4H ® He 3He ® C C + He ® O Carbon-Nitrogen and Oxygen contribute in this reaction Element synthesis CHNOPS: Essential elements for life Carbon is the backbone of organic molecules. Carbon can make complex molecules with the contribution of 6 chnops atoms. تنها کربن و در شرایط خاص سیلیس می تواند ملکولهای پیچیده ایجاد کند. Organic molecules in the interstellar medium Aim of biologist is Explaining how form initial building blocks of life, first cells eventually emerged ! Astrobiology lecture note: S.R, Sharif Univ. 2016 Formation of proto-planetary disk: collapsing cloud with an angular momentum produces a disk with the central part that produces star. Mass in solar system Overall mass of planets ~ 450 Earth mass Overall mass of metals ~ 50 Earth mass metals compose 1/100 of interstellar medium. So the mass of proto-planetary disk should be ~ 5000 Earth mass or at least 0.01 solar mass if condensation efficiency is 100 percent. Disk might be much lighter than star. Analytical approach for collapsing a proto-star & proto-planetary disk • Starting with the definition of moment of Inertia and time derivation. I = å mi ri 2 i • Time derivation results distribution of particles in phase space. • Second order derivative: • For stationary system the left-hand side is zero and we will have a stationary condition. • For the case of system collapse until we get equilibrium. Collapse of cloud in transparent and opaque medium. Let us start a cloud with the condition of . Cloud will collapse and if it is adiabatic then DK = -DU. In the new stage: and we may have and collapse stop. In order that collapse continues until the star forms, we need energy transport from cloud by radiation to outside. Jeans mass • Thermal energy as the kinetic energy of cloud 2K = 3kTM J m • Gravitational Potential energy: 3 GM J2 U =5 R Exercise (A) : Using virial theorem show: M = 5.1´10-13 T 3 J m 3r For typical interstellar medium with 10 Kelvin temperature and density of 10-21 g / cm,3 Jeans mass is 30M sun . Increasing the density makes mass smaller. Exercise (B): Show that typical time scale of collapsing cloud is about 2 million years. Angular momentum conservation in protoplanetary disk Taking into account the angular momentum of a cloud, if all the angular momentum is transformed to sun it should rotate with the period of 3 seconds. In fact sun has less than one percent of angular momentum of solar-system. Question: How central star lost Its specific angular momentum ? Proto-planetary disk. ALMA observation Jet in proto-planetary disk A Simple Model for Disk Our aim is to know the pressure of gas as a function of temperature in disk. This information provides us the condition for different materials in the disk to condense. Let us smearing out planets mass in solar system, we can n get obtain a column density of: ærö S(r) = S0 ç ÷ è r0 ø From the best fit: (-1.5, 0.01) & (-1.5, 0.02)& (-1.0, 0.1)& S =1700g / cm2 0 Rocky planet formation Gas Giant formations Asteroids transport ice to the surface of Earth Origin of Life Definition of life 1. Decrease the local Entropy, Using free energy, Self-organized system. 2- Growing 3- Data Storage (Genes) and evolution. 4- Self-Production amino acids: Building blocks of life. Where they produced ? Miller- Urey Experiment Lipids as the isolator of cell from the environment. Basic Structure of Cells و نیاز به یک سیال به عنوان حالل مواد شیمیایی و حامل Evolution of Genes … Darwin’s Theory (natural Selection) Living organisms on Earth Fight/struggle for: 1- Existence (food, light, territory, shelter …) 2- Sucsseful Reproduction Astrobiology lecture note: S.R, Sharif Univ. 2016 Evolution to Eukaryotes • A DNA is formed inside the membrane • Membrane is flexible and can swallow materials and digest them • Some of materials like Mitochondrions and Chloroplast trapped in the cell and stay with cell. Oxygen abundance The effect of Oxygen on Biosphere • • • • Oxidizing Fe on the surface of Earth Oxygen is toxic element and damage cells Oxygen inspiration is developed in Eukaryotes Oxygen combined with the methane decreases the greenhouse gas in the atmosphere and result is lower temperature of the Earth. Growth of Genes Before starting photosynthesis, The growth of number of genes was high where cells to find more food. After this point the rate of Complication slowed down. After Sexual production and Multicelluarity, the number of genes accelerate up the the present human. Advance organisms stared 570 million years ago. Harsh conditions for life Studying Harsh condition for life of bacteria reveals that they live in the range 100 degree and up to 100 atmosphere presure . Habitable parts of Galaxy Habitable parts around stars Which star is suitable for life • O-type stars have very short life time. Habitable zone: 450-900 AU • M-type stars, we have tidal lock. Habitable zone: 0.07-0.15 AU • The best is G-type star, long life stars with no tidal lock planets at habitable zone. Tidal Interaction of star with planet Moon keeps angular momentum of Earth Stable Statistics of Habitable planets orbiting G-type stars 22 % of Solar-type stars have Earth like planets. Considering the number of G-type Stars, they are few Billion habitable planet in Milky Way (PNAS 2013) Next Session Observation of Extra solar planets and searching life.