Download File1 - School of Astronomy, IPM

Exoplanets (1st session)
Sohrab Rahvar
physics Department, Sharif University of Technology
International School for Young Astronomers
Content of this lecture
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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
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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
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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.