Download Lecture 1: Astrophysics

Lecture 1: Astrophysics
Senior Astrophysics
2017-03-07
Senior Astrophysics
Lecture 1: Astrophysics
2017-03-07
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Outline
1
Introduction
2
What is astrophysics?
3
Website of the Week
4
Radiation
5
Next lecture
Senior Astrophysics
Lecture 1: Astrophysics
2017-03-07
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Course structure
18 sessions — last lectre ADV only
14 lectures + 4 computational labs
From week 2, Friday 12pm lectures will be in SNH Learning Studio 4003
Need to remember your Matlab!
Extra lab session on Wednesdays at 10 am; SNH Learning Studio. Only
need to attend one per week.
Also: plan to spend 10 minutes each week telling you about important
web research tools in astronomy: Website of the Week [WOTW]
Will be the basis for at least one assignment question, so pay attention!
Lecture 1: Astrophysics
Introduction
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Timetable
Week
week 1
week 2
week 3
week 4
week 5
week 6
week 7
week 8
Date
7 Mar
8 Mar
10 Mar
14 Mar
15 Mar
17 Mar
21 Mar
22 Mar
24 Mar
28 Mar
29 Mar
31 Mar
4 Apr
5 Apr
7 Apr
11 Apr
12 Apr
Day
Tue 1pm
Wed 9am
Fri 12pm
Tue 1pm
Wed 9am
Fri 12pm/Wed
Tue 1pm
Wed 9am
Fri 12pm/Wed
Tue 1pm
Wed 9am
Fri 12pm/Wed
Tue 1pm
Wed 9am
Fri 12pm/Wed
Tue 1pm
Wed 9am
26 Apr
1 May
Wed 9am
Mon 5pm
Lecture 1: Astrophysics
10am
10am
10am
10am
Topic
Lecture 1
Introduction
Lecture 2
Radiation processes
Lecture 3
Emission and absorption
Lecture 4
Sources of radiation
Lecture 5
Stellar structure
Lab 1
Lab 1: Line formation
Lecture 6
The main sequence
Lecture 7
Stellar evolution 1
Lab 2
Lab 2: Stellar evolution 1
Lecture 8
Stellar evolution 2
Lecture 9
Supernovae
Lab 3
Lab 3: Stellar evolution 2
Lecture 10
Stellar remnants
Lecture 11
Binary stars
Lab 4
Lab 4: Roche lobes
Lecture 12
Accretion energy
Lecture 13
Binary evolution
Mid-semester break
Lecture 14
ADV-only lecture
Assignment 1 due
Assignment 2 due
Introduction
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Assignments
All assignments will be submitted through Turnitin.
Either typeset (LATEX/Word etc.) or handwritten is acceptable
BUT quality must be legible (no unreadable photos from your phone!)
No more coversheets. Deadline is 11:59 pm on the due date.
Lecture 1: Astrophysics
Introduction
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Course outline
Radiation — lectures 1–4 + lab 1
How is radiation produced? How is it affected as it propagates?
Stellar structure and evolution — lectures 5–10 + labs 2 & 3
Modelling stars; the evolution of stars; stellar remnants
Binary stars – lectures 11–13 + lab 4
Binary stars; evolution of binaries; applications in modern astronomy
Final lecture (lecture 14): Adv-only: Problems in binary evolution
(examinable)
Lecture 1: Astrophysics
Introduction
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Textbooks
No required text.
Highly recommended:
Carroll & Ostlie, An Introduction to Modern Astrophysics
Hilditch, An introduction to close binary stars
Both on closed reserve in SciTech library.
Lecture 1: Astrophysics
Introduction
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Astrophysics
Astrophysics is a big subject.
Sometimes will just flag where a whole (possibly large!) field branches
off, e.g. won’t talk about how stars form
Sometimes will give qualitative description (with lots of pretty pictures);
unless I say otherwise, this is non-examinable
A few topics are amenable to analysis at our level in time available. I
will walk through these in class, and these will most naturally be the
subject of assignments and exams.
Lecture 1: Astrophysics
Introduction
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What is astrophysics?
Application of laws of physics to
understand the behaviour of astronomical objects
predict new phenomena that could be observed
Physics used can include electromagnetism, fluid mechanics, plasma physics,
general relativity, nuclear physics, and more.
Lecture 1: Astrophysics
What is astrophysics?
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What is astrophysics?
Main difference between astrophysics and other branches of physics:
controlled experiments are (almost) never possible!
Observational science: only information we have is via study of EM
radiation from objects (and, very recently, high energy particles)
Lecture 1: Astrophysics
What is astrophysics?
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What is astrophysics?
Consequences:
complex systems: can’t change variables separately to isolate their
effects, e.g. galaxies
timescales: often human lifetimes, so can’t follow many processes all
the way, e.g. stellar evolution
rare events: knowledge is limited, and will usually not occur nearby;
e.g. SNe
best way to add knowledge is to use new wavelength domains, e.g.
radio, X-ray
statistical arguments vital! more so than in many areas of lab physics,
e.g. γ -ray bursts
Lecture 1: Astrophysics
What is astrophysics?
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Physical conditions
Physical conditions we are studying are very diverse:
temperature:
T
3K
<
(CMB)
<
1012 K
gas near BH
density
10−20 kg/m3
(ISM)
<
ρ < 1018 kg/m3
(neutron star)
speeds:
v ∼ 0.99c in jets from BH
Lecture 1: Astrophysics
What is astrophysics?
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Units
Astronomers use many non-SI units. Partly historical, like magnitudes,
but we’ll try to avoid those in this course.
Other main problem is scale of astronomy: inconvenient orders of
magnitude involved with using SI units.
Principal ones we will worry about:
distance:
parsec (pc); 1 pc = 3.26 ly = 3.086 × 1016 m
Nearest star is 1.3 pc away
solar radius: 1R = 6.955 × 108 m
mass:
solar mass: 1M = 1.989 × 1030 kg
luminosity (energy/unit time)
solar luminosity: 1 L = 3.839 × 1026 W
Lecture 1: Astrophysics
What is astrophysics?
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Website of the Week:
APOD: Astronomy Picture of the Day
http://apod.nasa.gov/apod/
Annotated daily astronomical image
Lecture 1: Astrophysics
Website of the Week
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Part 1: Radiation
The physics of radiation (4 lectures + 1 lab)
1
2
How is radiation affected as it propagates to the observer?
Mechanisms that produce radiation
Blackbody radiation
Transitions within atoms
3
Use results to understand spectra of stars, nebulae
Lecture 1: Astrophysics
Radiation
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Radiation
Because all of astronomy is dependent on electromagnetic radiation, we need
to understand radiation itself: how it is produced, how it propagates, and
how it is affected as it propagates.
Lecture 1: Astrophysics
Radiation
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Interstellar gas
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Radiation
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Photons escaping star
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Radiation
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Basic properties of radiation
EM radiation: frequency ν , wavelength λ
λν = c
Individual photons have energy
E = hν
where h = Planck’s constant
Common to measure energies in eV, where
1 eV = 1.602 × 10−19 J
(energy of visible light photon ∼ few eV)
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Radiation
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Basic properties of radiation
Simplification: astronomical objects are normally much larger than λ, so
neglect diffraction
light travels along straight lines
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Radiation
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Need to be careful about direction of photon travel:
Far from source (e.g. light from distant star) can assume radiation is
travelling radially
But e.g. inside a star, photons move in many different directions, so have
to worry about angles and how much radiation is moving in each
direction
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Radiation
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Flux and luminosity
Define the radiant flux F from a source as the total amount of light
energy (of all wavelengths) that crosses a (perpendicular) unit area per
unit time
dE = F dA dt
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Radiation
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Flux and luminosity
For a spherically symmetric steady source with luminosity L (= total
amount of energy emitted per unit time): energy conservation means
L
4πr2
inverse square law: measured flux drops off as
square of distance
F (r) =
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Radiation
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Flux and luminosity
L is total luminosity emitted at all wavelengths, so F is also integrated
over all wavelengths.
In practice, often measure only part of spectrum, so need to consider
how radiation is distributed over frequency
Z
F = Fν (ν)dν
total energy flux = integral of Fν over all frequencies
Then
dE = Fν dA dt dν
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Radiation
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For astronomers only
Units of Fν are (energy)/(time) per area per frequency bin so W m−2
Hz−1
Special unit: 1 Jy = 10−26 W m−2 Hz−1
Fν called “flux density” — in order to get power received, need to
multiply by the area and by the bandwidth
Lecture 1: Astrophysics
Radiation
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Next lecture
Radiation processes
Intensity and brightness
Emission
Absorption
Lecture 1: Astrophysics
Next lecture
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