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Transcript
Activity 1 - Mathematical and Scientific Methods
Whereas
•
mathematics is the language of the Universe,
•
and is our “tool” for understanding the birth, life, death,
contents, events, everything about the Universe,
•
and your instructor & TAs want each student to have
command of these tools so that learning the astronomy
concepts becomes the ultimate goal,
•
we continue to search for a reasonable way for all to
master the mathematical basics of astronomy!
Have 11 scored participation
activities. Lowest 4 scores to
be dropped. Math review
counts as 2.
50 pts
10 quizzes; one with
lowest score will be
dropped.
65% of your grade will
come from active
involvement!
3
This is as far as we got on Monday, November 14.
Learning Goals: Be able to ….
! Explain why the much higher mass of some stars
causes their evolution to be so different from the Sun.
Masses have more mass and therefore more gravity
pushing down on the core.
Luminosity is greater, lifetime is shorter.
Core doesn’t go degenerate because next fusion cycle
sets in when pressures and temperatures reach high
enough level.
Learning Goals: Be able to ….
!Outline the basic stages of the evolution of a
massive star
Main sequence star - H fused He primarily CNO cycle
Core out of H, He to C fusion sets in
Once core ran of He, core contracted, heated up, gave
off heat, started shell fusion
C -> O fusion
etc. No degeneracy of the core.
until an iron core is reached.
No outward pressure provided
Core collapses
Supernova occurs
7
Supernovae
Neutron Stars
Pulsars (aka beaming neutron stars)
Fusion to iron marks irreversible doom for the once glorious star
10
11
M ~ 0.000003 Msun
R ~ 6500 km
Vesc ~ 0.00004 c
M ~ 1.5 Msun
R ~ 10 km
Vesc ~ 0.7c
13
☞
http://chandra.harvard.edu/photo/1999/0052/ (above series of images)
http://vimeo.com/71117055 (expansion of nebula at visible wavelengths from 1999 - 2012
Former core of a massive
star, called a neutron star.
Neutron degeneracy.
Neutron stars eventually
spin more and more slowly.
Stays a ball of neutrons.
Conservation of angular momentum means these creatures spin extremely
fast! Millisecond pulsars (1000 times per second)
http://www.jb.man.ac.uk/~pulsar/Education/Sounds/sounds.html
17
http://www.nasa.gov/centers/goddard/news/topstory/2003/0702pulsarspeed.html
18
http://www.noao.edu/image_gallery/images/d5/03036y.jpg
☞
http://www.parkes.atnf.csiro.au/people/sar049/eternal_life/supernova/pulsars.html
Activity 22: Post-Activity Quiz
(Got this far on Wednesday.)
http://hubblesite.org/newscenter/archive/releases/1996/22/video/a/
☞
http://youtu.be/VTVg6L0oz7E
Neutron Stars and Pulsars
All pulsars are neutron stars, but not all neutron stars are pulsars.
1. Theoretically, what is a pulsar?
A rapidly spinning neutron star beaming synchrotron radiation towards Earth.
2. Observationally, what is a pulsar?
An object whose radiation varies extremely rapidly.
3. What are the characteristics of a neutron star ?
Extremely dense, R~10 km, supported by neutron degeneracy
4. How do we know these objects aren’t just white dwarfs?
Material would be flying away due to insufficient centripetal force.
25