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Midterm

Midterm 2 Review Questions with Answers


Department
Astronomy & Astrophysics
Course Code
AST201H1
Professor
Stefan Mochnacki
Study Guide
Midterm

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Earths orbit will remain the same and the sun will just be a black hole. The force of gravity
depends on mass involved. The only way earth would getsucked” in is if the gravitational
force was changed (by the change in masses) but since the mass stays the same, the force of
gravi ty also remains the same between earth and black hole.
Death of the sun – low-mass star
-runs out of hydrogen to fuse in core (core= helium ash) so core cools and contracts, releasing
energy (sub-giant branch) while the hydrogen-shell bur ning produces enough energy (ra te of
bur ning increases) to expand the outer layers lowering the sur face temperature from yellow to
red (red giant!)
-suddenly helium will start to fuse (Helium f lash) as its hotter and fusion will continue until
helium in the core runs out leaving carbon ash (moves to the horizontal branch). Carbon cant
produce much energy so it cools and contracts (the core)
-electron degeneracy pressure, however, stops further contraction- law of physics
-however, the helium-shell burning creates enough energy to blow outer layers off as
planetary nebula, leaving a white dwarf
White dwarf because it is a low mass star (<8Msun) and it’ll blow up a planetary nebula as
well
The Monster” is in the centre of the galaxy- Milky Way. We cant see the centre (visible light
is blocked by dust) but x-rays, radio and infrared can. It was observed to have swirling gas
near the centre and stars orbiting a common centre of mass. The stars are also in nice ellipses
so that must mean that the object must be small (less than 1AU) and has a mass of around
4million Msun: indicating that theres a supermassive black hole in the centre of the galaxy.
Neutron star is what could remain after a high-mass star hits supernova (could just leave
nothing or a black hole). All pulsars are neutron stars but not all neutron stars are pulsars as it
depends on where the neutron star is situated in relation to our perspective. Pulsars (usually
radio waves) are beams of light from the hot spots of neutron stars that sweep across its path.
Since neutron stars very dense and small it spins very fast (up to 30 times a second)-
conservation of angular momentum. Pulsars are created by intense magnetic fields held by
neutron stars (2 beams of light). They arent aligned with the spinning axis.
Luminosity classes are measures of stars’ luminosities as determined from the width of stars
spectrums. It also indicates the stage of life of a star.
stars that have low-density, low-pressure atmospheres: narrow, faint absor ption lines:
supergiant
stars that have high-density, high-pressure atmospheres: dark, wise absorption lines: main
sequence stars
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