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Midterm 2 Review Questions with Answers

Astronomy & Astrophysics
Course Code
Stefan Mochnacki
Study Guide

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Type 1 supernovae (white dwarf supernovae) tend to dim faster (first few weeks) and the
luminosities decrease more gradually. Hydrogen isnt present in the spectral lines of white
dwarf supernovae while type 2 should have several hydrogen spectral lines since it high mass
stars have more hydrogen in its outer layers. Type 2 is also most often observed in elliptical
galaxies while type 1 is most often observed in spiral galaxies. Type 1 supernovae usually
dont leave behind a remnant while type 2 supernovae usually leaves either nothing, a neutron
star or a black hole.
Supernova type 1: white dwarf binary star system- engulfing chemicals/gas released by
binary star and since the mass > 1.4Msun it cant be supported by the electron degeneracy
Supernova type 2: core collapse of a high-mass star-once iron is reached in the core, no
pressure so it contracts and cools (gravity wins over pressure), overcomes electron degeneracy
pressure (electron capture e+p neutrons and neutrinos). Meanwhile, the outer layers of the
star is rushing at 20% speed of light and hits a stationary ball of neutrons supernovae
Star-gas-star cycle is the ongoing galactic recycling of remnant materials. Chemicals released
from supernovae (high-mass stars) or stellar wind created bubbles of hot gas blown from
high-mass stars, stellar winds from low-mass stars around the stage of red giant/giants or
planetary nebula before it turns into a white dwarf, are where most of the recycling occurs.
As one star dies, it releases the remnants and gas/dust particles of the star and it gets enriched
with other elements to form heavier elements.
Large spiral galaxies have spiral arms, a disk, central bulge and a halo (with globular
clusters). It contains an ISM with a lot of dust and gas, especially within the spiral arms. The
disk stars orbit in the same plane, same direction with slight up and down movements and
most of them are young so disk appears bluer (100 000ly across, 1000ly thick). Central
bulge/halo stars orbit with random orientations and most of the stars in the bulge and halo are
old stars (6500ly).
Answered in #35
Elliptical galaxies are spherical and follow more traits of the disk in spiral galaxies. The stars
are mostly red so it appears red (“dead for forming new stars- minimum amounts of gas or
dust, star orbits are random, elongated and closet to the centre) and has up to 1 trillion old
Irregular galaxies are usually full of young stars, dust and gas and have no defined shape.
They tend to be small (20 000ly in diameter- average) and it has more in common with disk
aspect of spiral galaxies
The temperature of the star (blackbodies)- or the Doppler shifts of a rotating star could also
be presented as the colour of a star
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