Unit 13 Homework (11)
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Polk State College *
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Course
1002
Subject
Astronomy
Date
Dec 6, 2023
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1.
Describe the differences between the main regions of the galaxy by describing the
following characteristics of the listed areas: the age of stars in the region, the amount of
gas and dust in the region, the amount of star formation in the region, and the orientation
of orbits in the region.
a) the galactic halo: The halo contains no gas or dust. Stars appear redder than the stars in the
disk. Is the oldest part of our galaxy, spherical and consist of primarily old stars formed long ago.
Stars in the halo orbit the galactic center. The absence of gas and dust means that no new stars
are forming there.
b) the galactic bulge: Gas and dust in common in the bulge and the disk. Stars in the bulge are
distinctly redder than those in the disk. Contains both young and old stars. Is it not flattened as
the disk but flatter than the halo. The gas density is very high in the inner part of the bulge
making this region the site of vigorous ongoing star formation.
c) the galactic disk: An immense, circular, flattened region containing most of our galaxy’s
luminous star and interstellar matter. The disk appears as a band of light, the center of the disk
lies in the direction of the constellation Sagittarius. The disk has young stars, gas, and dust that
cuts through the center od the halo. It is the site of ongoing star formation.
2.
Identify one particular type of celestial object that is unique to each of the following
regions of the galaxy, and give a brief description of the object.
a) the galactic halo: Stars are less abundant in heavy elements.
b) the core of the galactic bulge: High density gas, star formation
c) the galactic disk: Bright, blue stars.
3.
Explain how variable stars allow us to measure very long distances.
Knowing the luminosity, astronomers apply the inverse-square law to find the distance. The brightest
Cepheids can be seen at distances of millions of parsecs, extending the cosmic ladder well beyond our
own galaxy. RR Lryae stars lies far from the sun, close to the galactic center.
4.
Explain briefly why spiral arms are places of active star formation.
Galactic gas slows down and becomes denser as it passes through a spiral density wave, new stars are
formed because of the spiral waves passage through the spiral arm. Galactic material catches up with the
wav, is temporarily slowed down and compressed by the gravitational pull as it passes through, as it
enters the arms from behind the gas is compressed and form stars.
5.
Why is it much easier to study the center of the galaxy with radio waves than with
visible light?
Just as there's a limit to what we can see with our naked eyes, there's a limit to how much of the Milky
Way galaxy we can see using the visible light wavelength of the electromagnetic spectrum. Visible light
can't penetrate the dense accumulation of stars and gas that is found in the centre of the Milky Way—
the Galactic Bulge—so to investigate the galaxy's deep structure, we need to use measurements of
multiple different wavelengths of radiation within the electromagnetic spectrum.
6.
Briefly describe how our galaxy formed. How does this model explain two differences
between disk and halo stars?
It starts from an extended cloud of pergalactic gas. The first glactic stars and global clusters was spread
out over an irregular region of space spanning many tens of kiloparsecs. The distribution today (galactic
halo) reflects that fact, imprint of their birth. The first stars in smaller systems merged to create our
Galaxy. Many stars were born during this merger as interstellar gas clouds collided and collapsed. The
galactic halo is ancient with no new star formation as the disk is full of youthful activity.
7.
Describe two observed features of the galactic core that lead astronomers to believe that
there is a supermassive black hole in the center of our galaxy.
The observed activity of the black hole in the center of our galaxy is thought to be powered by the
accretion onto the black hole, as well as by supernova explosions in the cluster surrounding it.
8.
Briefly explain how observations lead astronomers to conclude that the Milky Way
galaxy is embedded in a volume filled with "dark matter"
Theory predicts that there should be more black holes than we've so far detected. Stars in the outer
regions of the Galaxy are orbiting faster than expected. Due to its large size, the light from stars on the
other side of the Milky Way has not reached us yet. Astronomers have detected neutrinos from unseen
sources
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