Astro Lab 3
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School
University of Washington *
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Course
101
Subject
Astronomy
Date
Dec 6, 2023
Type
Pages
3
Uploaded by SuperHarePerson760
Introduction
Galaxies are evolving, connected systems of billions of stars. In this activity you will investigate
how the appearance of a galaxy relates to its stellar composition. You will:
●
Classify the color, morphology, and features of a number of galaxies, and
●
Relate galaxy colors to stellar populations and star formation histories.
Your TA will present a series of galaxies to you in the planetarium. For each galaxy, record its
appearance in a table similar to the one below. Note that when we describe stars, the word “red”
is used to also include the colors orange and yellow--mostly it means "not blue". Dusty Features
are the appearance of large clouds where the light from stars is partially or fully obscured.
Spiral or
Elliptical or ?
Red
Stars?
Blue
Stars?
Dusty
Feature
s?
Spiral
Arms?
Anything
Odd?
1.
Spiral
Yes
Yes
Yes
Yes
example
galaxy
2. Elliptical
Yes
No
Yes
No
3. Elliptical
Yes
Yes
Yes
No
4. Spiral
Yes
Yes
Yes
Yes
5. Spiral
Yes
Yes
Yes
Yes
6. Elliptical
Yes
No
Yes
No
Seems
very
spread
out/dusty
7. Spiral
Yes
Yes
Yes
No
8. Spiral
Yes
Yes
Yes
Yes
9. Elliptical
Yes
Yes
Yes
No
10. Spiral
Yes
Yes
No
No
11. Elliptical
Yes
No
Yes
No
Questions
1.
Which type of galaxy is likely to contain many M-stars but few O-stars?
Elliptical is more likely to contain M-Stars over O-stars
2.
Which type of galaxies appear to have many young stars?
Spiral galaxies have more young stars
3.
Which type of galaxies are more likely to show evidence of dust?
Spiral galaxies are more likely to show evidence of dust
4.
Would you predict that a galaxy that is experiencing active star formation contains a
little or a lot of gas and dust? Do your observations, as recorded in your table,
support this assertion? Why or why not?
A galaxy experiencing active star formation is likely to contain a lot of gas and dust. In
the table the spiral galaxies contain more gas and dust than elliptical galaxies did.
5.
Do galaxies that have many young stars also contain many old stars? Do your
observations support this assertion? Why or why not?
Galaxies that have many young stars also can contain older stars. My observations do
support this assertion because within the spiral galaxies where there are the most young
stars there are still older stars in the middle that are bigger and brighter, although there
might not be as many as the young stars within those galaxies.
6.
Consider the following conversation among three students:
○
Student 1: Because there is mainly red light in this galaxy and no blue
light, I think that only small, red stars formed in this galaxy and not any
big blue ones.
○
Student 2: I disagree; it’s just that blue stars don’t last very long. I think
the blue stars that may have been there in the past have already evolved
into red giants, so the galaxy looks red due to the light from all the red
giants.
○
Student 3: I think you’re both wrong. I thought that both blue stars and
red giants live short lives, so they should both be gone. I think that all the
blue stars that formed early on have evolved into red stars that are there
now. So the galaxy appears red because it’s full of a lot of old, red stars
that used to be the blue stars.
7.
Write a response that corrects their misconceptions, and then explain why the galaxy
they are looking at looks red. Base your arguments on stellar evolution as described
in Astro 101.
Student 1 is incorrect because red stars often begin as blue stars. As they age their
surface temperature decreases and the red stars turn into blue stars. So big blue stars
could have existed in this galaxy, they most likely just aged into red stars.
Student 2 is correct because the blue supergiant stars don't last as long as smaller
stars. They are incorrect though about the red stars evolving into red giants because
according to stellar evolution, it's more likely that the stars evolved into supernovas.
Student 3 is technically right because red and blue supergiants don't live as long as
smaller red and blue stars. They are incorrect though because red giants don't live short
lives and do not start to form at the same time as blue stars.
8.
Astronomers used to think that galaxies starting off elliptical and turned into spirals
over time. Based on this lab, do you think this proposed evolutionary sequence is
correct? Explain why or why not.
This is incorrect because spiral galaxies are the ones that contain more younger stars
which wouldn't make sense if the galaxies were to start off elliptical because elliptical
galaxies often contain a higher amount of older stars than younger stars.
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