Final Exam Flashcards
What were the “computers” at the Harvard College Observatory? What did they do?
It was a team of women who worked as skilled workers to process astronomical data at the universities observatory
(studied photographic plates of stars and unveiled some of the most fundamental discoveries of the universe)
What are the seven Spectral Types? Which is hottest? Coolest?
O B A F G K M
hottest — coolest
O = hottest ; M = coolest
What spectral type is the Sun? Be able to locate the Sun’s position on an H-R Diagram
Sun spectral type = G2V (g)
In H-R diagram the sun is near the middle of the main sequence
IDENTIFY H-R DIAGRAM AND DIFFERENT STELLAR POPULATIONS AND SUN LOCATION
CHECK CAMERA ROLL
What powers the Sun?
Thermonuclear fusion (nuclear fusion)
What conditions are needed for thermonuclear fusion to take place?
- core temp: 15,000,000 K (27,000,000 Fahrenheit)
- core pressure: 3 trillion pounds
Very high temperature and pressure
When they are formed, all stars are made primarily of which two elements
Hydrogen and Helium (very hot gas)
What is a nebula
Cloud (giant molecular cloud)
What is the interstellar medium? What is it made of? What has to happen for a nebula to form a
star?
Interstellar medium (ISM): the gas and dust between the stars
MADE OF…
gas (99%): low in density, mostly hydrogen and helium 
dust: mostly carbon, oxygen, silicon
Formation: star needs to be cold in order to form
What is also formed along with a star?
Other elements?
What are the two things that all main sequence stars have in common?
Hydrostatic Equilibrium
radiation pressure and gravitational compression are equal
What does it mean to say that a star is in a state of hydrostatic equilibrium?
gravitational force is balanced; the body is neither expanding or contracting
What is nucleosynthesis
How the nucleus of an atom is formed from basic particles like protons and neutrons
If the nuclear reactions in the core of a star become hotter, what happens to the star?
The hot core pushes outer layers of star outward causing it to expand and cool transforming the start to a red giant
If the nuclear reactions in the core of a star stop, what happens to the star?
The star collapses because it no longer maintains equilibrium
Which stars age the fastest? Why?
High mass stars because their is fusion within their core (burnout faster?)
Why do main sequence M stars live so long?
Because a star with only half the mass of the sun can spend 80 billion years on the main sequence; they have not had time to evolve off it
What is a black dwarf?
A white dwarf that has cooled sufficiently and no longer emits heat or light
Describe the life cycle of a star like the Sun.
Nebula —> main sequence star —> red giant star —> planetary nebula —>white dwarf
How long total will the Sun be a main sequence star
~ 10 billion years
What percent of a star’s lifetime is spent as a main sequence star?
Roughly 90% (determined by their mass)
Over the course of its lifetime, what fusion reactions will the Sun have taking place in its core?
Why can’t these reactions continue to make heavier elements like they do in high mass
Not sure
What will be the fate of Earth when the Sun becomes a red giant star?
In a few billion years it will engulf the planet but before that earth will become uninhabitable because the sun will become hot enough to boil oceans
What is a planetary nebula? What do they have to do with planets?
giant and super giant star that is already dying; they begin life as a hotter main sequence star
What is found at the center of a planetary nebula?
The glowing leftover part of a star
Will the Sun’s spectral type change as it ages? If so, how?
Yes, it’s temperature and gravity change but they’re relatively slow
Describe white dwarf stars. What eventually happens to a white dwarf
White dwarf: earth sized, dead, dense, collapsed stellar core of an intermediate mass star
- composed of carbon ; all nuclear fusion has stopped
Eventually can become black dwarf but the universe isn’t old enough
As they cool they can crystallize (Possibly become diamonds)
What is the Chandrasekhar Limit for a white dwarf star?
Chandrasekhar Limit for a white dwarf mass is less than 1.4M ☉
Describe the life of a high mass star.
High mass stars live fast and die young
Low mass stars age slow and live long
What is the final element produced through fusion in the core of a high mass star?
Iron
What is a supernova?
Explosion of a star; largest explosion that takes place in space
What happens to produce elements heavier than iron?
Nuclear fusion stops, the core collapses (makes supernova)
How does a supernova change its surrounding interstellar medium?
The heavier elements get incorporated into the next generation of stars
What is a neutron star?
Essentially a giant atomic nucleus
-very dense -made of neutrons
What is a pulsar?
A rapidly rotating neutron star
What is the Chandrasekhar Limit for a neutron star?
1.4 M ☉
What happens to a white dwarf or neutron star if it exceeds its Chandrasekhar Limit?
It becomes a black hole
What is a black hole?
Not a hole.
it is a collapsed stellar core where the gravity is so strong that it’s escape velocity is greater than the speed of light; nothing not even light can escape
What is the minimum mass for a black hole?
3.0 M ☉
What is an event horizon? What determines the size of a black hole’s event horizon?
The event of a black hole is the boundary between it’s outside and it’s inside (things outside cannot know about things that happen inside)
Bigger mass = bigger event horizon
How does a black hole’s escape velocity differ at the Singularity vs. the at the Event Horizon vs.
outside of the black hole?
SINGULARITY: escape velocity is infinity
EVENT HORIZON: escape velocity is c (speed of light)
OUTSIDE OF BLACKHOLE: escape velocity < infinity
What is spaghettification? Why would it happen if a person (or a star) strayed too close to a
black hole?
Spaghettification: occurs near strong gravitational fields
The pull of gravity is stronger astronauts feet and it is in their head which causes the feet to have a greater acceleration which pull them apart
What are supermassive black holes & where do we find them?
Black holes where there is stuff being fed
to them with jets of high velocity gas (messy eaters)
Found at the center of all the big galaxies
Describe the Milky Way’s supermassive black hole
Called Sagittarius A
mass: 4.1million M ☉
26,000 light years away from Earth
What kind of galaxy is the Milky Way? What are the other types of galaxies?
Milky Way galaxy is a barred spiral galaxy
4 galaxies:
Barred Spiral, Spiral, Elliptical, and Irregular
CHECK PHONE FOR REFERENCE PICTURES
What part of the Milky Way are we located in?
We are near the Orion arm and the Sagittarius constellation
Describe open star clusters.
open space between clouds (further apart)
Describe globular star clusters
Like a glob of stars (closer together, bunched up)
What happens to the population of stars in a cluster as it ages? How would an H-R diagram of a
cluster change as the cluster aged?
As the cluster ages the more massive stars die or about to become giants and white dwarfs
You can tell the age of a cluster by looking the main sequence, as it leaves the older they are
Approximately how many stars are in the Milky Way? How many stars are in our Solar System?
It is estimated that there are 100 to 400 billion stars in our galaxy
How common are Earth-like planets in our galaxy?
It is estimated that there are 40 billion earth size planet inhabited zones of sunlight or red dwarf stars in our Milky Way
How do galaxies grow and evolve?
Through collisions and mergers (they don’t crash)
What is going to happen to the Milky Way Galaxy?
It will collide with the Andromeda galaxy
