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Astronomy 100 > Final Exam > Flashcards

Final Exam Flashcards

1
Q

What were the “computers” at the Harvard College Observatory? What did they do?

A

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)

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2
Q

What are the seven Spectral Types? Which is hottest? Coolest?

A

O B A F G K M
hottest — coolest
O = hottest ; M = coolest

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3
Q

What spectral type is the Sun? Be able to locate the Sun’s position on an H-R Diagram

A

Sun spectral type = G2V (g)

In H-R diagram the sun is near the middle of the main sequence

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4
Q

IDENTIFY H-R DIAGRAM AND DIFFERENT STELLAR POPULATIONS AND SUN LOCATION

A

CHECK CAMERA ROLL

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5
Q

What powers the Sun?

A

Thermonuclear fusion (nuclear fusion)

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6
Q

What conditions are needed for thermonuclear fusion to take place?

A
  • core temp: 15,000,000 K (27,000,000 Fahrenheit)
  • core pressure: 3 trillion pounds

Very high temperature and pressure

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7
Q

When they are formed, all stars are made primarily of which two elements

A

Hydrogen and Helium (very hot gas)

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8
Q

What is a nebula

A

Cloud (giant molecular cloud)

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9
Q

What is the interstellar medium? What is it made of? What has to happen for a nebula to form a
star?

A

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

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10
Q

What is also formed along with a star?

A

Other elements?

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11
Q

What are the two things that all main sequence stars have in common?

A

Hydrostatic Equilibrium

radiation pressure and gravitational compression are equal

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12
Q

What does it mean to say that a star is in a state of hydrostatic equilibrium?

A

gravitational force is balanced; the body is neither expanding or contracting

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13
Q

What is nucleosynthesis

A

How the nucleus of an atom is formed from basic particles like protons and neutrons

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14
Q

If the nuclear reactions in the core of a star become hotter, what happens to the star?

A

The hot core pushes outer layers of star outward causing it to expand and cool transforming the start to a red giant

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15
Q

If the nuclear reactions in the core of a star stop, what happens to the star?

A

The star collapses because it no longer maintains equilibrium

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16
Q

Which stars age the fastest? Why?

A

High mass stars because their is fusion within their core (burnout faster?)

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17
Q

Why do main sequence M stars live so long?

A

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

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18
Q

What is a black dwarf?

A

A white dwarf that has cooled sufficiently and no longer emits heat or light

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19
Q

Describe the life cycle of a star like the Sun.

A

Nebula —> main sequence star —> red giant star —> planetary nebula —>white dwarf

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20
Q

How long total will the Sun be a main sequence star

A

~ 10 billion years

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21
Q

What percent of a star’s lifetime is spent as a main sequence star?

A

Roughly 90% (determined by their mass)

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22
Q

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

A

Not sure

23
Q

What will be the fate of Earth when the Sun becomes a red giant star?

A

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

24
Q

What is a planetary nebula? What do they have to do with planets?

A

giant and super giant star that is already dying; they begin life as a hotter main sequence star

25
Q

What is found at the center of a planetary nebula?

A

The glowing leftover part of a star

26
Q

Will the Sun’s spectral type change as it ages? If so, how?

A

Yes, it’s temperature and gravity change but they’re relatively slow

27
Q

Describe white dwarf stars. What eventually happens to a white dwarf

A

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)

28
Q

What is the Chandrasekhar Limit for a white dwarf star?

A

Chandrasekhar Limit for a white dwarf mass is less than 1.4M ☉

29
Q

Describe the life of a high mass star.

A

High mass stars live fast and die young

Low mass stars age slow and live long

30
Q

What is the final element produced through fusion in the core of a high mass star?

A

Iron

31
Q

What is a supernova?

A

Explosion of a star; largest explosion that takes place in space

32
Q

What happens to produce elements heavier than iron?

A

Nuclear fusion stops, the core collapses (makes supernova)

33
Q

How does a supernova change its surrounding interstellar medium?

A

The heavier elements get incorporated into the next generation of stars

34
Q

What is a neutron star?

A

Essentially a giant atomic nucleus
-very dense -made of neutrons

35
Q

What is a pulsar?

A

A rapidly rotating neutron star

36
Q

What is the Chandrasekhar Limit for a neutron star?

A

1.4 M ☉

37
Q

What happens to a white dwarf or neutron star if it exceeds its Chandrasekhar Limit?

A

It becomes a black hole

38
Q

What is a black hole?

A

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

39
Q

What is the minimum mass for a black hole?

A

3.0 M ☉

40
Q

What is an event horizon? What determines the size of a black hole’s event horizon?

A

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

41
Q

How does a black hole’s escape velocity differ at the Singularity vs. the at the Event Horizon vs.
outside of the black hole?

A

SINGULARITY: escape velocity is infinity

EVENT HORIZON: escape velocity is c (speed of light)

OUTSIDE OF BLACKHOLE: escape velocity < infinity

42
Q

What is spaghettification? Why would it happen if a person (or a star) strayed too close to a
black hole?

A

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

43
Q

What are supermassive black holes & where do we find them?

A

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

44
Q

Describe the Milky Way’s supermassive black hole

A

Called Sagittarius A
mass: 4.1million M ☉
26,000 light years away from Earth

45
Q

What kind of galaxy is the Milky Way? What are the other types of galaxies?

A

Milky Way galaxy is a barred spiral galaxy

4 galaxies:
Barred Spiral, Spiral, Elliptical, and Irregular

CHECK PHONE FOR REFERENCE PICTURES

46
Q

What part of the Milky Way are we located in?

A

We are near the Orion arm and the Sagittarius constellation

47
Q

Describe open star clusters.

A

open space between clouds (further apart)

48
Q

Describe globular star clusters

A

Like a glob of stars (closer together, bunched up)

49
Q

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?

A

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

50
Q

Approximately how many stars are in the Milky Way? How many stars are in our Solar System?

A

It is estimated that there are 100 to 400 billion stars in our galaxy

51
Q

How common are Earth-like planets in our galaxy?

A

It is estimated that there are 40 billion earth size planet inhabited zones of sunlight or red dwarf stars in our Milky Way

52
Q

How do galaxies grow and evolve?

A

Through collisions and mergers (they don’t crash)

53
Q

What is going to happen to the Milky Way Galaxy?

A

It will collide with the Andromeda galaxy

Astronomy 100 (5 decks)

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