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Astro 150 Exam 2

Terms in this set (15)

What process causes protostars to shine?
The release of gravitational energy as the gas collapses inward
One of the H absorption lines in stars is the H𝜶 line with a rest wavelength of 656.3 nm. If you observe a star and observe its H𝜶 line at 656.5 nm.
a. Is it blue shifted or red shifted?

b. Is it coming towards you or away from you?

c. Can you tell how the star is moving in the plane of the sky?
a. Redshifted because the observed is larger than the rest

b. Redshifted means the star is moving away from you

c. No, you cannot tell because only radial motion is measured by light shift
What do stars with mass < 8 solar masses turn into at the end of their lives?
White dwarfs with the lost mass as planetary nebula
What do stars w mass > 25 solar masses turn into at the end of their lives?
Black holes with some mass blown away as a supernova
What is it about black holes that makes them black?
The escape velocity exceeds that of light. The light gets turned around before escaping due to the high gravity
Briefly explain how stars form.
1. Something disturbs the large cloud of mostly gas
2. Parts of the cloud fragment as it collapses producing multiple collapsing regions, each of which become a star
3. The highest density regions of the cloud collapse under their own gravity. They release heat as they collapse, but this heat is not enough to stop the collapse.
4. Eventually, the contraction is slowed down by this release of heat, but the contraction isn't halted completely.
5. Some of the collapsing cloud begins spinning up due to conservation of angular momentum.
6. This part separates itself from the forming star and forms a proto stellar disk
7. The protostar then receives some of the material from the proto stellar disk as the disk material moves inward.
8. Eventually, the protostar is hot enough for nuclear fusion of H into He to ignite in the core, at which point it is on the main sequence
What is the most common type of planet in the Galaxy, but that does not exist in our Solar System?
Planets of size between Neptune and Earth - called supes Earth or sub Neptunes
You observe two stars. They have the same brightness, yet you know that the luminosity of star #1 is larger than that of star #2. What can you infer about the distance of star #1 away from Earth compared to star #2?
If brightness is the same and Lum1>Lum2 then, Distance1>Distance2 --> star #1 is further away
Star #1 has a mass of 13 times the mass of the Sun. How long does it live on the main sequence?
tms=10^10 x m^3sun/m^3
= 10^10(1/13)^3
=4.55 million yr
Star #2 has a mass of 0.08 times the mass of the Sun. How long does it live on the main sequence?
tms=10^10 x m^3sun/m^3
=10^10(1/0.08)^3
= 1.95 x 10^13 yr
How many generations of 13 solar mass stars can live and die during the life of one 0.08 solar mass star?
Divide lifetime of 0.08 star by 13 star
1.95 x 10^13 (4.55 x 10^6)
= 4.3 million
What did Carl Sagan mean when he said, "We are star stuff"?
Most of the material that comprises us was once produced by a star - either in the core of a living star or during stellar death
Consider an astronaut falling into a black hole:
Assuming that the astronaut can withstand the tidal forces (so perhaps it's a supermassive black hole), what would they look like to an outside observer?
The astronaut would get redder and dimmer
Time would move slower and slower as they get closer and closer
Consider an astronaut falling into a black hole:
What would it look like from the astronaut's perspective?
The observer would look bluer and bluer
Time for the observer but seen by the astronaut would move faster and faster
Consider an astronaut falling into a black hole:
Would the astronaut be able to convey what they see to us?
Before they cross the event horizon, they could tell us what they see
After they cross the horizon, they would not be able to communicate
Light cannot escape and nothing moves faster than light
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