final Flashcards
What is the main thing that goes on inside a star?
nuclear fusion
In what way can a star be considered a “nuclear furnace”?
Its “burning” hydrogen as a fuel
How is the furnaces inside stars different from the ones inside our homes?
stars use hydrogen as fuel and produce helium, unlike home furnaces which use carbon source and release carbon dioxide.
In the most important nuclear process inside a star, four _______ atoms are converted
into one _______ atom.
hydrogen,helium
Why does the process described above result in the creation of energy?
the total mass of the resulting single nucleus is less than the mass of the two original nuclei. There is mass not accounted for, and that mass is converted into energy
What kind of weapon of mass destruction employs the same process that happens at the center of our sun?
Nuclear bomb/hydrogen bomb
What do we receive from stars as a direct result of the reactions that take place inside stars?
Light
What are the two main attributes of the light that comes from either a star or a light
bulb?
luminosity and temperature
Which is hotter, a light bulb filament that is red hot or one that is white hot?
White
Which is brighter, a light bulb filament that is red hot or one that is white hot?
cannot tell just from color
What is the difference between a star’s absolute brightness and its apparent brightness
(luminosity means the same thing as brightness)?
Absolute brightness is how bright it actually is, apparent brightness is how bright it appears from earth
Are the purplest stars the brightest stars? Are they the hottest stars?
purple are hotter than blue
What name do we give the luminosity - temperature chart used to classify stars?
Hr diagram
Where would a cool, but very bright star be found on the HR diagram? Where would a hot bright star be found?
upper right, upper left corner
What is the main sequence?
It’s the region on the HR diagram where stars spend most of their life, while they are consuming their core hydrogen
What factor, more than any other, determines how a star’s life will unfold?
Mass
What are stars before they become stars?
Cloud of gas
Why are there so many more main sequence stars then there are stars making their way towards the main sequence?
because the time it takes to reach the main sequence is far less than the time they are on the main sequence
When a protostar reaches the main sequence, it stops shrinking. What is it that makes this happen?
Because the gravity pulling the star in balances out with the atoms that are being pressured down and pushing out
What two things must be in balance if a star is to remain the same size?
Pressure and gravity
Of all the influences on a star, why is gravity the most implacable?
Gravity never stops
Stars cannot remain on the main sequence forever. Why?
only hydrogen in their core
The smallest stars, after they leave the main sequence will be composed mainly of _______.
helium
No red dwarf star has ever become a black dwarf “star”. How can we be so sure of this?
Because it will have to become a white dwarf, which will take trillions of years, which our galaxy has not been around long enough for.
What do medium mass stars become when they exhaust their core hydrogen? What do they become after that (sometimes)?
The outer shell begins to undergo fusion and expands, becoming a giant/supergiant
At the end of their lives, medium mass stars end up as ________ ________.
a white dwarf. Eventually cooling to black dwarf
The heaviest stars. After they have consumed their helium, they move on to consume what?
carbon nitrogen oxygen
Why does the cascade to larger and larger atoms inside a high mass star stop?
Because it eventually forms iron which stops nuclear fusion
Which atom cannot undergo fusion spontaneously?
iron
Stars with which mass are doomed to a core collapse supernova?
heavier than about 3 solar masses
When was the last supernova that occurred in our galaxy?
1604
How bright are supernovae when they occur?
Very, brighter than the all the other stars in the galaxy put together
What atoms are only formed in a supernova?
atoms heavier than iron
The Crab Nebula began as a supernova that was first observed in what year?
- AD
Why is it correct to state that each of us contains at least a tiny bit of stardust?
Because the elements only made in supernovas are also in our body
What are the two possible fates for the remaining core after a supernova?
neutron star or black hole
What is another name for a neutron star?
Pulsars
Neutron stars emit what kind of light in a regular, heartbeat-like manner?
radio, optical, X-ray or gamma-ray wavelengths
Which is more dense? A white dwarf star or a neutron star?
Neutron star
Why will we never know what happens inside the event horizon of a black hole?
light cannot escape
If a collapsed core is greater than about three solar masses, ______________ cannot be counteracted.
cannot be counteracted.
its gravity
How can we be sure that nothing can escape from a black hole?
Because not even light can escape inside
Why is the event horizon like a one-way road?
you can’t just cross over the road
What is the best evidence we have that black holes exist?
the radiation from matter that is being torn apart as it is sucked inside the event horizon
Does the Universe consist of only a handful of galaxies?
hundreds of billions
About how many stars are in the Milky Way galaxy, and about how large is it?
200-400 billion, 100,000 ly large
Where do you need to look in the sky to be looking at the galactic center?
Constellation of Sagittarius
If you point your eyes in the direction of the center of the Milky Way, you don’t see the great bulge of stars there. Why is this?
gas, dust, stars impact the view
What name is given to the unknown stuff that seems to make up a large part of the Milky Way’s mass?
black matter/hole
The Milky Way’s mass is about how large? The amount of mass in the galaxy is a mystery. Why is that?
1.5 trillion solar masses. Too much to count for
What is the name of the mysterious object at the center of our galaxy?
sagittarius A
What are the three main types of galaxies?
elliptical, spiral, and irregular.
If the universe extended infinitely, what would you see in any part of the sky, no matter where you looked?
Stars, sky would be bright as sun at all times
When we spot a distant galaxy in the sky, which way is it heading?
away from earth
When a galaxy is moving towards us, the light reaching us from that galaxy is _______shifted; when it is moving away from us, the light is _________shifted.
blue, red
The color shift from extragalactic objects (objects outside our own Milky Way Galaxy) is always in which direction?
away from us
When we add up all the stars in all the galaxies in all the universe, what sort of number would we get?
1x10^24 stars
If a galaxy is moving away from us faster, what can we say about its distance?
the further they are the faster they are moving away from us.
Are there any distant galaxies that are moving towards us? What does this answer tell us about where we are located in the universe?
No, everything in the universe is moving away from everything else. The whole universe is expanding
What name do we use to describe our universe in which everything is rushing away from everything else?
expansion
Where is the edge of the universe?
Doesn’t have an edge
Since it is possible to explore every square inch of the universe, the universe must be
_________.
finite
About how long ago did the Big Bang occur?
14.1 billion years ago
What was created at the moment of the Big Bang?
Space and time. The Big Bang created all the matter and energy in the Universe.
Was the Big Bang really a big bang (an explosion?)
No
What existed in the universe before there was any matter?
just energy: no massive particles
What is the name for the type of matter in the universe before there were any protons and neutrons formed?
quark and other elementary particles
What had to happen in the universe in order for matter as we know it today to be possible?
In the first moments after the Big Bang, the universe was extremely hot and dense. As the universe cooled, conditions became just right to give rise to the building blocks of matter - the quarks and electrons of which we are all made
What happened to all the quarks that were the first matter formed?
They combined into protons and neutrons
Which atoms were formed in the first million years of the universe?
Helium, hydrogen, lithium
What has the universe been doing ever since it formed?
expanding
What are two possible fates for the universe?
Universe is closed or open (Expansion or the big crunch)
What determines what our universe’s ultimate fate will be?
The amount of mass and rate of expansion
A star suddenly becomes ten times as luminous. How does it’s HR position change?
upwards
Black holes
A: Have no mass
B: Have no size
C:Are everywhere, but we don’t see them
D:Must exist, even if we don’t see them
D
Milky Way seems to have…
A: More stars than can be seen
B: more mass that can be accounted for
C:Less mass than it needs to have
D: Mass in wrong place
B
Two galaxies seen from Earth are getting further away from us: These galaxies are:
A:Getting closer together
B: Moving together
C: Getting further apart
D: Could be A, B, or C, no way to tell
C
