ASTRONOMY FINAL Flashcards
Describe in your own words the major stages in the lifecycle of a 1 solar mass star
Step 1- Molecular cloud which are clouds of gas and dust, as you zoom into clouds there are these blobs which are basically cloud of gas and dust that are collapsing. because of gravity as they collapse they get hotter and hotter and denser and denser and they form a protostar
Step 2 - Protostar - a more dense cloud of gas and dust, but because of gravitational collapse the center gets denser and denser as gas collapses in, and because we are compressing the gas it is also getting hotter - it continues to get more hot and dense until fusion occurs
Step 3 - main sequence star (no longer could of gas and dust) mostly plasma - the star needs to be a very high temperature which also means you need a high density for there to be enough fusion to keep it going. hydrogen fusion in the core - eventually we will use up all the hydrogen and the fusion stops in the core
Step 4 - hydrogen burning red giant when fusion is not keeping the core from collapsing it will collapse, and it gets hotter because it is collapsing and denser but not hot enough or dense enough for fusion to occur. - it does however get hot and dense enough in a layer outside of the core for hydrogen fusion, but the mass of the core is so great that it is pulling so the whole star puffs up because its hotter.
until eventually fusion in the shell stops. and it collapses
Step 5 - helium burning red giant - it collapses enough that helium burning in the core can occur and eventually it starts developing a carbon core (inert so it collapses)
Step 6 - helium shell burning red giant - where you have an inert carbon core, a helium burning shell and a hydrogen fusing shell around that.
now puffs up by another factor of like 1000 from its original size. that energy now is so great that it just blows off the envelope. gravity can no longer hold it all in.
Step 7a. - planetary nebula - And then something happens and poof There goes the envelope, and basically the envelope of the star has been puffed out. it’s the envelope of the stars has been blown off
Step 7b. - White dwarf - the core turns into a white dwarf the rest of it forms into a new molecular cloud.
Explain how the chemical composition of the Sun and its core have changed over the last 5 billion years and will change over the next 5 billion years
the Sun is about 4.6 billions years old so before that it was a molecular cloud then protostar it is composed of about 3/4 hydrogen and 1/4 helium where it then goes into the main sequence stage which is where the sun has been since and it is fusing hydrogen into helium in its core. over the next 5 billion years the sun will continue in its main sequence stage until it uses up all the hydrogen in the core.
when fusion is not keeping the core from collapsing it will collapse, and it gets hotter because it is collapsing and denser but not hot enough or dense enough for fusion to occur. - it does however get hot and dense enough in a layer outside of the core for hydrogen fusion
it collapses enough that helium burning in the core can occur and eventually it starts developing a carbon core (inert so it collapses)
puffs up by another factor of like 1000 from its original size. that energy now is so great that it just blows off the envelope. gravity can no longer hold it all in.
the core turns into a white dwarf the rest of it forms into a new molecular cloud.
Draw a cross-sectional diagram of the Sun at the present day, at the end of its main-sequence lifetime, and just before it becomes a red giant
draw on ipad
Explain why hydrogen fusion will eventually end in the Sun’s core
Because when the sun is in the main sequence it is constantly burning hydrogen so we will eventually run out of hydrogen in the core and it will cause the core to collapse - As more and more hydrogen is converted into helium, the core’s composition changes - it becomes rich in helium. This buildup of helium changes the conditions in the core.
Explain why hydrogen shell burning eventually begins in the Sun
When the hydrogen in the core eventually depletes it causes the core to collapse which stops hydrogen fusion in the core - and it gets hotter because it is collapsing and denser but not hot enough or dense enough for fusion to occur. - it does however get hot and dense enough in a layer outside of the core for hydrogen fusion, but the mass of the core is so great that it is pulling so the whole star puffs up because its hotter.
Explain why stars tend to puff up and turn red when they die
the mass of the core is so great that it is pulling so the whole star puffs up because its hotter. The increased energy production in the shell exerts an outward pressure, causing the outer layers of the star to expand. As the star’s outer layers expand, they cool and become less dense. The expanded, cooler outer layers emit light at longer wavelengths, which is why the star appears red. The star’s surface temperature is cooler compared to its earlier main sequence phase,
Describe what a white dwarf is and what it’s made of
this is the final stage in the life cycle of a star - fusions finishes in the core and all that’s left is carbon and oxygen as the core - this is the white dwarf
it is very dense and inerts and is initially very hot but cools down for billions of years.
Describe the main steps in the Sun’s post main-sequence evolution, both in your own words and by drawing the steps on an H-R diagram
check ipad
Estimate the time taken for the various steps in the above sequence
Explain why white dwarf stars don’t collapse under their own gravity, concentrating on electron degeneracy
White dwarfs are incredibly dense, meaning their electrons are packed very closely together. As gravity compresses the star, electrons are squeezed into the smallest space possible. But there’s a limit to how close they can get.
electrons are ‘pushing back’ just as hard as gravity is pulling in.
Explain what a planetary nebula is and distinguish it clearly from a planet
this is step 7a of the life cycle of a star and basically during the end of the stars red giant phase the star expands by a factor of 1000 - that energy now is so great that it just blows off the envelope. gravity can no longer hold it all in. And then something happens and poof There goes the envelope, and basically the envelope of the star has been puffed out. and eventually disperses into space where it joins with gas from other dead stars forming a new molecular cloud
Compare and contrast a white dwarf with Earth, in terms of size, density, temperature, and chemical composition
Typically, a white dwarf is about the size of Earth. The average radius of a white dwarf is similar to that of Earth - White dwarfs are incredibly dense. Despite their Earth-like size, they contain a mass comparable to that of the Sun. Their densities can be millions White dwarfs are extremely hot when they first form much hotter than earth
Most white dwarfs are composed primarily of carbon and oxygen, which are the products of helium fusion from their earlier stages as stars
Earth is composed of a variety of elements, with a core mainly made of iron and nickel, a mantle of silicate rocks
Distinguish between high-mass and low-mass stars, explaining why there is a difference
High - mass stars have a different process occuring during the helium burning red giant. they will instead have carbon fusing in the core because they are much hotter and more dense, and you will eventually end with a iron core and the star will also have a silicon and Neon shell too.
low mass stars will blow off the shell leaving the carbon core and a white dwarf.
Explain how the sequence of steps in the evolution of a high-mass star differs from that of a low-mass star, focusing on evolution in the core of the star
in a high mass star the core will turn in carbon, but from this point since it is much hotter and denser - carbon fusion can begin and then you will get new cores and new shells until you finally reach an iron core. where fusion can no longer happen.
for a low mass start the carbon core causes the star to puff up until energy is so great that it will blow off the envelope leaving only the core behind.
Use a graph of the binding energy per nucleon in atomic nuclei to predict whether fission or fusion of that atom with another will produce or consume energy
When u do the nuclear reactions it’s like u convert H4 -> C12
Fusion involves combining lighter nuclei (like hydrogen or helium) to form heavier ones.
Fission involves splitting heavier nuclei (like uranium or plutonium) into lighter ones.
Use the nuclear binding energy graph to describe why nuclear fusion in stars doesn’t tend to produce elements heavier than iron
Fusion doesn’t produce elements heavier than iron because you can’t break apart iron or create iron without it requiring energy (usually fusion and fission releases energy, so it’s energetically unfavourable if u do it with iron)
On the graph it’s just like u take the final binding energy - initial binding energy =
And for iron it would be negative meaning it uses energy
Draw an onion diagram of the interior of a massive star just before it dies
check Ipad
Explain how a supernova explosion occurs
when a core collapses to the density of an atomic nucleus it releases an enormous amount of energy. - and this is a supernova - you have an iron core that collapses and forms the atomic nuclei
Compare the energy of a supernova to the lifetime energy output of the Sun
a Supernova is as bright as every star in the galaxy - 100 billion stars and a supernova is the same. forms either a neutron star or a black hole.
Describe the basic characteristics of a neutron star, such as its mass, density, and size
weighs between one and a half and three times the mass of the sun
about the size of downtown toronto or 11km across
Compare the properties of neutron stars to those of white dwarfs
the lightest stars collapse to form a white dwarf, heavier stars collapse to form either a neutron star or black hole.
a white dwarf is just a carbon core and the rest of the properties blew off into a new molecular cloud
a neutron star is basically a star that had an iron core and the iron core collapsed and exploded into a super nova creating a neutron star.
Use a diagram to show how neutron stars and pulsars are related
Neutron stars are pulsars - they are neutrons star rotating with a strong magnetic field (pulsating beam of light)
Describe and draw the main steps in the star-gas-star cycle
for a high mass star it pops up to a giant or super giant, and then super nova occurs and get blown away (cloud of gas and dust is blown away) you end up with either a black whole or a neutron star
Neutron star (can merge or etc..)
Black hole (nothing happens to them ever again)
This gas and dust goes out to form the gas and dust of space forms a new generation of stars.
new star with a low mass * red giant planetary nebula that blows off the envelope. You get a white dwarf which gradually cools and it cools and eventually call it a black dwarf because it’s not glowing anymore, because it’s not hot anymore. (So a black dwarf is just a cold white dwarf that’s been waiting for a very, very long time and it’s gotten cold.)
the nebula blows off, becomes part of the interstellar medium, which in turn comes back and forms a new generation of stars.
Explain the sense in which we are “star stuff”
because earth and every living thing. in it is composed of the elements that are created from sundry start events.
Given a chemical element (e.g. hydrogen, helium, carbon, iron, uranium) explain how and where it was ultimately produced
helium and hydrogen came from the beginning of the universe.
everything else came from various sundry star events.
grey and purple elements came from exploding white dwarfs and merging neutron stars.
origin of iron - if you add enough mass to a white dwarf it can become massive enough to undergo carbon fusion all the way to iron.
why aren’t there any low mass red giants
because the universe is not old enough yet.
Describe the overall properties of the Milky Way, including its size, mass, number of stars, shape, and parts
the milky way has about 200 billion stars, and a diameter of about 100,000 light years. the galaxy is shaped as a disk and stars orbit the center of the galaxy. has three parts disk, bulge, halo and bobular clusters. 1.5 trillion solar masses.
Name the three major components of the Milky Way
disk, bulge, and halo
disk is relatively thin 3,000 light years.- most of the gas and dust, and most star formation occurs in the disk
