Stellar Nurseries
Stages of Star Birth
Masses of Newborn Stars
Life as a Low-Mass Star
Life as a High-Mass Star
100
The interstellar medium.
What is the gas and dust between stars in a galaxy?
100
This is how a protostar forms.
What is when a molecular cloud contracts so much that pressure is strong enough to push back against gravity and slow its contraction and no radiation can escape?
100
The least and greatest masses that stars can have.
What are 0.08 M(Sun) and 150 M(Sun)?
100
The mass of an low-mass star.
What is less than 2 M(Sun)?
100
The mass of a high-mass star.
What is greater than 8 M(Sun)?
200
Molecular clouds.
What are the cold, dense places where stars are born with temperatures 10-30 K and density 300 molecules/cubic cm?
200
This is how a protostellar disk is formed.
What is...Random motion of gas particles gives a cloud some small overall rotation that increases as the cloud contracts because of the law of conservation of angular momentum. The rotation prevents gas from falling directly onto the protostar so it forms a protostellar disk...?
200
Degeneracy pressure depends only on ___, not ___.
What are density and temperature? in that order!
200
This is how a star turns into a red giant.
What is...the core runs out of hydrogen so the core shrinks from gravity. The outer layers expand and the luminosity increases.
200
The CNO cycle.
What is the catalyst for hydrogen fusion in high-mass stars that exists because gravity compresses their cores to higher temperatures so protons can hit C, O, or N nuclei which make the reaction faster?
300
Stars near the edge of a molecular cloud appear redder because dust grains block shorter-wavelength photons more easily than longer-wavelength photons.
What is interstellar reddening?
300
This is why old stars rotate more slowly than young ones.
What is because rotation of disk generates a magnetic field which transfers angular momentum to outer material and slows the rotation and because the magnetic field helps generate strong winds which can transfer out additional material and momentum?
300
This is how a brown dwarf comes to be.
What is...A protostar with mass below 0.08 M(Sun) doesn't have a lot of space for electrons, so it stops contracting before hydrogen burning can begin and becomes a brown dwarf that slowly radiates away its thermal energy (in IR)...?
300
Hydrogen shell burning.
What is when gravity contracts the hydrogen shell around the red giant's core until the hydrogen is hot enough for fusion?
300
This is how a high-mass star becomes a supergiant.
What is...when a high-mass star runs out of hydrogen in its core, it develops a hydrogen-burning shell and its outer layers expand into a supergiant.
400
Gravity can only create stars if it overcomes this.
What is the outward push of thermal pressure?
400
Protostellar jets.
What are the things that young protostars often fire into interstellar space in opposite directions along their rotation axes? (perhaps because magnetic field lines get twisted by rotation?)
400
This is what happens to protostars with mass greater than 150 M(Sun).
What is...Radiation pressure causes them to blow away their outer layers and extra mass?
400
Helium burning.
What is when the helium core reaches 100 million K, helium fuses 3 He nuclei into 1 C nucleus and the lost mass becomes energy?
400
This is why there is no helium flash in a high-mass star.
What is because core temperatures are so high that thermal pressure remains strong and prevents degeneracy pressure from being a factor, so helium burning just ignites gradually?
500
This helps to prevent a pressure buildup in molecular clouds.
What is the ability of molecular clouds to get rid of thermal energy (that is formed when regions contract and gravitational potential energy is converted into thermal energy) because collisions of gas molecules convert it into photons which can escape?
500
Name the four stages of birth of a star.
Formation of a Protostar, Convective Contraction (energy released through convection), Radiative Contraction (energy released by radiative diffusion), Self-Sustaining Fusion (star settles into main sequence)
500
Radiation pressure.
What is a pressure exerted by photons when they strike matter that becomes prevalent in large-mass stars when they can exert a pressure greater than thermal pressure?
500
Helium flash.
What is when the rising temperature in the core causes the helium fusion rate to increase without changing pressure in the core (because degeneracy pressure doesn't change with temperature), and then thermal pressure becomes dominant again and a lot of energy is suddenly released into the core?
500
This is how a high-mass star dies.
What is when the core is iron and gravity pushes the electrons past the quantum mechanical limit, they combine with protons to form neutrons, so the star collapses into a ball of neutron with neutron degeneracy pressure which releases a lot of energy. The outer layers are driven off into space in a supernova and a neutron star is left behind. Or, if the mass is so large that it overcomes neutron degeneracy pressure, it collapses into a black hole too...?
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