chapter 13

what primarily triggers the contraction of a cloud of interstellar gas to form a star

gravity overcoming the internal gas pressure

what characteristic is common among star-forming clouds

low temperature and high density

why are molecular clouds ideal for star formation

they have low temperatures and high densities, which help gravity overcomegas pressure

what is a protostar

a dense clump of gas in a molecular cloud that will become a new star

what causes the central temperature of a protostar to rise dramatically during its formation

he trapping of infrared radiation due to increasing density

at what core temperature does a protostar become a true star

10 million K

why do protostars often have spinning disks around them

collisions between gas particles cause the cloud fragment to flatten along its rotation axis due to conservation of angular momentum

what role do jets play in the development of a protostar

they help clear away surrounding gas, revealing the protostar within and reducing angular momentum by carrying material off into space

how does angular momentum affect binary star systems

it allows neighboring protostars to orbit each other without colliding, forming binary systems with varying orbital distances based on their angular momentum

what determines whether a newborn star will be massive or low-mass

the processes governing clumping and fragmentation in star-forming clouds, which are not yet fully understood but observable through young star clusters’ demographics

why are high-mass stars relatively rare compared to low-mass stars in young star clusters

high-mass stars require specific conditions that are rarely met during star formation episodes, while low mass stars form more easily under typical conditions found in molecular clouds

what is the primary characteristic that determines a star’s luminosity, surface temperature, and ultimate fate

its mass

which of the following is considered a low-mass star: 5 solar masses, 1.5 solar masses, 10 solar masses

a star with 1.5 solar masses

what is the primary source of energy for a low-mass star during its main-sequence stage

hydrogen fusion in the core

approximately how long will our sun remain in its main-sequence stage

10 billion years

what process keeps the sun’s fusion rate and overall luminosity steady during its main-sequence stage

gravitational equilibrium and energy balance

during which phase does a low-mass star spend about 90% of its total lifetime

main-sequence stage

what happens to a low-mass star’s outer layers when it enters the red giant stage

they expand outward significantly

what causes the sun to become a red giant after its main-sequence stage

the depletion of hydrogen in the core leading to hydrogen shell fusion around an inert helium core

how much larger will the sun be at the peak of its red giant stage compared to its current size

about 100 times larger in radius and around 1000 times more luminous

what is required for helium nuclei to overcome their repulsion and fuse together

extremely high temperatures and speeds for collisions between nuclei

what is the result of the helium flash in a low-mass star like the sun

the core rapidly heats up, causing thermal pressure to dominate over degeneracy pressure, leading to expansion of the core and reduction in luminosity from red giant peak levels

which reaction describes helium fusion commonly known as the triple-alpha process

three helium nuclei fuse to form one carbon nucleus, releasing energy as mass is converted according to E=mc²

what happens when a low-mass star like our sun exhausts its core helium supply

it expands again into an even larger red giant powered by double shell-fusion

why can’t carbon fusion occur in a low-mass star like our sun

because degeneracy pressure halts contraction before tempertures reach necessary levels for carbon fusion

what phenomenon marks the final stages of life for a low-mass star like our sun

planetary nebula formation

how will earth’s environment change as the sun becomes more luminous over time during its main-sequence life

earth will undergo a runaway greenhouse effect causing oceans to boil away within 1-4 billion years

during which phase will earth’s surface temperature rise dramatically above current levels due primarily increased solar luminosity reaching over thousands times present value before the sun’s final death stages begin

first red giant phase

after exhausting all possible nuclear fuel sources what will be left behind once sun ejects outer layers forming planetary nebula

white dwarf

what is the primary difference between the early stages of life for high-mass stars and low-mass stars

high-mass stars proceed through their early stages much more rapidly

what process initiates hydrogen fusion in a high-mass star

gravitational potential energy released by the contracting protostar

hoe does hydrogen fusion in high-mass stars differ from that in low-mass stars

it occurs through the cno cycle

what elements are involved in the cno cycle during hydrogen fusion in high-mass stars

carbon, nitrogen, and oxygen

what is the overall reaction result of both the proton-proton chain and the cno cycle

four hydrogen nuclei fuse into one helium-4 nucleus

why does hydrogen fusion proceed more rapidly in high-mass stars compared to low-mass stars

the core temperature is higher due to greater gravitational compression

what happens to a high-mass star when it begins to run low on hydrogen fuel

it develops a hydrogen-fusing shell and expands into a supergiant

during which phase does a high-mass star become a supergiant

when it starts fusing helium into carbon in its core

what prevents degeneracy pressure from becoming significant during helium core fusion in high-mass stars

the core temperature is so high that thermal pressure remains strong enough to prevent degeneracy pressure from becoming significant

why can high-mass stars fuse elements heavier than carbon while low-mass stars cannot

low-mass stars lack sufficient gravitational compression to heat their cores enough for heavy element fusion

which reaction type primarily contributes to the creation of elements heavier than carbon in high-mass stars

helium-capture reactions fusing helium nuclei with other nuclei to form heavier elements

at what temperature does carbon fusion typically occur within a high-mass star’s core

600 million K

what element accumulates in the core of a high-mass star just before it explodes as a supernova

iron

why can’t iron generate energy through nuclear reactions within a stellar core

iron has the lowest mass per nuclear particle, making it unable to release energy through either fusion or fission

what event marks the final collapse of a high-mass star’s core leading to a supernova explosion

the combination of electrons with protons forming neutrons and releasing neutrinos