BGSU ASTR 2010 Study Guide for Final
Exam Q&A 100% Solved | Graded A+
Interstellar Medium - ✔✔The gas and dust that fills the space between
stars in a galaxy.
Interstellar medium composition (ISM) - ✔✔A thin (few atoms/cubic
centimeter) distributions of primarily hydrogen and helium.
~74% Hydrogen, ~24% Helium, <2% other (by mass)
99% gas, rest dust
Average 1 atom per cm^3
How do we know that interstellar gas exists? - ✔✔Because of optical
emission lines (produced by hot hydrogen), radio emission (produced by
cold gas), and absorption features in stellar spectra added by cold
interstellar gas.
What is the cause of astronomical 'reddening'? - ✔✔It is the effect of dust
in interstellar space absorbing blue light more readily than red light;
therefore as star light passes through dust more of the red light makes it
through making the star appear redder than it otherwise would.
1
©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
,What is the original source of energy which heats up the core of a
collapsing cloud? - ✔✔Gravitational potential energy of the cloud.
What event sets the final mass of a forming star during the process of star
formation? - ✔✔The development of strong winds from the forming star
halts the flow of material onto the core, which fixes the mass of the soon-to-
be star.
General Theory of Star Formation - ✔✔Begins with a giant cloud of gas
and dust. The dust begins the reddening effect. It is slowly rotating. Infrared
cannot detect it. Very cold, low pressure, spread apart. A few 100 particles
per/cm^3
Gets a "kick" from something external - bumping into another cloud or a
nearby explosion of a star. This puts additional pressure on the outside.
The external pressure makes it being to collapse. It now has gravitational
potential energy. As it begins to collapse it the energy changes to the
kinetic energy of motion (from moving faster). The gas particles start to fall
towards the core and the energy then transfers to thermal energy in the
core. And then to infrared energy.
2
©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
,What happens to the energy of the cloud? - ✔✔Gravitational potential
energy > Kinetic Energy of collapse > Thermal Energy in core > Infrared
radiation
What happens to the spin of the cloud? - ✔✔Large cloud > Slow spin
As the cloud shrinks > rotation rate increases
Fragmentation of the cloud into individual stellar nebulae - ✔✔Denser
regions collapse faster, leading to clumping of the cloud into individual
stellar nebulae. Material continues to fall onto the Stellar nebulae, which
becomes opaque in the infrared.
Why does the cloud initially stay cool, but then begin to heat up? - ✔✔Due
to the gravity of the stellar nebulae they are pulling more and more material
from the collapsing cloud. Eventually the density of the stellar nebulae
becomes high enough to begin to trap the infrared radiation. (from
becoming opaque to infrared). Develops enough density to begin heating
up.
Protostar - ✔✔A contracting cloud of gas and dust; the earliest stage of a
star's life. When the stellar nebulae starts to trap infrared within it.
What happens to stop mass falling into the protostar? - ✔✔The protostar
develops mass wind/jets that halts mass inflow.
3
©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
, Why does a collapsing cloud flatten? - ✔✔Collisions in the vertical direction
tend to cancel out vertical motion, leaving only rotation.
pre-main-sequence star - ✔✔A ball of gas in the process of slowly
contracting to become a star as it heats up before beginning nuclear fusion.
Source of materials which makes up planets - ✔✔Planets form from
particles in a disk of gas and dust, colliding and sticking together as they
orbit the star. The planets nearest to the star tend to be rockier because the
star's wind blows away their gases and because they are made of heavier
materials attracted by the star's gravity.
Evolution sequence of a 0.5 solar mass star - ✔✔
What is the root cause of stars not existing as main sequence stars
forever? - ✔✔Stars have a finite fuel supply (the amount of hydrogen that
has a temperature over 10 million Kelvin, so they will run out eventually.
What is the significance of the helium core becoming degenerate in a one
solar-mass evolving star? - ✔✔The switch to degeneracy in the helium core
allows the core of the star to stop collapsing since electron degeneracy
supplies a new outward pressure to balance gravity.
When does hydrogen fusion completely stop in a one solar-mass star? -
✔✔Once the star has blown off most of its outer envelope as a planetary
4
©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
Exam Q&A 100% Solved | Graded A+
Interstellar Medium - ✔✔The gas and dust that fills the space between
stars in a galaxy.
Interstellar medium composition (ISM) - ✔✔A thin (few atoms/cubic
centimeter) distributions of primarily hydrogen and helium.
~74% Hydrogen, ~24% Helium, <2% other (by mass)
99% gas, rest dust
Average 1 atom per cm^3
How do we know that interstellar gas exists? - ✔✔Because of optical
emission lines (produced by hot hydrogen), radio emission (produced by
cold gas), and absorption features in stellar spectra added by cold
interstellar gas.
What is the cause of astronomical 'reddening'? - ✔✔It is the effect of dust
in interstellar space absorbing blue light more readily than red light;
therefore as star light passes through dust more of the red light makes it
through making the star appear redder than it otherwise would.
1
©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
,What is the original source of energy which heats up the core of a
collapsing cloud? - ✔✔Gravitational potential energy of the cloud.
What event sets the final mass of a forming star during the process of star
formation? - ✔✔The development of strong winds from the forming star
halts the flow of material onto the core, which fixes the mass of the soon-to-
be star.
General Theory of Star Formation - ✔✔Begins with a giant cloud of gas
and dust. The dust begins the reddening effect. It is slowly rotating. Infrared
cannot detect it. Very cold, low pressure, spread apart. A few 100 particles
per/cm^3
Gets a "kick" from something external - bumping into another cloud or a
nearby explosion of a star. This puts additional pressure on the outside.
The external pressure makes it being to collapse. It now has gravitational
potential energy. As it begins to collapse it the energy changes to the
kinetic energy of motion (from moving faster). The gas particles start to fall
towards the core and the energy then transfers to thermal energy in the
core. And then to infrared energy.
2
©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
,What happens to the energy of the cloud? - ✔✔Gravitational potential
energy > Kinetic Energy of collapse > Thermal Energy in core > Infrared
radiation
What happens to the spin of the cloud? - ✔✔Large cloud > Slow spin
As the cloud shrinks > rotation rate increases
Fragmentation of the cloud into individual stellar nebulae - ✔✔Denser
regions collapse faster, leading to clumping of the cloud into individual
stellar nebulae. Material continues to fall onto the Stellar nebulae, which
becomes opaque in the infrared.
Why does the cloud initially stay cool, but then begin to heat up? - ✔✔Due
to the gravity of the stellar nebulae they are pulling more and more material
from the collapsing cloud. Eventually the density of the stellar nebulae
becomes high enough to begin to trap the infrared radiation. (from
becoming opaque to infrared). Develops enough density to begin heating
up.
Protostar - ✔✔A contracting cloud of gas and dust; the earliest stage of a
star's life. When the stellar nebulae starts to trap infrared within it.
What happens to stop mass falling into the protostar? - ✔✔The protostar
develops mass wind/jets that halts mass inflow.
3
©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
, Why does a collapsing cloud flatten? - ✔✔Collisions in the vertical direction
tend to cancel out vertical motion, leaving only rotation.
pre-main-sequence star - ✔✔A ball of gas in the process of slowly
contracting to become a star as it heats up before beginning nuclear fusion.
Source of materials which makes up planets - ✔✔Planets form from
particles in a disk of gas and dust, colliding and sticking together as they
orbit the star. The planets nearest to the star tend to be rockier because the
star's wind blows away their gases and because they are made of heavier
materials attracted by the star's gravity.
Evolution sequence of a 0.5 solar mass star - ✔✔
What is the root cause of stars not existing as main sequence stars
forever? - ✔✔Stars have a finite fuel supply (the amount of hydrogen that
has a temperature over 10 million Kelvin, so they will run out eventually.
What is the significance of the helium core becoming degenerate in a one
solar-mass evolving star? - ✔✔The switch to degeneracy in the helium core
allows the core of the star to stop collapsing since electron degeneracy
supplies a new outward pressure to balance gravity.
When does hydrogen fusion completely stop in a one solar-mass star? -
✔✔Once the star has blown off most of its outer envelope as a planetary
4
©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
