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BGSU ASTR 2010 Study Guide for Final Exam Q&A 100% Solved | Graded A+
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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% Hydroge...

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  • 21 december 2024
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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.

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©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.




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©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.


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©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.

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