Astronomy Exam Two

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What happens to the rotation of a molecular cloud as it collapses to form a star?

The rotation rate increases and results in a disk of material around a protostar

When does a protostar become a true star?

When nuclear fusion begins in the core

What is the smallest mass a newborn star can have?

80 times the mass of Jupiter

What is the greatest mass a newborn star can have?

100 solar masses

For ever star with a mass greater than 10 solar masses, about how many stars are there with masses less than a solar mass?

100

What do astronomers mean when they say that we are all "star stuff"?

That the carbon, oxygen, and many elements essential to life were created by nucleosynthesis in stellar cores

What type of star is our Sun?

low-mass

What can we learn about a star from a life track on an H-R diagram?

What surface temp. and luminosity it will have at each stage of its life.

How many helium nuclei fuse together when making carbon?

3

What is planetary nebula?

The expanding shell of gas that is no longer gravitationally held to the remnant of a low-mass star.

What happens to the core of a star after a planetary nebula occurs?

It becomes a white dwarf.

Compared to the star it evolved from, a white dwarf is

hotter and dimmer

What is the CNO cycle?

A type of hydrogen fusion that uses carbon, nitrogen, and oxygen atoms as catalysts.

Which element has the lowest mass per nuclear particle and there fore cannot release energy by either fusion or fission?

Iron

What happens when the gravity of a massive star is able to overcome neutron dgeneracy pressure?

The core contracts and becomes a black hole.

What types of stars end their lives with supernovae?

stars that are at least several times the mass of the sun.

Suppose the Betelguese (the upper left shoulder of Orion) were to become a supernova tomorrow (as seen here on Earth). What would it look like to the naked eye?

Would remain a dot of light but would suddenly become so bright that, for a few weeks, we'd be able to see it during the day time.

After a supernova event, what is left behind?

either a neutron star or a black hole.

Degeneracy Pressure

pressure on an atomic level where things are so dense that electrons try to occupy the same space but cannot, creating a pressure. (ex: the people trying to sit in chairs at the same time)

Thermal Pressure

Pressure dictated by temp. (ex: a balloon expanding with heat)

Explain why degeneracy pressure can support a stellar core against gravity even when the core becomes very cold.

When the core becomes cold, the density would increase and push the molecules of the core closer together. Degeneracy pressure will not let this happen b/c no two electrons can occupy the same space which will create a pressure and support itself against gravity.

Brown dwarf

an object too small to become an ordinary star because electron degeneracy pressure halts its gravity collapse before fusion becomes self-sustaining; brown dwarfs have a mass less than 0.08Msun

What is the minimum mass for a star and why can't objects with lower masses be true stars?

The smallest mass for a star to form is 0.08Msun. Objects with lower masses can't self-sustain fusion and therefore can't really be stars.

What is the max. mass of a star? What kind of pressure limits how massive a star can be?

The max. mass of a star is about 150 times that of our sun. The pressure that limits how massive a star can be is radiation pressure which is when the photons of light exerting a slight pressure when they strike matter causing an outward pressure of the star.

Why is mass so important to a star's life?How and why do we divide stars into groups by mass?

The birth mass determines the fusion progression within the core of the star. We divide these into groups because lower mass stars usually live longer than higher mass stars and they can produce different elements through fusion

When a star exhausts its core hydrogen fuel, the core contracts but the star as a whole expands. Why?

Hydrogen burns around a helium core increasing heat and causing the star to expand.

Planetary Nebula

a glowing cloud of gas ejected from a low mass star at the end of its life.

What happens to the core of a star after a planetary nebula occurs?

Afterwards, what is left behind is a small inert core which will become a white dwarf.

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