Download ASTRONOMY: WHAT DO YOU NEED TO KNOW

ASTRONOMY: WHAT DO YOU NEED TO KNOW?
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ABOUT HOW STARS ARE BORN: (Chapter 9)
What is the interstellar medium and what is it made of?
Low density dust and gas
What is a nebula?
A visible cloud of dust and gas
Be able to identify the three types of nebulae and give their characteristics: (formation, color)
Emission nebulae: are produced when a star (temperatures > 25000K) excites the gas in the cloud near
it to produce a light emission spectrum. The nebula is a distinctive pink form the blending of the colors
of excited gaseous hydrogen.
Reflection nebulae: are produced when starlight is scattered off of a dusty nebula. The nebula is blue
because the dust particles are very small thus able to scatter blue photons.
Dark nebulae: are produced when very dense clouds of dust and gas obstruct the view of the stars
behind it. They don’t glow because there are no nearby stars to ionize the gas.
What triggers star formation in an interstellar gas cloud?
Shock waves from the explosions of nearby stars
What is a protostar?
A collapsing cloud of gas and dust destined to become a star but not yet glowing as a star
What is a star cluster?
Stars held together in a stable group by their common gravity; from 10-1000 stars
What is the CNO cycle and what is formed through this cycle? How massive are stars that follow this cycle?
This cycle is found in stars more massive than our Sun. The cores of such stars are hotter than the Sun
and use the CNO cycle to produce helium instead of the hydrogen to helium formation of the Sun. The
cycle uses carbon nuclei to nitrogen nuclei to oxygen nuclei back to unchanged carbon nuclei to produce
four hydrogens that are then fused to helium.
What does the stability of a star depend upon?
The stable relation between gas pressure and temperature
What is hydrostatic equilibrium?
The balance between weight and temperature
Energy flows outward from the inner core as…………………………… conduction and radiation
Energy flows outward from the outer layers as……………………….. convection
What are the four laws of stellar structure? (p. 185)
1) Total mass = sum of the shell masses
2) Total luminosity = the sum of the energy generated in each shell
3) The weight on each layer is balanced by the pressure in the layer
4) Energy moves from hot to cool by conduction, radiation, and convection
What is a brown dwarf (its size and color)
Below 0.8 solar masses without a core temperature to begin hydrogen fusion (appear red)
Know about the lifespan of high mass stars (25+ Suns) versus lower mass stars (Sun = 1 mass):
Massive stars burn up in a few million years up to 7 million years
What is the temperature range of the red stars regardless of size? (H-R diagram)
2000K-4000K
What is the temperature range of yellow main sequence stars? (H-R diagram)
4000K-10,000K
What is the temperature range of the blue starts regardless of size? (H-R diagram)
>10,000K
HOW STARS DIE: (Chapter 10)
How long do main sequence stars spend as an energy-generating star?
Main sequence stars spend 90 percent of their lifespan generating energy
What is a hydrogen-fusion shell, when does it form, and why does it make a star expand?
In hydrogen-fusion a helium core is produced that acts like ash because it’s too cool to fuse further. Still
it gets hotter because it contracts and converts gravitational energy to heat. This core heats the
hydrogen around it, starting fusion, and further heating the outer layers and causing expansion of the
entire star. As each layer further out is heated it expands outward thus producing a giant.
What is degenerate matter? Where is it found?
Degenerate matter is high density matter whose temperature no longer depends on temperature. It is a
gas but resists compression. It is found in white dwarfs near the end of a star’s lifetime.
Know the characteristics and lifespan characteristics of red dwarfs.
Less than 0.4 solar masses; totally convective; lowest-mass stars can exist for hundreds of billions of
years (none have likely burned out yet)
Know the characteristics and lifespan characteristics of medium-mass stars (i.e. like our Sun).
1.0-10 solar mass stars; may or may not be convective; create shells and expand as they age; eject gas
into space and contact into white dwarfs
What is a planetary nebula and what does it look like?
Ionized gasses surrounding a white dwarf seen as the result of slow gas ejected by the red giant being
compressed by the fast gases as the red giant collapses into a white dwarf
Know the characteristics and lifespan characteristics of white dwarfs.
Does not undergo nuclear fusion but rather contains degenerate matter; contains no gas but radiates
energy into space which can take many billions of years for it to cool from its very small surface
What is a binary star and how is mass transferred in these systems?
A massive star paired with a smaller star; the gravity of the ore massive star pulls mass form the lesser
star creating an accretion disk of material flowing between them
What is an accretion disk and when does it form?
Because of angular momentum matter travels in the form of a flat disk form one star to the other (See
Fig. 10-10 p. 212)
What is the general definition of a nova?
Novas occur with the sudden brightening of a star associated with transfer of matter from one star to
another in binary systems and also with the collapse and destruction of massive stars and the
accompanying release of massive amounts of energy
What is a supernova and what types of stars cause these types of nova?
Type II is…… collapse and explosion of a massive star
Type Ia…..… a white dwarf gaining mass in a binary system and collapsing
Type Ib…..… a massive star in a binary system loses its outer layers to its companion
What happens to a star when it goes nova?
Electrons spiral through the magnetic fields of nova and produce a blue glow. The star collapses within
seconds as the outer envelope of the star is blasted outward. It produces a right light that fades over
time.
What type of star is formed from a supernova?
A neutron star
NEUTRON STARS AND BLACK HOLES:
Know the mass of a neutron star compared with its radius:
A sugar cubed size lump of neutron star material would weigh 100 million tons
What range of solar mass stars form neutron stars? Stars from 8-20 solar masses become neutron stars
What happens to stars of lesser solar mass? Stars less than 8 solar masses become white dwarfs
What happens to stars of greater solar mass? Stars great than 20 solar masses become black holes
How do the magnetic fields and rotation of neutron stars compare with normal stars?
Magnetic fields 1000 times that of the sun; rotation rates of 10-100 times per second
What is a pulsar and does it actually pulse? What does it do?
It is a spinning neutron star that emits radio waves form excited gases trapped in the star’s magnetic
field. It doesn’t actually pulse, rather it appears to blink on and off as it rotates towards and away from
the sight-line of Earth
What is a pulsar wind?
The high energy particles blowing away from a neutron star
What causes binary pulsars?
A pulsar whose period changes as the pulsar rotates around a companion star or other center of mass.
Because the pulsar is further away from Earth at some times and closer at others the time of the pulses
varies.
How do accretion disks from a binary system affect the x-ray beams of some pulsars?
Accretion disks of a normal star obscure our view of the pulsar as the neutron star rotates around the
accretion disk. The gasses of the disk block out the radio pulse of the neutron star.
How many solar masses must a star have to create a black hole?
Greater than 20 solar masses
What is a singularity?
A point of infinite gravity and density but of zero radius
What is the event horizon?
The point beyond which light and matter can’t escape the black hole
What happens to light at the event horizon?
Light will not escape and space-time curves back on itself
As energy or matter flows into a black hole, the spinning ejects jets of what? (see p. 245)
As matter spins into a black hole the rotation creates an accretion disk that energies the gasses and
emits gamma ray energy along the line of rotation
What are gamma-ray bursts and where are they coming from? How were they discovered?
They were discovered when American scientists were looking for evidence of Russian Soviet nuclear
tests; but in fact the gamma ray bursts were coming in from space They are the tell-tale evidence of
supernova collapses of massive stars to black holes. They occur only for seconds at a time.