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Astronomy > Week 8 > Flashcards

Week 8 Flashcards

1
Q

Is the space between stars empty?

A

No it is just full of particles in lower density

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2
Q

interstellar medium

A

the matter and radiation that exists in the space between the star systems in a galaxy. made up of Hydrogen, Helium, ~2% “metals”

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3
Q

Nebula

A

a cloud of dust and gas in space

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4
Q

warm clouds

A

mostly atoms and ions

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5
Q

Cold clouds

A

atoms, molecules, dust,

“molecular clouds”

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6
Q

Can IR light shine through nebula?

A

yes it can shine through dust

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7
Q

How are stars formed?

A
  • Interstellar gas cloud starts to contract (shrink) due to their own gravity
  • Getting smaller, denser, and hotter
  • Spins faster
  • Densest parts of the cloud become opaque and trap heat
  • H-fusion begins when core reaches ~5 million degrees
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8
Q

What determines whether the gas cloud will become a star?

A

Mass (related to gravity + pressure)

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9
Q

What starts the collapse of a gas cloud?

A

Supernova shockwave, Colliding clouds, Turbulence in galaxy, Spontaneous cooling

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10
Q

Why do stars heat up as they form?

A

Gravitational Energy -> Kinetic Energy

Kinetic Energy = Thermal Energy

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11
Q

Protostar

A

a contracting mass of gas which represents an early stage in the formation of a star, before nucleosynthesis has begun.

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12
Q

What determines how small a star can be?

A

Mass affects temperature, and temperature must be high enough for fusion to occur (Mass > 0.08 Msun required for fusion)

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13
Q

Brown dwarf

A

no fusion, but still heat from gravitational contraction.

All about the same radius (~0.1 Rsun), regardless of mass.

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14
Q

How big can stars get?

A

As protostars collapse, core is so hot radiation pressure
blows off their outer layers. Less mass, less pressure
needed to counteract gravity, lower temp. Largest stable(ish) mass is ~120-150 Msun?

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15
Q

Low mass star

A

< 2 times the Sun

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16
Q

High mass star

A

> 8 times the Sun

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17
Q

Main Sequence stage

A
  • Where a star begins and is for 90% of its life
  • Fusing is occuring
  • Stellar thermostat keeps luminosity and temperature stable
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18
Q

Intermediate mass star

A

2-8 times the Sun

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19
Q

What initially happens when a star runs out of hydrogen

A
  • No more fusion
  • Temp not hot enough to fuse helium
  • Core will collapse (gravity overcomes pressure)
  • Increase in pressure = hotter in shell
  • Now hot enough for hydrogen fusion in shell around core.
20
Q

What answer most accurately describes the end life of a star 8-20 times more massive than our Sun?

A

Deep in the star’s core, elements fuse into ever heavier elements until no more energy is available to hold itself up against gravity; the star explodes as a Supernovae and the core is crushed into a Neutron Star.

21
Q

The Sun is a low mass star, what is the most likely sequence of events in its future?

A

It will use up it’s fuel in another 5 billion years, expanding to become a Red Giant, eventually it’s core will be a White Dwarf.

22
Q

What are the most common stars in the Universe?

A

Low mass stars (K, M types) are the most common.

23
Q

What happens in the core of a star fusing helium into carbon after all the helium is used up in the reaction?

A

Energy generation through fusion stops because carbon fusion requires higher temperature. The core collapses and helium starts fusing in shell.

24
Q

The core of a star 1.5 times more massive than our Sun is crushed into a dense object, which of the following most accurately describes this state?

A

The degeneracy pressure from electrons stops the core’s further collapse, leaving behind a White Dwarf.

25
Q

The majority of stars in the galaxy formed in which two structures?

A

Globular cluster and open clusters.

26
Q

Star formation in giant gas clouds is a result of competition between which forces?

A

Gravity and gas pressure

27
Q

There are hundreds of elements in the Universe, which of the following best describes how they were created?

A

The Big Bang produced mostly Hydrogen and Helium, fusion in stars and during supernova explosions made the rest.

28
Q

What effect sets the largest size a star can have?

A

The forming star is shining so strongly that it blows the collapsing gas cloud apart

29
Q

When astronomers look at globular clusters they don’t see any stars hotter/more luminous than our Sun. What does this mean for the age of the globular cluster?

A

The globular cluster is older than the typical lifetime of a star like our Sun.

30
Q

Red giant

A
  • Occurs when star core runs out of hydrogen and hydrogen fusion begins to occur in shell
  • Fusion is closer to star surface
  • outer layers will expand (increase pressure) and cool
  • Radiation can leave more easily
  • cooler on average (hence red) but overall larger amount of heat (more luminous)
  • Core is continuing to shrink getting denser and hotter eventually will be hot enough to fuse 3 4He -> 1 12C
31
Q

Helium “flash”

A

-When core contracts enough to heat to 100 million K,
helium starts to fuse into carbon
-will heat up and expand core (pressure wins)

32
Q

After the helium flash

A
  • He fused to C in hotter increasing core size
  • H fusion in shell decreases
  • becomes Horizontal Branch Star
  • Core stabilizes, luminosity decreases
  • Gravitational equilibrium is restored
33
Q

Double-Shell Red Giant

A
  • when He in core runs out
  • heat not enough for C fusion
  • C core will collapse
  • Outerlayers expand He fusion in shell (and H)
  • Star becomes very luminous
34
Q

Carbon fusion temp

A

600 million K, Electron degeneracy pressure becomes a
factor before the core reaches that
temperature

35
Q

Electron Degeneracy Pressure

A

-When atoms are subjected to extremely high temperature and pressure, the atoms are stripped of their electrons.
-Restricts how tightly packed particles can
become

36
Q

Low mass stars planetary nebula stage

A

-Temperature never gets high enough for carbon fusion
-Shell fusion becomes violent
• (no stellar thermostat)
• Outer layers blown off (due to temp sensitive He): Planetary nebula formed
- white dwarf formed

37
Q

Planetary nebula

A
  • explosions of dying star shells resulting in shell of gases
  • core is a small carbond left over rock, i.e. white dwarf
38
Q

Where are elements heavier then carbon produced

A

high mass stars

39
Q

High mass stars life

A
  • faster fusion in core (high temp and pressure)
  • early stages after main sequence similar to low mass stars but faster
  • C core will get hot enough to fuse other elements
40
Q

Onion model of high mass stars

A

-Concentric shells of increasing temperature and pressure produce heavier and heavier elements.
-Energy created by each new shell is enough to balance
gravity
-Successive shells are hotter, denser, and “burn out” in shorter times, until you reach iron

41
Q

Supernova

A

-After core begins to collapse as iron atoms get
compressed into pure neutrons it stops
-casues star to explode
-Energy of the explosion enables the production of elements heavier than iron
-huge energy release from neutrinos
-disperses heavy elements through the galaxy
-Inside may be a neutron star

42
Q

neutron star

A

remnant core of pure neutrons

43
Q

Where did our atoms come from?

A

Our atoms were once parts of stars that exploded
more than 4.6 billion years ago, whose remains were
swept up into the cloud out of which our Sun (& Solar
System) formed

44
Q

Why Neutron Stars Spin So Fast

A

Vast shrinking conserves angular momentum

45
Q

Collapse to a neutron star

increases?

A

Both rotation and magnetic field

46
Q

Neutron star speed over time

A

Gradually slows down as angular momentum is lost (slower =older)

47
Q

Pulsar

A

rotating neutron star

Astronomy (12 decks)

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