Astronomy: Chapter 8 Flashcards
Describe the evolution of a main-sequence star into a red giant.
- red Giants were once main sequence stars.
- Red Giants are Helium Burning stars. main sequence stars are hydrogen burning stars.
- Hydrogen fuses with hydrogen, to create helium. Gravity goes in, pressure pushes out. when gravity squeezes the core, nuclear fusion speeds up and temperature goes up. because the outer part gets more energy, it expands and cools. the core gets smaller and hotter when the core reaches 50mk, Helium begins to fuse, He+he=C. outside of the core reaches 10mk. Hydrogen still exists outside which burns up helium (shell). Electron degeneracy: helium flash to red giants.
On the H-R diagram, trace the path of a typical star during its formation and its evolution into a red giant. how can star clusters help us check this theory?
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Describe the steps in the formation of a white dwarf star and planetary nebula beginning at the red giant stage.
- Red Giants: eventually helium runs out. The core gets smaller and reaches 100mk. Core gets smaller and starts to burn carbon. it puffs up and forms into a planetary nebula. the core remains to be a white dwarf.
- the outer nebula is cool
Describe the properties of a white dwarf.
- second most common star in space.
- they are the remains of median mass stars.
- White dwarfs are astonishingly dense.
- White Dwarfs cannot generate energy by nuclear fusion. it has exhausted its hydrogen and helium fuel and produced carbon and oxygen.
- Thermal energy, interior becomes very hot, but it cannot get hot enough to fuse carbon into heavier elements.
- as it radiates energy into space, its temperature gradually falls, but it cannot shrink any smaller because its degenerate electrons cannot get closer together.
What is a “nova” and how does it work?
- Nova: a sudden and temporary brightening of a star making it appear as a new star in the sky, evidently caused by an explosion of nuclear fuel on the surface of a white dwarf.
- mass transferred onto a white dwarf can build and erupt as a nova explosion.
- produced by an eruption around a stellar remnant
- an old star flaring up.
- a nova is evidently an explosion involving a white dwarf.
Describe the evolution and deaths of the most massive stars, including type II supernovae and supernova remnants.
- First, there is a protostar.
- Temperature will increase in the core until nuclear fusion begins and protostar and protoplanets form.
- active young star.
- star will emit uv light and radiation.
- young solar system.
- eventually forms into a young solar system.
- Once a star turns into a red giant, it can form into a planetary nebula, which becomes a white dwarf. or it can become a supernova, which will create a black hole or neutron star.
Discuss the main events in the occurrence of a type Ia supernova.
a type Ia super nova is thought to occur when a white dwarf in a binary system receives enough mass to exceed the Chandrasekhar limit and collapse. the collapse of a white dwarf is different from the collapse of a massive star because the core of the white dwarf contains usable fuel. as the collapse begins, the temperature and destiny shoot up, and the carbon-oxygen core begins to fuse in violent nuclear reactions. in a few seconds, the carbon oxygen interior is entirely consumed, and the outermost layers are blasted away in a violent explosion that, at its brightest is about six times more luminous than a type II supernova. The white dwarf is entirely destroyed; no neutron star or black hole is left behind.
Describe the nature and properties of a neutron star.
- A highly dense star composed almost entirely of tight packed neutrons.
- Neutron stars spin rapidly and are hot with strong magnetic fields.
- About the size of washington dc.
- Jets of particles move around neutron stars, just about their magnetic fields.
- mass = 1.5 solar mass - 20km diameter.
- solid crust.,, 2km deep
- fluid core.
Describe the discovery and nature of pulsars.
- discovered by Jocelyn Bell in 1967
- observed with her radio telescope.
They are sources of short, precisely timed radio bursts spinning around a neutron star. - first believed to be signals from LIttle Green Men. LGM
Describe the nature and properties of a black hole.
- Black hole: a mass that has collapsed to such a small volume that its gravity prevents the escape of all radiation. also, the volume of space from which radiation may not escape.
- hard to see because light could not leave it.
- Time Dilation: clocks will move slower in strong gravitational fields.
- Gravitational redshift: the lengthening of the wavelength of a photon as it escapes from a gravitational field.
Describe observational attempts to verify the existence of black holes.
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What is meant by the terms “event horizon” and “schwarzschild radius” and what is their relation to the mass of a black hole?
Event Horizon: the boundary of the region of a black hole from which no radiation may escape. no event that occurs within the event horizon is visible to a distant observer.
- Schwarzchild radius: the radius of the even horizon around the black hole.
- the size of a black hole, its schwarzchild radius, is simply proportional to its mass.
