Solar System Final- 2
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- Which of the following was observed (not only predicted) well before the observational revolution of the 1980 and 1990s?
- Extinction of starlight by interstellar grains.
- How do we know that nearly all distant stars are made of Hydrogen and Helium, just like our Sun is?
- From observing their spectra.
- What phenomenon prevents the Sun from collapsing under the weight of its own matter and become a neutron star or even a black hole?
- Gas pressure.
- What happens to a star before thermonuclear reactions start?
- The star contracts.
- What happens when thermonuclear reactions start in the center of a star, or just before they start?
- T Tauri winds clear gas from the surrounding nebula.
- Why do Hydrogen atoms fuse into Helium in the core of the sun only and not everywhere in a sun?
- Because protons repel and never get close enough to fuse except at the core where the pressure and temperature are su#ciently high.
- When does Helium burning in the Sun\'s core start?
- The temperature cools down when the Hydrogen in the core has been mostly used up. This triggers a contraction resulting in even higher pressure and temperatures at which Helium can fuse.
- Where are interstellar grains first made? The question refers to solid grains, not to the atoms.
- In the outflow from stars including supernovae as the gas expands and cools.
- Why are interstellar grains not made of only ice or of only rock?
- Because rock and ice need a nucleus to condense onto.
- How do we know that interstellar grains are small, submicron sized
- (2) The mass of matter which is not in stars or gas is so low so the light blocking effciency of the material must be near optimum. (3) Blue light is scattered and blocked more than red light which is a signature of particles that are smaller than the wavelength of light.
- Is the slower than originally expected spin of the Sun finally understood?
- Yes, it is due to magnetic coupling between the forming star and plasma in the accretion disk.
- Complete the answer to the question \"What causes some molecular clouds to collapse and form stars?\" Answer: ........... imbedded in the cloud .......... but ......... This ........... triggers collapse.
- Interstellar grains + blocks high energy visual wavelengths and shorter starlight from penetrating to the interior + allows infrared light to escape and cool the cloud. + lowers the gas pressure and.
- It used to be believed that interstellar grains could only be made of metals. Why is it now believed that also silicates (rocky materials), carbons and in some places ices can be on the grains?
- The grains are believed to cycle in and out of cold molecular clouds where they can rebuild by condensing mantles of the less stable materials.
- Where was gold, uranium and other elements with more nuclear mass than iron made?
- In supernova explosions
- What phenomenon in a molecular cloud results in the formation of clusters of stars rather than one or a few more massive stars?
- Turbulence
- We have seen that according to the Virial Theorem only clouds with a certain set of properties collapse under gravity. What are those properties?
- A larger mass or higher density than a threshold value at a given temperature.
- Why is the gas disk surrounding a forming star fared up while the dust is in a thin disk?
- The gas pressure that causes the gas disk to flar up is ine#ective on the dust because of the much lower surface area to mass ratio of dust than of gas molecules.
- What causes the gas outflow from forming stars to be in well collimated bipolar jets?
- The gas was heated into a plasma before it was ejected and therefore has to follow the magnetic field generated by the forming star.
- Which of the following answers best describes how the overall structure of accretion disks was discovered?
- Theoretical predictions were dramatically confirmed by Hubble Space Telescope pictures of forming stars showing flaring disks and bipolar gas outflows.
- What is the most important component of planet building blocks by volume in the outermost parts of the nebula where appreciable heating has not taken place?
- Volatiles such as ices of water and carbon dioxide.
- What is the Kuiperbelt?
- A remnant of the nebula and its accretion disk where icy planetesimals formed
- Why is the pure ice model for a comet nucleus (ice of water, carbon dioxide or other ices) now believed to not be realistic?
- Because ice needed a condensation nucleus to form the grains out of which comet nuclei accreted.