Astronomy Test 2
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- Rate of nuclear fusion is extremely sensitive to temperature
- Neutrinos? No interaction because they are gone
- Positrons? Quickly find electrons in the core to annihilate with
- No longer redirects photons, now absorbs them
- Cooled to visible energies
- Photons can be seen at Earth 8 minutes later
The sun suddenly stops fusing hydrogen and loses its energy source. Which is true?
- Magnetic fields trap gas in huge bubbling loops
- Cooler areas at liftoff cause dark sunspots
- Energy and light released (flares)
- Charged particles are spewed out into space (coronal mass ejections)
Which is most likely the cause of the extreme heating in the chromosphere and corona?
- Can: damage satellites, harm astronauts, induce current on Earth and destroy electric transformers on the ground, cause swelling in Earth’s atmosphere
How do we know when a coronal mass ejection is on its way?
- The corona is constantly “evaporating”
- But replenished from below
- Apparent movement is caused by Earth’s actual movement around the Sun
- Parsec: (parallax-arcsecond)
- An object at a distance of one parsec has a parallax of 1 arcsecond
- 1 parsec: 1 pc: 3.26 light years
- Brightest stars were of first magnitude
- Dimmest stars were of sixth magnitude
- Everything else was sorted in between
- Fragile types are easily ionized or knocked apart by collisions in high temperature regions (high temp: high energy of particles)
- Hotter temperatures (more gravitational pressure= higher temp)
- Higher luminosity (higher temperature= much higher fusion rates)
high luminosity, short-lived, large radius, hot, blue
You discover a star and its spectrum reveals that it’s a G-type main sequence star. How old is it?
- Molecular clouds: cold enough to form molecules (T: 10 to 30 K)
- Often dusty (infrared light goes through cloud)
- Cloud collapses due to gravity (must be triggered)
If angular momentum is conserved what happens if r goes down (no change in m)?
Protostars start out relatively cool and dark (compared to stars). If the axes of the HR diagram were stretched to these temperatures a protostar would appear at the:
- Stable hydrogen turns into helium in the core
- Stellar thermostat keeps luminosity and temperature stable for billions of years
- Most stars in the galaxy are loss mass, main sequence stars
What happens if the cloud collapses but never quite gets to stardom?
- If they are too massive they will blow themselves apart (theoretical limit is 150 times the mass of the sun)
What will happen when the hydrogen in the core runs out?
- Not hot enough for hydrogen fusion
- Hydrogen shell burning pushes outer layers of the star out
With fusion again supporting the core, our star rests on the Horizontal Branch:
- Outer layers blown off (planetary nebula formed)
- Small, hot carbon “rock” left over (white dwarf)
A star moves upwards and to the right on the HR diagram. What is happening in its core?
- Main sequence lifetimes are shorter
Supernova 1987A was the most recent nearby supernova. Where did it occur?
- There is no way iron can produce any energy to push back against the crush of gravity in the star’s core
- This takes less than 0.01 seconds for the entire core
- Electron degeneracy pressure gone (core collapses completely)
- Last one “observed” in the Milky Way: 1604
- Last one we know about the Milky Way: 1868
- 1 every 100 years for each galaxy means that monitoring 100 galaxies should get you one supernova per year
- Heats surface layers and fuses hydrogen for while (only on surface, does not destroy star)
- Dimmer than supernova but still impressive
About this deck
Textbook: Cosmic Perspective, The (5th Edition)
Essential Cosmic Perspective, The (5th Edition)
Size: 102 flashcards