Exploring the Cosmos - Degree Exam 2012 - Life and Death of Stars (Part 2)
1. Synchrotron radiation is
a pulsed source of radio interference.
a feature of radiation from a neutron star.
caused by radioactive decay in a Type-II supernova.
a feature of the heat from a red giant.
2. Supermassive black holes are
found at the centre of nearly every galaxy.
only found in distant galaxies.
thought to be very rare in the universe.
usually violent sources of energy that can destroy galaxies.
3. The best evidence of black holes comes from
direct observation of black areas in space.
signs of the effect of strong gravitational fields.
evidence of their extreme magnetic fields.
x-ray sources which are always black holes.
4. Pulsars typically spin
about once a day.
many times per second.
about once a year.
many thousands of times per second.
5. Neutron degeneracy
causes supernova explosions.
prevents the collapse of a white dwarf in a supernova.
leads to the formation of heavy metals like gold in supernovae.
stops collapse in a supernova.
6. An emission nebula is
blue as it scatters the light from stars.
usually dark as it blocks the light from stars.
internally heated by stars.
red as it scatters the light from stars.
7. A protostar forms due to
gravitational attraction due to a nearby star.
collapse of a low density region containing hydrogen.
changes in the early stage of a main sequence star.
collapse of a high density region of gas.
8. Main sequence stars
are continuously contracting.
are continuously cooling.
stay approximately constant in size.
are hydro-dynamically unstable.
9. If 4 hydrogen nuclei fuse to form a helium nucleus
the mass-energy increases by about 1 %.
the mass drops by about 1 %.
energy is absorbed.
the mass is conserved.
10. Given that the radius of the Sun is about 700,000 km
energy from fusion appears almost instantly at the photosphere.
light takes 2 to 3 seconds to travel from the core to the photosphere.
it takes a few hours for light to travel from the core to the photosphere.
energy from fusion takes about 1 million years to travel this distance.
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