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