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