Exploring the Cosmos - Degree Exam 2013 - Life and Death of Stars (Part 2)
1. Open clusters within the Galaxy
contain about 1 million stars in a sphere of typically 25 parsecs diameter.
usually contain only very old stars which have then spread apart.
often contain metal-rich stars.
are never surrounded by dust clouds.
2. White dwarfs are
cold and tiny compared to the Sun.
so hot that IR radiation dominates, but smaller than the Sun.
typically hot enough to be strong X-rays emitters and about the size of the Earth.
about as hot as the Sun but typically smaller.
3. The crab pulsar is seen to pulse brightly
about 30 times each second.
nearly 30,000 times each second.
only very rarely.
about once a day.
4. Protostars are normally visible in which two bands of the electromagnetic spectrum?
Radio and visible.
IR and x-ray.
visible and UV.
UV and gamma.
5. The helium flash occurs
in a star of 1 solar mass near the end of the main sequence stage.
when a 1 solar mass black hole forms from a white dwarf.
when fusion begins in a proto-star of about 1 solar mass.
in the few seconds before a supernova explosion in a 10 solar mass star.
6. Pulsars are
always observed as optical objects.
never observed as gamma-ray objects.
seen in all the main observing bands within the EM spectrum.
too hard to detect to be able to make any clear statements about them.
7. Supermassive stars
live longer than all other types of star, as they have a greater store of fuel.
are the usual precursors of white dwarfs.
are too large to form black holes.
form iron cores in the final stages of their development
8. Type II supernovae
typically show hydrogen lines in their spectra.
are well-recognised standard candles.
are rare but exceedingly bright night-sky objects lasting many years.
are thought to be due to gravitational collapse of a white dwarf.
9. Sirius B is
a black hole that is difficult to observe because it is so close to Sirius a which is a very bright star.
the "dog star"
a star slightly heavier than Sirius A that causes Sirius A to wobble.
a white dwarf close to Sirius A.
10. Neutron degeneracy
determines the size of black holes smaller than 3 solar masses.
prevents white dwarfs from collapsing to form neutron stars.
affects how neutrons react within the proton-proton chain.
prevents neutron stars from collapsing to form black holes.
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