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