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