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