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.
are never surrounded by dust clouds.
contain about 1 million stars in a sphere of typically 25 parsecs diameter.
often contain metal-rich stars.
2. White dwarfs are
about as hot as the Sun but typically smaller.
cold and tiny compared to the Sun.
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.
3. The crab pulsar is seen to pulse brightly
about 30 times each second.
about once a day.
only very rarely.
nearly 30,000 times each second.
4. Protostars are normally visible in which two bands of the electromagnetic spectrum?
visible and UV.
Radio and visible.
UV and gamma.
IR and x-ray.
5. The helium flash occurs
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 a star of 1 solar mass near the end of the main sequence stage.
in the few seconds before a supernova explosion in a 10 solar mass star.
6. Pulsars are
always observed as optical objects.
too hard to detect to be able to make any clear statements about them.
seen in all the main observing bands within the EM spectrum.
never observed as gamma-ray objects.
7. Supermassive stars
are too large to form black holes.
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.
8. Type II supernovae
typically show hydrogen lines in their spectra.
are thought to be due to gravitational collapse of a white dwarf.
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 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.
10. Neutron degeneracy
prevents white dwarfs from collapsing to form neutron stars.
determines the size of black holes smaller than 3 solar masses.
prevents neutron stars from collapsing to form black holes.
affects how neutrons react within the proton-proton chain.
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