Nats: Chapter 11B
12. What was developed in the 1960s to extend the limits of the observable Universe
in radio light?
Bernard Lovell’s largest radio telescope in the world was completed. Multiple radio
dishes (radio arrays) were combined to achieve the power of one enormous
13. Describe the radio emission from a pulsar. What did Hewish initially suspect that
the signal was coming from? What is the true explanation for the pulses?Are all
neutron stars pulsars? Why/why not?
a) Named “pulsars”, these are neutron stars whose radio beams are periodically
aimed at Earth. This radiation can only be observed when the beam of
emission is pointing toward the Earth, much the way a lighthouse can only be
seen when the light is pointed in the direction of an observer, and is
responsible for the pulsed appearance of emission.
b) Hewish initially suspected that the signal was coming from man made
interference.After that was disproved, it crossed his mind that they could be
looking at a deliberate signal from an extraterrestrial civilization.
c) The true explanation for the pulses are energy emitted from neutron stars.A
neutron star is a cosmic zombie: the collapsed core of a heavyweight star that
blows itself apart at the end of its short life in a supernova explosion, it has
no nuclear reaction to hold it up.
d) If a neutron star is rotating so that a beam of radiation that it emits from its
magnetic poles sweeps across the Earth's location, we see it as a pulsar. Only
a neutron star is dense enough to rotate quickly enough without tearing itself
apart, so all pulsars are neutron stars. If the beam does NOT intercept the
Earth, or if the neutron star is not rotating, or does not emit a beam, it is not
seen as a pulsar. Thus not all neutron stars are pulsars.
14. What is time dilation? How was it proven to exist using pulsars in binary
a) Time dilation is an actual difference of elapsed time between two events as
measured by observers either moving relative to each other or differently
situated from gravitational masses.
b)A binary system is a system of two objects in space (usually stars, but also brown
dwarfs, planets, galaxies, or asteroids) which are so close that their
gravitational interaction causes them to orbit about a common center of
mass. Binary pulsars were found to tick slower when closest to their centre of
mass, providing the prediction of General Relativity that time slows down in
strong gravity field (time dilation)
15. What is a radio galaxy? Radio galaxies are typically giant elliptical with jets of radio emission from the
16. What does "quasar" stand for? What do quasars look like in visible light? What
do they look like in radio light? What revealed that quasars are distant galaxies?
Quasar – quasi-stellar radio source. In visible light they look like star, that’s why we
call them quasi-stellar but they are not really stars. In radio light they are
not normal stars because there is radio emission from quasar and it is not a
point source like a star, it is strongly extended. Their spectra revealed that
they are distant galaxies, they have galaxy spectra meaning they have
continuum emission, they have absorption line and emissions lines
(signatures of a galaxy) – their spectra are hugely red-shifted (moving very
quickly away from us meaning it is very far away).
17. What is currently believed to be the cause of the radio emission produced by