Review Quiz No. 20
1.
:60
Question 1:
Could a rapidly rotating neutron
star, in which the axis of the
magnetic field structure is the
same as the axis of rotation, be
observed as a pulsar?
20% 20% 20% 20% 20%
1
2
3
4
5
2.
3.
4.
5.
Yes, because all that matters is that it
rotates quickly.
Yes, because all that matters is that the
neutron star has a strong magnetic field.
No, because the beams of light would
always point in the same direction, so
the lighthouse effect couldn’t work.
No, because such a neutron star
wouldn’t emit any light at all.
No, because such a neutron star
wouldn’t rotate.
The Lighthouse Model of Pulsars
A Pulsar’s
magnetic field
has a dipole
structure, just
like Earth.
Radiation
is emitted
mostly
along the
magnetic
poles.
Question 2:
If an object is
collapsed to
the size of its
Schwarzschild
radius,
1.
2.
3.
4.
5.
the escape velocity from its surface would be the
speed of light.
light emitted from its surface would barely be able to
escape from it.
any object on its surface would experience no time,
no matter how long a (finite) time an observer at
large distance would wait.
All of the above.
:45
None of the above.
0%
1
0%
2
0%
0%
3
4
0%
5
Question 3:
What is the Schwarzschild
radius of an object with a
mass of 15 solar masses?
1.
2.
3.
4.
5.
:45
0.2 km
3 km
5 km
15 km
45 km
20% 20% 20% 20% 20%
1
2
3
4
5
Question 4:
If we can detect (indirectly) a
collapsed, compact object, and
we can figure out that its mass is
more than 6.5 solar masses, we
can conclude that …
:45
1.
2.
3.
4.
5.
it must be a white dwarf.
it must be a neutron star.
it must be a black hole.
it could be a neutron star or a
black hole.
it could be a white dwarf, a
neutron star, or a black hole.
20% 20% 20% 20% 20%
1
2
3
4
5
Black Holes
Just like white dwarfs (Chandrasekhar limit: 1.4 Msun),
there is a mass limit for neutron stars:
Neutron stars can not exist
with masses > 3 Msun
We know of no mechanism to halt the collapse
of a compact object with > 3 Msun.
It will collapse into a single point – a singularity:
=> A Black Hole!