Astro 20 Chapter 11

None of the pulsars emit pulses of visible light because

A few pulsars do emit visible light pulses.

____ occurs when light travels out of a gravitational field, loses energy, and its wavelength grows longer.

A gravitational redshift

Why does our theory predict that neutron stars will spin rapidly?

According to physicists, the conservation of angular momentum principle explains why neutron stars should spin rapidly. When a star collapses, physics says that it must rotate faster to conserve this momentum, just like the example with the figure skater spinning.

What observational evidence do we have that black holes exist?

Although the black hole itself is not visible, astronomers can observe the effects around it. The acceleration disk around a black hole is made up of hot gas and dust being sucked into the black hole, which can be seen. Black holes can also be a part of binary systems, which distorts the star next to it. X-ray radiation from black holes is also used to detect their presence.

How are neutron stars and white dwarfs similar?

Both objects are formed as a result of a dying star. While both have different sizes, they have about the same mass. The neutron star is the denser of the two.

If the sun and stars are supported by gas pressure, what supports a neutron star?

Degenerate neutrons support the weight of a neutron star. These form when neutrons are packed together extremely tight.

The escape velocity of an object depends on I. the mass of that object. II. the mass of the object trying to escape. III. the distance from the center of the object and the escaping object. IV. the speed of light.

I & III

The peculiar system SS 433 I. is emitting beams of energy and matter. II. is producing a spectrum with both a red and a blue shift. III. probably contains an accretion disk. IV. is the result of a planetary nebula.

I, II & III

A pulsar requires that a neutron star I. rotate rapidly. II. have a radius of at least 10 km. III. have a strong magnetic field. IV. rotate on an axis that is different from the axis of the magnetic field.

I, III & IV

Which of the following objects is considered to possibly contain a black hole?

LMC X-3

If neutron stars contain no nuclear fuel, why are they hot?

Neutron stars spin very fast, which contracts the material and makes it hot. When the gas particles in the neutron star fall inward, they pick up speed, which is converted into thermal energy.

Fraud in science is rare because it is difficult to commit. Why is it difficult to commit fraud in science?

Science requires that experimental and theoretical findings be reproducible. Scientific journals only allow certain highly trusted individuals to publish their work. (a and c)

Why don't all supernova remnants contain pulsars?

The pulsar may be tipped so that the beams do not sweep past Earth.

The search for black holes involves searching for

a stellar core greater than 3 solar masses

Pulsars cannot be spinning white dwarfs because

a white dwarf spinning that fast would fly apart.

The density of a neutron star is

about the same as an atomic nucleus.

The event horizon

has a radius equal to the Schwarzschild radius.

The orbit of the binary pulsar, PSR 1936+16, studied by Taylor and Hulse

is growing smaller, presumably by emitting gravitational waves.

The singularity of a black hole

is located within the event horizon.

Cygnus X-1 and LMC X-3 are black holes if the masses of the unseen companions are

more than 5 solar masses.

The density of a ____ is greater than the density of a ____.

pulsar, white dwarf

Which of the following can you never know about a black hole?

the elements of the material that has fallen in

Similar to the sun, pulsars' rotations are believed to slow down because

they are losing angular momentum into space via outward streaming particles.

A neutron star is expected to spin rapidly because

they conserved angular momentum when they collapsed.

Although neutron stars are very hot, they are faint and not easy to see at visual wavelengths because

they have only a small surface area from which to emit. the peak of their thermal emission is at much shorter wavelengths than visual. (both c and d)