Quiz 3

The _____ shift describes how a wave is stretched or compressed as the source of the wave moves toward us or away from us.

Doppler

A pulsar can have a Doppler _____.

shift

The terms 'period' and 'frequency' describe the same thing—namely, some sort of repetitive phenomenon—but they are the _____ of each other.

inverse

We can’t use the Doppler shift unless we see the _____ change.

period

The observed _____ of every pulsar changes all the time because we’re observing pulsars from a moving platform—the Earth.

period

The Earth goes around the Sun at about _____ kilometers per second.

30

The Doppler effect is stronger in some parts of the sky than _____ .

others

Radio noise comes from our electronic equipment, the galactic nonthermal background, the _____, and other sources.

atmosphere

The amplitude of the noise decreases as the square root of the number of _____ that you have.

samples

We measure the dispersion and the shift quite accurately, and the _____ is easy.

shift

The pulsar found by Hulse and Taylor confirmed Einstein’s theory and provided direct experimental proof that changes in _____ travel at the speed of light.

gravity

Pulsars can be used to probe the curvature of space predicted by Einstein’s _____ of relativity.

theory

Blobs in the Earth’s turbulent atmosphere act like little _____ or prisms, making the star dance and twinkle.

lenses

The technical term for the twinkling of stars is _____.

scintillation

The Moon, Sun, and planets don’t _____ due to their large angular size.

scintillate

A type of radio galaxy called a _____ is very bright and very distant and can look like a point source to us.

quasar

Scintillation increases with the wavelength _____.

squared

Antony Hewish built a telescope to discover quasars by their scintillation from blobs in the _____.

solar wind

Hewish’s graduate student, Jocelyn Bell _____, was involved in the construction and operation of the telescope.

Burnell

The scintillation is strongest at low frequencies, so Hewish designed his telescope to operate around ____ megahertz.

80

Bell Burnell discovered scintillating sources as well as a strange faint signal which didn’t look like _____ interference.

terrestrial

They had discovered something new: _____.

pulsars

A pulsar is the remnant of a massive star that exploded as a _____.

supernova

A neutron particle left by itself in free space decays in just a few minutes into a _____ and electron.

proton

The neutron star has a diameter of just a few _____ .

kilometers

Earth’s north magnetic pole is not at the North Pole; similarly, a neutron star’s magnetic pole can be offset from its _____ pole.

rotational

The first pulsars that were detected had periods of about ____ second.

1

The discovery of pulsars initiated a flurry of _____ around the world.

observations

Pulsars lose energy as they rotate, so they are _____ slightly, but very predictably.

slowing

Nearly 50 years after their discovery, there’s still a lot of _____ about the basic pulsar emission mechanism.

mystery

The delay in a pulse's arrival time, which increases as frequency decreases, is called _____.

dispersion

The amount of dispersion gives us an estimate of the _____ to the pulsar.

distance

Every object distorts the space around it at least a little; this is fundamental to the understanding of Einstein’s theory of _____.

relativity

When the pulsar is behind its companion, the pulses are delayed by the extra path they need to travel due to the distortion of _____.

space

The _____ found by Hulse and Taylor confirmed Einstein’s theory and provided direct experimental proof.

pulsar

Joseph Taylor, a faculty member at the University of Massachusetts, sought funds to search for new pulsars using the Arecibo radio telescope, which is _____ feet across.

1000

At the time of Taylor’s proposal, there were about _____ known pulsars.

100

Taylor got the grant, began to buy the hardware necessary to build a digital pulsar _____ system.

detection

They found 40 new pulsars, one in particular had a period of around ____ milliseconds.

60

The two neutron stars in the system have about 1.4 times the mass of the _____.

Sun

The two neutron stars orbit around each other every ____ hours.

7.7

According to classical physics, nothing prevents 2 objects from orbiting each other _____ .

forever

Eventually, the two neutron stars will merge as their orbit _____ through radiation of gravitational waves.

decays

Albert Einstein's theory states that under this theory, space is curved around massive objects, radiating _____ waves.

gravitational

The rapid orbit of the neutron stars produces a large Doppler _____ in pulse arrival times.

shift

The discovery of pulsars provided direct experimental proof that changes in gravity travel at the speed of _____.

light

Both Taylor and Hulse were awarded the _____ prize in Physics in 1993 for their groundbreaking work.

Nobel

A _____ inch of a neutron star contains the same mass as Mount Everest.

cubic

The average pulse shape of a pulsar is very _____.

stable

Pulsars produce nonthermal emission, meaning the radio emission is not dependent on _____ physics.

thermal

Energetic particles in magnetic fields produce _____ emission.

nonthermal

The arrival time of pulses from a pulsar depends on the frequency that was observed; higher frequencies arrive _____ first.

first

The delay of celestial pulses due to ionized gas between us and the pulsar is a significant aspect of radio _____.

astronomy

Dispersion is crucial for distinguishing between signals from space and _____ interference.

terrestrial

The faster the spinning of a pulsar, the smaller the time interval between emitted _____.

pulses

A neutron star’s magnetic field is created when the star collapses and drags the field down with it, _____ it enormously.

amplifying

Pulsars emit radio beams, and when the magnetic pole sweeps past us, we see it as a _____ pulse.

radio

Pulsars are often studied in the frequency range of _____ to 3 megahertz.

300

The stronger the magnetic field, the more likely charged particles are to produce radio _____ at a distance.

emission

Pulsars have been instrumental in confirming theories about space-time, particularly those posited by _____ .

Einstein

The immense pressure inside a neutron star is what allows it to maintain such a high density without collapsing into a black _____.

hole