ASTR 123 (Test 3-4) - Modules 5 and 6

describe E = mc^2

-"a little bit of mass can be converted into a large amount of energy" -E.g. nuclear fusion in stellar cores

According to General Relativity, an object in free fall represents the situation where no forces are acting on it. what is this called?

Called an "inertial reference frame" (e.g. the ISS) • E.g. tapping on an orange in free fall will result on it moving in a straight line at constant speed

describe the equivalence principle

Cannot distinguish between a gravitational field and an acceleration -An object in free fall has no forces acting on it.

Gravitational Waves (GWs)

General Relativity describes gravity in terms of a spacetime which is deformable • "ripples in spacetime"

what is "special relativity?"

It is "special" because it describes situations where there are no forces or accelerations acting on an object. • The main postulate is simple: The speed of light is an absolute constant.

where is the origin of gravity from?

The origin of gravity is the curvature of spacetime

True or False: No object (of finite mass) can travel at the speed of light or faster

True

what is time dilation?

a physical phenomenon in which time moves differently for different observers in the same inertial frame

To predict whether a star will ultimately become a black hole, what is the key property of the star we should look at? a. mass b. surface temperature c. color d. distance e. Diameter

a. mass

Spacetime effects like time dilation are only noticeable when... a. objects move close to the speed of light b. we have proper telescopes c. events in spacetime are connected by light beams d. very massive objects are involved e. we are within a black hole's event horizon

a. objects move close to the speed of light

The speed that gravitational waves travel is a. the speed of light b. one half the speed of light c. the speed of sound in empty space d. dependent on the black hole mass e. twice the speed of light (start of quiz 6-2)

a. the speed of light

Einstein suggested that the regular change (advance) in the perihelion of the planet Mercury could be explained by: a. the presence of a planet inside the orbit of Mercury, whose gravity influenced Mercury b. a distortion in spacetime caused by the gravity of the Sun c. the pull of a small black hole that orbits our Sun so closely that we are not able to see it d. the presence of a strong magnetic field in the Sun, which causes huge outburst of material

b. a distortion in spacetime caused by the gravity of the Sun

When laser beams in an interferometer combine... a. the resulting light only gets brighter b. an interference pattern of bright and dark light is formed c. the resulting light travels at twice the speed of light d. the increased laser power melts the camera e. the photons are destroyed

b. an interference pattern of bright and dark light is formed

General Relativity predicts that light passing near a massive object like the sun will... a. be spread into a spectrum of wavelengths b. appear bent when observed from Earth c. be the same as always d. make the sun's mass exceed 1.4 solar masses e. be reflected back

b. appear bent when observed from Earth

Current measurements of the Hubble constant H0... a. all agree on a single value b. disagree depending on the method used c. all use Type Ia supernovae as standard candles d. indicate the universe will someday contract to a single point e. are meaningless (end of quiz 6-2)

b. disagree depending on the method used

When astronauts aboard the International Space Station (ISS) in space let go of an orange, it just floats there. Why is that? a. the ISS is so far from the Earth, the gravity there is essentially zero b. the ISS is falling around the Earth, and in free fall, things feel no weight c. spacetime is so different aboard the ISS, that time stops, and so nothing can fall d. the law of gravity only works on the Earth, it doesn't work in space (end of quiz 5-1)

b. the ISS is falling around the Earth, and in free fall, things feel no weight

The main postulate of special relativity is that... a. the speed of gravity is zero b. the speed of light is an absolute constant c. cosmic rays should be able to reach the earth d. space and time should be discarded e. the speed of thought is nonexistent in Wil 100 (start of quiz 5-1)

b. the speed of light is an absolute constant

Massive stars with initial mass greater than about 40 M will collapse to ______________ in range of about 5 to 60 M

black holes

The object(s) created by the merger of two black holes is... a. a neutron star b. a pair of black holes with slightly lower mass c. a single black hole with mass slightly lower than the sum of the merging ones d. a single black hole with mass equal to the sum of the merging ones e. a supernova

c. a single black hole with mass slightly lower than the sum of the merging ones

Special relativity gives a "speed limit", meaning that... a. time slows down in rockets b. elliptical galaxies have smaller redshifts c. objects cannot move faster than the speed of light d. vehicles in Bern, Switzerland move too fast e. Einstein did not watch Star Trek

c. objects cannot move faster than the speed of light

Merging black holes can be observed... a. only at night b. by their radio wave emissions c. only by their gravitational wave emission d. by radio and gravitational wave emissions e. by their x-ray and gravitational wave emissions

c. only by their gravitational wave emission

According to the general theory of relativity, the presence of mass... a. causes motion at the speed of light squared b. is equivalent to the presence of light c. causes curved paths to straighten out until they are exactly straight lines d. causes a curvature (or warping) of spacetime e. will cause a black hole to form, unless there is motion (start of 5-2 quiz)

d. causes a curvature (or warping) of spacetime

What is a key reason that gravitational waves are so much harder to detect than electromagnetic waves? a. gravitational waves don't create any kind of disturbance the way electromagnetic waves do b. gravitational waves are so strong, they really shake our detectors, making measurements difficult c. gravitational waves get all mixed up with sound waves in the Earth's atmosphere, and are therefore hard to distinguish from all the sound d. gravitational waves are much weaker than electromagnetic waves, and therefore require very, very precise equipment to detect e. because the GW scientists are incompetent (start of 6-1 quiz)

d. gravitational waves are much weaker than electromagnetic waves, and therefore require very, very precise equipment to detect

We now know that most heavy elements such as gold are produced in... a. factories in China b. supernova explosions of massive stars c. black hole mergers d. neutron star mergers e. white dwarf mergers

d. neutron star mergers

When scientists say that "black holes have no hair", what do they mean? a. that the event horizon of a black hole is very smooth and does not have parts that jut out b. that if you threw something toward a black hole (a furry animal, say) it would quickly be ripped apart into smaller pieces c. that time near a black hole slows down so much our hair would not grow at a normal rate d. that once a black hole forms, very little information can be extracted from it about the material that is now inside e. no one knows what this means; regular people are not meant to figure out some of the weird things physicists say about black holes (end of quiz 5-2)

d. that once a black hole forms, very little information can be extracted from it about the material that is now inside

The region around a black hole where everything is trapped, and nothing can get out to interact with the rest of the universe, is called... a. the singularity b. the neutron star radius c. the gravitational redshift zone d. the event horizon e. television

d. the event horizon

The location of the 170817 neutron star merger was first determined using... a. radio telescopes b. texts by ancient Chinese astronomers c. the iterative guess method d. three gravitational wave detectors e. the earth's rotation

d. three gravitational wave detectors

In the 2015 gravitational wave discovery event, the two black holes a. were supermassive b. combined to form a neutron star c. were each about 1 solar mass d. were each about 30 solar masses e. never merged (end of quiz 6-1)

d. were each about 30 solar masses

Spacetime is a __________________ medium

deformable • bending and lensing of light • black holes • gravitational waves •the expanding universe

The 170817 event demonstrated that neutron star mergers... a. produce gamma ray bursts b. produce gravitational waves c. produce most of the heavy elements on earth d. produce kilonova afterglows e. all of the above

e. all of the above

A student shines a flashlight out the window of a very fast rocket. If the normal speed of light is c, then ... a. if she shines it forward, the light travels a bit faster than c b. if she shines it backwards, the light travels a bit slower than c c. if she shines it forward, the light travels a bit slower than c d. if she shines it backwards, the light travels a bit faster than c e. the light always travels at speed c

e. the light always travels at speed c

Whereas electromagnetic signals (light) are produced by individual atoms, GWs are produced by _________________ , and it is the only way to directly observe black holes and mergers of black holes and/or neutron stars

full objects

what are the 4 Forces of Nature?

gravitational, weak, electromagnetic, strong

Energetic protons from ancient Type II supernovae are circulating the Milky Way and hit Earth's atmosphere, making a shower of new particles, many of which are called __________.

muons

Objects with zero mass must travel at the speed ____________, e.g. the photons which make up light

of light -Light emitted from a rocket moving at speed v still moves at c

GWs are _________________ of that spacetime, propagating at speed __ .

oscillations c

Gravitational lensing: Light bending as a tool for astronomy Note that the power of the lens depends on the ____________, both visible and invisible (dark matter) (start of 5-2 content)

total mass

Einstein 1905 - 3 famous papers (start of 5-1 slides content)

• Description of Brownian motion (Proved the atomic theory of matter) • Photoelectric effect (birth of quantum physics) • Special relativity

Gravity is "different." describe this...

• by far the weakest • there is no quantum theory of gravity (yet) • is manifest in the structure of spacetime itself (General Relativity)