Physics 004 Final Review

Flashcards based on Physics 004 Final Review Lecture Notes

What causes gamma ray bursts?

Formation of black holes, supernova explosions, or collisions between neutron stars.

What happens when black holes and/ or neutron stars merge?

Black holes produce gravitational waves detectable by LIGO, while neutron-neutron star mergers produce light.

What does our galaxy look like?

We see it edge on (100,000 light years wide). Primary features: Disk (1000 light years thick), Bulge (27,000 light years from the Sun), Stellar halo, Globular clusters, and 4 spiral arms.

What is the mass within the Sun’s orbit?

1.0 x 10^11 Msun

How do stars orbit in our galaxy?

Stars in the disk orbit in circles going in the same direction with a little up-and-down motion. Stars in the halo and bulge have random orientations.

How is gas recycled in our galaxy?

The galaxy uses the cycle: Molecular clouds (cool and dense) -> Star formation -> Nuclear fusion -> Returning gas -> Hot bubbles -> Atomic hydrogen clouds.

What gas is within the milky way?

New elements made by a supernova mix into the interstellar medium.

Where will the galaxy’s gas be in 1 trillion years?

Locked into white dwarfs and low-mass stars.

How do we observe the star-gas-star cycle in the Milky Way?

We use many different wavelengths of light.

What do radio waves, emitted by atomic hydrogen and carbon monoxide, show?

21-cm radio waves show where gas has cooled and settled into the disk. Radio waves from carbon monoxide show the locations of molecular clouds.

What do infrared emissions show?

Long-wavelength infrared emission shows where young stars are heating dust grains. They also show where stars are, whose visible light is blocked by gas clouds.

Where are x-rays observed?

X-rays are observed from hot gas above and below the Milky Way's disk.

What do gamma rays show?

Gamma rays show where cosmic rays from supernovae collide with atomic nuclei in gas clouds.

Where does star formation happen?

It usually happens in the spiral arms of a galaxy.

What are spiral arms?

Spiral arms are waves of star formation.

Where do stars tend to form in our galaxy?

Active star-forming regions contain molecular clouds, hot stars, and ionization nebulae. Much of the star formation in our galaxy happens in the spiral arms.

Gas is added to the interstellar medium by supernovae and planetary nebulae. What kind of gas would you expect that to be?

Mostly hydrogen and helium, with a mix of heavier elements in it, such as carbon, oxygen, silicon, iron, and so on.

Why is it difficult to get a good picture of what the Milky Way Galaxy looks like?

Dust blocks our view when we look toward the center or in the disk. It is very large, and the edges are far away and faint, plus we’re inside the Milky Way and therefore cannot see it from the outside.

About how long does light take to reach us from the nearest star besides the Sun? (The Sun takes 8 minutes.)

About four years.

Why did the remaining gas for our galaxy settle into a spinning disk?

It was due to friction between dust and gas & conservation of angular momentum.

What happens in the disk as the galaxy grows older?

Stars continuously form.

What is the problem with the simple model?

The halo is littered with streams of stars and faint dwarf galaxies.

What is the better model?

Some halo stars formed in small galaxies early on that later merged to build-up our halo over time.

What is the simple model and better model good for?

Simple model is good for explaining disk stars; better model explains all of the stars in the stellar halo.

How are galaxies and the universe closely related?

A galaxy's age, its distance, and the age of the universe are all closely related. We see that galaxies formed when the universe was young and have aged along with the universe.

Why does ongoing star formation lead to a blue-white appearance?

Short-lived blue stars outshine the others.

What is a lenticular galaxy?

It has a disk like a spiral galaxy but much less dusty gas (intermediate between spiral and elliptical)

What are elliptical galaxies?

They are all spheroidal and their red-yellow color hints at old star formation.

What is the Hubble Tuning Fork?

A way to organize galaxies based on appearance.

Where are spiral galaxies found?

Spiral galaxies are often found in groups of galaxies (up to a few dozen galaxies). Our Milky Way and our nearest big spiral neighbor, Andromeda, are a part of the Local Group.

Where are elliptical galaxies found?

Elliptical galaxies are much more common in huge clusters of galaxies (hundreds to thousands of galaxies).

What types of galaxies fall into each group?

Blue and star-forming: Spirals and irregulars; Red & Dead: Ellipticals

Where is gas, dust, and star formation more abundant?

They are more abundant in spiral and irregular galaxies.

How do we measure the distances to galaxies?

We use the distance ladder. Brightness alone does not provide enough information to measure distance to an object. Although, if you know an object’s luminosity and brightness, you can determine distance.

How do we build up our distance ladder?

Step 1: Solar system size using radar. Step 2: Distances of stars using parallax. Step 3: Cepheid variable stars as standard candles. Step 4: White dwarf supernova brightness tells us the distance.

What does the relationship between apparent brightness and luminosity depend on?

Distance.

How do we determine a star’s distance?

We can determine a star's distance if we know its luminosity and can measure its apparent brightness.

What is a standard candle?

A standard candle is an object whose luminosity we can determine without measuring its distance. White dwarf supernovae can also be used as standard candles.

What statement is true about elliptical galaxies?

They consist mostly of older stars and are common in large galaxy clusters.

How was the Great Debate settled?

Hubble settled the debate by measuring the distance to the Andromeda Galaxy using Cepheid variables as standard candles.

How is distance and redshift related?

Distance=𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦/𝐻0

How did Hubble prove that galaxies lie far beyond the Milky Way?

He measured the distance to the Andromeda Galaxy using Cepheid variable stars as standard candles.

What can we compare the expanding universe to?

One example of something that expands but has no center or edge is the surface of a balloon.

How is matter distributed?

Matter is evenly distributed on very large scales in the universe.

What does Hubble’s constant tell us?

It tells us the age of the universe because it relates the velocities and distances of all galaxies.

What is cosmological redshift?

Expansion stretches photon wavelengths, causing a cosmological redshift directly related to lookback time.

What is the cosmological horizon?

It marks the limit of the observable universe; a horizon in set by time rather than space.

What was the main issue debated during the Great Debate of 1920?

Whether spiral nebulae were galaxies outside the Milky Way.

Why do more distant galaxies appear to be moving away from us faster?

There is more expanding space between us and distant galaxies, so the total velocity is greater.

What do quasars indicate?

The highly redshifted spectra of quasars indicate large distances. Variability shows that all this energy comes from a region smaller than our solar system.

What do orbits of stars and direct imaging indicate?

They indicate a mass closer to 6 billion MSun.

What is the development of a central black hole related to?

The development of the central black hole must be related to galaxy evolution.

What is the primary evidence that quasars are extremely distant?

Their highly redshifted spectra.

The center of galaxy M87 has been shown to host a black hole with a mass of approximately?

2-6 billion solar masses.

What key process converts gravitational potential energy into thermal radiation near a black hole?

Friction in an accretion disk.

What relationship has been observed between galaxies and their central black holes?

Black hole mass correlates with the galaxy's bulge mass.

What does the evidence for a supermassive black hole at the center of the Milky Way include?

Detection of X-ray flares from the black hole’s core and measurement of star orbits indicating a 4 million solar mass object.

What was the early universe like?

It was extremely hot and dense.

What did photons convert to?

Photons converted into particle–antiparticle pairs and vice versa.

What are the four known forces in the universe? Which ones are the strongest and weakest?

Strong force (strongest), Electromagnetism, Weak force, Gravity (weakest)

What eras of forces were there?

Electroweak era, Gut era, Planck era

What is T.O.E.?

Theory of Everything (during Planck era.)

What happens at the end of the nucleosynthesis era?

Nuclei begins to fuse, and at the end of the era there is 75% H, and 25% He.

What happens at the end of the nuclei era?

Soup of nuclei, electrons & photons. Lasts ~380,000 years.

What happened during the era of atoms?

Atoms form and background radiation is released.

What are the 2 primary pieces of evidence for the Big Bang?

The Cosmic Microwave Background (CMB) and the Big Bang theory correctly predicts the abundance of helium and other light elements.

How does inflation work?

Inflation can make all the structure by stretching tiny quantum ripples to enormous size.

How does inflation affect the overall geometry of the universe?

Inflation of the universe flattens its overall geometry.

Why is the cosmic microwave background now in the form of microwaves?

The universe stretched the light into longer wavelengths.

According to CMB data, what makes up most of the universe’s energy?

Dark energy.

What is dark matter and dark energy?

Dark matter: An undetected form of mass that does not interact with light. Dark energy: An unknown form of energy that accelerates the expansion of the universe.

How do galaxies rotate?

Inside the galaxy: Like a merry-go-round. Outside the galaxy: Like the solar system

How much more dark matter is there than ordinary visible matter?

5.5 times more dark matter than there is ordinary visible matter.

What does the fate of the universe depend on?

The fate of the universe depends on the abundances of all matter and dark energy. It also depends on the rate of acceleration of the expansion.

What best fits the supernova data?

An accelerating universe.

What is the rotation curve of the spiral galaxy?

A plot of rotation speed vs. distance from the center.

Observations indicate that spiral galaxies rotate much faster than would be expected based on their visible gas and stars alone. This has led astronomers to conclude what?

There must be a lot of dark matter whose gravity can be felt but which cannot be seen.

What would a rotation curve of the moons orbiting Jupiter look most similar to?

A rotation curve for the planets within the solar system.

What do the fast speeds of stars in elliptical galaxies tell us?

There must be a lot of dark matter whose gravity can be felt but which cannot be seen.

What would happen to the galaxies within a cluster of galaxies if the dark matter was instantly removed from the cluster?

The galaxies within the cluster would have escape velocity from the cluster.