AST1002 UF Final Exam

What does the Milky Way Galaxy look like?

Thin disk, 100,000 light years in diameter, central bulge and spherical halo that surrounds the entire disk

What type of galaxy is the Milky Way?

Spiral Galaxy

What are the Milky Way's different components

Fairly flat disk of stars, central bulge, halo, spiral arms. Clouds of interstellar gas and dust make up the interstellar medium

Where are young stars located in the Milky Way?

Spiral arms of disk

Where are old stars in the Milky Way?

Globular clusters, halo

Where are the new forming stars located in the Milky Way?

Spiral arms because this where stars die and become the material for new stars. Also galactic center.

Why is the metallicity of very old and young stars different?

Old stars contain smaller proportions of heavy elements than younger stars. This is because the halo does not contain the cold dense molecular clouds required for star formation.

Orbit of Disk Stars

Orbit the galactic center in circular paths that go in the same direction in nearly the same plane. They bob up and down like a merry-go-round

Orbit of Halo Stars

Halo stars orbit the galactic center, but their orientations are completely random, and neighboring stars may circle the galactic center in opposite directions. Orbit is high and low

Orbit of Bulge Stars

Complex orbit, some have random orientations like halo stars while other orbit in the same general direction as disk stars but with more elongated orbits. Orbit is high and low

How can we know the amount of mass in our galaxy?

Newton's Law of Motion and Gravity, orbital motions of stars allow us to determine the distribution of mass in our galaxy. i.e. use sun's orbital velocity and distance from the galactic center to determine the mass of our galaxy lying within the sun's orbit.

How much mass is in the sun's orbit?

100 billion times the mass of the sun

What does the observed rotation curve of our galaxy tell us about the mass in the galaxy?

We can determine the mass on large scales by measuring the orbital motion of stars and gas at greater distances from the galactic center

What do we know about the amount of mass in our galaxy beyond the orbit of the sun? Is it less or more, and what type

There's more matter beyond the orbit of the sun made of stars, star clusters, spiral arms, dark matter

What are the spiral arms?

Pinwheel like structure originating close to the galactic bulge and extending outward throughout the galactic disk

What is to be expected at the center of our galaxy and how do we know about it?

A supermassive black hole, producing radio emissions called Sagittarius A

Standard Candles

An object for which we have some means of knowing its true luminosity, so that we can use its apparent brightness to determine its distance with the luminosity-distance formula

White Dwarf Supernovae

A supernova that occurs when an accreting white dwarf reaches the white-dwarf limit, ignites runaway carbon fusion, and explodes like a bomb, often called type 1a sequence

RR Lyrae Variables

A pulsing variable star that is recognizable by the characteristic shapes of their light curves, all pulsate with only small differences in period between them (every .5-1 day). Used as standard candles. Pre-main sequence

Cepheid Variables

Pulsating variable star that is recognizable that pulsate in a "sawtooth" pattern (every 1-100 days). Post main sequence

Tulley-Fisher Relationship

A relationship among spiral galaxies showing that the faster a spiral galaxy's rotation speed, the more luminous it is. We can determine the distance to a spiral galaxy once we measure its rotation rate and apply the luminosity-distance formula

3 Major Types of Galaxies

Spiral, Elliptical, Irregular

Spiral Galaxies

Flat, white disks with bulges at their centers, have spiral arms. Cool gas and dust, interspersed with hot ionized gas

Elliptical

Rounder and redder than spiral galaxies and are usually football shaped. Very little cool gas and very hot ionized gas. Stars orbit randomly

Irregulars

Neither disk-like nor round. Dominated by young blue stars and large amounts of gas give the galaxies their irregular shapes

Which elliptical galaxies are the most round and which are most elongated?

E0 on the E0-E7 elliptical scale is the roundest, and E7 is most elongated

What types of stars do we find in ellipticals

Old, cool (red) stars

What is the amount of dust and gas in an elliptical galaxy compared to other galaxies?

Very little dust or cool gas. Some contain a lot of very hot gas and are red or yellow because of it

How are the masses of elliptical galaxies?

They are among the largest in the universe

Which spiral have the largest bulge and tighter spiral arms?

Sa has the largest bulge/tighter arms

Which have the smaller bulge and looser smaller arms?

Sc and SBc have the smallest bulge and looser spiral arms

Barred Spiral Galaxies

Appear to have a straight bar of stars cutting across the center with spiral arms curling away from the ends of the bar

Lenticular Galaxies

Lens-shaped, have disk and spheroidal components but appear to lack spiral arms. Hybrid between spiral and elliptical

What types of stars do we find in spirals?

New stars

What is the amount of dust and gas of a spiral galaxy?

Contains more gas than other galaxies, especially in the disk. The bulge and halo contain little to no gas or dust

Why are galaxy collisions common?

Galaxies are gravitationally bound in small groups or big clusters. The gravity pulls them together

Cluster

Few dozen or more galaxies bound by gravity

Groups

Smaller than a cluster

How are spiral galaxies distributed in space?

Tend to collect in groups with several dozen galaxies

How are elliptical galaxies distributed in space?

Clusters of galaxies with up to hundreds and thousands all bound together by gravity

What is the local group?

The Local Group is the group of about 40 galaxies to which the milky way belongs. Largest are Andromeda and Milky Way

How many galaxies are in the Local Group

40

What are quasars?

Extremely bright center of a distant galaxy thought to be powered by a supermassive black hole

What are Radio Galaxies?

Galaxy that emits unusually large quantities of radio waves. Thought to contain a galactic nucleus powered by a supermassive black hole

What are Seyfert Galaxies?

Galaxies that are found relatively nearby and have nuclei much like those of quasars, but are less luminous

Hubble's Law

Mathematical expression of the idea that more distance galaxies move away from use faster at speed which is proportional to its distance

When galaxies move away from us, how is their light shifted?

The wavelengths are red, and the faster they move, the redder they are

When galaxies move towards us, how is its light shifted?

The wavelengths are blue and the faster they move, the bluer they are

What is Hubble's constant?

Expresses current rate of expansion of the universe

How old is the universe?

About 14 billion years

What does Hubble's law imply about the expansion of the universe?

That the universe is expanding as a result of the Big Bang

What is dark matter?

Matter we infer to exist from its gravitational effects but from which we have not detected any light

Evidence for Dark Matter

Orbital speeds in the Milky Way remain high even very far from the center, total mass in clusters of galaxies

3 Ways of Measuring Dark Matter in Clusters

Galaxy orbits around the cluster center, X-rays from very hot gas inside cluster, gravitational links and effects as predicted by Einstein

What is gravitational lensing?

Occurs when a massive object bends light beams that are passing nearby, enabling us to measure the mass of a cluster without relying on Newton's laws

When does gravitational lensing occur?

When a distant galaxy lies directly behind the lensing cluster

Why is the amount of dark matter important to determine the fate of the universe?

Dark matter is the glue that holds the universe together. The gravity from dark matter probably caused protogalactic clouds to become galaxies and galaxies to group into clusters

What is dark energy?

Name given to energy that could be causing the expansion of the universe to accelerate

How much dark energy to we estimate from observations?

Dark energy is much less dense than dark matter but the amount present is outstanding and always will be

What is the composition of the universe?

72% dark energy, 23% dark matter, 5% gas and stars

Big Crunch (Possible Expansion Scenario)

Collapsing universe. If gravity dominates, the universe will stop expansion and the subsequent contraction will make the universe end up in a big crunch, all matter will crash back together

Big Freeze (Possible Expansion Scenario)

If the expansion dominates, the universe will grow until it is so big that the overall energy densities will be too low for even stars to form, and the universe will freeze

Critical Density (Possible Expansion Scenario)

In between Big Crunch and Big Freeze, average mass and energy density would need for the strength of gravity to eventually halt the expansion and remain forever in equilibrium

Accelerating Universe (Possible Expansion Scenario)

Believe the universe expansion rate will grow with time, propagated by dark energy

Decoupling

Separation of classes of particles from regular interaction with one another, as in the decoupling of photons from particles of matter that produced the cosmic background radiation

Oblers' Paradox

If the universe were infinite in both age and size, then the sky would not be dark at night

Big Bang Theory

Scientific theory of the universe's earliest moments, all the matter came into being at a single moment in time

Evidence for Big Bang

Theoretical, observation, and experimental evidence, cosmic radiation field is also evidence

What cannot be explained by the Big Bang?

The origin density that makes galaxies and planets, the overall smoothness of the universe on large scales, the fact that the actual density of matter and energy is close to the critical density

Cosmic Microwave Background

Remnant radiation from the Big Bang, which we detect using radio telescopes sensitive to microwaves, confirming first prediction of big bang theory

The Sun's surface, as we see it with our eyes, is called the ________________.

photosphere

Io's surface appears very smooth because it

is continuously resurfaced by volcanic activity.

While observing the Sun, you note a large number of sunspots. What can you conclude?

There are likely to be an above average number of flares and prominences.

If two different stars were to form at the same time, with one three times as massive as the other, how would the lifetime of the heavier star compare to that of the less massive one?

The less massive star would last fifteen times as long as the more massive one

What interesting feature does Saturn's satellite Titan has on its surface?

Lakes of liquid methane

Two stars have the same temperature with one having twice the radius of the other. How do their luminosities differ?

The larger star is four times brighter.

Order the following objects in increasing radius (smallest to largest size):

neutron star, white dwarf, Jupiter, Sun

Nuclear fusion, the process by which the Sun shines, fuses four ___________ atoms to produce one __________ atom + energy and some neutrinos.

hydrogen, helium

Since dust scatters blue light more than red light, it is best to observe in the_________ wavelength to avoid this obscuration.

infrared

What would happen to the planets orbits if the Sun will collapse into a black hole?

There will be no change in the orbits of the planets

The solar spectrum is a good example of what kind of spectrum?

absorption line spectrum

The tail of a comet consist of

dust and gas

Suppose the temperature of the surface of a star were to rise. How would this affect the star's color and the wavelength of the lines seen in the spectrum?

The color will shift to shorter wavelength, but the lines that are seen will not show any shift

If professor Sarajedini were to hover near a black hole while carrying a standard flashlight, how would her light appear different from your standard flashlight as you observe her from a safe distance?

Her light would appear redder.

A star has a parallax of 0.1 arcsec. What is its distance?

10 parsecs

A stellar remnant that is greater than 3 times the mass of the Sun will become a

black hole

What marks the transition from protostar to star

hydrogen fusion begins

Why do star clusters provide excellent tests for theories of stellar evolution?

The stars in any particular cluster formed roughly at the same time from the same primary material and hence are approximately the same ages as each other.

Which main sequence star will have the shortest lifetime?

O because they are the hottest

If two stars were to form at the same time in different locations, with one star twice as massive as the other, how would their lifetimes compare?

The less massive star would live four times as long as

the more massive one.

Proxima Centauri has the largest parallax of any known star, about three quarters of an arcsecond. This corresponds to a distance of about

1.3 pc.

A white dwarf in a binary system which is accreting matter from a larger companion can manifest itself as a repeating phenomenon known as a

Nova

Which one of these effects does NOT originate in the Sun's magnetic activity cycle?

Neutrinos which pass through the Earth.

A protostar typically radiates most of its energy in the _____________ part of the electromagnetic spectrum.

infrared radio

Why do asteroids and comets differ in composition?

Asteroids formed inside the frost line, while comets formed outside.

The Oort Cloud is believed to be

a spherical cloud of cometary nuclei far beyond the Kuiper Belt

The tops of convection cells can be seen just below the surface of the Sun are called

solar granules

What types of stars end their lives as supernovae?

Stars that are much more massive than the Sun

A cloud fragment too small to collapse into a main sequence star becomes a

brown dwarf.

A loop of gas following the magnetic field lines between sunspots' poles is

a prominence