Final Exam Astronomy

Milky Way Galaxy

Milky Way Galaxy

A barred spiral galaxy made up of stars, gas, and dust, with spiral arms and a central bar.

Bulge

A spherical region in the center of the Milky Way that contains a central bar and old stars.

Disk

Shaped like a frisbee, the disk of the Milky Way includes spiral arms and is divided into a thin disk and a thick disk.

Thin Disk

Part of the Milky Way's disk that contains the youngest stars and is denser.

Thick Disk

Part of the Milky Way's disk that contains older stars and is puffier, formed from stars that have moved out of the thin disk over time.

Halo

A spherical region that surrounds the disk of the Milky Way and contains very old, faint stars.

Central Bulge

The very center of the Milky Way, which contains a supermassive black hole known as Sgr A*.

Global Clusters

Groups of very old stars that live above the disk of the Milky Way.

Dark Matter

Unseen matter that makes up about 95% of the Milky Way's mass and is believed to exist in a large halo around the galaxy, speeding up the orbits of stars on the edge of the stellar disk.

Sgr A*

Our own supermassive black hole located at the center of the Milky Way, detected through radio wavelength imaging and the tracing of star orbits in the central bulge.

Population I

Bright, blue stars found in the spiral arms within the disk of the Milky Way, characterized by their younger age and higher abundance of heavy elements.

Population II

Fainter, redder stars found in the halo and globular clusters of the Milky Way, characterized by their older age and lower abundance of heavy elements.

Spiral Galaxies

Galaxies that are about 1 million times larger than our solar system, including the Milky Way, with central bulges, halos, disks, and spiral arms.

• star-forming galaxies ( population 1 and 2 )

• Spiral galaxies rotate around their centers

• some have bars

Elliptical Galaxies

Galaxies that contain almost entirely old stars, lack spiral arms, and have a reddish color due to low ongoing star formation.

Irregular Galaxies

Galaxies that do not have regular spiral or ellipsoidal shapes, are disorganized, and often exhibit significant star formation. Form both pop I and pop II stars.

Standard Candles

Objects with known intrinsic luminosity used to measure distances in the universe, such as variable stars like Cepheid variables and Type 1a supernovae.

Cepheid Variable

A type of variable star with a period of time between its brightest phases, allowing astronomers to determine its intrinsic luminosity and calculate its distance.

Type 1a Supernova

An explosion that occurs when a white dwarf in a binary system explodes, with all Type 1a supernovae having the same intrinsic luminosity, making them useful for distance measurements.

Hubble's Law

The observation that the further away a galaxy is, the faster it is moving away from us, described by the equation v = H x d, where v is velocity, d is distance, and H is the Hubble constant.

Quasars

Bright, blue objects that resemble stars but are actually active galactic nuclei (AGN) powered by accreting supermassive black holes at the centers of galaxies.

Supermassive Black Holes

Extremely massive black holes are found at the centers of galaxies, including quasars, which emit large amounts of energy.

Galaxy Mergers

The collision and merging of galaxies, which can trigger star formation and lead to the formation of larger elliptical galaxies.

Cosmological Principle

The idea that the universe is the same everywhere, with isotropic (looking the same in every direction) and homogeneous (essentially the same in any large volume of space) properties.

Cosmic Web

The large-scale structure of the universe, consisting of galaxies connected by filaments and regions without galaxies called voids.

Galaxy Formation

The process by which galaxies form, either through the monolithic collapse of large clouds of gas and dark matter or through the mergers of smaller galaxies.

Big Bang Theory

The theory of cosmology that explains the expansion of the universe, beginning with a primordial explosion of space, time, matter, and energy, and leading to the formation and evolution of galaxies and other cosmic structures.

Observable Universe

The region of space visible to us from Earth, beyond which the time it would take light to reach us is longer than the age of the universe itself.

Dark Matter

The unseen matter that makes up about 27% of the matter-energy in the universe and plays a crucial role in the formation and evolution of galaxies.

Dark Energy

The dominant type of energy in the universe, making up about 68% of

Orbital period

Time to complete one full orbit

Semi-major axis

Distance to center of milky way

Evidence of Sgr A*

• Radio wave length image of the center of the universe

• Astronomers traced the orbits of stars in the central bulge by trackinf their orbits they could figure out the mass concertratedbat the center of the milky way.

• Lots of mas > no light emitted = supermassive black hole

Red light

from star forming regions in the spiral arm

Blue light

form hot young massive stars in the spiral arms

Hubble system for classifying spiral galaxies

Grouped by their morphology or shape.

• Barred spirals start with ( SB )

• Un-barred spiral start with ( S )

Methods for measuring the mass of galaxies

method 1 > measure the time it takes stars to orbit the center of the galaxy at different distances out.

method 2 > measure the spectrum of the galaxy ( combines the light of all its satrs) Look for doppler shifts due to the rotation of the gaalxy.

Edwin Hubble

measured their ditance from us and their velocity ( of galaxies )

Parts of Quasars

• supermassive black hole

• Accretion disk

• jets

Galaxies life cycle

Galaxy evolution is much longer than human life scales. We cannot see individual galaxies grow and chnage. We observe different galaxies of different ages in order to figure put their evolution

Cosmological principle

The universe is the same everywhere the universe is isotropic and homogenous

Isotropic

looks the same in every direction

Homogenous

A large volume of space is essentially the same as any other large volume of space

Universe expansion

universe is curently expanding, the obersvable universe has gotten larger

Rate of Expansion

If we know how much the observable universe has expanded we can figure out how long it has been expanding for.

Formula (expansion)

time= distance / velocity ( time equals distance divided by velocity)ss

Why was the universe hot and dense ?

Because density pressure and temperature are related, if you cram the whole universe into a small space it will have high density, and pressure, and temp. as it expands it cools down.

Hot soup ( 0 - 375,000 years after bing bang )

Universe was hot and dense plasma, first subatomic particles form as well as, hyfrogen atoms, some helium ( through nuclear fusion)

The Cosmic Microwave Background ( 375,000 years after the big bang)

The universe expands and cools enough, that there is no longer plasma. There was a time when the universe went from being opaque to being transparent. We see the cosmic microwave background. We observe this glow from the early universe in all directions.

The Dark Ages ( 375,000-400 million years after the big bang)

The universe had expanded/cooled enough to be transparent. No stars or galaxies yet. Nothing was able to shine so it was very dark.

The first stars formed ( 400 million years after Big Bang)

Has cooled long enough for cool clouds of gas to collapse and form the first stars

The development of galaxies, stars, and planets ( 400 my- 5 billion years after the big bang)

First stars formed then galaxies and planets formed. The universe was still expanding bu the expansion was not accelerating (speeding up)

 The expansion of the universe starts accelerating

after it was 5 billion years old, dark energy became the dominant type of matte/energy in the universe. Dark energy energy of space, expansion is speeding up.

Big freeze

aka heat death of the universe, if the universe keeps expanding forever eventually galaxies and solar systems will drift apart. there won’t be enough gas to form new stars. Black holes will eventually evaporate. Space will be big empty and very cold.

Big rip

The expansion will speed up things will keep drifting apart, and even subatomic particles will get ripped apart.

Big crunch

In this theory the universe will stop expanding at one point n will begin to collapse again. This would be kind of like a reverse big band that would lead to another big bang and the creation of th universe all over again.