Astronomy Final 17-29

Imaging/ photometry

Using images of s star to measure its brightness or position

spectroscopy

uses a prism/grating to spread starlight out, examining color in high detail

luminosity

total amount of energy a star emits in all wavelengths

features of luminosity

1. measures a stars true energy output independent of distance

2. more luminous stars burn fuel faster than fainter stars, leading to a shorter lifetime

Apparent brightness

measures how much stars light reaches the earth

light prorogation

as light radiates away from the source, its energy spreads out leading to a decrease

temperature of stellar colors

hot stars emit blue and ultraviolet light

cooler stars emit more red and infrared light

UBV system

measures apparent magnitudes

Color index

measures a stars B-V

1. Hotter stars are brighter in blue light and have lower B-V

2. Cooler stars are fainter in blue light, leading to a higher bV

UBV system color names

• U: ultraviolet magnitude

• B: Blue

• V: visual magnitude

• R: red magnitude

• I: infrared

starlight spectra

when starlight is spread into a spectrum, dark absorption lines appear at specific wavelengths

star spectra in terms of temperature

• cool stars have more absorption lines from neutral atoms

• hot stars get absorption lines from ionized atoms

spectral category

Hottest —> coolest

• O

• B

• A

• F

• G

• K

• M

corresponds to temperature range

Brown Dwarfs

objects with masses to low to sustain hydrogen fusion in the core

• emit infrared

• very faint

features of giant stars

extended atmospheres, low pressure, narrow spectral lines

features of dwarf stars

compact and dense atmosphere, broader spectral lines

metallicity

the fraction of a stars mass composed of metals

key aspects of metallicity

1. traces the chemical evolution of the galaxy

2. young stars have a higher metallicity than older stars

Center of mass for binary stars

center of mass of the binary star system lays closer to the more massive stars center of mas s

Visual binary

a pair of stars gravitationally bound together, but are observed separately through a telescope

• keplers 3rd law

Spectroscopic binary

absorption lines from either star in the system show varying doppler shifts during orbit *cannot be seen through visual binary

eclipsing binary

one star blocks the light of the other during orbit

*cannot be seen through visual binary

• measures the radius/diameter of both stars

optical double

stars that lie in the same line of sight but are not gravitationally bonded

Hertzprung-russel

calculated the Radii of stars with known temperature and luminosity

Luminosity classes

I: supergiant

II: bright giant

III: giant

IV: subgiant

v: main sequence dwarf

VI: subdwarf

D: white dwarfs

Absolute Magnitude “M”

The apparent magnitude a star would have if the distance was 10 pc

m-M = -2.5log₁₀ (d/10pc) or d= 100 ^{m-M +5/5}

Giant molecular cloud (GMC

composed of hydrogen H20 and Hydrocarbons

• if its mass is high enough it can withstand pressure from gas

Jeans Mass

the critical limit for gravitational collapse

Order of star Formation

1. the GMC contains dense clumps (core)

2. center of core is a protostar taking gas from cloud converting potential energy to heat and light

3. the rotating core flattens into a disk

4. protostar forms bipolar outflow— removing remaining metal

5. Protostar is now T Tauri star still collecting material

Main sequence evolution

1. hydrogen fusion at the equilibrium rate

2. time on MS relies on stellar mass

3. MS lifetime is 80-90% of total stellar lifetime

Planetary Nebula formation

1. ejects cloud of gas and dust

2. star ejects gas from surface

3. gas is channeled into directly opposing streams

Very massive stars in Main sequence

explode as a supernova, eventually becoming a black hole

Massive stars Main sequence

explode as a supernova but form as a neutron star

intermediate mass star Main sequence

becomes white dwarfs

low mass stars Main sequence

has some connective layers with strong magnetic fields

Very Low mass stars Main sequence

fully connective layers converting all hydrogen into helium, with a long lifetime

Core-collapse supernova

cycles of fusion in the core produce layers of heavy elements, fusion stops once iron forms. the core implodes once it reaches critical mass

Open clusters

Groups of thousands of stars

Features of open clusters

young stars, loosely shaped, located in the galactic disk

globular clusters

denser groups of thousands of stars

features of globular clusters

earliest formation in our galaxy, low metallicity, only low mass stars left in main sequence, located in galactic halo

Roche Lobe

the surface surrounding each star where the gravitational influences are equal

Ordinary Nova

when white dwarfs accumulate enough hydrogen to surface letting out a breif burst of H fusion

Type Ia supernova

generally produced by gathering white dwarfs or the merging of 2 WD

• type of standard candle

Standard Candle

a star with a intrinsic luminosity, lets astronomers measure intrinsic distances

Henrietta Levitt

discovered the relationship between cepheids intrinsic luminosity and pulsation period. measures distances within milky way and nearby galaxies

“Levitt Law”

Log₁₀ <L>/ L_sun = 1.15 log10 P +2.47

Edwin Hubble

calculated distance to spiral nebula

white dwarfs

dense, hot, earth size cores, made up of carbon and oxygen, no fusion in core

Pauli-exclusion principal

requires each electron to have its own space, once the minimum volume is reached electrons create pressure to withstand collapse

Type II Supernova

this occurs in massive star in MS, core electrons disappear fusing into protons, neutrinos fly outwards and the remaining core is stabilized by neutron degeneracy. leaving a neutron star remnant

features of a black hole

star builds iron core, when fusion stops the outer shell cannot stop collapse

1. iron core collapse and becomes dense

2. nuetron degeneracy pressure cannpt support collapsing core

3. core reaches its critical radius as gravity prevents light from escaping

event horizon

where velocity surpasses speed of light, and strength of gravity is so strong nothing escapes

singularity

remnants from black hole that contains all the mass concentrated into a singular small region

supermassive black holes

found at the center of most galaxies, mass measured by keplers 3rd law, stars closer to galactic center orbit faster eventually overtaking those in larger orbits, leading to spiral arms

spiral arms

the problem that came with understanding the orbit of stars, its believed that stars orbit within the disk of a spiral galaxy, creating dense clumps that created spiral arms.

*like a traffic jam caused by diff orbiting stars

Vera ruben

first evidence of dark matter

Dark matter

flat curves that indicate unidentified material

features of dark matter

1. emits no wavelengths = invisible

2. has a gravitational effect on stars and gas

3. 95% of total galaxy mass

Spiral galaxies

1. Sa/ Sba

2. Sb/ SBb

3. Sc/ SBc

Sa galaxy features

tightly wounded with smooth arms and light central bulge

Sb galaxy

the milky way, fainter bulge and less tightly wound

Sc Galaxy

loose spiral arms, clear stellar clusters, smaller bulge

features of spiral galaxies

young stars, star forming regions, dust in the spiral arms

central bulge appears due to older star population

global clusters are distributed aroung galactic halo

elliptical galaxies

smooth and featurless, most common galaxy, large range in size and mass, contains highly evolved, low mass, low metallicity population of stars, limited dust or gas.

lecticular galaxies

intermediate between ellipticals and spirals, appears disk like but lacks spiral arms, SBo classification

irregular galaxies

don’t fit into hubble sequence

tully-fisher relation

as the galaxy rotates one gas moved towards us and gas on the other side moves away. this links a galaxies luminosity to its rotational velocity

Minor mergers

dwarf galaxies get taken over by other large galaxies— galactic cannabolism. this does not disrupt the larger galaxy

major mergers

two large galaxies merge causing major disruption. this can strip gas out of a galaxy or cause a starburst galaxy

galaxy cluster

members of a galaxy cluster are gravitationally bound to each other

supercluster

contains dozens of galaxy clusters that are not bound by gravity

voids

regions of the universe where no galaxies are found

geroge lamatire

“expansion of the universe” —> clusters of galaxies are not moving apart but space time of universe is moving

cosmological redshift,z.

caused by stretching of photons wavelengths as it passes through the expanded universe

Big bang

marks creation of the universe. the universe was originally a dense singularity where time and space were created

evidence of big band

1. expansion of the universe

   1. most other galaxies are moving away from our milky way

   2. the farther the galaxy the faster it recedes

2. cosmic wave background

   1. big banged produced a hot explosion filling universe with high energy short-wave photons

3. cosmic neutrino background

dark energy

a mysterious force that causes the universe's expansion to accelerate, there is no known orgin, makes up 73 % of space

Horizon problem

the universe is the same almost everywhere due to thermal equilibrium (shouldn’t happen)

the addition of a period — expansion of universe — created a isotropic universe

Inflation

is the reason temperatures increase exponentially together throughout the universe