Quant. Astronomy Exam 4

nebula

a cloud of interstellar gas or dust; the term is most often used for clouds that are seen to glow with visible light or infrared

spectral class

(or spectral type) the classification of stars according to their temperatures using the characteristics of their spectra; the types are O, B, A, F, G, K, and M with L, T, and Y added recently for cooler star-like objects that recent survey have revealed

pulsar

a variable radio source of small physical size that emits very rapid radio pulses in very regular periods that range from fractions of a second to several seconds; now understood to be a rotating, magnetic neutron star that is energetic enough to produce a detectable beam of radiation and particles

black hole

a region in spacetime where gravity is so strong that nothing—not even light—can escape

dark matter

nonluminous material, whose nature we don’t yet understand, but whose presence can be inferred because of its gravitational influence on luminous matter

binary stars

two stars that revolve about each other

white dwarf

a low-mass star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size; such a star is near its final state of life

main sequence

a sequence of stars on the Hertzsprung–Russell diagram, containing the majority of stars, that runs diagonally from the upper left to the lower right

exoplanet

a planet orbiting a star other than our Sun

neutron star

a compact object of extremely high density composed almost entirely of neutrons

type II supernova

a stellar explosion produced at the endpoint of the evolution of stars whose mass exceeds roughly 10 times the mass of the Sun

event horizon

a boundary in spacetime such that events inside the boundary can have no effect on the world outside it—that is, the boundary of the region around a black hole where the curvature of spacetime no longer provides any way out

interstellar medium

(or interstellar matter) the gas and dust between the stars in a galaxy

protostar

a very young star still in the process of formation, before nuclear fusion begins

transit

when one astronomical object moves in front of another

accretion disk

the disk of gas and dust found orbiting newborn stars, as well as compact stellar remnants such as white dwarfs, neutron stars, and black holes when they are in binary systems and are sufficiently close to their binary companions to draw off material

cepheid

a star that belongs to a class of yellow supergiant pulsating stars; these stars vary periodically in brightness, and the relationship between their periods and luminosities is useful in deriving distances to them

nova

the cataclysmic explosion produced in a binary system, temporarily increasing its luminosity by hundreds to thousands of times

type Ia supernova

a supernova formed by the explosion of a white dwarf in a binary system and reach a luminosity of about 4.5 × 10⁹ L_Sun; can be used to determine distances to galaxies on a large scale

singularity

the point of zero volume and infinite density to which any object that becomes a black hole must collapse, according to the general theory of relativity

Schwarzchild radius

the radius of the event horizon

HR Diagram

a plot of luminosity against surface temperature (or spectral type) for a group of stars

luminosity

the rate at which a star or other object emits electromagnetic energy into space; the total power output of an object

which type of star is the largest and coolest

red supergiant

which type of star is the smallest and hottest

white dwarf

where do most stars in the universe fall on the HR diagram

the main sequence

what color of stars are the coolest

red

what color of stars are the hottest

blue and white

what is the metric of the HR diagram based on (what kind of star)

our sun

where do the most luminous stars fall on the HR diagram

the top

where do hot stars fall on the HR diagram

the left

where do the cooler stars fall on the HR diagram

the right

how long do stars in the main sequence typically stay there

90% of their lifetime

what is the color of spectral class O

blue-violet

what is the surface temperature of spectral class O

30,000-50,000 K

what is the color of spectral class B

blue-white

what is the surface temperature of spectral class B

11,000-30,000 K

what is the color of spectral class A

white

what is the surface temperature of spectral class A

7500-11,000 K

what is the color of spectral class F

yellow-white

what is the surface temperature of spectral class F

5900-7500 K

what is the color of spectral class G

yellow

what is the surface temperature of spectral class G

5200-5900 K

what is the color of spectral class K

orange

what is the surface temperature of spectral class K

3900-5200 K

what is the color of spectral class M

red-orange

what is the surface temperature of spectral class M

2500 - 3900 K

what size is a dwarf star

smaller than the sun

what size is a giant star

1-10 times bigger than the sun

what size is a supergiant star

10-1500 times bigger than the sun

what is the horizontal axis of an HR diagram

surface temperature of the star

what is the vertical axis of an HR diagram

luminosity of the star

what portion of the apparent brightness scale is visible with the naked eye

-25 to +6

what stars are the brightest on the apparent brightness scale

-25 ranked celestial bodies

how do we “see” nebula

some emit their own light (emission)
some scatter blue light off their dust (reflection)

look with radio telescopes with 21 cm wavelength radiation

what is 21 cm wavelength radiation

light produced from the transition & spin in the hydrogen atom

how do stars form from nebula

gas and dust from nebula get stored up by supernova explosion, leading to collapse and heating up. once it heats up enough to start the hydrogen-helium fusion reactions at the core, it’s officially a star

what is hydrostatic equilibrium

when the inward force of gravity and the outward thermal force of a star are balanced

what is the conservation of angular momentum

Spinning objects change rotation speeds as they change shape

think figure skates spinning slower with their arms out and faster with their arms in

how does a solar system form from a nebula

the star forms from the nebula material, left over material flattens out around the budding star into a disk, planets begin to form from the material, planets finish forming and solar winds blow excess materials out of system

how many exoplanets have been found so far

6158

how do we find exoplanets

astrometry & doppler shift

occultation

direct imaging

how do we use astrometry and doppler shift to find exoplanets

stars wobble as exoplanets orbit them, so observing the wobble and the doppler shift from the orbit works to identify exoplanets

what is occultation

the dipping in light of the star as the planet passes in front of it

what is the transit method

watching the slight dips in star’s light as exoplanet passes in front of the star to observe the size, orbital period, and presence of the exoplanet

describe the Kepler Mission Satellite and exoplanets

launched in 2009 and lasted 9 years

orbits the sun and not earth

pointed towards constellations cygnus, lyra, and draco

used transit method to observe exoplanets

describe the TESS (Transiting Exoplanet Survey Satellite) mission and exoplanets

Launched in April 2018

able to find smaller exoplanets, looking for Earth-like planets.

Uses transit method

Orbits Earth, can look at a huge portion of the sky

Has found approx. 7000 candidates, and 600 confirmed exoplanets

describe a low-mass star’s death process

on the main sequence 90% of lifespan

runs out of fuel and leaves main sequence

helium builds up in the core and the layers heat up and expand and then cool down creating a red giant

helium fuses in to carbon during the helium flash, stopping fusion and causing the core to collapse

becomes planetary nebula with white dwarf core left at the center

how does a nova occur in the low-mass star death

white dwarf in binary system steals hydrogen off of the binary partner, and the hydrogen spirals down onto the white hot surface and explodes

uses accretion sphere

what is a variable star

stars in the instability strip

instability strip is block spanning from near the bottom of the main sequence up to red supergiant territory - first bit of the path of star death on HR diagram

describe the fusion reactions that occur during star death for a high-mass star

reactions press further than helium—> carbon —> progresses all the way to iron in the core of the star & this stops any fusion reactions causing the collapse of the star core

what type of explosion occurs from the fusion into iron in high-mass stars

type II supernova

is there anything left after a type II supernova

yes; the core remnant

what are the types of core remnants left over after a type II supernova

neutron star & black hole

what is the difference between neutron stars and black holes as core remnants

neutron stars are lower solar mass (1-1.3 x mass of the sun) remnants and the neutrons keep the core from further collapsing inward

black holes stem from larger solar mass (1.4- 3 x the mass of the sun) remnants and the neutrons are no longer able to keep the core from further collapsing —> all of the mass collapses down to single point in space time (singularity)

describe the relationship between neutron stars and pulsars

neutron stars are incredibly small with lots of mass crammed into that space

they also have very concentrated magnetic fields after the collapse, and when the star spins incredibly fast, the magnetic field axis and rotational axis may not line up

when they don’t line up, there’s a very rapid radio signal that can be detected from the charged radio particles stuck in the magnetic field lines —> those are pulsars

special relativity theory

a theory about the physics of very fast motion (close to speed of light) where time passes slower for objects that are moving fast (time dilation) and length/space gets smaller for objects that are moving fast (length contraction)

general relativity

a theory about physics of motion near very massive objects where space and time are inter-connected, like a fabric called the “fabric of space-time”

if one component changes, so does the other

light follows the lines/flow of space-time

larger objects create larger warps/stretches of space-time

gravitational lensing

light can be bent around massive objects

escape velocity

the speed a body must achieve to break away from the gravity of another body

what are the parts of a galaxy

nuclear bridge

disk

spiral arms

halo

globular clusters

what do most galaxies have at their center

supermassive black holes

what are globular clusters

some of the first stars to form in the universe

small groups of very old stars

do we know what makes up the halo surrounding a galaxy

no; theories that is is dark matter, but we do not know what makes up dark matter

what measurement units do we use to measure galaxy distances

megaparsec (mpc = 1 million parsec)

what methods do we use to measure galaxy distance from Earth

Cepheid Star Method

Standard Candle Method

what is the cepheid star method of measurement

The time it takes a variable star to complete one cycle of brightness as related to the star’s luminosity, and then using that information with the inverse-square law to measure distance

What is the standard candle method of measurement

pick an object that is bright enough to be visible at enormous distances that has a known luminosity and compare its apparent brightness using the inverse square law to measure distance

what are the different shape classifications of galaxies

spiral

barred

ellipticals

irregulars

what type of galaxy is the milky way

barred spiral galaxy