Astronomy

Astronomy science bowl vocab

Chandrasekhar limit

-1.44 solar masses, max mass a white dwarf can support through electron degeneracy pressure

Eddington Luminosity

-the maximum luminosity a star can achieve when there is a balance between radiation pressure and gravitational force

Hayahsi Track

-luminosity temperature relationship is followed by pre-main-sequence stars <3M

-stars move vertically on the H-R diagram, keeping the same surface temp but becoming less luminous.

-stars are fully convective

Henyey track

-luminosity temperature relationship followed by stars +0.5M pre-mian sequence after thje core is hot enough

-stars move diagonally towards the main sequence, they heat up but remain just as luminous

-not fully convective

Asymptotic giant branch

-final phase of low-intermediate mass start(0.6-8M), 2nd giant phase

-highly luminous and low surface temp

-AGB stars have C-O cores, He burning shells, H burining shells, and convective envolope

-no fusion in core, low mass loss, thermal pulses every 10,000-100,000 He shell will have a fusion burst

Red Giant Branch

-first giant phase for stars up to 2.3M

-core is inert He, fusion only occuring in thin H shell

-convective envelop expands due to H shell burning

-surface temp around 3000-5000k, massively increased luminousity

Hellium flash

-occurs in stars with mass less then 2.3M

-at end of RGB electron-degenerate helium core is developed

-at 10^8k the triple alpha proccess starts, runaway fusion starts until pressure is brought off the core

-stable He-burning occurs

Horizontal branch

-He fusion occurs in the core, no longer degenerate

-triple alpha proccess occurs, all have roughly the same luminousity

-stable period

Proton-proton chain

-2 protons fuse, then beta+ decay occurs creating deuterium

-deuterium and a proton fuses to create He3(releases gamma array), then 2 He3 fuse to make He4 and two H1(this is pp1)

-pp2(lithium burning), Li7 is formed, then fuses and spilts into 2 He4

-pp3, fusion occurs until Beryllium 8 which then splits, creates high energy neutrinos

CNO cycle

-catalytic fusion proccess where C12, N13, N14, and O15/16 are used as catalysts for the reaction 4H→He4+2e+

-used in main sequence at higher core temps(15-20m K), and needs >1.3M

-Used in O, B and early A class stars

Triple-Alpha Proccess

-post main-sequence

-2 He4 fuse into Be8, and quickly before decay another He4 fuses, creating stable C12

-O16 can also be formed

-requires 100m K core temperatures

Wolf-Rayet star

-Late stage of massive stars(>20M)

-spectra dominated by He, N, C, and O(not H)

-Strong stellar winds and mass loss

Cepheid Variable

-pulsating stars whose brightness changes

-period ranges 1-100 days

-pulsation period and luminosity have relationship, this allows it to be a standard candl;e

RR Lyrae Variable

-pulsating variable stars, but older and less lyuminous then cepheid variables

-period usually less then a day

-low mass(0.6-0.8M)

T Tauri star

-very young pre-main sequence stars

-in process of contracting towards main sequence

-surrounded by protoplanetary disk

-less than 10 million years old, strong stellar winds and mass loss

-strong emission lines and infrared radiation

Brown Dwarf

-failed stars, can’t fuse hydrogen

-masses between 0.0013M and 0.08M

-can fuse deuterium and lithium

-emit mostly infrared

White Dwarf Cooling

-intial temp of 100,000-200,000K

-heat lost over billions of years, C/O core crystal

-heat lost through blackbody radiation

Stellar Nucleosynthesis

-Hydrogen burn: PP chain, CNO cycle

-Helium burning:Triple alpha proccess
-Alpha proccess:Successive helium capture builds elements up to Iron 56

S proccess

-known as slow neutron capture, happens when neutron capture rate is slower than beta decay rate

-causes elements like strontium, barium, lead

-comes from C13(from third dredge up) reacting with He4

-additionally comes from Ne22, where O22 fuses with He4

-occurs along with thermal pulses in AGB

R Proccess

-rapid neutron capture, forms when neutron capture rate is faster than beta decay

-occurs during sopernovae and neutron star mergers, can create elements far heavier then Uranium

Dredge ups

-dredge ups are mixing events between interior and convection envelope

-1st dredge up: as star enters RGB hydrogen burning shell mixes with interior CNO cycle(C12 depleted, more N14, He brought in)

-2nd dredge up:occrs after core He exhuastion(He brought up, N14 further increasedm 16O brought up)

-3rd dredge up: occurs in thermal pulse cycles in AGB(C12 brought up, s-proccess elements brought up as well)

Hydrostatic Equilibrium

-Pressure graident matches gravitational compression

-breakdown of hydrostatic equilibrium leads to new stellar evolution

Virial theorem

-theorem relates kinetic and potential energy for bound systems

• 2(T)= -(U) fir gravitational systems

• E = T + U= -T - U/2

-as star contracts T must increase, while U decreases

-adding energy causesx cooling in gravitational systems

Thorne-Żytkow object

-conjectured hybird star, where a red giant contains a neutron star as its core

-formed through neutron star/red giant collusion

-only likely to occur in globular clusters

Technetium Star

-star which has a stellar spectrum that includes absorbtion lines for Tc

-signifies S-proccess is ongoing

-Likely AGB

Roche Lobe Overflow

-Robe lobe is the equipotential surface around each star in a binary system

-when mass exceeds this point mass is transfered between stars

Urca procces

-neutrino cooling through combinbed electron capture and beta decay reactions

-coupled reactions no nuclear charge change but neutrinos carry away energy

-cooling rate proportional to T^6

-reduces stellar lifetime by 10%~

Nu-proccess

-neutriono included nuleosynthesis in cure collaspe in supernovae

-during core collaspe an immense amount of neutrinos are realsed, these interact with outershell elements

-these interactions often know out protons/neutrons or further destabilize atoms causing new reactions

Spiral Density Wave

-A model that explains how spiral arms don’t disapear due to differential rotation

-states theres a pressure wave throughout the galatic disk, so starts exist and enter the spiral periodically

Bar instability

-gravitational instability creates elongated bar-shaped structures in a galaxy’s center

-the bar rotates as a rigid body and can drive spiral arms outwards

-2/3 of spiral galaxies are barred

Lindblad Resonance

-orbital resonances where star rotation matches spiral wave density rotations

-inner Lindblad resonance means stars orbit faster than the wave

-outer Lindblad resonance means stars orbit more slowly than the wave

-resonances determine boundaries for where spiral waves are

Galactic Halo

-spherical componet surrounding the galaxy’s disk and bulge

-contains old metal-poor stars, globular clusters, and dark matter

-extends far beyond the visible disk

-dark matter halo provides most of a galaxy’s mass as well

-lays above thick disk

Thin Disk

-where most visual stars reisde

-contains young to intermediate age star, high metallicitiy

-lots of rotational motion, star formation site, low velocity dispersion

-scale height of 300pc~

-contains open clusters

Thick Disk

-intermediate properties between thin disk and halo

-contains older stars with higher velocity dispersion

-scale height of 1kpc

-lays on top of the thin disk

Galactic Bulge

-spherical bound cluster of old stars, low metallicity

-located at center of galactic near supermassive blackholes and nuclear star clusters

-little rotation and random orbital mechanics

Globular cluster

-gravitational bound cluster of 10,000-1000,000 old, low metallicity stars

-found in galactic halos

-very dense cores with radii of ~pc

-used as tracers of galactic history

Open Cluster

-loosly bound, 50-1000 young new stars from the same molecular cloud

-found in galactic disks, and spiral arms

Stellar association

-unbound groups of new young stars

-have hot surface temp(O&B classification)

-have t tauri stars

-disperse quickly due to stellar winds

OB Association

-groups of O and B type stars formed together but not bound

-10-100 stars over 30-200 pc

-short-lived, 10-30million years

H II Region(Strömgren sphere)

-ionized gas clouds surrounding massive O and B type stars

-UV radiation ionizes surrounding H gas

-causes a bright emission nebulae

-marks star formation

Planetary Nebula

-shell of ionized gas ejected by low-intermediate mass stars(0.8-8M)

-white dwarfs will eject their envelope

Supernovea Remnant

-shockwave of heated gas from explosion

-contains interstellar medium and ejected material

-can triger star formation

Interstellar Medium(ISM)

-all matter and radiation between stars

-99% gas, 1% dust

-70% H, 28%He

-1atom per cm³

Molecular Cloud

-dense regions of ISM

-molecules can form and survive

-giant molecular clouds are primary star formation sites

Bok Glubole

-isolated dark nebulae(dense nebulae that absorb visable light)

-star formation sites

-found within H II regions, and are between 2-50M

Herbig-Haro Objects

-bright nebular jets created from ionized gas ejected due to newborn stars colliding with clouds of gas and dust at high speeds

-found in star forming regions

Shock front

-boundary where supersonic motion creates abrupt changes in a gases properties

-gas is compressed and heated as it crosses the shock boundary

-shock boundary causes supernova, and stellar winds to cause compression and heating

-can create high energy phenomena

Turbulence

-chaotic fluid motion, contains eddies and rapid velocity and pressure fluctuations

-high velocity particles can cause turbulence, along with galactic rotation, and magneto-hydrodynamic effects

Pulsar

-rapidly rotating neutron star with strong magnetic fields

-charged particles get accelerated along magnetic field lines, emitting radiation

-this radiation creates the periodic pulsing light

Synchrotron Radiation

-radiation from relativistic electrons being accelerated in magnetic fields

-power is proportional to Lorentz factor^4

-highly polarized(linear)

-continuous spectrum

Cyclotron Radiation

-radiation emitted by non-relativistic charged particles from acceleration in magnetic fields

-polarization can be circular or elliptical

Inverse Compton Scattering

-high-energy electrons collide with low-energy photons

-boosts frequency by a factor of Lorentz factor²

-creates xray and gamma ray emission

Bremsstrahlng

-radiation emitted when electrons decelerate in electric fields

Cherenkov Radiation

-radiation emmited when a charged particle travels through a medium faster than the speed of light in that medium

-produces a blue glow

-detection mechanism for particles in ice/water

Gamma-Ray Burst

-caused by most energic explosions

-lasts less then 2 seconds for neutron star merges(kilonova), longer ones due to core collaspe and blackholes(hyper nova)

-energy admitted in jets

Active Galactic Nucleus

-super massive (10,000-10,000,000M) blackholes that are accreting matter

-outshines entire host galaxy

-powers quasars, blazars, Seyfert galaxies

Quasar

-found in AGN, most luminous objects in the universe

-highly redshifted

-broad spectual lines

Blazar

-AGN with jets pointed at Earth, or within 10 degrees

-highly variable brightness

-BL Lac objects(no emission lines), and flat spectrum radio quasars

Serfert Galaxy

-(mostly)spiral galaxy with compact nucleus

-type 1:have broad and narrow emission lines

-type 2:only narrow lines

-less intense than quasars

-seen nearby

Jet

-highly collimated outflow of plasma

-Blankdford-znajek mechanism(converts rotational energy into electromagnetic energy)

-Synchrotron radiation

-very relativistic speeds

Schwarzschild Radius

-critcal radius for blackhole formation R=2GM/C²

-earth radius=9mm, sun=3km

Hawking Radiation

-causes blackhole evaporation

-virtual particles form at horizon, one falls in, one excapes, energy gets depeleted from blackhole

-proportional to mass

Ergosphere

-in Kerr blackholes there is a zone where spacetime is framedragged

-rotational energy reservoir, can be extracted by Penrose proccess

Frame Dragging(Lense-Thirring Effect)

-Spacetime rotation, means you can’t stay “still” within spacetime itself

-proportional to Angular momentum/(c²r³)

1a Supernova

-caused by a white dwarf accreting matter, pushing it above the chandesekar limit

-used as standard candles, silicon absorption lines are present

1b Supernova

-caused by core collapse of a massive star

-He lines are present, no H

-lost H envelope

1c

-caused by core collapse of a massive star

-no He or H lines are present

-can create gamma rays(hypernova)

-lost H and He envelope

Type II

-all type 2 have H lines present, and it’s the core collapse of a massive star that still has H in its outer layers

-II-P, long plateau phase where brightness stays constant for awhile

-II-L, brightness decreases linearly

-IIn, narrow hydrogen lines are caused due to interactions between ejecta and circumstellar material

IIb, stars with hydrogen lines then fade to He lines, lost most of its envelopes before explosion

Stromgren Sphere

-area in HII region where ionization overcomes recombination

Population I, II, III

-I: highest metallicity, less then a few billion years old, found in galactic disk

-II: low but nonzero metallicity, often older than 10 billion years old, found in halo bulge and globular clusters

-III: first stars to ever form, made all of H, He and trace Li, likely all dead, haven’t been observed ever

Friedmann Equations

-cosmology equations that describe how the size of the universe evolves

-contains hubble paremeter, p(energy density of the universe), k(curvature parameter), and lamda

-k=0 means flat universe, k=1 means closed universe, k=-1 means open universe

-FLRW metric scales geometry of the universe

Lamda-CDM Model

-math model of the universe with lamda, CMD, and ordinary matter

-has three postulates, the cosmological principle(the universe is the same everywhere), geodesics only intersect at one point in spacetime and space represents an expanding fluid(Weyl’s postulate), general relativity exists

Plank Era

-0s after the big bang to plank tme

-all forces were unified and quatum gravity dominated

Grand Unification Era

-10^-43s → 10^-36s

-gravity seperates, electroweak and strong are still together

-inflationary epoch 10^-36s → 10^-32s, rapid expansion and quatum fluctions are strentched to cosmic scales

Electroweak Era

-10^-36s → 10^-12s

-weak and electromagnetic still acts as one form

-at end of epoch the forces seperate

Radiation Era

-10^-12s → 47,000

-Quarks, Hadrons, Leptons, photons all have their own epochs in that order

-nucleosynthesis epoch starts at 3minutes

Matter Era

-47,000 to 9.8billion years

-past this era expansion starts accelorating again

-recombination epoch at 380,000 years, where neutral atoms are allowed to form

-380,000 → 150-400 million years, dark age epoch(no stars year)

-reionization epoch 150m → 1b years, first stars form and UV light reionizes the IGM

Dark Energy Era

-universe expansion is being accelerated

-goes till the present

Hubble constant

-70km/s/Mpc

-relates recession velocity to distance

-furthest on the cosmic distance ladder

Critcal Density

-density needed for a flat universe

-p_c= 10^-29g/cm²

-above the value the universe is closed, below its open

Omega parameter

-ratio of actual density to critical density

-Omega = Omega_matter + Omega_{dark energy} + Omega_radiation

-observed value to be 1.000

Flatness problem

-fine tuning problem where omega is exactly equal to one

-inflation drives omega to 1

Baryon Acoustic Oscillations

-sounds waves in early plasma, explained through universe expansion

-150Mpc is the standard distance of these rings, deviations can

Red shift

-z= (wavelength_observed - wavelength_emitted)/(wavelength_emitted)

-the stretching of wavelengths through cosmic expansion

-Hubble’s law v = H₀d

-three types: gravitational, Doppler, and cosmological

Luminosity and angular distance Distance

-distance based on apparent brightness vs absolute brightness

• d_L= (c/H₀)*z

-angular distance is calculated based on a known physical size and apparent angular size

• d_A= D/θ (non expan ding universe

• d_A= d_L/(1+z)²(expanding universe)

Peculiar Velocity

-velocity of an object relative to motion from pure cosmic expansion

-caused by gravitational attraction

Photometry

-measurement of brightness of objects

• m = observed brightness(apparent)

• M = brightness at 10 parsecs(absolute brightness

• m - M = 5log(d)-5

Spectroscopy

-analysis of light separated by wavelength to determine composition, temp, density, and motion

-3 types of spectra for Kirchoffs laws: 1st→continous(hot solid or dense gas), 2nd → emission lines(hot thin gas), and 3rd→absorption lines(cool gas infron of hot source)

Astrometry

-measurements of positions and motions of celestial bodies

-uses parallax, proper motion, and radial velocity

-Parallax is the shift in a star’s position due to Earth’s rotation

• arcseconds of parallax = 1/distance in parsecs

-proper motion is angular movement acorss the sky, in arcseconds per year

• Combined with distance, it can give transverse velocity

-radial velocity is how fast something is moving towards or away from us

• measured with Doppler shift of spectral lines, - means towards, + means away

Hydrogen Spectral Lines

-Lyman series, n_f is 1, involes UV light

-Balmer series, n_f is 2, involes visable light

-Paschen series, n_f is 3, involes infrared light, 1875nm

-Brackett series, n_f is 4, involes infrared light, 4050nm

-Pfund series, n_f is 5, involes infrared light, 7460nm

-notable lines, Lyman-alpha(intergalatic medium 121.6nm), H-alpha(656.3nm, red)

Stark/Zeemen effect

-spilting of spectral lines from electric and magnetic fields

Spectral line broadening