Astronomy 2022 November 21-23

massive collection of gravitationally bound star, dust and gases. Made when gravity causes dark matter to gravitationally collapse into clusters of stars that are attracted together and merge

20% Ellipticals (E0 E3 E5 E7 S0), 75% spirals (Sa Sb Sc S0 SBa SBb SBc), barred spirals, 5% irregulars.

classified by extent and brightness of the nucleus and openness curvature of the spiral arms. Subclasses SAa, SAb, SAc

differential rotation? The winding problem, 500 million years. Density wave theory: created as density waves pass through disk of stars and gas, one of the evidences of dark matter

grand design galaxy, gravitational influence of NGC 5195. Barred spiral, diameter 140k ly. Disk of stars 1 kpc thick at the location of the sun, 1.5 trillion solar masses. Carina Sagittarius arm, Norma arm, crux scutum arm, Perseus arm, local/Orion arm

classified by the extent and brightness of the nucleus and the openness curvature of the spiral arms. Sublcasses SBa, SBb, SBc

SB barred spiral galaxy, UGC 12158. Strong nucleus and tight arms

SB barred spiral galaxy. NGC 1365

SB barred spiral galaxy. NGC 1080. Small nucleus and loose, well defined arm

astronomers expect that as you get more distant from galaxy’s center, teh velocities of clusters and stars should slow due to Kepler’s third law. That’s not actually what happens.

can’t be seen, doesn’t interact with anything, not composed of atoms. We know it exists by the way it gravitationally affects the expansion of the universe, paths of light ray, orbits of stars in galaxies. Without dark matter, stars, galaxies, clusters of galaxies and the universe will fall apart.

cold neutral hydrogen, dust, neutrinos, axions, black holes, neutron stars

disk of stars, dust and gas, and a halo (sphere of stars), which is the outer region of the galaxy, composed of mostly population 2 stars, RR lyrae stars, and globular clusters.

located in halo and globular clusters. Oldest stars, more than 10 Gyr. Composed of 75% hydrogen, 24.99% helium, poor metal .01%

ellipses over galactic plane, halo stars. Disordered, elliptical orbits at all inclinations. Prograde and retrograde orbits. Wide ranges of orbital speeds.

variable stars. Old, low mass, metal poor stars older than 10b years. 50 L luminosity ranges 2-3, periods 12-24 hours. Using HST, visible out to about 1M parsecs. Valuable for measuring distances in the Milky Way. Found in globular clusters, galactic bulge, halo, anywhere there are old stars

clusters of ancient stars 10-12 billion years old, as old, or older, than galaxies. Mostly cool red stars K and M. Population 10k-1M stars. Stars separated by light weeks/months

1918 used the orbital motions of teh globular clusters to determine the location of the center of the Milky Way, determined sun’s location 8 kpc away from the center

flat pancake pinwheel, rotation and angular momentum

Sagittarius A, supermassive black hole. 4.6M mass. Center of the galaxy has many RR lyrae stars and very little gas/dust.

composed of dust and gas, active area of star formation, Sagittarius A.

Milky Way has 2 main ones: Centaurus and Perseus. Mostly composed of population 1 stars, young O and B stars. 70% hydrogen, 28% helium, rich 2% metals. Neutron stars, pulsars, and black holes also found here

found in spiral arms, ordered circular orbits in the plane, all orbit in the same general direction, orbit speeds similar at any given radius.

galactic clusters. Young newly formed blue and white stars. 10-300 stars, found within plane of galaxy. M45, h and x persei

interstellar medium, emission nebulae (H II regions, site of active star formation, ionized O and B stars), absorption nebulae (dust clouds that absorb light), reflection nebulae (formed as starlight reflects off left over dust grains), giant molecular clouds, planetary nebulae (ejected envelopes of low mass red giants), supernovae remnants

Discovered the first galaxy outside our own using the period luminosity relationship (Andromeda galaxy)

a way galaxies differ. Galaxies vary in percent of population 1 stars and population 2 stars

a way galaxies differ. The stars in some galaxies are found in organized, circular, planar orbits around the nucleus. Stars in some are found in chaotic, elliptical orbits with high inclinations around the Nucleus

a way galaxies differ. Some galaxies have large amounts of dust and gas available for active star formation. Some galaxies have small amounts of dust and gas, little to no star formation.

a way galaxies differ. Spiral galaxies (75%), elliptical galaxies (20%), irregular galaxies (5%)

type E. big, featureless puffballs with a bright center. Elliptical shaped spheroids of old stars, mostly M and K, cool red giants, population 2 stars. Internal structure lacks spiral arms, dust lanes, and have little to no gas or dust. Chaotic, irregular orbits, star formation ended around 8-10 billion years ago. Formed the same way we see them today or through mergers

type SO. Galaxies in transitions, lost spiral arms. Thin disks, nucleus, no spiral arms. Formed from spiral galaxies after star formation shut off, collisions from other galaxies. Some are barred, most have older population 2 stars and large nuclei/halos.

Type 1. Show an irregular structure or no structure. Little evidence of rotation. Can range up to 90% gas, shows evidence of on-going star formation. Dominated by young, blue population 1 stars.

type D. Most common type of galaxy by numbers. Low luminosity Ellipticals and irregulars. Simple, smaller versions of larger irregular galaxies (dwarf irregulars with small and large Magellanic Clouds)

interactions give galaxies their shapes and a path to growth. Collisions of spiral galaxies results in heavy star formation as GMC and HII regions collide and combine. Individual stars unlikely to combine.

created by differential gravitational interactions. With 3 bodies A, B, and C, C is closest to M and therefore the attraction is greater. So since C is accelerating faster, tidal stretching creates tidal tails

a way galaxies merge. Passing by interactions, slow encounter between a large and small galaxy. A small galaxy can be torn apart by tides from larger galaxies, so gas and stars join the larger. Or nuclei of galaxies slowly spiral together and may be the way Ellipticals glow.

a way galaxies merge. May play a pivotal role in the formation assembly of irregular galaxies. Will eventually merge into a single galaxy. Gas clouds combine and form many O and B stars. One day the Milky Way and Andromeda may merge

fast moving smaller galaxy passes right through the middle of a larger disk galaxy. Results in tidal splash, circular density wave moving outward towards the target galaxy. Wave triggers massive star formation