astronomy

Question 1

Iron Core Collapse

Answer 1

Stars burn until they reach their iron core. After this there are no fusion fuels left for the star to tap. Iron core collapse follows. There is an explosion and only raw material for planets/next generation of stars is left

Question 2

The Race to Explosion for BH

Answer 2

The baby neutron star is supported by neutron degeneracy pressure. Neutron star mass is growing because of inflating matter. If M> 2.5 Msun, neutron degeneracy pressure fails and BH is formed. Neutron stars are left behind. They shine by residual heat. Pulsars also remain.

Question 3

Neutron Stars

Answer 3

proposed to explain extreme energy of supernovae

Question 4

Pulsars

Answer 4

pulsating radio sources. Rapidly spinning, magnetized neutron stars

Question 5

Black Holes

Answer 5

gravity wins, core collapses, so all mass goes into infinitely small point, the singularity of a new BH

Question 6

No Hair Theorem

Answer 6

BH can only have mass, charge, and spin. Any other differences will be radiated away as gravitational waves or electromagnetic radiation.

Question 7

Electric Charge

Answer 7

BH should be neutral. A charged BH will accrete particles of the opposite charge due to electrostatic force.

Question 8

Spin

Answer 8

the rate at which an object revolves around an axis

Question 9

Equatorial Bulge

Answer 9

The earth has an equatorial bulge due to rotation. This is because the centrifugal force from rotation slightly counteracts the gravitational force. Spinning BHs also develop equatorial bulge.

Question 10

Frame Dragging

Answer 10

The Static Limit is as close as a fixed observer can get with a rocket. Any closer and the rocket must route with BH. Anyone at the event horizon will appear to rotate exactly with the black hole.

Question 11

Static Limit

Answer 11

edge of the ergosphere. Closest you can get and remain stationary

Question 12

Finding BHs

Answer 12

gravitational lensing. Binary systems. Accretion.

Question 13

Binary systems

Answer 13

star-BH will orbit around center of mass. Causes wobbling stars. Doppler effect

Question 14

Accretion

Answer 14

the gravity of the BH will capture some of this gas. The infalling gas particles will collide and create an accretion disk. Most particles don’t fall directly in but get caught in its orbit and slowly spiral in. The gas gets hot as it falls in and emits light.

Question 15

Light emitted by accretion disks

Answer 15

x-ray light

Question 16

Stellar mass BH

Answer 16

are formed as a result of stellar evolution. They are much smaller than supermassive BHs.

Question 17

Neutron stars emit:

Answer 17

x-ray light. Measurement of the unseen mass is one way to separate BHs from neutron stars

Question 18

Infall Energy

Answer 18

Most objects don’t fall directly into a BH. They either experience spaghettification or begin to orbit

Question 19

Orbiting material has angular momentum

Answer 19

MVR (r= radius of orbit) Angular momentum does not change but is conserved. Particles not on perfectly circular orbits will collide, exchanging angular momentum.

Question 20

ISCO

Answer 20

Innermost stable orbit. Inside the ISCO matter likely plunges directly into the BH without radiating energy.

Question 21

Temperature Structure of the Disk

Answer 21

more energy comes out closer to the center. Hotter and smaller near center

Question 22

Max Luminosity/Eddington Luminosity

Answer 22

If great enough, pressure can equal gravitational pull of BH and shut off accretion. More massive BH have higher max luminosities.

Question 23

Spinning BH are:

Answer 23

hotter

Question 24

Jets

Answer 24

a small fraction of matter in accretion disks can be ejected perpendicular to the disk at a high velocity

Question 25

Evidence for BHs

Answer 25

X-ray emissions from normal stars. Velocity measurements indicate unseen massive objects. X-ray study of iron accretion disks show large velocities and gravitational redshift. Low minimum luminosity indicate accretion into event horizon

Question 26

BHs and brightness

Answer 26

They do not always stay very bright

Question 27

Conservation on accretion disks

Answer 27

if some particles in an accretion disk moves inward, conservation of angular momentum requires: other particles to move outward.

Question 28

Spiral Galaxies

Answer 28

blue colors of young stars. Lots of dust and gas

Question 29

Elliptical Galaxies

Answer 29

Light distribution is smooth. lower mass, red, older stars: little gas.

Question 30

Irregular galaxies

Answer 30

often blue young stars. Usually much smaller

Question 31

Expansion

Answer 31

most nebula appear to be receding away from us rapidly

Question 32

redshift

Answer 32

light from other galaxies is shifted to longer wavelengths

Question 33

rate universe is expanding

Answer 33

the universe is expanding at a nearly constant rate

Question 34

observers in all galaxies see:

Answer 34

the same expansion, there’s no center

Question 35

Quasars:

Answer 35

lass than one light week in size. Very red shifted. Powered by BH accretion

Question 36

Active Galactic Nuclei

Answer 36

Quasars: most luminous, outshine their host galaxies. Seyfert: galaxies, low luminosity quasars. Radio galaxies: AGN that are unusually bright at radio wavelengths

Question 37

How do SMBHs get so big?

Answer 37

Start with the collapse of massive stars.

Question 38

Possible solutions as to why SMBHs are so big

Answer 38

Accretion faster than the eddington luminosity rate? Initial stars and their black holes are unusually massive. SMBHs may have formed directly in early universe?

Question 39

Disk and Bulge Structure

Answer 39

disk: plate-like structure orbiting stars and gas. younger stars and active star formation. Bulge: inner spherical distribution of stars; older stars, little gas.

Question 40

The mass of central SMBH:

Answer 40

is correlated to the total stellar velocity dispersion and total stellar luminosity. Also affects availability of material falling into BH

Question 41

Star Formation

Answer 41

Start with cloud of gas and dust. Gravity makes it collapse. It needs to cool to continue collapsing. Cloud will eventually ignite nuclear fusion and become a star.