Neutron Stars and Black Holes Remnant cores of massive stars: produce pulsars, jets and gamma-ray bursts Relativity theory is needed!

Results of 2nd Exam Raw mean: 54.92; so curve of 20 pts Curved mean: 74.92;  = 9.80 Distribution: High, 100; Low, 54 ≥ 90: 3 ≥ 80: 15 ≥ 70: 16 ≥ 60: 13 < 60: 3 Random guessing: 52 (after curve) -- no one did that badly

It’s Hard to Find Black Holes They don’t emit (significant) radiation Light bending means they don’t even show up as dark spots:  Unless distance is close to RS, gravity is close to that of a regular star of the same mass

Origin of Black Holes Collapse of very massive stars (>30 M) can lead to BHs of ~3-25 M (neutron stars must have masses below about 2 M ). A NS could accrete more gas from a binary companion, kicking it over the upper mass limit Collapse of densest regions of forming galaxies, either directly or through merger of stars in dense clusters can yield BHs with M > 1000 M . Quantum fluctuations in the early universe could give primordial BHs of a wide range of masses.

Accretion Disks Form when gas spirals down into a massive object. Seen in: Stars (and planetary systems) being born (earlier) Binary stellar systems with compact component: white dwarf neutron star black hole Active Galactic Nuclei (later)

In an Accretion Disk Mass moves inward Angular momentum is carried outward Friction (viscosity) in the gas heats it up Usually most of this heat is radiated from the disk surface giving: Ultraviolet radiation from white dwarfs X-rays from neutron stars and stellar mass BHs Mostly visible and UV from AGN BHs Most logical way to launch jets

One famous X-ray binary with a very likely black hole is in the constellation Cygnus

Cyg X-1: Radio Image & X-ray light curve Combining observations: optical of blue giant; Doppler shifted lines of star and gas stream we conclude star has M>15 M and X-ray emitting companion has M>10 M, so

Cygnus X-1 is a Black Hole Binary

Accretion Disks are Efficient E = mc2 Complete conversion of mass to energy is only possible in matter-antimatter annihilation But normal accretion disks can convert > 5.7% but probably < 32% of mass to energy This is far better than chemical reactions (~ 0.0001 %) or even nuclear fusion (~0.7 %) Full conversion of 1 M /year = 5.7  1039W

Jets Launched From Disks Artist’s rendition of jets launched from vicinity of BH in the center of an AD.

Gamma-Ray Bursts Tremendous powers in high energy photons emitted in just a few seconds First discovered by spy satellites in 1960s looking for atomic bomb tests: isotropic in the sky Usually have “afterglows”: emission in X-rays, optical and radio bands that decay more slowly Generic model: a “fireball” of very hot plasma, bursting out as a very relativistic jet (~100) This makes it look even brighter if jet points at us, but still involves great powers, since many are very distant

Where do gamma-ray bursts come from?

GRB Light Curves and Locations

GRBs are Far Away Since 1997 many have had galaxies identified as their hosts; at large cosmological redshifts, therefore billions of parsecs away

Competing Models: NS-NS Mergers or Hypernovae (or both)?

Some GRBs are Hypernovae Light curves brightening and looking like SN have been seen in a few cases, making it likely that some (many?, all?) GRBs are exceptionally powerful SN But could just be long GRBs, w/ short ones NS-NS mergers.

End of Stars We now turn to collections of stars Galaxies, starting with our Home Galaxy Clusters and superclusters of galaxies Then the whole Universe: Cosmology and the Big Bang