Exam on Wednesday

•  Short answer and essay questions •  Mostly qualitative •  Don’t need to memorize formula, but do

need to know which way formula go

•  Review session today, 4:30, here Tuesday, 5:00, 4421 Sterling Hall

Evidence for Black Holes

•  Stellar Mass Black Holes – X-ray binaries – Accretion Disks – Orbits

•  Supermassive Black Holes – Spectra – Masers –  Jets

Type Ia

•  Start with a White Dwarf •  Somehow get above Chandrasekhar limit

– Accretion from companion? – Merger?

•  Start a little nuclear burning in the core

Type Ia Supernova

•  Burn most of the star up to Fe/Ni

•  No compact remnant left, no pulsar

Tycho’s SN (1572) remnant

HOW TO DETECT A BLACK HOLE •  Effects on matter/light outside the horizon

–  gravitational attraction of other bodies – “dark star” with mass

•  distinguish from normal star, white dwarf, neutron star

•  Accretion (swallowing) of gas –  gas heated by compression/turbulence in strong gravity

field X-rays –  but need a source of gas

•  accretion from interstellar matter insignificant •  mass transfer in binaries to the rescue

SunM3>

HOW TO DETECT BLACK HOLES

1. Mass of “compact “ companion in close binary system (stellar remnants only)

X-ray binary (artist’s impression)

HOW TO DETECT BLACK HOLES

2. Orbital motion of stars or gas clouds (supermassive holes)

M87 disk

HOW TO DETECT BLACK HOLES

3. Random motions of stars in galaxy’s nucleus (supermassive holes)

Globular cluster M3 (similar appearance to a galactic nucleus)

Gas almost never falls directly into a black hole

Too much “swirl” (angular momentum) …

Too much “swirl” (angular momentum) … …makes it more

like a whirlpool

Gas almost never falls directly into a black hole

ACCRETION DISK •  Like a flattened whirlpool

•  Gas must give up angular momentum to go down the drain

VISCOSITY (~FRICTION)

ACCRETION DISKS ALLOW US to PROBE the HORIZON

GRAVITY

MOTION

HEAT

RADIATION (X-rays, UV…)

Energy flows from one form to another...

matter swirling inward

friction

ENERGY FLOW IN ACCRETION DISK

GRAVITATIONAL POTENTIAL ENERGY

KINETIC ENERGY

HEAT

RADIATION

Energy flows from one form to another...

falling matter

compression/turbulence

particle collisions, etc.

CAN WE IMAGE BLACK HOLES?

CAN WE IMAGE BLACK HOLES?

•  HUBBLE: read newspaper @ 1 mile –  Optical/UV telescope in space –  Falls short by 100,000

•  VLBA: read newspaper in Chicago –  Transcontinental radio telescope –  Falls short by 1,000

•  Event Horizon Telescope: read paper in LA – High frequency VLBA (being built) – Can do if for 2 Black Holes

•  MAXIM: Read newspaper on moon –  X-ray interferometer in space (2040?)

…NOT YET, BUT SOMEDAY…?

MAXIM = Micro- arcsecond X-ray Imaging Mission

DETECTOR SPACECRAFT

CONVERGER SPACECRAFT

200 M

COLLECTOR SPACECRAFT (32 PLACES EVENLY SPACED)

10 KM

5000 KM

CONSTELLATION BORESIGHT

Hub Spacecraft

SPACECRAFT DELAY LINE

Why is it easier to image a supermassive black hole?

Why is it easier to image a supermassive black hole?

•  Black hole radius scales as M

•  Even though they are far away, still appear large

2 biggest apparent Black Holes

•  Sag A* - Milky way center –  26,000 light years away –  4.3 million Msun

•  M87 –  54 million light years away –  6.6 billion Msun

•  Which looks bigger?

EVOLUTION OF CLOSE BINARIES

•  “Algol Paradox” and its resolution •  Roche lobe = “sphere” of influence

–  actually teardrop shaped

•  Matter flows across Lagrange point •  Too much angular momentum

ACCRETION DISK

ALGOLS CAN EVOLVE INTO X-RAY BINARIES

•  Crucial that mass ratio flips –  otherwise stars can fly apart

•  Compact star either NS or BH –  depends on mass of precursor

•  Two modes of mass transfer –  stellar wind: star smaller than Roche

lobe –  “Roche lobe overflow”: star swells to

fill Roche lobe

NEUTRON STAR VS. BLACK HOLE: …how to tell

•  BH if: – mass > 3 Msun (reliable) – distinctive spectrum (unreliable ????)

•  NS if: – pulsing (X-ray pulsar) – evidence of nuclear explosions on surface

(X-ray burster)

X-ray pulsar (accretion)

X-ray burster (thermonuclear)

BINARY MASS FUNCTION depends on...

•  Orbit period: easy •  Doppler shift of

normal star: easy •  Mass of normal star:

hard •  Orbit inclination: hard

0.1 10 1 100

Log Mass (solar units)

about 15 Msun

Sag A* Orbits