1. ASTR 1020 – March 7 Homework 4 due today . Homework 5 due Thursday
Second mid-term exam next Tuesday March 14
Next Observatory Opportunity Tonight at 7:30 .
Website

2. SN1987A First naked eye supernova since 1604.
Discovered by Ian Shelton. Feb 23, 1987 UT
Showed hydrogen escaping at 30,000km/s
In Large Magellanic Cloud
Tiny galaxy orbiting the Milky Way.
Huge international response of the astronomy community.

3. Progenitor Star that exploded was tracked down.
Not terribly prominent. SK
B3 Supergiant m= M=-7.8
T=16,000K, R= 40R
Distance 55,000pc – actually outside Milky Way.

4. Stellar History Burned H 10,000,000 years He 1,000,000 C 300
Ne months O
Si days
POW!!!!

5. Rings HST image of SN1987A a few years after the event. Center is dim
3 Bright rings
Illuminated by the flash
Hourglass shape again
Means there was mass loss
prior to the explosion

6. Impending Collision
Blast wave is about to hit the ring.

7. Big Rings 30 Light Years With this geometry there is only a few light
months delay.

8. Neutrino Astronomy Ground Level Fill mineshaft with water
Put photo detectors around the inside

9. Neutrino Going Through Water
(scattering)
light produced
by secondary interactions n

10. Super Kamiokande

11. Detection of SN1987A Kamiokande II Japan 12 events 15s
IMB Ohio 8 events 5.6s
Mont Blanc neutrino detector saw a marginal signal 4.7 hours earlier. Real???
In 1987A we detected the formation of a new neutron star!

12. Pulsars Neutrons Stars considered unobservable
Forgot the effect of magnetic fields
When a magnetic spins it creates electric fields
Electric fields create accelerated electrons
Accelerated electrons create strong radio signals
Pulsar is a spinning, magnetized neutron star

13. Intense Magnetic Field
Field not necessarily aligned with spin axis
Particles get thrown out along the polar axes (cannot cross field lines)
Beam radio signal along magnetic axis too.

14. From Above
Every time beam sweeps by we see a pulse

15. Lighthouse Analogy Some of the Cosmic Rays that
reach Earth could have been
created in Pulsars

16. Pulse Trains Listen to the Pulsars: PSR B0329+54 1.4Hz
Vela Pulsar 11Hz

17. Center of the Crab Nebula
Chandra (X-rays) and HST (Visible)

18. Pulsar Power Energy Source is the Rotation
As Pulsar emits, rotation slows
As pulsar slows, it becomes less luminous
Rapidly fade out
Period
Glitches or Starquakes
Time

19. The Binary Pulsar Pulses get closer on approaching
side of orbit (Doppler)
Can map out orbit
Two neutron stars spiraling
toward each other. Will merge
into black hole in about 200,000
years
Friction that causes the inward
spiral caused by Gravity Waves
First confirmation of Einstein’s
prediction
Period
Time

20. An X-ray Pulsar Hercules X-1 Discovered in 1971
Pulses every 1.24 seconds in the x-ray
Eclipses every 1.7 days due to binary orbit
Turns off every 35 days due to accretion disk wobble
The Rosetta Stone of X-ray Astronomy
Proved the bright x-ray sources were mass transfer binaries
with a neutron star.
There are about 100 of these “Classical X-ray Binaries” in the Milky Way

21. X-ray Bursters A Neutron Star Nova Intensity Time
Every few hours the x-ray source will “burst” for 30 seconds
Explanation: Helium accumulates on surface of the neutron star in binary
Periodically it explosively burns
Nuclear release insufficient to blow it out into space
Collapses back and cools
A Neutron Star Nova

22. Black Holes YES. Are there any Black Holes?
Just 20 years ago, the answer was “probably”.
The term didn’t exist until 1969

23. What Happens when a neutron star exceeds its Chandrasekhar Limit?
Must Collapse
No known force powerful enough to halt the collapse
Result: Black Hole

24. Things that don’t happen
Collapse to Singularity
Winks out of universe
Explodes by some new force
Einstein’s prediction wasn’t a “sure thing”

25. Formation Neutron Star Collapses
Now it’s inside event horizon and can never be seen again.

26. A Newtonian Black Hole Energy Falling To Surface Kinetic Energy OR
if v=c

27. Schwarzschild Radius Two errors cancel.
This is the radius of the “Event Horizon”
The event horizon is a true singularity in space-time.
It is a place where time and space cease to exist.

28. Geometry of Black Hole Can you boost the signal?
No, that doesn’t help.
Space Curves
in on itself
There’s no path
out!

29. Curved Space

30. Rubber Sheet Analogy

31. Properties - Size The radius of a black hole is 3km per solar mass
There is no limit on size or mass.
Note: Volume rises as the cube of the mass. Implies the larger the black
hole gets, the lower is its density.
A sphere of water the size of Saturn’s orbit would be a black hole!

32. Properties – Escape Velocity
No way.
Not even light can escape.
No signal can escape
No particle
Nothing

33. Properties – Orbital Period
Material orbiting a black hole will have milli-second periods

34. Properties - Basic Mass (Schwarzschild Black Hole)
Electric Charge (doesn’t happen)
Angular Momentum (Kerr Black Hole)
No “Surface” Features
No Magnetic Fields
No Pulsing
“No Hair”

35. Jump on In
You won’t make
it, but it would be quite
a ride!

36. Properties – Energy Emitted
Energy Released from accretion
about 0.1mc2

38. Time Dilation Now it gets weird!
Time does not run at the same rate everywhere in the universe.
Twins are not always the same age.
Clocks run a little bit faster in Colorado than in Washington DC.
Folks in DC are actually a little slower than us.
About one part in a trillion.
That’s a millisecond over a lifetime.

39. Time Dilation Some event takes dt∞ out in free space.
Same event takes place at radius r from center of a black hole.
Now view it from free space.
Takes dt instead. Longer. It looks like things are moving slower.
If you are near the black hole, the rest of the universe appears to be moving faster.

40. Time Dilation As r approaches Rs dt gets longer and longer.
When r reaches the event horizon, time stops.
We know how to make a time machine with a forward switch only!
Just fly to a black hole and orbit above the surface.
But you can fall in really fast as viewed from outside.

41. A “frozen star” If time stops above the surface, it can’t go in.
How does the hole form?
Is the material still stuck in temporal limbo just above the surface?
What’s inside?
If nothing can get out, then how can gravity?

42. Hawking Radiation The vacuum makes pairs of
electrons and positrons that pop
into existence and then annihilate
without any net effect.
Above a black hole, one can get
sucked in. The other annihilates
above the surface to cause
radiation.
Since its close to the surface, the
light gets redshifted escaping,
but it carries energy with it!

43. Temperature
Hawking derived that the temperature of a black hole is thermal.
Energy for the radiation comes from the mass of the hole.
The black hole shrinks with time.
That’s a really long time unless the black hole is tiny.
A 1kg black hole would last only 10-16s.

44. Artist’s impression of Cyg X-1 (NASA)
6M0 BH orbiting an O9 star.
2000pc away in Cygnus