1. What is a black hole?

2. The end state is called a ‘Black Hole’
What Happens When a Super Massive Red Giant Is Too Massive and collapses?
The end state is called a ‘Black Hole’
A black hole is a tiny, spherical, collapsed stellar core that has enormous gravity, so much gravity that even photons of light cannot escape.

3. Black Holes first suggested in 1783!
5/14/2018
Black Holes
first suggested in 1783!
require a mass at least 3-5 solar masses
evidence?

4. Black Hole Verification
Need to measure mass
Use orbital properties of companion
Measure velocity and distance of orbiting gas
It’s a black hole if it’s not a star and its mass exceeds the neutron star limit (~3 M)
A new Phenomena may point the way!!

5. Gamma Ray Bursts (GRB)
Cosmic -rays must be observed from above our atmosphere.
since the 1960s, satellites have detected strong bursts of -rays
they occur daily, for a few minutes
-rays are hard to focus, so determining their direction is tough
Since 1997, we have detected the afterglows of GRBs at other wavelengths.
we can pinpoint their sources to distant galaxies
What they are is still a mystery.
most luminous events since the Big Bang
best theory: they are hypernovae … gigantic supernovae which form black holes
Hubble ST image of GRB afterglow
in a distant galaxy

6. Gamma ray bursts may signal the births of new black holes

7. At least some gamma ray bursts come from supernovae in very distant galaxies

8. The star has collapsed into oblivion. GRAVITY HAS FINALLY WON!!
The star becomes infinitely small.
it creates a “hole” in the Universe a singularity
‘Size’ of a black hole – the Schwarzschild radius – is about 3km for each solar mass of material.
Since 3 M or more are compressed into an infinitely small space, the gravity of the star is HUGE!
WARNING!!
Newton’s Law of Gravity is no longer valid !!

9. Some black hole candidates include:
LMC X-3 in the Large Magallenic Cloud orbits its companion every 1.7 days and might be about 6 M.
Monoceros A orbits an X-ray source every 7 hours and 45 minutes and might be more than 9 M.
V404 Cygnus has an orbital period of 6.47 days which causes Doppler shifts to vary more than 400 km/s. It is at least 6 M.

10. Cygnus X-1 must have a mass of about 7 times that of the Sun

11. But…
The best Black Hole candidate (thus far):

15. Supermassive black holes may exist at the centers of most galaxies

17. What would it be like to visit a black hole?

18. No Escape
Nothing can escape from within the event horizon because nothing can go faster than the speed of light.
No escape means there is no more contact with something that falls in. It increases the hole mass, changes the spin or charge, but otherwise loses its identity.

19. Since gravity depends on mass – why is light affected?
Einstein had the right idea – the spacetime gets distorted by mass and light travels through and is influenced by the space time.

20. Just as the spacetime is stretched by the large mass, so is the wavelength of light!

22. The Schwarzschild radius defines
the Event Horizon
the point at which nothing can escape!

23. Warping Space the Gravity of a Black Hole
Gravity imposes a curvature on space.
even though it has no mass, light will be affected by gravity
its path through space will be bent and gravity will redshift it
within the event horizon, it is redshifted to infinite wavelengths (zero energy)
As matter approaches the event horizon…
the tidal forces are tremendous
the object would be “spaghettified”

24. Tidal forces near the event horizon of a black hole would be lethal to humans
Spaghettified!!!
Tidal forces would be gentler near a supermassive black hole because its radius is much bigger

25. In the gravity field due to a point mass or spherical mass, for a uniform rope or rod oriented in the direction of gravity, the tensile force at the center is found by integration of the tidal force from the center to one of the ends. This gives
where Dr is the length of the rod, m is its mass, and R is the distance to the massive body.

26. Ultimate tensile strength of bone is:
130 Mpa (M Newtons/meter2)
For steel it is:
Mpa

27. Without integrating:
Maclauren series:

28. Thought Question Is it easy or hard to fall into a black hole? A. Easy
B. Hard
Hint: A black hole with the same mass as the Sun wouldn’t be much bigger than the Manoa campus

29. Matter in a black hole becomes much simpler than elsewhere in the universe
No electrons, protons, or neutrons
Event horizon
the shell from within light cannot escape
Schwarzschild radius (RSch)
the distance from the center to the event horizon
gravitational waves
ripples in spacetime which carry energy away from the black hole
Only three properties of a black hole
mass, angular momentum, and electrical charge

31. Structure of a Kerr-Newman (Rotating) Black Hole
In the Ergoregion, nothing can remain at rest as spacetime here is being pulled around the black hole

32. Retardation of Time by Gravity
In the vicinity of the black hole, time slows down.
If we launched a probe to it, as it approached the event horizon:
50 min of time on mother ship would be only 15 min on the probe
from the mother ship’s view, the probe takes forever to reach event horizon
light from the probe is red-shifted
probe would eventually disappear as light from it is red-shifted beyond radio
From the probe’s view:
it heads straight into the black hole
light from the mother ship is blue-shifted

33. 5/14/2018
Do Black Holes Suck?
At a distance, a black hole exerts gravitational force according to Newton’s Law.
just like any other star with the same mass
if our Sun was replaced by a 1-M black hole, the planet’s orbits would not change
Only at a distance of 3 Rsch from the black hole will the gravity increase from what Newton’s Law predicts.
then one could eventually fall into the black hole
A black hole does not suck in everything around it!

34. Finding Black Holes
5/14/2018
We look for strange motions of stars with perhaps unseen companions.
We may detect them in BINARY STARS

35. Primordial black holes may have formed in the early universe
The Big Bang from which the universe emerged might have been chaotic and powerful enough to have compressed tiny knots of matter into primordial black holes
Their masses could range from a few grams to more massive than planet Earth
These have never been observed
Mathematical models suggest that these might evaporate over time.

36. How do black holes evaporate?
“Virtual” particles and anti-particles are constantly being produced out of the vacuum of space!

37. What about near the event horizon of a black hole?

38. Black holes evaporate
Virtual particles that appear in pairs near a event horizon may not be able to mutually annihilate each other if only one manages to survive a trip along the event horizon.

39. The time it takes for a black hole to evaporate only depends on its mass:
a black hole that lives for only a second has a mass of ~2 x 105 kg

40. Do black holes really exist?

41. Disney Studios presents “THE BLACK HOLE”
The Black Hole Story:
Disney Studios presents
“THE BLACK HOLE”
introduced by
Dr. William J. Kaufmann III B.S. M.S. Ph.D.