Download Black Holes - Chabot College

Black Holes & Relativity
In this chapter you will discover…

Einstein’s theory of general relativity

space and time are not separate entities

how black holes arise

surprisingly ‘simple’ theoretical properties of
black holes

X rays and jets of gas are created near many
black holes
Relativity

Einstein’s vision

Theorized Time &
Distance cannot be
measured absolutely

Time & Distance only
have meaning when
measured relative to
something
The “Up” Paradox


In childhood, we regard “up” as a single direction
above our head.
When we realize that people in Australia do not
stand upside-down…


we revise our common sense
“up” is defined relative to the center of the Earth
What is Relative?

A plane flies WEST from Nairobi to Quito at 1,000 mi/hr.

The Earth rotates EAST at the equator at 1,000 mi/hr.

What an observer sees depends on her/his position!
What is Relative?

A plane flies WEST from Nairobi to Quito at 1,000 mi/hr.

The Earth rotates EAST at the equator at 1,000 mi/hr.

An observer on the Earth’s surface?
=> Would see the plane fly westward overhead
What is Relative?

A plane flies WEST from Nairobi to Quito at 1,000 mi/hr.

The Earth rotates EAST at the equator at 1,000 mi/hr.

An observer far away in space?
=> Would see the plane not seem to move at all, and the
Earth turn under it!
Motion & Reference
•Objects moving relative to one other are in different
reference frames.
•They experience time and measure distance & mass in
different ways
Einstein’s Vision

1905: Special Relativity

Speed of Light is the same for ALL observers

No matter how fast they are moving!

No matter what direction they are moving!
Einstein’s Vision
 1915:
General Relativity
 Acceleration
“upward” is
equivalent to gravitation
“downward”
 We
can’t tell the
difference!!
Einstein’s Vision
 1915:
General Relativity
 Matter
will bend space and time
Time is affected by gravity
Light is affected by gravity
According to Einstein’s Theory of
Relativity, gravity is really the warping of
spacetime about an object with mass.
 This means that even light is affected by
gravity.

Proof!

Deflection of Starlight by the Sun

1919 Total Solar Eclipse

Precession of Mercury’s orbit

Gravitational Redshift of light moving up

Delay in signals from Spacecraft on Mars
Radio Signals from Mars
Mars Orbiters & Landers
send signals to Earth
Signals travel at speed of
light across solar system
Radio Signals from Mars
Signals bent by gravitation
of the Sun
Signals take longer to
reach us than predicted
Special Relativity Consequence

Length is different for moving observers
 Stationary
observers measure longer lengths
 Moving objects appear to be shorter

Time is different for moving observers
 Stationary
observers measure longer times
 Time for Moving objects appears to be less

Energy and Mass are related (E = mc2)
A ball in moving train…
Seen from INSIDE the train, the ball
simply goes UP and DOWN in a certain time
tinside observer
A ball in moving train…
Seen from OUTSIDE the train, the ball goes
UP and DOWN, but ALSO sideways at the
speed of the train, say in a certain time
toutside observer
A ball in moving train…
The faster the train is moving, the faster the ball
appears to be going to an outside observer
A ball in moving train…
The faster the train is moving, the faster the ball
appears to be going to an outside observer,
covering a longer distance in that same time
toutside observer
So what??

Replace the Ball with a Beam of Light
And…

Suppose both inside and outside
observers assume the speed of light is
the same
A light beam in moving train…
For the observer in the train, the light moves up
and down at the speed of light, in a time
tinside observer
A light beam in moving train…
For the observer OUTSIDE the train, the light
travels farther ….
A light beam in moving train…
For the observer OUTSIDE the train, the light
travels farther ….
– but if it moves at the same speed of light –
it must take longer! toutside > tinside
Consequences!
Time measured by someone moving is different
than time measured by someone who isn’t!
toutside observer > tinside observer
Consequences!
Time measured by someone moving is different than
time measured by someone who isn’t!
toutside observer > tinside observer
The faster you go, the greater the difference in your
perception of time vs. for someone not moving!
Proof!

Decay of Subatomic Particles (Muons)
(cf. https://www.youtube.com/watch?v=qgC-NDpt-mw)

Actual Aircraft Travel (Hafele-Keating exp.)
(cf. http://www.youtube.com/watch?v=gdRmCqylsME)

GPS satellites!
(cf. https://www.youtube.com/watch?v=30KfPtHec4s
(cf. https://www.youtube.com/watch?v=zQdIjwoi-u4 )

Nuclear Colliders
Additional Consequences of
Special Relativity
• Time as measured by stationary observer is longer
• Length as measured by stationary observer is longer
• Mass as measured by stationary observer is more
All compared with measurements made by moving
observers…
Additional Consequences of
Special Relativity
• Time is relative!
(https://www.youtube.com/watch?v=02tchltLm3c)
• Length as measured by stationary observer is longer
• Mass as measured by stationary observer is more
All compared with measurements made by moving
observers…
Traveling
to the
Stars
The Doppler Shift Explained through
Relativity
Speed of light is measured to be identical but…
observed frequency (wavelength) is not!
So what
happens to
light near a
VERY massive
object?
Black Holes
& General Relativity
Black Holes – Theory!
 After
massive star supernova,
if core mass > 3 M, gravity will be
too strong for even neutron
degeneracy to stabilize star.
Black Holes – Theory!
 The
star will collapse into
a singularity
“zero” size
 Infinite density
 Enormous gravitational
pull IF you get too close

Black Holes - Theory

The star becomes infinitely small.

it creates a “hole” in the Universe

Since 3 M or more are compressed into
an infinitely small space, the force of
gravity NEAR to the star is HUGE!!!

WARNING!!

Newton’s Law of Gravity is no longer valid !!
Black Holes - Theory
 Defined
 Radius
by their event horizon
inside of which light cannot
escape (Schwarzschild radius)
Black Holes - Theory
 Defined
by their rotation
 Rapidly
rotating holes will affect space
around them
Rotating Black Holes “drag”
space around them
Black Holes - Theory
 Defined
by their event horizon
 Radius
inside of which light cannot
escape (Schwarzschild radius)
 Defined
by their rotation
 Rapidly
rotating holes will affect space
around them
 But
how can they be observed??
Black Holes affect Time
in nearby space
Black Holes affect matter
in nearby space, too
Cygnus X-1
•A candidate for a
*stellar-sized*
black hole
•~ 11x more
massive than Sun.
•8000 ly away.
Black Holes can emit
“jets” of radiation
Black Holes come in
different sizes…
Black Holes at the
Centers of Galaxies
Black Hole at Center of Milky Way!
Intermediate Mass
Holes?
Gamma Ray Bursters
Gamma Ray Bursts as
indicators of Black Holes
Detecting the
“Gravitational Dance” of
Black Holes?