Universe 8e Lecture Chapter 22 Black Holes

1
Roger A. Freedman William J. Kaufmann III
Universe Eighth Edition
CHAPTER 22 Black Holes
2
(No Transcript)
3
The Speed of Light Is the Same to All Observers
The speed you measure for ordinary objects
depends on how you are moving. Thus, the batter
sees the ball moving at 30 m/s, but the
outfielder sees it moving at 40 m/s relative to
her.
4
The Speed of Light Is the Same to All Observers
Einstein showed that this commonsense principle
does not apply to light. No matter how fast or in
what direction the astronaut in the spaceship is
moving, she and the astronaut holding the
flashlight will always measure light to have the
same speed.
5
Length Contraction and Time Dilation The
faster an object moves, the shorter it becomes
along its direction of motion. Speed has no
effect on the objects dimensions perpendicular
to the direction of motion.
6
Length Contraction and Time Dilation The faster
a clock moves, the slower it runs. This graph
shows how many seconds (as measured on your
clock) it takes a clock that moves relative to
you to tick off one second. The effect is
pronounced only for speeds near the speed of
light c.
7
The Equivalence Principle The equivalence
principle asserts that you cannot distinguish
between (a) being at rest in a gravitational
field and (b) being accelerated upward in a
gravity-free environment This idea was an
important step in Einsteins quest to develop the
general theory of relativity.
8
The Gravitational Curvature of Spacetime
According to Einsteins general theory of
relativity, spacetime becomes curved near a
massive object. To help you visualize the
curvature of four-dimensional spacetime, this
figure shows the curvature of a two-dimensional
space around a massive object.
9
The Gravitational Deflection of Light Light
rays are deflected by the curved spacetime around
a massive object like the Sun. The maximum
deflection is very small, only 1.75 arcsec for a
light ray grazing the Suns surface. By contrast,
Newtons theory of gravity predicts no deflection
at all. The deflection of starlight by the Sun
was confirmed during a solar eclipse in 1919.
10
The Gravitational Slowing of Time and the
Gravitational Redshift (a) Clocks at different
heights in a gravitational field tick at
different rates. (b) The oscillations of a light
wave constitute a type of clock. As a light wave
climbs from the ground floor toward the top
floor, its oscillation frequency becomes lower
and its wavelength becomes longer.
11
The Gravitational Slowing of Time and the
Gravitational Redshift The oscillations of a
light wave constitute a type of clock. As a light
wave climbs from the ground floor toward the top
floor, its oscillation frequency becomes lower
and its wavelength becomes longer.
12
The Formation of a Black Hole (a)(c) These
illustrations show four steps leading up to the
formation of a black hole from a dying star. (d)
When the star becomes a black hole, not even
photons emitted directly upward from the surface
can escape they undergo an infinite
gravitational redshift and disappear.
13
Curved Spacetime around a Black Hole This
diagram suggests how space time is distorted by a
black holes mass.
14
(No Transcript)
15
The Environment of an Accreting Black Hole If a
black hole is rotating, it can generate strong
electric and magnetic fields in its immediate
vicinity. These fields draw material from the
accretion disk around the black hole and
accelerate it into oppositely directed jets along
the black holes rotation axis. This illustration
also shows other features of the material
surrounding such a black hole.
16
(No Transcript)
17
Gamma-Ray Bursters This map shows the same sky
as in part (a) but at visible wavelengths.
Comparing part (b) with part (a) shows that
unlike X-ray bursters, which originate in the
disk of the Milky Way Galaxy, gamma-ray bursters
are seen in all parts of the sky.
18
The Host Galaxy of a Gamma-Ray Burster This
false-color image was made on February 8, 1999,
16 days after a gamma-ray burster was observed at
this location. The host galaxy of the gamma-ray
burster has a very blue color (not shown in this
image), indicating the presence of many recently
formed stars. The gamma-ray burst may have been
produced when one of the most massive of these
stars became a supernova.
19
The Collapsar Model of a Long-Duration Gamma-Ray
Burster These illustrations show the final few
seconds in the life of a massive, rapidly
rotating supergiant star that has lost its outer
layers of hydrogen and helium. After the jets
have subsided, what remains is a Type Ic
supernova with a black hole at its center.
20
A Supermassive Black Hole The galaxy NGC 4261
lies some 30 million pc (100 million ly) from
Earth in the constellation Virgo. (a) This
composite view superimposes a visible-light image
of the galaxy (white) with a radio image of the
galaxys immense jets (orange). (b) This Hubble
Space Telescope image shows a disk of gas and
dust about 250 pc (800 ly) across at the center
of NGC 4261. Observations indicate that a
supermassive black hole is at the center of the
disk.
21
An Intermediate-mass Black Hole? M82 is an
unusual galaxy in the constellation Ursa Major.
The inset is an image of the central region of
this galaxy from the Chandra X-ray Observatory.
The bright, compact X-ray source varies in its
light output over a period of months. The
properties of this source suggest that it may be
a black hole of roughly 500 solar masses or more.
22
The Structure of a Nonrotating (Schwarzschild)
Black Hole A nonrotating black hole has only two
parts a singularity, where all of the mass is
located, and a surrounding event horizon. The
distance from the singularity to the event
horizon is called the Schwarzschild radius
(RSch). The event horizon is a one-way surface
Things can fall in, but nothing can get out.
23
(No Transcript)
24
(No Transcript)
25
A Rotating Supermassive Black Hole This artists
impression shows the accretion disk around the
supermassive black hole at the heart of the
galaxy MCG6-15-30. The arching magnetic field
allows the accretion disk to extract energy and
angular momentum from the black hole.
26
Falling into a Black Hole (a) A cube-shaped
probe is dropped from a distance of 1000
Schwarzschild radii from a 5-M black hole. (b),
(c), (d) As the probe approaches the event
horizon, it is distorted into a long, thin shape
by the black holes extreme gravity. A distant
observer sees the probe change color as photons
from the probe undergo a strong gravitational
redshift.
27
(No Transcript)
28
Key Ideas

• The Special Theory of Relativity This theory,
  published by Einstein in 1905, is based on the
  notion that there is no such thing as absolute
  space or time.
• The speed of light is the same to all observers,
  no matter how fast they are moving.
• An observer will note a slowing of clocks and a
  shortening of rulers that are moving with respect
  to the observer. This effect becomes significant
  only if the clock or ruler is moving at a
  substantial fraction of the speed of light.
• Space and time are not wholly independent of each
  other, but are aspects of a single entity called
  spacetime.

29
Key Ideas

• The General Theory of Relativity Published by
  Einstein in 1915, this is a theory of gravity.
  Any massive object causes space to curve and time
  to slow down, and these effects manifest
  themselves as a gravitational force. These
  distortions of space and time are most noticeable
  in the vicinity of large masses or compact
  objects.
• The general theory of relativity is our most
  accurate description of gravitation. It predicts
  a number of phenomena, including the bending of
  light by gravity and the gravitational redshift,
  whose existence has been confirmed by observation
  and experiment.

30
Key Ideas

• The general theory of relativity also predicts
  the existence of gravitational waves, which are
  ripples in the overall geometry of space and time
  produced by moving masses. Gravitational waves
  have been detected indirectly, and specialized
  antennas are under construction to make direct
  measurement of the gravitational waves from
  cosmic cataclysms.
• Black Holes If a stellar corpse has a mass
  greater than about 2 to 3 M?, gravitational
  compression will overwhelm any and all forms of
  internal pressure. The stellar corpse will
  collapse to such a high density that its escape
  speed exceeds the speed of light.

31
Key Ideas

• Observing Black Holes Black holes have been
  detected using indirect methods.
• Some binary star systems contain a black hole. In
  such a system, gases captured from the companion
  star by the black hole emit detectable X rays.
• Many galaxies have supermassive black holes at
  their centers. These are detected by observing
  the motions of material around the black hole.

32
Key Ideas

• Gamma-Ray Bursters Short, intense bursts of
  gamma rays are observed at random times coming
  from random parts of the sky.
• By observing the afterglow of long-duration
  gamma-ray bursters, astronomers find that these
  objects have very large redshifts and appear to
  be located within distant galaxies. The bursts
  are correlated with supernovae, and may be due to
  an exotic type of supernova called a collapsar.
• The origin of short-duration gamma-ray bursters
  is unknown.

33
Key Ideas

• Properties of Black Holes The entire mass of a
  black hole is concentrated in an infinitely dense
  singularity.
• The singularity is surrounded by a surface called
  the event horizon, where the escape speed equals
  the speed of light. Nothingnot even lightcan
  escape from inside the event horizon.
• A black hole has only three physical properties
  mass, electric charge, and angular momentum.
• A rotating black hole (one with angular momentum)
  has an ergoregion around the outside of the event
  horizon. In the ergoregion, space and time
  themselves are dragged along with the rotation of
  the black hole.
• Black holes can evaporate, but in most cases at
  an extremely slow rate.