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Black Holes - Observation
How do you see something you
can’t see ?????
How do objects emit em waves?
When an charged object accelerates, it must change it’s energy if the acceleration
causes a change in speed.
If the acceleration of the charged object results in a loss of energy of the object,
that energy will be released in the form of electromagnetic energy.
How do objects emit em waves?
Peculiar discovery of Einstein
Electromagnetic energy is not released in the form of an electromagnetic “wave”
but rather is released in the form of an electromagnetic “particle” called a photon.
The energy of motion of this photon is not the usual kinetic energy, but the energy
of the photon is given by
E=hf
Where h is called Planck’s constant and f is the frequency of the EM wave.
h = 6.6 x 10-34 J sec
Photon
Black Holes – Observation
Accretion
A black hole will accrete nearby matter through the event horizon because
of the black hole’s strong gravitational field.
Black Holes – Observation
Accretion
As the matter falls into the event horizon, it experiences strong
accelerations. As this happens, they will radiate energy in the form of
photons (recall the Aurora Borealis)
Black Holes – Observation
Accretion
The accelerations are very high for the particles as they collapse into and
through the event horizon. Calculations show that the photons emitted should
be in the X-ray region of the electromagnetic spectrum.
These X-ray photons can be distinguished from X-ray bursters because there is
no regularity (or periodicity) to the emission.
The emission of X-rays as matter collapses into the event horizon is somewhat
continuous.
Black Holes – Observation
Effect on the Motion of Objects in Orbit
Recall:
vorbit =
1/2
( )
GM
R
Black Holes – Observation
Effect on the Motion of Objects in Orbit
vorbit =
1/2
( )
GM
R
Speeds of objects and the orbital radius can be determined by direct
observation (we have talked about this in the past). Once these are known, it is
possible to determine the mass of the object producing the warpage of space.
Space Warps
Orbit with Space Warps
R
vorbit
Black Holes – Observation
Effect on the Motion of Objects in Orbit
Calculation of the mass of the object occupying the focus is strong (but
circumstantial?) evidence for a black hole if the mass is above the minimum
mass required to form a black hole (3M)
Black Holes – Observation
Gravitational Waves - Ripples in Space
Current evidence remains indirect and therefore
inconclusive. To confirm that black holes actually exist,
we'll need to be able to observe the gravitational waves
they produce as they form or interact.
If scientists could build gravitational wave detectors of
sufficient sensitivity, they should be able to measure
the vibrations in spacetime generated by black holes as
they form from a collapsing star, when they ingest
large amounts of matter, or if they interact, even collide
with a second black hole or another massive object,
such as a neutron star. Certain patterns of gravitational
waves emitted would reveal the "smoking gun."
So far, the wavelike disturbances in spacetime have
eluded detection. In a relativistic universe, there should
be no shortage of places in which to hunt for black
holes. Much larger and more sensitive detectors are
now under construction. With luck, soon gravitation
scientists may be shouting "Eureka!"
Black Holes - Observation
Laser Interferometer Gravitational Wave Observatory (LIGO)