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 = h fWhere h is called Planck’s constant and f is the frequency of the EM wave.

h = 6.6 x 10-34 J sec

Photon

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

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

vorbit = G M

R( )1/2

Recall:

Black Holes – Observation

Effect on the Motion of Objects in Orbit

vorbit = G M

R( )1/2

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)