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------------ 1878 - Magnetic structures in the Galaxies.
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- Our world is made of atoms. We are made of atoms. Atoms are made of charged particles. Protons in the nucleus have positive electric charge. Electrons orbiting the nucleus have negative electric charge. Put them together in an atom and the neutron has a “ neutral” charge. Separate these electric charges and set them in motion and they create an electro-magnetic field.
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- Light itself is traveling waves of electro-magnetic fields. Light photons are massless and can travel at only one speed in space 670,633,500 miles per hour. All other charged particles that have mass travel at slower speeds. Light also travels at slower “net” speeds when it travels in media other than a vacuum. Light’s “net speed” slows down because it is being absorbed and re-emitted by all the atoms in that medium.
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- Traveling charged particles and spiraling magnetic fields are everywhere in space. There is an unseen Cosmic web of magnetism. Electricity and magnetism are not separate forces but actually work together in amazing ways.
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- Earth creates its magnetic field through its rotation causing its molten iron core to move creating an electric dynamo that generates a magnetic field. The field is actually about 10 times weaker that the common refrigerator magnetic.
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- Earth’s magnetosphere is a shield that protects us from charged space particles striking the Earth’s surface. Cosmic rays and other charged particles from the Sun, called the Solar Wind, are constantly bombarding the planet. Our magnetosphere deflects this bombardment into the North and South magnetic poles.
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- You can witness the result as these incoming charged particles excite atoms and gas molecules in the upper atmosphere creating the Aurora, the Northern Lights.
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- For some unknown reason the Earth’s North-South magnetic field reverses itself every few hundred thousand years. It actually disappears for a few thousand years between the poles flipping. The last flip occurred 780,000 years ago. We can not predict the next flip but the magnetic field today is 35% weaker than it was a few thousand years ago.
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- Magnetic fields span the entire galaxy. James Clark Maxwell’s equations from 1865 tells us that the energy in a magnetic field is its strength multiplied by its volume. The strength of the Galaxy’s enormous volume creates magnetic fields equivalent to the radiation pressure of all of the stars within it.
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- Astronomers are trying to “ see” the magnetic fields by detecting the “polarization” of the light. Light being an electromagnetic wave acquires a particular orientation, called polarization, as it travels through a galactic magnetic field. Astronomers can measure this polarization using radio telescopes. Discoveries are starting to present the picture of magnetic structures. Rather than being a tangled web they appear to acquire an orderly, spiral structure.
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- This magnetic structure may play a significant role in the formation of stars inside the galaxy. Observing the structure in the Whirlpool Galaxy M51, and NGC 5195, discovered galaxy interactions in the form of density waves, waves of compression that sweep through the galaxy disk. The strength of the galaxy’s magnetic field correlates with the density of the interstellar gas within the galaxy.
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- Explaining star birth by gravity alone does not work. A proto-star would spin itself apart long before it could reach the mass needed to start a fusion core. Current thinking is that the strong magnetic field creates a drag on rotation allowing the proto-star to gain the mass needed to become a star.
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- Our Milky Way Galaxy disk is 150,000 lightyears across and 1,000 lightyears thick. Gravity alone would allow the spinning disk to collapse into the plane and loose mass like a lawn sprinkler. It appears it is the magnetic pressure that is providing the buoyant force that interacts with gravity and centrifugal forces. Discoveries to date suggest that galaxies can generate magnetic fields quickly, within 100 million years. But, how they do this is a mystery.
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- Our Milky Way appears as though each spiral arm has its own magnetic field, independent of the other arms. The field direction can change from one arm to the other. Two bar magnets would repel, push each other apart, but how can we explain why that does not happen inside galaxies?
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- New, larger, radio telescopes are being built in order to discover how galactic magnetic fields get generated and how they affect star formation and how they affect this structure of the galaxy.
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- Since 1998 the Sloan Digital Sky Survey has been mapping the cosmic web of galaxies. The survey is measuring the faint imprint of cosmic sound waves that have reverberated throughout the Universe since the Big Bang.
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- SDSS had charted 1.5 million galaxies inside a cube of 7.5 billion lightyears on a side. The map shows that on cosmic scales the giant galaxy clusters, filaments, and walls of galaxies are separated by giant voids 500,000,000 lightyears across. These massive structures began as tiny density variations in the early hot plasma filled Universe shortly after the Big Bang.
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- Cosmic Inflation Theory has the Universe expanding at a gigantic rate in a fraction of a second. The Universe grew in size 100 billion times, from smaller that a proton to one meter across. This earliest plasma of charged particles contained quantum fluctuations which were small variations in density.
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- The photons within density clumps produced enormous outward pressures. The force of photons and particles in motion created “ sound waves”, density waves. There were no stars or galaxies , the sound waves rushed about in the hot plasma. Electrons and protons were too hot to settle down into neutral atoms.
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- In this plasma soup the “ speed of sound” reached 57% the speed of light. Protons and neutrons are together called “ baryons”. And, the sound waves are called “ baryon acoustic oscillations”.
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- After 380,000 years of expansion and cooling the electrons and protons combined into hydrogen atoms. In this neutral charge environment the photons flew free, not bouncing off any charged particles. The Universe went from opaque to transparent. The release of pressure slowed down the speed of the sound waves.
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- This expanding spherical shell would have a radius of 500,000,000 lightyears today. Precise measurements show minuscule variations in temperature of a few parts in 100,000 due to these inflation - enhanced density fluctuations. These “ baryon acoustic oscillations” result in “hot” and “cold” spots 1 degree in angular size across the sky.
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- The radius of this 1 degree in the sky is 500,000,000 lightyears. These sound waves have affected the abundance of galaxies in a specific pattern separated by 500,000,000 lightyears. So, if we can make a Cosmic Map of these sound waves they could become “standard rulers” to measure cosmic distances.
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- The other two methods used to measure cosmic distances is with Redshifts and with “standard candles”. Redshifts are based on a known light source wavelength being stretched out as it travels through expanding space. Wider wavelengths are shifted towards the “red” end of the light spectrum. The amount of redshift is used to calculate the distance to the light source.
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- The other method using standard candles depends on the source having a known luminosity. By measuring dimness as light spreads out through space we can calculate distance. Apparent Brightness versus Intrinsic Brightness of the source.
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----------------------- Apparent Brightness = Luminosity / 4*pi*distance^2
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- “ Standard Rulers” offer a third alternative. If we can map out the voids between galaxy clusters we can count the number of sound waves, 500 million lightyears each. Combining the three methods have provided the most precise extragalactic distances measure to date.
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- The result yields the conclusion that the Universe is 31% Ordinary Matter and Dark Matter, and 69% Dark Energy. The further conclusion is that the geometry of the Universe is “ flat”. It is not “spherical” on our scales of measurement.
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- Put a circle on flat paper and the circumference is 2 * pi * radius, or 6.3 times the radius. However, the circumference over a sphere is 4 * pi. The equator forms a circle on Earth, 24,902 miles circumference. The distance from the North Pole to the equator is 6,214 miles. That is 1/4th the circumference. The circumference is 4 times the arc on the sphere.
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- Now make these same measurements on the circumference of the spherical sound waves in the Cosmic Microwave Background. The answer is the 3-D Universe is geometrically flat like a 2-D sheet of paper. ( or, a sphere that is so enormous, enormously large that it appears flat.)
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- And, comparing the void between galaxies over a range of Redshifts tells us the density of Dark Energy ( whatever is expanding the Universe) is constant over time. When the Universe doubles in size the density of Normal Matter drops by a factor of 1.5. Dark Energy comes from empty space and remains constant over time and space (location). This combination means that the Universe is always accelerating in its expansion.
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- Does Dark Matter have its own electro-magnetic force different from our Normal Matter? We assume its interaction with gravity is the same as Normal Matter. That is how we conclude that it exists. Do you get the idea that there is a lot more to learn? Stay tuned, an announcement will be made shortly.
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