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--------------------------------- 1887 - Galaxies Galore
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- As astronomers continue to measure the distances to stars and galaxies , to measure their velocities, speed and directions, we gather a 3-D picture of the structure of the Universe
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- What we are seeing is stars that gather into galaxies, galaxies that gather into “ clusters” of galaxies, and galaxy clusters that group into “ super clusters”. These galaxy clusters are interconnected by “filaments” of galaxies, sheets ad “strings” of galaxies on the surface of giant “voids“. The voids are like bubbles of expanding space. The galaxies are like bubble surfaces that grow as galaxies separate apart.
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- Even these super clusters seem to group into an even larger super-super structure. Astronomers call this larger cluster “ Laniakea” . The word is Hawaiian which means “immeasurable heaven”
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- We are located in this 3-D map on the “ Orion Spur”, a spiral arm of the Milky Way Galaxy just 27,400 lightyears from the center traveling at 504,000 miles per hour. The Milky Way galaxy is 100,000 lightyears diameter. This is 0.1 million lightyears, or, 10% of a million lightyears, 0.1MLY, which I will use as the galactic unit of measure in this review.
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- Within a diameter of 7 MLY there is a “ Local Group” of 26 galaxies. The Milky Way and the Andromeda are the two biggest galaxies in this group. Our Local Group of galaxies are part of the “ Virgo Cluster” of galaxies 50 MLY across. The Virgo Cluster contains more that 1,000 large galaxies.
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- The Virgo Cluster is part of a super cluster of 100’s of galaxy clusters spanning 100 MLYs. These super clusters are interconnected by filaments and sheets of galaxies that are like the surface of bubbles. The voids are empty of any galaxies at all.
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- For some time astronomers believed this super cluster represented one part of a homogeneous structure for the entire Universe. But, since 2014 evidence has compiled that this structure is part of an even larger structure that is a collection of 100,000 large galaxies across 400 MLY. This is Laniakea.
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- Measuring these structures ad their dynamics will hopefully lead to understanding “Dark Matter”. This invisible matter is only evident by its gravity with no interactions with electromagnetic radiation, ie. with light. The laws of gravity indicate that this Dark Matter composes 80% of all matter. It represents 23% of all matter-energy in the Universe.
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- The dynamics of Laniakea will hopefully also help astronomers explain “ Dark Energy“, the 73% of all the mass-energy in the Universe. Dark Energy is the energy that is expanding space separating galaxies at an ever increasing rate. Today it is measured at 47,000 miles per hour per million lightyears of separation in space.
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- There may be even larger super clusters to be discovered. All these structures are resulting from the “ tug of war” between gravity that is holding galaxies together and bringing them together and expanding space that is accelerating their separation.
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- Measuring the velocities resulting from this “ tug of war” concludes that there is missing Dark Matter that is exerting the extra gravitational forces. Measuring the positions and distances conclude with a structured distribution of matter and its accelerating rate of expansion. How these measurements are made are footnoted at the end of this review.
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- The 3-D map that begins to define the structures within the Universe is a dynamic structure of counter balancing forces that cause galaxies to flow in currents, swirl in eddies, collect in pools and nest into moving structures, nested into even larger moving structures.
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- In 2008 astronomers had 1,800 galaxies measured and catalogued in this 3-D structure spanning 130 MLY. In 2013 the catalogued included 8,000 galaxies spanning 650 MLY. From this picture astronomers found that clusters of galaxies spanning 400 MLY were all moving together towards a “ Great Attractor”. Only 20% of the galaxies have been measured in this group called “Laniakea”.
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- Let’s begin with you reading this review sitting perfectly still. Well not really. Here is some of the dynamics you are experiencing and don’t feel it. You will need your imagination to begin to realize these dynamics. California is rotating on the Earth’s surface traveling east at 700 miles per hour. Your path around the Sun is traveling 67,000 miles per hour. Your path around the center of the Milky Way Galaxy is traveling at 504,000 miles per hour.
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- As a member of the Local Group of 26 galaxies you are moving toward the Constellation Centaurus at 1,342,000 miles per hour. Inside this Local Group the Milky Way and Andromeda galaxies are gravitationally moving towards each other at 246,000 miles per hour. The two galaxies will merge in 4 billion years from now.
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- Beyond the Local Group of galaxies within 25 MLY is a Local “Sheet” of galaxies only 3 MLY thick. Below this plane of galaxies is a “ filament” of galaxies called the Leo Spur. Below that is emptiness called the “ Local Void”.
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- The Local Void is expanding , inflating like a balloon, with a surface of under dense and over dense regions piling up at the boundaries. Inside is a volume spanning 13 MLY containing 300 local group’s worth of galaxies, moving at 1,565,000 miles per hour. This group is called the Virgo Cluster of galaxies at 50 MLY distance from the Milky Way.
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- The Great Attractor in that direction is an area with seven clusters of galaxies the size each the size of the Virgo Cluster spanning 100 MLYs. The Laniakea boundaries span 500 MLYs and encompass Normal and Dark Matter mass equivalent to 100 million billion Solar Mass. These structures are separating at 1,565,000 miles per hour, but there are gravity wells that create “ peculiar velocities” of only 1,342,000 miles per hour.
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- God only knows what all these structures are expanding into. They extend out to the boundary of our Observable Universe 13.8 billion lightyears from us. The 3-D map described above is only 10% , or , 1.4 billion lightyears of this distance. What more is there out there to learn? Stay tuned, an announcement will be made shortly.
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- (1) How are these distance and velocity measurements being made?
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- If we know the wavelength of a particular light source, such as the radiation emitted by the element hydrogen, and we measure this wavelength to be much wider, that is redder.
Wider wavelengths are stretched towards the red end of the light spectrum, redshifted when moving away from us. The amount of redshift can be used to calculate the receding velocity of this expanding light source. The amount of redshift is also a rough estimate of the distance to the light source.
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-------------- Redshift = (wavelength observed - intrinsic wavelength) / intrinsic wavelength
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-------------- Receding velocity = speed of light * Redshift.
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-------------- Hydrogen intrinsic wavelength = 656.3 nanometers.
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--------------- Observed wavelength is 662.9 nanometers.
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------------- Redshift = 6.6 nm / 656.3 nm = 0.01
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-------------- Receding velocity = 3*10^5 km/sec * 1% = 3,000 km/sec
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-------------- Receding velocity = 6,711,000 miles per hour.
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- Another method to measure the distance is to use the Apparent Brightness of a light source. If the Intrinsic Luminosity is known the distance can be calculated as the dimness increases as the square of the distance from the source.
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-------------- Apparent Brightness = Luminosity / 4*pi*(distance)^2
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---------------- d^2 = Intrinsic Luminosity / 4*pi* ( Measured Brightness)
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- Light sources that have known intrinsic luminosities include pulsating stars called Cepheid Variables that have a luminosity related to their rate of pulsation. And, Type 1a Supernovae that explode at 1.4 Solar Mass and can outshine an entire galaxy for a brief moment of time. A third method is the brightness of a spiral galaxy itself where rotation rate is related to its total luminosity. This is called the Tully-Fisher relationship.
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- The visible part of the Universe is being catalogued in this manner. The invisible part, the Dark Matter, is inferred due to the gravitational attractions required to form the structures and to create the velocities encountered.
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----- 707-536-3272 ---------------- Friday, July 1, 2016 -----
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