- 3075 - DARK MATTER - Investigating Dark Matter? Whatever Dark Matter is it has mass, it is influenced by gravity, it is not homogeneous throughout space, it has some structure with galaxies and clusters of galaxies yet to be understood.
--------------- 3075 - DARK MATTER - Investigating Dark Matter?
- Pity the poor astronomer whose career changed from seeing the beautiful wonders of the Cosmos, stars, galaxies, nebular, supernovae, to the biggest wonder, the “Darkness” that is 96% that he cannot see.
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- The challenges in astronomy today are to figure out what the 24% Dark Matter and the 76% Dark Energy that occupy the darkness really are? How do we begin to understand the 96% of the Cosmos that we cannot see?
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- Neither Dark Energy ,nor Dark Matter, interact with the electromagnetic energy. They do interact with gravitational energy. Dark Energy is an anti-gravity force that is expanding the space between all the matter. Dark Matter interacts with gravity in the opposite direction trying to pull matter back together.
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- The matter that we understand because it interacts with both gravity and electromagnetism is Ordinary Matter made up of protons, neutron, and electrons. It is the 4% that we can see. The ratio of the 4% we can see to the 24% of Dark Matter that we can not see is ( 1 to 6) , ordinary visible matter to invisible Dark Matter.
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- Astronomers studying galaxies and galaxy clusters find that the velocities of the stars orbiting the center are moving too fast to be held by the gravity created by the mass in the center. Galaxy’s stars should be flying off into space according to our calculations. On average there must be 6 times more gravity holding things together than we can account for as Ordinary Matter.
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- Performing these calculations on the Milky Way Galaxy and the Andromeda Galaxy require the stars orbiting at the outer edges of the galaxy to be traveling much slower in order to avoid being slung into outer space.
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- The galaxy’s outer star orbits have just as fast orbiting velocities as inner star orbits. Gravity falls off as the inverse square of distance from the central mass. Like our solar system the outer orbits have lower velocities:
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------------------------------------------------ ORBITAL VELOCITIES:
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------------------ Mercury -------------- 106,000 miles per hour
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------------------ Venus ------------------ 78,300 miles per hour
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------------------ Earth ------------------- 66,663 miles per hour
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------------------ Mars ------------------- 54,000 miles per hour
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------------------ Jupiter ------------------ 29,300 miles per hour
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------------------ Saturn ------------------ 21,700 miles per hour
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------------------ Uranus ------------------ 15,200 miles per hour
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------------------ Neptune ----------------- 12,080 miles per hour
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- But, in galaxies the orbital velocities are nearly the same all the way out to the edge of the disks, or spheres. To explain this there must be a halo of unseen mass surrounding the galaxy and adding at least 6 times more gravitational force holding the galaxy together.
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- This unseen halo is the Dark Matter that we do not understand. It can not be stars, it cannot be any of the 92 natural elements, it cannot be neutrinos or Blackholes. The best theory is that it is a new type of weakly interacting, massive, particle that we have yet to discover.
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- Astronomers are busy measuring the mass of galaxies and comparing the ratio of visible to Dark Matter. Most galaxies in our neighborhood are ( 1 to 8 ) ratio. However, when measuring the ratio for the colliding Antenna Galaxies it is ( 1 to 4 ).
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- Then, to add to the confusion, a nearby Dwarf Galaxy has a ratio of ( 1 to 1,000 ). This Dwarf Galaxy called Seque 1 is 75,000 lightyears away in the Constellation Leo the Lion. The galaxy is essentially a Dark Matter Galaxy. It is 1 billion times fainter than our Milky Way with the lumination equivalent to only 300 Suns yet it has the mass of 600,000 Suns.
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------------- Seque 1 weighs 600,000 Solar Mass
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------------- It is 400 lightyears across
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------------- It is a spheroidal galaxy
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------------- It is emitting light of only 300 Suns
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------------- It has no Blackhole at its core
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------------ It has no blocking dust or hydrogen gas clouds.
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- How it can weigh 1,000 times more than the matter we can identify is a mystery. The Answer: Dark Matter is a mystery.
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- Dark matter is thought to be concentrated in halos surrounding galaxies. But, it is not consistent between individual galaxies. Dark Matter does not appear to be homogeneous throughout space.
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- The question came up, is it a consistent concentration within a Cluster of galaxies?
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- Fortunately we have a way of measuring this. There is a particular cluster of galaxies 4.5 billion lightyears away that is in our direct line of sight to 12 other galaxies that are in the background. The Cluster of 100 galaxies is an enormous concentration of gravity. (named: MACS J12062).
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- The light from the background galaxies passes by this immense gravity lens on its way to us. The light beams are bent as they pass creating multiple images from our viewpoint. 47 background images appear to our point of view.
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- This is like holding the bottom of a wine glass up to your line of sight of a candle flame. What you see is multiple images of candle flames through the glass lens. The same concept occurs in this case and it is called “gravitational lensing“.
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- The breakthrough here is that by measuring the amount the light beams are bent astronomers can calculated the amount of gravitational force needed to cause it.
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----- Inside a radius of 515,000 lightyears the calculated mass is 130 * 10^12 Solar Mass
------- Inside a radius of 312,000 lightyears the calculated mass is 80 * 10^12 Solar Mass.
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------------- For comparison, our Milky Way Galaxy is 100,000 lightyears across and inside 50,000 lightyears the mass is 0.5 * 10^12 Solar Mass.
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- To learn how Dark Matter is distributed inside the Galaxy Cluster the density is calculated for the two concentric volumes.
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- First we calculate the density of the inside sphere:
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------------------ Volume of a sphere = 4/3 *pi* radius^3
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------------------- Volume = 4/3 * pi * (312,000 lightyears)^3
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------------------ Volume = 1.3 * 10^17 lightyears^3
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------------------ Mass = 8.0*10^13 Solar Mass
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------------------ Density = Volume / Mass = 0.00062 Solar Mass / lightyears^3
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- Next calculate the density between the outer sphere and the inner sphere.
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------------------ Volume of a sphere = 4/3 *pi* radius^3
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------------------- Volume = 4/3 * pi * (515,000 lightyears)^3
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------------------ Volume = 4.4 * 10^17 lightyears^3
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------------------ Mass = (13*10^13 - 8*10^13) Solar Mass
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------------------ Mass between the shells = 5 * 10^13 Solar Mass
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------------------ Density = 0.00011 Solar Mass / lightyears^3
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- From a comparison between the density of the outer shell and the sphere around the core the density is 6 times greater near the center. Therefore, Dark Matter is not evenly distributed inside a Galaxy Cluster.
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- It is concentrated towards the center of the Cluster. This is in contrast with individual galaxies where Dark Matter is thought to be concentrated in a halo surrounding the galaxy.
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- Whatever Dark Matter is it has mass, it is influenced by gravity, it is not homogeneous throughout space, it has some structure with galaxies and clusters of galaxies yet to be understood. An announcement will be made shortly, stay tuned.
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March 4, 2021 DARK MATTER - Investigating? 1342 3075
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--------------------- --- Thursday, March 4, 2021 ---------------------------
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