- 2861 - DARK MATTER - how we know it is there? - The big idea of dark matter is that there’s something other than these known particles contributing in a significant way to the total amounts of matter in the Universe. We look at the motions of these objects, we look at the gravitational rules that govern orbiting bodies, whether something is bound or not, how it rotates, how structure forms, and we get a number for how much matter there has to be in there.
--------------------------- 2861 - DARK MATTER - how we know it is there?
- When you collide any two particles together, you probe the internal structure of the particles colliding. If one of them is not “fundamental“, but is rather a composite particle, these experiments can reveal its internal structure.
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- We have not yet directly found dark matter in the form of an interaction with another particle. However, the indirect evidence all shows that it must be real.
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- The particles and antiparticles of the Standard Model have now all been directly detected, with the last holdout, the Higgs Boson, falling at the LHC earlier in the 2010 decade. All of these particles can be created at LHC energies, and the masses, or energy levels, of the particles lead to fundamental constants that are absolutely necessary to describe them fully.
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- These particles can be well-described by the physics of the quantum field theories underlying the Standard Model, but they do not describe everything. They do not describe “dark matter“.
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- The Universe consists of all the protons, neutrons and electrons that make up our bodies, our planet and all the matter we’re familiar with, as well as some photons, in light, radiation, etc.
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- Protons and neutrons can be broken up into even more fundamental particles, the quarks and gluons, and along with the other Standard Model particles, make up all the known “matter” in the Universe.
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- There is something other than these known Standard Model particles contributing in a significant way to the total amounts of matter in the Universe.
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- How much mass is there in these structures at every level. We look at the motions of these objects, we look at the gravitational rules that govern orbiting bodies, whether something is bound or not, how it rotates, how structure forms, and we get a number for how much matter there has to be in there.
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- How much mass is present in the stars contained within these structures. we know how stars work, so as long as we can measure the starlight coming from these objects, we can know how much mass is there in stars.
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- The two bright, large galaxies at the center of the Coma Cluster, NGC 4889 and the slightly smaller NGC 4874, each exceed a million light years in size. But the galaxies on the outskirts, zipping around so rapidly, point to the existence of a large halo of dark matter throughout the entire cluster. The mass of the normal matter alone is insufficient to explain this bound structure.
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- These two numbers don’t match, and the mismatch between the values we obtain for them is spectacular in magnitude, they miss by a factor of approximately 50. There must be something more than just stars responsible for the vast majority of mass in the Universe. This is true for the stars within individual galaxies of all sizes all the way up to the largest clusters galaxies in the Universe, and beyond that, the entire cosmic web of galaxies.
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- The predicted abundances of helium-4, deuterium, helium-3 and lithium-7 as predicted by Big Bang Nucleosynthesis, is that the Universe is 75–76% hydrogen, 24–25% helium, a little bit of deuterium and helium-3, and a trace amount of lithium by mass.
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- After tritium and beryllium decay away, this is what we’re left with, and this remains unchanged until stars form. Only about 1/6th of the Universe’s matter can be in the form of this normal, “baryonic“, or atom-like matter.
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- When we extrapolate the laws of physics all the way back to the earliest times in the Universe, we find that there was not only a time so early when the Universe was hot enough that neutral atoms couldn’t form, but there was a time where even nuclei couldn’t form!
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- When nuclei finally can form without immediately being blasted apart, that phase is where the lightest nuclei of all, the different isotopes of hydrogen and helium, originally formed..
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- The formation of the first elements in the Universe after the Big Bang, Nucleosynthesis, tells us with very, very small errors how much total “normal matter” is there in the Universe. Although there is significantly more than what’s around in stars, it’s only about one-sixth of the total amount of matter we know is there from the gravitational effects. Not only stars, but normal matter in general, isn’t enough.
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- Additional evidence for dark matter comes from another early signal in the Universe: when neutral atoms form and the Big Bang’s leftover glow can travel, at last, unimpeded through the Universe. It’s very close to a uniform background of radiation that’s just a few degrees above absolute zero. But when we look at the temperatures on microkelvin scales, and on small angular (< 1°) scales, we see it’s not uniform at all.
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- The fluctuations in the cosmic microwave background tell us what fraction of the Universe is in the form of normal (protons+neutrons+electrons) matter, what fraction is in radiation, and what fraction is in non-normal, or dark matter, among other things. Again, they give us that same ratio: that dark matter is about five-sixths of all the matter in the Universe.
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- When we look at the Universe on the largest scales, we know that gravitation is responsible, in the context of the Big Bang, for causing matter to clump and cluster together. Based on the initial fluctuations that begin as over dense and under dense regions, gravitation and the interplay of the different types of matter with one another and radiation determine what we’ll see throughout our cosmic history.
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- This is particularly important, because we can tell that the dark matter is cold, or moving below a certain speed even when the Universe is very young. These pieces of knowledge lead to outstanding, precise theoretical predictions.
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- According to models and simulations, all galaxies should be embedded in dark matter halos, whose densities peak at the galactic centers. On long enough timescales, of perhaps a billion years, a single dark matter particle from the outskirts of the halo will complete one orbit.
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- The effects of gas, feedback, star formation, supernovae, and radiation all complicate this environment, making it extremely difficult to extract universal dark matter predictions.
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- All together, they tell us that around every galaxy and cluster of galaxies, there should be an extremely large, diffuse halo of dark matter. This dark matter should have practically no collisional interactions with normal matter; upper limits indicate that it would take light-years of solid lead for a dark matter particle to have a 50/50 shot of interacting just once.
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- However, there should be plenty of dark matter particles passing undetected through Earth, every second. Dark matter should also not collide or interact with itself, the way normal matter does. That makes direct detection difficult. But, there are some indirect ways of detecting dark matter’s presence. The first is to study what’s called “gravitational lensing“.
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- When there are bright, massive galaxies in the background of a cluster, their light will get stretched, magnified and distorted due to the general relativistic effects known as gravitational lensing.
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- By looking at how the background light gets distorted by the presence of intervening mass (solely from the laws of General Relativity), we can reconstruct how much mass is in that object. This tells us that there must be about six times as much matter as is present in all types of normal Standard Model-based matter alone.
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- There’s got to be dark matter in there, in quantities that are consistent with all the other observations. When we examine colliding clusters of galaxies, we learn something even more profound. The dark matter really does pass right through one another, and accounts for the vast majority of the mass; the normal matter in the form of gas creates shocks, and only accounts for some 15% of the total mass in there.
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- In other words, about five-sixths of that mass is dark matter! By looking at colliding galaxy clusters and monitoring how both the observable matter and the total gravitational mass behaves, we can come up with an empirical proof for the existence of dark matter.
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- There is no modification to the law of gravity that can explain why two clusters, pre-collision, will have their mass and gas aligned, but post-collision, will have their mass and gas separated.
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- Unfortunately, we don’t know what’s beyond the Standard Model. We’ve never discovered a single particle that isn’t part of the Standard Model, and yet we know there must be more than what we’ve presently discovered out there.
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- As far as dark matter goes, we don’t know what dark matter’s particle, or particles, properties should be, should look like, or how to find it. We don’t even know if it’s all one thing, or if it’s made up of a variety of different particles.
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- All we can do is look for interactions down to a certain cross-section, but no lower. We can look for energy recoils down to a certain minimum energy, but no lower. We can look for photon or neutrino conversions, but all these mechanisms have limitations. At some point, background effects, natural radioactivity, cosmic neutrons, solar cosmic neutrinos, etc., make it impossible to extract a signal below a certain threshold.
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- To date, the direct detection efforts having to do with dark matter have come up empty. There are no interaction signals we’ve observed that require dark matter to explain them, or that aren’t consistent with Standard Model-only particles in our Universe.
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- Direct detection efforts can disfavor or constrain specific dark matter particles or scenarios, but does not affect the enormous suite of indirect, astrophysical evidence that leaves dark matter as the only viable explanation.
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- When it comes to looking for the great cosmic unknowns, we might get lucky, and that’s why we try. But absence of evidence is not evidence of absence. When it comes to dark matter, don’t let yourself be fooled.
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--------------------------- To learn more request these earlier reviews;
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- 2823 - DARK MATTER - needs to be a new 2020 discovery? Researchers remain unsure about what exactly dark matter is. Originally, some conjectured that the missing mass in the universe was made up of small faint stars and black holes, though detailed observations have not turned up nearly enough such objects to account for dark matter's influence.
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- 2790 - DARK MATTER - to discover what it is? - There is a race to discover “dark matter“. Dark matter is that elusive substance that has mystified science since the 1930s, when astronomers first realized galaxies needed some kind of invisible gravitational glue to hold them together. No one knew what it was, so it was named “dark matter“.
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- 2768 - DARK MATTER - What is the Universe Made of? Since 1970 astronomers have believed Dark Matter existed because studying the orbits of galaxies and stars around galaxies could not be calculated based on the stars and matter they could see. Either Kepler’s and Newton’s formulas for the laws of gravity and motion were incorrect, or there was matter there that they could not find.
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- 2767 - DARK MATTER - confirmed by new measurements? - The first Fast Radio Burst detected came from a galaxy that is about 4 billion light-years away from Earth. Using dispersion measurements for these FRB’s, astronomers are able to make a rough calculation of how much dark matter the radio waves passed through before reaching earth.
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- 2718
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- 2631 - DARK MATTER - dark coffee would help? Astronomer’s observations have determined the average density of matter in our universe to very high precision. But this density turns out to be much greater than can be accounted for with “ordinary atoms“. Is there some other matter that we still don’t know about?
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- 2497 - DARK MATTER - What is it exactly? To explain the Observable Universe we are continuously learning new things. Astronomers have three major unproven theories, Dark Matter, Dark Energy, and Cosmic Inflation. We know something exists with each of these but we just do not know what it is or what causes it.
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- 2401 Science is examining the evidence for Dark Matter making up 80% of all the matter in the Universe. But, we can not find what it is? Matter and Energy are two forms of the same thing according E = mc^2. ALL MATTER is 30% of the total and ALL ENERGY is 70% of the total. Of the 30% of all matter 25% is Dark and only 5% is “Ordinary matter” that we see as our Ordinary Universe. 95% is unknown Dark stuff with 30% holding things together and 70% ever expanding and separating all the matter in its expansion.
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- 2214 - Dark Matter is what is holding our own galaxy together. This same observation is repeated with every other galaxy that astronomers have studied. Their math formulas would not work if there was not some unknown gravity pull holding galaxies together.
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- 2082 - Dark matter throws us a curve.
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- 1934 - Can Dark matter make blackholes?
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- 1888 - What is the Universe made of? What we observe , know , and think we understand is less than 5% of what is out there. The research is accelerating to discover, what is Dark Matter?
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- 1850 - Dark Mater is 23% of the Universe. It is 90% of all matter. Do we need new math to discover this? Is it new mass or is it undiscovered energy acting like mass?
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- 1823 - Dark Matter and the extinction of the dinosaurs? Earth passes through the disk of our Galaxy every 32 million years. How might this event be involved in the evolution of life on Earth?
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- 1820 - Dark Matter - What do we know about it matters. It is 25% of all the mass-energy in the Universe. It does not interact with light but does interact with gravity.
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- 1777 - Dark Matter - New clues keep coming in but the mystery of what Dark Matter is remains a mystery. Soon some new breakthrough in physics will help explain this.
- 1722 - Dark Matter, what is it? If you include Dark Energy than 95% of the Universe is made of this stuff. Remember matter and energy are the same thing, E = mc^2.
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- 1658 - Gravity grows weaker with distance, 1 / r^2, therefore distant objects must orbit more slowly or they would fly off into space.
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- 1636 - What does Dark Matter look like? - #1636 - Dark Matter accounts for 5.4 times as much mass as Ordinary Matter in the Universe.
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- 1594 - 4% Ordinary Matter and the rest is Dark Matter and Dark Energy. Several methods are used to calculate the structure of the Universe and each reaches the same conclusion. 73% is Dark Energy that we do not understand and another 23% is Dark Matter that we can figure out what it is made of. This Review uses simple methods that you can understand to reach these same conclusions.
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- 1585 - Today the space is expanding due to Dark Energy at 47,000 miles per hour per million lightyears, but, it is also accelerating faster and faster.
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- 1596 - Using Redshift calculation to learn how fast the Universe is expanding. This is one step in understanding that 73% of the mass-energy of the Universe is some sort of anti-gravity causing the galaxies to recede away from each other.
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- 1597 - Using the Brightness Method to calculate the distance to galaxies. To illustrate we will again use the familiar star Vega.
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- 1598 - Stars and galaxies would be flying our of their orbits if it were not for unseen mass existing around the galaxies. The previous Review 1597 calculated that 73% of the Universe was composed of Dark Energy, leaving the 27% composed of matter. How did we learn that 85% of that matter was “ Dark Matter” and not ordinary matter?
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- 1599 - We need a breakthrough in physics to explain Dark Matter. Why is 96% of the Universe “ Dark”? What else could explain how these conclusions could not be true.
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- 1576 - - We need a breakthrough in physics to explain Dark Matter. WIMPs should be colliding with us all the time at 536,880 miles per hour. That is how fast the Sun is going through the Galaxy. There have been unexplained WIMP detections that change with the seasons. Change with the Earth’s rotation around the Sun. Going with the wind of WIMPs or against the galactic wind of WIMPS. Dark Matter will soon be discovered.
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- 1535 - Gravitational lensing has come form theory to being an essential tool for astronomers . Hubble Telescope has used the lensing as a magnifying glass to see galaxies back to years after the Big Bang. An announcement will be made shortly, stay tuned.
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- 1517 - What is the universe made of - 5 calculations used to measure Dark Matter.
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- 1485 - Where is the Dark Matter?
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- 1427 - The picture of Dark Matter Collision
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- 1341 - Investigating Dark Matter
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- 1218 - Could Dark Matter be another Universe?
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- 1204 - Dark Matter, wht do we think it is?
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- 1075 - Dark Matter
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- 837 - Weighing Galaxies using Hot Gas?
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- 718 - What could Dark Matter be?- Dark Matter is there, but, what is it? There are at least three candidates being studied: MACHOS, WIMPS, Hydrogen Gas
There are at least three reasons why astronomers believe that Dark Matter is there: Hot Gas, Colliding Galaxies, Rotating Galaxies
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- 692 - Dark Matter and Blackholes.
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- 594 - Dark Galaxy
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- October 13, 2020 2861
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--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
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--- to: ------ jamesdetrick@comcast.net ------ “Jim Detrick” -----------
--------------------- --- Wednesday, October 14, 2020 ---------------------------
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