- 3448 - DARK MATTER - missing mass in the Universe? Dark Matter is one of the most confusing mysteries ever! But, the most widely accepted theories of the Universe don’t make sense without out. Thanks to Einstein’s Theory of General Relativity, scientists can calculate how massive objects behave on the largest cosmic scales.
------------- 3448 - DARK MATTER - missing mass in the Universe?
- Throughout the 1950s and 60s (the “Golden Age of Relativity”), astrophysicists noticed that the gravitational behaviors they were observing did not conform to the amount of “luminous” , visible matter.
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- Listing the evidence for dark matter there’s the rotation curves of galaxies. There’s the temperatures of galaxy clusters. There’s the bending of light around massive structures. There’s the large-scale structure of the Universe itself. There’s the cosmic microwave background, and there is still more:
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- What we have learned about Dark Matter (DM) states that it conforms to three parameters: Cold, Collision less, and Abundant. This forms the basis for the most widely accepted model of the Universe, which is the “Lamba Cold Dark Matter” (LCDM) model.
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- The rotational velocities of galaxies (a result of their mass distribution) show how luminous matter alone cannot account for what we see. There’s also the presence of “Dark Matter Halos,” which every galaxy in the Universe appears to have.
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- This scale of density and scale radius are different numbers for every single halo, but no matter what, they all share this common shape and the shape looks like this, density as a function of radius, starts like this and then goes down. The scale radius tells us where this breaking point is. It tells us something interesting about the evolution of dark matter halos.
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- These Halos suggest DM forms as a dense, centralized, ball-like structure that accumulates more DM particles over time. The formation of these halos is intrinsically linked to the formation and evolution of galaxies and the large-scale structure of the Universe.
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- Dark matter candidates include WIMPs, self-interacting dark matter, axions, and axion-like particles, primordial blackholes and sterile neutrinos and on and on and on.
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- All these different theories predict how dark matter might behave in our universe. Existing efforts to detect dark matter candidate particles include neutrino detectors like the IceCube Observatory in Antarctica, the SNOLAB facility in Ontario, and the Super-Kamiokande Observatory in Japan.
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- These facilities are usually located underground and operate in total darkness to ensure no background interference from electromagnetic sources. The detectors can spot the tiniest releases of energy that may result from interaction between dark matter candidate particles or a one-in-a-million chance of interaction with normal matter.
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- Neutrinos are absolutely a physical undeniable verifiable example of dark matter. They do not interact with light. They have all the properties of dark matter, but they’re not heavy enough or abundant enough to explain the extreme dominance in the energy pie. For the energy pie chart of the universe, dark matter is taking up like some twenty-five percent.
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- Are there really heavy neutrinos? Science is looking for WIMPs that are much, much heavier than neutrinos and that don’t fit into our standard understanding of particle physics.
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- Dark-matter particles known as “neutralinos” annihilate each other, creating a cascade of particles and radiation that includes medium-energy gamma rays.
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- There are many unresolved questions concerning dark matter involvement in the evolution of the Universe. This goes beyond the evolution of galaxies and includes questions about “baryogenesis” and matter/anti-matter asymmetry.
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- These refer to the birth of baryonic (normal) matter in the Universe and how matter must have exceeded anti-matter in the early Universe .
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- We know that for some reason, matter is preferred over anti-matter. Should dark matter play a role in that? Probably. Dark matter is more than a hypothesis. It’s a framework for understanding vast swaths of phenomena across the Universe. It’s why dark matter is on the edge of knowledge.
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- Over 80% of all matter in the universe is made up of dark matter and we only assume it exists because without it, the behavior of stars, planets and galaxies simply wouldn't make sense.
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- Dark matter is completely invisible. It emits no light or energy and thus cannot be detected by conventional sensors and detectors. The key to its elusive nature must lie in its composition.
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- Visible matter, called “baryonic matter“, consists of baryons, an overarching name for subatomic particles such as protons, neutrons and electrons. Scientists only speculate what dark matter is made of. It could be composed of baryons but it could also be non-baryonic, that means consisting of different types of particles.
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- Most scientists think that dark matter is composed of non-baryonic matter. The lead candidate, WIMPS are believed to have ten to a hundred times the mass of a proton, but their weak interactions with "normal" matter make them difficult to detect. Neutralinos, massive hypothetical particles heavier and slower than neutrinos, are the foremost candidate.
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- Sterile neutrinos are another candidate. Neutrinos are particles that don't make up regular matter. A river of neutrinos streams from the sun, but because they rarely interact with normal matter, they pass through Earth and its inhabitants.
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- There are three known types of neutrinos; a fourth, the ‘sterile neutrino“, is proposed as a dark matter candidate. The sterile neutrino would only interact with regular matter through gravity.
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- One of the outstanding questions is whether there is a pattern to the fractions that go into each neutrino species. The smaller neutral “axion” and the uncharged “photinos“, both theoretical particles, are also potential placeholders for dark matter.
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- There is also such a thing as antimatter, which is not the same as dark matter. Antimatter consists of particles that are essentially the same as visible matter particles but with opposite electrical charges.
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- These particles are called “antiprotons” and “positrons” (or antielectrons). When antiparticles meet particles, an explosion ensues that leads to the two types of matter cancelling each other out. Because we live in a universe made of matter, it is obvious that there is not that much antimatter around, otherwise there would be nothing left. Unlike dark matter, physicists can actually manufacture anti-matter in their laboratories.
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- But if we cannot see dark matter, how do we know it exists? The answer is gravity, the force exerted by objects made of matter that is proportional to their mass. Since the 1920s, astronomers have hypothesized that the universe must contain more matter than we can see because the gravitational forces that seem to be at play in the universe simply appear stronger than the visible matter alone would account for.
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- Motions of the stars tell you how much matter there is. Astronomers examining spiral galaxies in the 1970s expected to see material in the center moving faster than at the outer edges. Instead, they found the stars in both locations traveled at the same velocity, indicating the galaxies contained more mass than could be seen.
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- Studies of gas within elliptical galaxies also indicated a need for more mass than found in visible objects. Clusters of galaxies would fly apart if the only mass they contained was the mass visible to conventional astronomical measurements.
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- Different galaxies seem to contain different amounts of dark matter. In 2016 astronomers found a galaxy called “Dragonfly 44“, which seems to be composed almost entirely of dark matter. On the other hand, since 2018 astronomers have found several galaxies that seem to lack dark matter altogether.
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- The force of gravity doesn't only affect the orbits of stars in galaxies but also the trajectory of light. Albert Einstein showed in the early 20th century that massive objects in the universe bend and distort light due to the force of their gravity. The phenomenon is called “gravitational lensing“. By studying how light is distorted by galaxy clusters, astronomers have been able to create a map of dark matter in the universe.
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- Several astronomical measurements have corroborated the existence of dark matter, leading to a world-wide effort to observe directly dark matter particle interactions with ordinary matter in extremely sensitive detectors, which would confirm its existence and shed light on its properties. However, these interactions are so feeble that they have escaped direct detection up to this point, forcing scientists to build detectors that are more and more sensitive.
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- Despite all the evidence pointing towards the existence of dark matter, there is also the possibility that no such thing exists after all and that the laws of gravity describing the motion of objects within the solar system require revision.
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- Dark matter appears to be spread across the cosmos in a network-like pattern, with galaxy clusters forming at the nodes where fibers intersect. By verifying that gravity acts the same both inside and outside our solar system, researchers provide additional evidence for the existence of dark matter and dark energy.
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- Things are even more complicated as in addition to dark matter there also appears to be “dark energy“, an invisible force responsible for the expansion of the universe that acts against gravity.
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- Dark matter might be concentrated in blackholes, the powerful gates to nothing that due to the extreme force of their gravity devour everything in their vicinity. Dark matter would have been created in the Big Bang together with all other constituting elements of the universe as we see it today.
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- Stellar remnants such as “white dwarfs” and “neutron stars” are also thought to contain high amounts of dark matter, and so are the “brown dwarfs“, failed stars that didn't accumulate enough material to kick-start nuclear fusion in their cores.
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- There are two approaches to learning more about this mysterious stuff. Astronomers study the distribution of dark matter in the universe by looking at the clustering of material and the motion of objects in the universe. Particle physicists are on a quest to detect the fundamental particles making up dark matter.
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- An experiment mounted on the International Space Station called the “Alpha Magnetic Spectrometer” (AMS) detects antimatter in cosmic rays. Since 2011, it has been hit by more than 100 billion cosmic rays, providing fascinating insights into the composition of particles traversing the universe.
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- We have measured an excess of positrons, the antimatter counterpart to an electron, and this excess can come from dark matter.
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- Beneath a mountain in Italy, the “ LNGS's XENON1T “ is hunting for signs of interactions after WIMPs collide with xenon atoms. A new phase in the race to detect dark matter with ultra-low background massive detectors on Earth has just begun with “XENON1T”.
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- The “Large Underground Xenon” dark-matter experiment (LUX), seated in a gold mine in South Dakota, has also been hunting for signs of WIMP and xenon interactions. But so far, the instrument hasn't revealed the mysterious matter.
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- Nonetheless, a null result is significant as it changes the landscape of the field by constraining models for what dark matter could be beyond anything that existed previously.
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- The “IceCube Neutrino Observatory“, an experiment buried under the frozen surface of Antarctica, is hunting for the hypothetical sterile neutrinos. Sterile neutrinos only interact with regular matter through gravity, making it a strong candidate for dark matter.
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- Experiments aiming to detect elusive dark matter particles are also conducted in the powerful particle colliders at the “European Organization for Nuclear Research” (CERN) in Switzerland.
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- Several telescopes orbiting Earth are hunting for the effects of dark matter. The European Space Agency's Planck spacecraft, retired in 2013, spent four years in the Lagrangian Point 2 (a point in the orbit around the sun, where a spacecraft maintains a stable position with respect to Earth), mapping the distribution of the cosmic microwave background, a relic from the Big Bang, in the universe. Irregularities in the distribution of this microwave background revealed clues about the distribution of dark matter.
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- In 2014, NASA's “Fermi Gamma-ray Space Telescope” made maps of the heart of our galaxy, the Milky Way, in gamma-ray light, revealing an excess of gamma-ray emissions extending from its core.
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- The signal we found cannot be explained by currently proposed alternatives and is in close agreement with the predictions of very simple dark matter models. The excess can be explained by annihilations of dark matter particles with a mass between 31 and 40 billion electron volts.
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- The James Webb Space Telescope, launched after 30 years of development on December, 2021, is also expected to contribute to the hunt for the elusive substance. With its infrared eyes able to see to the beginning of time, the telescope of the century won't be able to see dark matter directly, but through observing the evolution of galaxies since the earliest stages of the universe, it is expected to provide insights that have not been possible before.
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------------------------------------- Other Reviews available upon request:
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- 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.
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- 3062 - DARK MATER - is it real? We have known about Dark Matter for a long time Back in the 1930’s, a Swiss astronomer named Fritz Zwicky noticed that galaxies in a distant cluster were orbiting one another much faster than they should have been given the amount of visible mass they had. He proposed than an unseen substance, which he called “dark matter“, might be tugging gravitationally on these galaxies.
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- 3049 - DARK MATTER - is real but what is it? Dark matter is still an unconfirmed model, yet , the detractors have yet to convince the larger field of their ideas. And the latest evidence? It also suggests that dark matter is real. But what is it?
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- 2931 - DARK MATTER - explorations? - Researchers remain unsure about what exactly dark matter is. Originally, some scientists 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 the significant amount of dark matter's influence.
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- 2897 - DARK MATTER - produces many new theories? When something seems a little mysterious or we just don’t understand what is going on we like to describe it with the adjective ‘dark’. This is one of the reasons why the term ‘dark’ matter got coined which was first proposed to explain the anomaly observed in the rotational velocities of galaxies.
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- 2886 - DARK MATTER - mysteries? When something seems a little mysterious or we just don’t understand what is going on we like to describe it with the adjective ‘dark’. We do not understand 95% of the universe we live in. The 5% that is left is everything we know about and are still learning about.
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- 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.
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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. 2/7/22Either 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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February 7, 2022 - DARK MATTER - missing mass in the Universe? 3448
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