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  • richardmitnick 9:05 am on May 31, 2021 Permalink | Reply
    Tags: "Looking deep into the universe", , , , , Frtiz Zwicky and Vera Rubin, HIRAX telescope in the Karoo semidesert in South Africa, , , , ,   

    From Swiss Federal Institute of Technology in Zürich [ETH Zürich] [Eidgenössische Technische Hochschule Zürich](CH): “Looking deep into the universe” 

    From Swiss Federal Institute of Technology in Zürich [ETH Zürich] [Eidgenössische Technische Hochschule Zürich](CH)

    31.05.2021
    Felix Würsten

    How is matter distributed within our universe? And what is the mysterious substance known as dark energy made of? HIRAX, a new large telescope array comprising hundreds of small radio telescopes, should provide some answers. Among those instrumental in developing the system are physicists from ETH Zürich.

    2
    Hartebeesthoek Radio Astronomy Observatory, located west of Johannesburg South Africa.
    How the final expansion of the HIRAX telescope in the Karoo semidesert in South Africa should look once completed. (Image: Cynthia Chiang / HIRAX.)

    “It’s an exciting project,” says Alexandre Refregier, Professor of Physics at ETH Zürich, as he considers the futuristic-​looking visualisation from South Africa. The image shows a scene in the middle of the Karoo semidesert, far away from larger settlements, with rows upon rows of more than 1,000 parabolic reflectors all directed towards the same point. At first glance, one might assume this is a solar power station, but it’s actually a large radio telescope that over the coming years should provide cosmologists with new insights into the makeup and history of our universe.

    Key element: hydrogen

    HIRAX stands for Hydrogen Intensity and Real-​time Analysis eXperiment and marks the start of a new chapter in the exploration of the universe. The new large telescope will collect radio signals within a frequency range of 400 to 800 MHz. These signals will make it possible to measure the distribution of hydrogen in the universe on a large scale. “If we can use hydrogen, the most common element in the universe, to discover how matter is distributed in space, we could then draw conclusions about what dark matter and dark energy are made of,” Refregier explains.

    Dark Energy and Dark Matter are two mysterious components that together make up the vast majority of the universe. They play a major role in the formation of structures and in the universe’s accelerated expansion. But experts remain puzzled about exactly what dark energy and dark matter are made of. HIRAX should help home in on the precise nature of these two components. The researchers also hope that the new system will deliver insights into fast radio bursts and pulsars.

    Combining hundreds of individual signals

    Not only will Refregier and his team be involved in the scientific analysis of the data, the professor is also helping to develop the new system together with his postdoc Devin Crichton and engineer Thierry Viant. “HIRAX is a remarkable undertaking, not just from a scientific point of view, but also because it represents a significant technological challenge,” Refregier says. As part of their subproject in collaboration with scientists from the University of Geneva [Université de Genève](CH), the ETH researchers are developing what’s known as a digital correlator, which will combine the signals recorded by each of the approximately six-​metre telescopes. “Rather than consisting of a single large telescope, the HIRAX array is made up of numerous smaller radio telescopes that are correlated with each other,” Refregier says. “This enables us to build a telescope with a collection surface and resolution much greater than a measuring device with only one parabolic reflector.”

    Tested in Switzerland

    The physicists first tested the technology for the digital corrector in Switzerland using a pilot system. To do so, they used the two historic radio telescopes housed at the Bleien facility in the Swiss canton of Aargau. They will now use the results of these tests to develop a digital corrector capable of linking 256 reflectors. “The HIRAX telescope is being set up in stages, which allows us to develop and refine the technology we need as we go along,” Refregier says. The funding required for this subproject was recently secured.

    For their digital correlator, the ETH Zurich physicists are using high-​performance graphics processing units that were originally developed for video and gaming applications. The researchers are also breaking new ground when it comes to calibration. To synchronise the measurement signals received by the individual antennas, they use a radio signal transmitted by a drone. It is crucial to pinpoint the position of these signals so that the telescope can then provide the required precision.

    An ideal location

    It’s no accident that the HIRAX telescope is being installed in the Karoo semidesert. As a protected area, it is still largely free of disruptive signals from mobile communications antennas. “It’s actually quite ironic,” Refregier says. “On the one hand, mobile communications technology is a massive help in developing telescopes. On the other, that same technology makes life difficult for radio astronomers because mobile communications antennas transmit within similar frequency ranges.

    Another reason why the Karoo region is an ideal location is that this is also where part of the planned Square Kilometre Array will be erected.


    Once completed, this will be the world’s largest radio telescope, connecting systems in South Africa and Australia and representing yet another giant leap forward in radio astronomy. “Despite its remote position, the Karoo location is well connected by power and data lines,” Refregier says. In this respect, the undertaking presents a challenge because the new telescope will generate 6.5 terabytes of data every second. “This is why we’re going to install the digital corrector directly on site, so that the amount of data can first be reduced before it is sent somewhere else for further processing,” Refregier says.

    Opening the door for the next large-​scale project

    A collaboration among numerous other universities from different countries, the HIRAX project is also important with respect to research policy. First, it strengthens the collaboration between South Africa and Switzerland, enabling young scientists from the former to conduct research in the latter. Second, Refregier says he is grateful that the work we are doing on the development of HIRAX is opening the door to Switzerland’s participation in the Square Kilometre Array: “This means that we can do our part to ensure that Swiss universities are involved in this pioneering project and can keep pace with the latest developments in radio astronomy.”

    _____________________________________________________________________________________
    Dark Energy Survey

    ]

    The Dark Energy Survey (DES) is an international, collaborative effort to map hundreds of millions of galaxies, detect thousands of supernovae, and find patterns of cosmic structure that will reveal the nature of the mysterious dark energy that is accelerating the expansion of our Universe. DES began searching the Southern skies on August 31, 2013.

    According to Einstein’s theory of General Relativity, gravity should lead to a slowing of the cosmic expansion. Yet, in 1998, two teams of astronomers studying distant supernovae made the remarkable discovery that the expansion of the universe is speeding up. To explain cosmic acceleration, cosmologists are faced with two possibilities: either 70% of the universe exists in an exotic form, now called dark energy, that exhibits a gravitational force opposite to the attractive gravity of ordinary matter, or General Relativity must be replaced by a new theory of gravity on cosmic scales.

    DES is designed to probe the origin of the accelerating universe and help uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision. More than 400 scientists from over 25 institutions in the United States, Spain, the United Kingdom, Brazil, Germany, Switzerland, and Australia are working on the project. The collaboration built and is using an extremely sensitive 570-Megapixel digital camera, DECam, mounted on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory, high in the Chilean Andes, to carry out the project.

    Over six years (2013-2019), the DES collaboration used 758 nights of observation to carry out a deep, wide-area survey to record information from 300 million galaxies that are billions of light-years from Earth. The survey imaged 5000 square degrees of the southern sky in five optical filters to obtain detailed information about each galaxy. A fraction of the survey time is used to observe smaller patches of sky roughly once a week to discover and study thousands of supernovae and other astrophysical transients.
    _____________________________________________________________________________________

    Dark Matter Background
    Fritz Zwicky discovered Dark Matter in the 1930s when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, some 30 years later, did most of the work on Dark Matter.

    Fritz Zwicky from http:// palomarskies.blogspot.com.


    Coma cluster via NASA/ESA Hubble.


    In modern times, it was astronomer Fritz Zwicky, in the 1930s, who made the first observations of what we now call dark matter. His 1933 observations of the Coma Cluster of galaxies seemed to indicated it has a mass 500 times more than that previously calculated by Edwin Hubble. Furthermore, this extra mass seemed to be completely invisible. Although Zwicky’s observations were initially met with much skepticism, they were later confirmed by other groups of astronomers.
    Thirty years later, astronomer Vera Rubin provided a huge piece of evidence for the existence of dark matter. She discovered that the centers of galaxies rotate at the same speed as their extremities, whereas, of course, they should rotate faster. Think of a vinyl LP on a record deck: its center rotates faster than its edge. That’s what logic dictates we should see in galaxies too. But we do not. The only way to explain this is if the whole galaxy is only the center of some much larger structure, as if it is only the label on the LP so to speak, causing the galaxy to have a consistent rotation speed from center to edge.
    Vera Rubin, following Zwicky, postulated that the missing structure in galaxies is dark matter. Her ideas were met with much resistance from the astronomical community, but her observations have been confirmed and are seen today as pivotal proof of the existence of dark matter.

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science).


    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL).


    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu.


    _____________________________________________________________________________________

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    ETH Zurich campus
    Swiss Federal Institute of Technology in Zürich [ETH Zürich] [Eidgenössische Technische Hochschule Zürich](CH) is a public research university in the city of Zürich, Switzerland. Founded by the Swiss Federal Government in 1854 with the stated mission to educate engineers and scientists, the school focuses exclusively on science, technology, engineering and mathematics. Like its sister institution Swiss Federal Institute of Technology in Lausanne [EPFL-École Polytechnique Fédérale de Lausanne](CH) , it is part of the Swiss Federal Institutes of Technology Domain (ETH Domain)) , part of the Swiss Federal Department of Economic Affairs, Education and Research.

    The university is an attractive destination for international students thanks to low tuition fees of 809 CHF per semester, PhD and graduate salaries that are amongst the world’s highest, and a world-class reputation in academia and industry. There are currently 22,200 students from over 120 countries, of which 4,180 are pursuing doctoral degrees. In the 2021 edition of the QS World University Rankings ETH Zürich is ranked 6th in the world and 8th by the Times Higher Education World Rankings 2020. In the 2020 QS World University Rankings by subject it is ranked 4th in the world for engineering and technology (2nd in Europe) and 1st for earth & marine science.

    As of November 2019, 21 Nobel laureates, 2 Fields Medalists, 2 Pritzker Prize winners, and 1 Turing Award winner have been affiliated with the Institute, including Albert Einstein. Other notable alumni include John von Neumann and Santiago Calatrava. It is a founding member of the IDEA League and the International Alliance of Research Universities (IARU) and a member of the CESAER network.

    ETH Zürich was founded on 7 February 1854 by the Swiss Confederation and began giving its first lectures on 16 October 1855 as a polytechnic institute (eidgenössische polytechnische Schule) at various sites throughout the city of Zurich. It was initially composed of six faculties: architecture, civil engineering, mechanical engineering, chemistry, forestry, and an integrated department for the fields of mathematics, natural sciences, literature, and social and political sciences.

    It is locally still known as Polytechnikum, or simply as Poly, derived from the original name eidgenössische polytechnische Schule, which translates to “federal polytechnic school”.

    ETH Zürich is a federal institute (i.e., under direct administration by the Swiss government), whereas the University of Zürich is a cantonal institution. The decision for a new federal university was heavily disputed at the time; the liberals pressed for a “federal university”, while the conservative forces wanted all universities to remain under cantonal control, worried that the liberals would gain more political power than they already had. In the beginning, both universities were co-located in the buildings of the University of Zürich.

    From 1905 to 1908, under the presidency of Jérôme Franel, the course program of ETH Zürich was restructured to that of a real university and ETH Zürich was granted the right to award doctorates. In 1909 the first doctorates were awarded. In 1911, it was given its current name, Eidgenössische Technische Hochschule. In 1924, another reorganization structured the university in 12 departments. However, it now has 16 departments.

    ETH Zürich, EPFL (Swiss Federal Institute of Technology in Lausanne) [École polytechnique fédérale de Lausanne](CH), and four associated research institutes form the “ETH Domain” with the aim of collaborating on scientific projects.

    Reputation and ranking

    ETH Zürich is ranked among the top universities in the world. Typically, popular rankings place the institution as the best university in continental Europe and ETH Zürich is consistently ranked among the top 1-5 universities in Europe, and among the top 3-10 best universities of the world.

    Historically, ETH Zürich has achieved its reputation particularly in the fields of chemistry, mathematics and physics. There are 32 Nobel laureates who are associated with ETH Zürich, the most recent of whom is Richard F. Heck, awarded the Nobel Prize in chemistry in 2010. Albert Einstein is perhaps its most famous alumnus.

    In 2018, the QS World University Rankings placed ETH Zürich at 7th overall in the world. In 2015, ETH Zürich was ranked 5th in the world in Engineering, Science and Technology, just behind the Massachusetts Institute of Technology(US), Stanford University(US) and University of Cambridge(UK). In 2015, ETH Zürich also ranked 6th in the world in Natural Sciences, and in 2016 ranked 1st in the world for Earth & Marine Sciences for the second consecutive year.

    In 2016, Times Higher Education WorldUniversity Rankings ranked ETH Zürich 9th overall in the world and 8th in the world in the field of Engineering & Technology, just behind the Massachusetts Institute of Technology(US), Stanford University(US), California Institute of Technology(US), Princeton University(US), University of Cambridge(UK), Imperial College London(UK) and

     
  • richardmitnick 10:26 pm on February 9, 2021 Permalink | Reply
    Tags: "Astronomers offer possible explanation for elusive dark-matter-free galaxies", , , , , Frtiz Zwicky and Vera Rubin, Illustris Project, Lambda Cold Dark Matter cosmological model,   

    From UC Riverside: “Astronomers offer possible explanation for elusive dark-matter-free galaxies” 

    UC Riverside bloc

    From UC Riverside

    February 9, 2021
    Iqbal Pittalwala

    1
    UC Riverside-led study finds extreme tidal mass loss in dwarf galaxies formed in a simulation.

    A team led by astronomers at the University of California, Riverside, has found that some dwarf galaxies may today appear to be dark-matter free even though they formed as galaxies dominated by Dark Matter in the past.

    Galaxies that appear to have little to no dark matter — nonluminous material thought to constitute 85% of matter in the universe — complicate astronomers’ understanding of the universe’s dark matter content. Such galaxies, which have recently been found in observations, challenge a cosmological model used by astronomers called Lambda Cold Dark Matter, or LCDM, where all galaxies are surrounded by a massive and extended dark matter halo.

    Lamda Cold Dark Matter Accerated Expansion of The universe http scinotions.com the-cosmic-inflation-suggests-the-existence-of-parallel-universes
    Alex Mittelmann, Coldcreation.

    Dark-matter-free galaxies are not well understood in the astronomical community. One way to study the possible formation mechanisms for these elusive galaxies — the ultradiffuse DF2 and DF4 galaxies are examples — is to find similar objects in numerical simulations and study their time evolution and the circumstances that lead to their dark matter loss.

    Jessica Doppel, a graduate student in the UC Riverside Department of Physics and Astronomy and the first author of research paper published in the MNRAS, explained that in a LCDM universe all galaxies should be dark matter dominated.

    “That’s the challenge,” she said. “Finding analogs in simulations of what observers see is significant and not guaranteed. Beginning to pin down the origins of these types of objects and their often-anomalous globular cluster populations allows us to further solidify our theoretical framework of dark matter and galaxy formation and confirms that no alternative forms of dark matter are needed. We found cold dark matter performs well.”

    For the study, the researchers used cosmological and hydrodynamical simulation called Illustris, which offers a galaxy formation model that includes stellar evolution, supernova feedback, black hole growth, and mergers.

    The Illustris Simulation

    The researchers found a couple of “dwarf galaxies” in clusters had similar stellar content, globular cluster numbers, and dark matter mass as DF2 and DF4. As its name suggests, a dwarf galaxy is small, comprising up to several billion stars. In contrast, the Milky Way, which has more than 20 known dwarf galaxies orbiting it, has 200 to 400 billion stars. Globular clusters are often used to estimate the dark matter content of galaxies, especially dwarfs.

    The researchers used the Illustris simulation to investigate the origin of odd dwarf galaxies such as DF2 and DF4. They found simulated analogs to dark-matter-free dwarfs in the form of objects that had evolved within the galaxy clusters for a long time and lost more than 90% of their dark matter via tidal stripping — the stripping away of material by galactic tidal forces.

    “Interestingly, the same mechanism of tidal stripping is able to explain other properties of dwarfs like DF2 and DF4 — for example, the fact that they are ‘ultradiffuse’ galaxies,” said co-author Laura Sales, an associate professor of physics and astronomy at UCR and Doppel’s graduate advisor. “Our simulations suggest a combined solution to both the structure of these dwarfs and their low dark matter content. Possibly, extreme tidal mass loss in otherwise normal dwarf galaxies is how ultradiffuse objects are formed.”

    In collaboration with researchers at the MPG Institute for Astrophysics [MPG Institut für Astrophysik], Garching (DE), Sales’ group is currently working with improved simulations that feature more detailed physics and a numerical resolution about 16 times better than the Illustris simulation.

    “With these data, we will be able to extend our study to even lower-mass dwarfs, which are more abundant in the universe and expected to be more dark matter dominated at their centers, making them more challenging to explain,” Doppel said. “We will explore if tidal stripping could provide a path to deplete dwarfs of their inner dark matter content. We plan to make predictions about the dwarfs’ stellar, globular cluster, and dark matter content, which we will then compare to future observations.”

    The research team has already been awarded time at the W. M. Keck Observatory to help answer some of the questions pertaining to observations of dwarfs in the Virgo cluster.

    W.M. Keck Observatory, two ten meter telescopes operated by Caltech and the University of California, Maunakea Hawaii USA, altitude 4,207 m (13,802 ft). Credit: Caltech.

    Virgo Supercluster Credit: NASA.

    Sales and Doppel were joined in the research by Julio F. Navarro of the University of Victoria (CA); Mario G. Abadi and Felipe Ramos-Almendares of the National University of Córdoba (AR); Eric W. Peng of Peking University (CN); and Elisa Toloba of the University of the Pacific in California.

    The study was supported by grants from NASA and the National Science Foundation.

    Dark Matter Background
    Fritz Zwicky discovered Dark Matter in the 1930s when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, some 30 years later, did most of the work on Dark Matter.

    Fritz Zwicky from http:// palomarskies.blogspot.com.


    Coma cluster via NASA/ESA Hubble.


    In modern times, it was astronomer Fritz Zwicky, in the 1930s, who made the first observations of what we now call dark matter. His 1933 observations of the Coma Cluster of galaxies seemed to indicated it has a mass 500 times more than that previously calculated by Edwin Hubble. Furthermore, this extra mass seemed to be completely invisible. Although Zwicky’s observations were initially met with much skepticism, they were later confirmed by other groups of astronomers.
    Thirty years later, astronomer Vera Rubin provided a huge piece of evidence for the existence of dark matter. She discovered that the centers of galaxies rotate at the same speed as their extremities, whereas, of course, they should rotate faster. Think of a vinyl LP on a record deck: its center rotates faster than its edge. That’s what logic dictates we should see in galaxies too. But we do not. The only way to explain this is if the whole galaxy is only the center of some much larger structure, as if it is only the label on the LP so to speak, causing the galaxy to have a consistent rotation speed from center to edge.
    Vera Rubin, following Zwicky, postulated that the missing structure in galaxies is dark matter. Her ideas were met with much resistance from the astronomical community, but her observations have been confirmed and are seen today as pivotal proof of the existence of dark matter.

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science).


    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL).


    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    UC Riverside Campus

    The University of California, Riverside is one of 10 universities within the prestigious University of California system, and the only UC located in Inland Southern California.

    Widely recognized as one of the most ethnically diverse research universities in the nation, UCR’s current enrollment is more than 21,000 students, with a goal of 25,000 students by 2020. The campus is in the midst of a tremendous growth spurt with new and remodeled facilities coming on-line on a regular basis.

    We are located approximately 50 miles east of downtown Los Angeles. UCR is also within easy driving distance of dozens of major cultural and recreational sites, as well as desert, mountain and coastal destinations.

     
  • richardmitnick 3:02 pm on October 28, 2020 Permalink | Reply
    Tags: "Solved: the mystery of how dark matter in galaxies is distributed", , , , , , Frtiz Zwicky and Vera Rubin,   

    From Instituto de Astrofísica de Canarias – IAC (ES): “Solved: the mystery of how dark matter in galaxies is distributed” 

    IAC

    From Instituto de Astrofísica de Canarias – IAC (ES)

    1
    Dark matter in two galaxies simulated on a computer. Credit: Image taken from the article Brinckmann et al. (2018, MNRAS, 474, 746; https://doi.org/10.1093/mnras/stx2782 The structure and assembly history of cluster-sized haloes in self-interacting dark matter).

    28/10/2020
    Jorge Sánchez Almeida
    jos@iac.es

    Ignacio Trujillo
    itc@iac.es

    The gravitational force in the Universe under which it has evolved from a state almost uniform at the Big Bang until now, when matter is concentrated in galaxies, stars and planets, is provided by what is termed Dark Matter. But in spite of the essential role that this extra material plays, we know almost nothing about its nature, behaviour and composition, which is one of the basic problems of modern physics. In a recent article in Astronomy & Astrophysics Letters, scientists at the Instituto de Astrofísica de Canarias (IAC) (ES) /University of La Laguna (ULL)(ES) and of the National University of the North-West of the Province of Buenos Aires (Junín, Argentina) have shown that the dark matter in galaxies follows a ‘maximum entropy’ distribution, which sheds light on its nature.

    Dark matter makes up 85% of the matter of the Universe, but its existence shows up only on astronomical scales. That is to say, due to its weak interaction, the net effect can only be noticed when it is present in huge quantities. As it cools down only with difficulty, the structures it forms are generally much bigger than planets and stars. As the presence of dark matter shows up only on large scales the discovery of its nature probably has to be made by astrophysical studies.

    MAXIMUM ENTROPY

    To say that the distribution of dark matter is organized according to maximum entropy (which is equivalent to ‘maximum disorder’ or ‘thermodynamic equilibrium’) means that it is found in its most probable state. To reach this ‘maximum disorder’ the dark matter must have had to collide within itself, just as gas molecules do, so as to reach equilibrium in which its density, pressure, and temperature are related. However, we do not know how the dark matter has reached this type of equilibrium.

    “Unlike the molecules in the air, for example, because gravitational action is weak, dark matter particles ought hardly to collide with one another, so that the mechanism by which they reach equilibrium is a mystery”, says Jorge Sánchez Almeida, an IAC researcher who is the first author of the article. “However if they did collide with one another this would give them a very special nature, which would partly solve the mystery of their origin”, he adds.

    The maximum entropy of dark matter has been detected in dwarf galaxies, which have a higher ratio of dark matter to total matter than have more massive galaxies, so it is easier to see the effect in them. However, the researchers expect that it is general behaviour in all types of galaxies.

    The study implies that the distribution of matter in thermodynamic equilibrium has a much lower central density that astronomers have assumed for many practical applications, such as in the correct interpretation of gravitational lenses, or when designing experiments to detect dark matter by its self-annihilation.

    This central density is basic for the correct interpretation of the curvature of the light by gravitational lenses: if it is less dense the effect of the lens is less. To use a gravitational lens to measure the mass of a galaxy one needs a model, if this model is changed, the measurement changes.

    The central density also is very important for the experiments which try to detect dark matter using its self-annihilation. Two dark matter particles could interact and disappear in a process which is highly improbable, but which would be characteristic of their nature. For two particles to interact they must collide. The probability of this collision depends on the density of the dark matter; the higher the concentration of dark matter, the higher is the probability that the particles will collide.

    “For that reason, if the density changes so will the expected rate of production of the self-annihilations, and given that the experiments are designed on the prediction of a given rate, if this rate were very low the experiment is unlikely to yield a positive result”, says Sánchez Almeida.

    Finally, thermodynamic equilibrium for dark matter could also explain the brightness profile of the galaxies. This brightness falls with distance from the centre of a galaxy in a specific way, whose physical origin is unknown, but for which the researchers are working to show that it is the result of an equilibrium with maximum entropy.

    SIMULATION VERSUS OBSERVATION

    The density of dark matter in the centres of galaxies has been a mystery for decades. There is a strong discrepancy between the predictions of the simulations (a high density) and that which is observed (a low value). Astronomers have put forward many types of mechanisms to resolve this major disagreement.

    In this article, the researchers have shown, using basic physical principles, that the observations can be reproduced on the assumption that the dark matter is in equilibrium, i.e., that it has maximum entropy. The consequences of this result could be very important because they indicate that the dark matter has interchanged energy with itself and/or with the remaining “normal” (baryonic) matter.

    “The fact that equilibrium has been reached in such a short time, compared with the age of the Universe, could be the result of a type of interaction between dark matter and normal matter in addition to gravity”, suggests Ignacio Trujillo, an IAC researcher and a co-author of this article. “The exact nature of this mechanism needs to be explored, but the consequences could be fascinating to understand just what is this component which dominates the total amount of matter in the Universe”.

    Dark Matter Background
    Fritz Zwicky discovered Dark Matter in the 1930s when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

    Fritz Zwicky from http:// palomarskies.blogspot.com.

    Coma cluster via NASA/ESA Hubble.

    In modern times, it was astronomer Fritz Zwicky, in the 1930s, who made the first observations of what we now call dark matter. His 1933 observations of the Coma Cluster of galaxies seemed to indicated it has a mass 500 times more than that previously calculated by Edwin Hubble. Furthermore, this extra mass seemed to be completely invisible. Although Zwicky’s observations were initially met with much skepticism, they were later confirmed by other groups of astronomers.

    Thirty years later, astronomer Vera Rubin provided a huge piece of evidence for the existence of dark matter. She discovered that the centers of galaxies rotate at the same speed as their extremities, whereas, of course, they should rotate faster. Think of a vinyl LP on a record deck: its center rotates faster than its edge. That’s what logic dictates we should see in galaxies too. But we do not. The only way to explain this is if the whole galaxy is only the center of some much larger structure, as if it is only the label on the LP so to speak, causing the galaxy to have a consistent rotation speed from center to edge.

    Vera Rubin, following Zwicky, postulated that the missing structure in galaxies is dark matter. Her ideas were met with much resistance from the astronomical community, but her observations have been confirmed and are seen today as pivotal proof of the existence of dark matter.

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science).


    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL).


    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu.

    The Vera C. Rubin Observatory currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    LSST Data Journey, Illustration by Sandbox Studio, Chicago with Ana Kova.

    See the full article here.


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.


    Stem Education Coalition

    The Instituto de Astrofísica de Canarias(IAC) (ES) is an international research centre in Spain which comprises:

    The Instituto de Astrofísica (ES), the headquarters, which is in La Laguna (Tenerife).
    The Centro de Astrofísica en La Palma (CALP) (ES)
    The Observatorio del Teide (OT) (ES), in Izaña (Tenerife).

    These centres, with all the facilities they bring together, make up the European Northern Observatory(ENO).

    The IAC is constituted administratively as a Public Consortium, created by statute in 1982, with involvement from the Spanish Government, the Government of the Canary Islands, the University of La Laguna and Spain’s Science Research Council (CSIC).

    The International Scientific Committee (CCI) manages participation in the observatories by institutions from other countries. A Time Allocation Committee (CAT) allocates the observing time reserved for Spain at the telescopes in the IAC’s observatories.

    The exceptional quality of the sky over the Canaries for astronomical observations is protected by law. The IAC’s Sky Quality Protection Office (OTPC) regulates the application of the law and its Sky Quality Group continuously monitors the parameters that define observing quality at the IAC Observatories.

    The IAC’s research programme includes astrophysical research and technological development projects.

    The IAC is also involved in researcher training, university teaching and outreachactivities.

    The IAC has devoted much energy to developing technology for the design and construction of a large 10.4 metre diameter telescope, the ( Gran Telescopio CANARIAS, GTC), which is sited at the Observatorio del Roque de los Muchachos ES.

    Gran Telescopio Canarias at the Roque de los Muchachos Observatory on the island of La Palma, in the Canaries, Spain, sited on a volcanic peak 2,267 metres (7,438 ft) above sea level

     
  • richardmitnick 11:53 am on July 28, 2020 Permalink | Reply
    Tags: "What dark matter is (probably) not", , , , , Frtiz Zwicky and Vera Rubin, , ,   

    From Symmetry: “What dark matter is (probably) not” 

    Symmetry Mag
    From Symmetry<

    07/28/20
    Meredith Fore

    No one knows for sure what dark matter is. But we know we need something to explain what we see in the universe, and we’ve crossed a few ideas off of our list.

    1
    Illustration by Sandbox Studio, Chicago with Corinne Mucha

    For a recent YouTube video, a theorist with a postdoctoral fellowship at CERN named Dorota Grabowska discussed dark matter with popular science figure Dianna Cowern (more commonly known as Physics Girl). Below the video, a viewer typed the comment, “Dark Matter is science speak for ‘we don’t have a clue.’”

    Grabowska says she was surprised at the number of commenters who seemed to believe physicists knew nothing about the subject.

    “They were saying, ‘Oh, it’s just a miscounting of space dust’ or, ‘We really just don’t understand magnetism,’” Grabowska says. “People weren’t realizing the steps that physicists go through to actually test a hypothesis and say, ‘This doesn’t work; let’s think differently.’”

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    The birth of a dark matter theory

    Science hypotheses often come from an abnormal observation—something that appears unexpectedly or acts in an unexpected way. Three commonly cited unusual astrophysical observations credited to dark matter are abnormal galaxy rotation speeds, patterns in the large-scale structure of the universe, and the Bullet Cluster.

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    Abnormal galaxy rotation speeds

    Based on the visible matter in galaxies, physicists can use the laws of gravity to predict how quickly stars revolve around galaxies. The prediction was that matter closest to the center of a galaxy would move the fastest, with matter farther from the center feeling less of the pull of gravity and moving more slowly.

    However, astronomers first noticed in the early 20th century that the opposite was happening: The matter in the outer regions of galaxies was moving much faster than expected [see below Dark Matter Background]. Finding these abnormal dynamics was one of the first hints that we might be missing something. If invisible matter makes up much of the mass of a galaxy, then the faster-than-expected regions can be explained.

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    Large-scale structure

    The hot early universe was in part made up of charged nuclei and electrons. Photons could drag on these particles, preventing growth. But dark matter was immune to this interaction and, with the help of gravity, began to form its own structures. When the universe cooled enough that atoms could form, these atoms (“baryons”) were pulled into the dark matter structures, falling into their gravitational potential wells. This has left a signature in the sky called baryon acoustic oscillations, reminiscent of the ripples of a stone splashing into water.

    Comparing the predictions of a dark matter theory to observational data from these oscillations, called BAOs, and the overall shape of our universe’s “cosmic web” are necessary tests of the theory’s strength.

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    The Bullet Cluster

    Bullet Cluster NASA Chandra NASA ESA Hubble, evidence of shock

    The Bullet Cluster is a cluster of galaxies created by a collision between two other galaxy clusters. The clusters interacted gravitationally, causing the matter in both to slow down as they passed through each other. The gas from each collided, heating up and creating a bright signal in X-rays.

    But while there are two bright X-ray clusters of galaxies near the point of collision, a significant amount of mass is located in two dark “lobes” even farther from the center. It’s like the galaxies collided, but some of their matter didn’t care and kept going unimpeded. Dark matter seems to be passing through regular matter like a ghost.

    The Bullet Cluster is considered a crucial piece of evidence for the existence of dark matter. It is famous for being the first galaxy merger to be deeply studied, but astronomers have since found many more galaxy mergers that show the same dark “lobe” structure.

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    To be viable, any theory of dark matter must adequately explain all three of these phenomena. “The baton gets passed from the astrophysical observers to the theorists, to the experimentalists,” Grabowska says.

    Observers announce an unexpected phenomenon to theorists, who think of a possible explanation for it; experimentalists then devise a way to test that explanation through detection methods such as looking for a gravitational signature or a particle interaction. “It’s this massively collaborative process where no one really has the one way to look at it. You need everyone to put the whole picture together.”

    Scientists may not yet know what the explanation for these unusual astronomical observations is, but they do have some idea what it is not.

    Disfavored: The theories that have fallen behind

    Grabowska is careful to note that it’s difficult to completely throw away a theory of dark matter. The range of possible masses for a dark matter particle spans many orders of magnitude, all the way from the axion (its mass a tiny fraction of that of a proton) to stellar black holes (thousands of times more massive than the sun).

    “It is much easier to say you know what dark matter could be than what dark matter can’t be,” she says. “You can’t say a candidate is disfavored until you actually look for it, and dark matter is very hard to look for.”

    One thing physicists are sure of? They haven’t miscounted any mass.

    Galaxy rotation curves could be explained if there were simply regular matter that observers didn’t measure or account for. Some theories posited that perhaps there was more regular mass out there, but it consisted of things like brown dwarfs, burnt-out stars, and small, ancient black holes that are too dim to see properly. Scientists posited that these massive compact halo objects (or “MACHOs”) could make up the missing matter.

    But not only do MACHOs not explain other phenomena that point to the existence of dark matter, widespread searches for these objects have not found enough of them to represent all of dark matter.

    Another set of dark matter theories that many scientists consider to have fallen short is modified Newtonian dynamics (or “MOND”).

    Mordehai Milgrom, MOND theorist, is an Israeli physicist and professor in the department of Condensed Matter Physics at the Weizmann Institute in Rehovot, Israel http://cosmos.nautil.us

    These theories propose a modification to Newton’s laws of motion that would apply only at very small accelerations, which would adequately explain the abnormal rotation speed of galaxies. But like MACHOs, these theories are inadequate to explain BAOs or the dynamics of larger-scale galaxy clusters. They also struggle to describe the Bullet Cluster.

    Some of the strongest candidates for dark matter—which would explain abnormal galaxy rotation speeds, the Bullet Cluster, BAOs and the large-scale structure of the universe—are weakly interacting particles (or “WIMPs”). But so far, thorough, decades-long searches have not yet turned up any evidence for the existence of WIMP dark matter candidates; instead, they have set stricter and stricter limits on their possible properties.

    The range of viable candidates for a dark matter particle is still vast. It includes axions, sterile neutrinos and WIMPs with rare interactions or extremely low masses.

    Expanding the field even further is the possibility that there isn’t just one answer to dark matter: It could be a combination of different types of particles or objects, or there could be an entire “dark sector” of dark matter particles, like a mirror-universe version of the Standard Model.

    Definitively disproving a dark matter theory or a specific dark matter candidate is challenging—when do you stop searching for a particle that could have nearly any mass? But the breadth of evidence for dark matter allows for very thorough vetting. A dark matter theory has so much to explain; and as experiments get more precise and telescopes get sharper, we may be able to cross a few more off our list.

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    Dark Matter Background
    Fritz Zwicky discovered Dark Matter in the 1930s when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

    Fritz Zwicky from http:// palomarskies.blogspot.com

    Coma cluster via NASA/ESA Hubble

    In modern times, it was astronomer Fritz Zwicky, in the 1930s, who made the first observations of what we now call dark matter. His 1933 observations of the Coma Cluster of galaxies seemed to indicated it has a mass 500 times more than that previously calculated by Edwin Hubble. Furthermore, this extra mass seemed to be completely invisible. Although Zwicky’s observations were initially met with much skepticism, they were later confirmed by other groups of astronomers.

    Thirty years later, astronomer Vera Rubin provided a huge piece of evidence for the existence of dark matter. She discovered that the centers of galaxies rotate at the same speed as their extremities, whereas, of course, they should rotate faster. Think of a vinyl LP on a record deck: its center rotates faster than its edge. That’s what logic dictates we should see in galaxies too. But we do not. The only way to explain this is if the whole galaxy is only the center of some much larger structure, as if it is only the label on the LP so to speak, causing the galaxy to have a consistent rotation speed from center to edge.

    Vera Rubin, following Zwicky, postulated that the missing structure in galaxies is dark matter. Her ideas were met with much resistance from the astronomical community, but her observations have been confirmed and are seen today as pivotal proof of the existence of dark matter.

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)


    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)


    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

    The Vera C. Rubin Observatory currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    LSST Data Journey, Illustration by Sandbox Studio, Chicago with Ana Kova

    See the full article here .


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    Please help promote STEM in your local schools.


    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
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