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On July 23, 1928, Vera Rubin, American astronomer who discovered dark matter, born in Philadelphia, Pennsylvania (d. 2016). From the article:
"Rubin held various academic appointments for the next eleven years. She served for a year as an Instructor of Mathematics and Physics at Montgomery County Community College, then worked from 1955-1965 at Georgetown University, as a Research Associate Astronomer, Lecturer (1959-1962), and finally, Assistant Professor of Astronomy (1962-1965).[1][16] She joined the Carnegie Institute in 1965, as a staff member in the Department of Terrestrial Magnetism,[1][16][17] where she met her long-time collaborator, instrument-maker Kent Ford.[7] Because she had young children, she did much of her work from home.[8]
In 1963, Rubin began a year-long collaboration with Geoffrey and Margaret Burbidge, during which made her first observations of the rotation of galaxies at the McDonald Observatory's 82 inch telescope.[7] During her work at the Carnegie Institute, Rubin applied to observe at the Palomar Observatory in 1965, despite the fact that the building did not have facilities for women.[18] She created her own women's restroom, sidestepping the lack of facilities available for her and becoming the first female astronomer to observe there.[1][3][19]
At the Carnegie Institution, Rubin began work related to her controversial thesis regarding galaxy clusters[16] with Ford, making hundreds of observations using Ford's image-tube spectrograph.[20] This instrument allowed Rubin to amplify starlight seen through the telescope so they could view astronomical objects that were previously too dim to see.[7][20] The Rubin–Ford effect, an apparent anisotropy in the expansion of the Universe on the scale of 100 million light years, was discovered through studies of spiral galaxies, particularly the Andromeda Galaxy, chosen for its brightness and proximity to Earth.[9][21] First appearing in journals in 1976, the idea of peculiar motion on this scale in the universe was a highly controversial proposition, dismissed by leading astronomers but ultimately shown to be valid.[3][9] The effect is now known as large scale streaming.[19] The pair also briefly studied quasars, which had been discovered in 1963 and were a popular topic of research.[7][9]
Wishing to avoid controversial areas of astronomy, including quasars and galactic motion, Rubin began to study the rotation and outer reaches of galaxies, an interest sparked by her collaboration with the Burbidges.[7] She investigated the rotation curves of spiral galaxies, again beginning with Andromeda, by looking at their outermost material, and observed flat rotation curves: the outermost components of the galaxy were moving as quickly as those close to the center.[22] This was an early indication that spiral galaxies were surrounded by dark matter haloes.[3][7] She further uncovered the discrepancy between the predicted angular motion of galaxies based on the visible light and the observed motion.[23] Her research showed that spiral galaxies rotate quickly enough that they should fly apart, if the gravity of their constituent stars was all that was holding them together; because they stay intact, a large amount of unseen mass must be holding them together, a conundrum that became known as the galaxy rotation problem.[3][22]
Rubin's calculations showed that galaxies must contain at least five to ten times as much dark matter as ordinary matter.[24][25] Rubin's results were confirmed over subsequent decades,[1] and became the first persuasive results supporting the theory of dark matter, initially proposed by Fritz Zwicky in the 1930s.[1][9][26] This data was confirmed by radio astronomers, the discovery of the cosmic microwave background, and images of gravitational lensing.[7][9] Her research also prompted a theory of non-Newtonian gravity on galactic scales, but this theory has not been widely accepted by astrophysicists.[3]
Another area of interest for Rubin was the phenomenon of counter-rotation in galaxies. Her discovery that some gas and stars moved in the opposite direction to the rotation of the rest of the galaxy challenged the prevailing theory that all of the material in a galaxy moved in the same direction, and provided the first evidence for galaxy mergers and the process by which galaxies initially formed.[19]
Rubin's perspective on the history of the work on galaxy movements was presented in a review, "One Hundred Years of Rotating Galaxies," for the Publications of the Astronomical Society of the Pacific in 2000. This was an adaptation of the lecture she gave in 1996 upon receiving the Gold Medal of the Royal Astronomical Society, the second woman to be so honored, 168 years after Caroline Herschel received the Medal in 1828.[3][27] She continued her research and mentorship until her death in 2016."
"Rubin held various academic appointments for the next eleven years. She served for a year as an Instructor of Mathematics and Physics at Montgomery County Community College, then worked from 1955-1965 at Georgetown University, as a Research Associate Astronomer, Lecturer (1959-1962), and finally, Assistant Professor of Astronomy (1962-1965).[1][16] She joined the Carnegie Institute in 1965, as a staff member in the Department of Terrestrial Magnetism,[1][16][17] where she met her long-time collaborator, instrument-maker Kent Ford.[7] Because she had young children, she did much of her work from home.[8]
In 1963, Rubin began a year-long collaboration with Geoffrey and Margaret Burbidge, during which made her first observations of the rotation of galaxies at the McDonald Observatory's 82 inch telescope.[7] During her work at the Carnegie Institute, Rubin applied to observe at the Palomar Observatory in 1965, despite the fact that the building did not have facilities for women.[18] She created her own women's restroom, sidestepping the lack of facilities available for her and becoming the first female astronomer to observe there.[1][3][19]
At the Carnegie Institution, Rubin began work related to her controversial thesis regarding galaxy clusters[16] with Ford, making hundreds of observations using Ford's image-tube spectrograph.[20] This instrument allowed Rubin to amplify starlight seen through the telescope so they could view astronomical objects that were previously too dim to see.[7][20] The Rubin–Ford effect, an apparent anisotropy in the expansion of the Universe on the scale of 100 million light years, was discovered through studies of spiral galaxies, particularly the Andromeda Galaxy, chosen for its brightness and proximity to Earth.[9][21] First appearing in journals in 1976, the idea of peculiar motion on this scale in the universe was a highly controversial proposition, dismissed by leading astronomers but ultimately shown to be valid.[3][9] The effect is now known as large scale streaming.[19] The pair also briefly studied quasars, which had been discovered in 1963 and were a popular topic of research.[7][9]
Wishing to avoid controversial areas of astronomy, including quasars and galactic motion, Rubin began to study the rotation and outer reaches of galaxies, an interest sparked by her collaboration with the Burbidges.[7] She investigated the rotation curves of spiral galaxies, again beginning with Andromeda, by looking at their outermost material, and observed flat rotation curves: the outermost components of the galaxy were moving as quickly as those close to the center.[22] This was an early indication that spiral galaxies were surrounded by dark matter haloes.[3][7] She further uncovered the discrepancy between the predicted angular motion of galaxies based on the visible light and the observed motion.[23] Her research showed that spiral galaxies rotate quickly enough that they should fly apart, if the gravity of their constituent stars was all that was holding them together; because they stay intact, a large amount of unseen mass must be holding them together, a conundrum that became known as the galaxy rotation problem.[3][22]
Rubin's calculations showed that galaxies must contain at least five to ten times as much dark matter as ordinary matter.[24][25] Rubin's results were confirmed over subsequent decades,[1] and became the first persuasive results supporting the theory of dark matter, initially proposed by Fritz Zwicky in the 1930s.[1][9][26] This data was confirmed by radio astronomers, the discovery of the cosmic microwave background, and images of gravitational lensing.[7][9] Her research also prompted a theory of non-Newtonian gravity on galactic scales, but this theory has not been widely accepted by astrophysicists.[3]
Another area of interest for Rubin was the phenomenon of counter-rotation in galaxies. Her discovery that some gas and stars moved in the opposite direction to the rotation of the rest of the galaxy challenged the prevailing theory that all of the material in a galaxy moved in the same direction, and provided the first evidence for galaxy mergers and the process by which galaxies initially formed.[19]
Rubin's perspective on the history of the work on galaxy movements was presented in a review, "One Hundred Years of Rotating Galaxies," for the Publications of the Astronomical Society of the Pacific in 2000. This was an adaptation of the lecture she gave in 1996 upon receiving the Gold Medal of the Royal Astronomical Society, the second woman to be so honored, 168 years after Caroline Herschel received the Medal in 1828.[3][27] She continued her research and mentorship until her death in 2016."
Vera Rubin - Wikipedia
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“Dark Matter” introduces the concept of Dark Matter by applying Newton’s Law of gravitation to estimate the speed of a star in a rotating galaxy as a functio...
Thank you my friend SGT (Join to see) for making us aware that July 23 is the anniversary of the birth of American mathematician, physicist, and astronomer Vera Florence Cooper Rubin.
Images: Vera Rubin, the astronomer who helped to discover about dark matter. The Coma Cluster, which provided the first evidence for dark matter. Source: © NASA, JPL-Caltech, SDSS, Leigh Jenkins, Ann Hornschemeier (Goddard Space Flight Center) et al.; : Observed and predicted rotation curves for the galaxy M33, also known as the "Triangulum Galaxy." Source: © M33 Image: NOAO, AURA, NSF, T. A. Rector.More info
1. Background from learner.org/courses/physics/unit/text.html?unit=10&secNum=2
Initial Evidence of Dark Matter
"Fritz Zwicky, an astronomer at the California Institute of Technology, stumbled across the gravitational effects of dark matter in the early 1930s while studying how galaxies move within the Coma Cluster. The Coma Cluster consists of approximately 1,000 galaxies spread over about two degrees on the sky—roughly the size of your thumb held at arm's length, and four times the size of the Sun and the Moon seen from Earth. Gravity binds the galaxies together into a cluster, known as a galaxy cluster. Unlike the gravitationally bound planets in our solar system, however, the galaxies do not orbit a central heavy object like the Sun and thus execute more complicated orbits.
To carry out his observations, Zwicky persuaded Caltech to build an 18-inch Schmidt telescope that could capture large numbers of galaxies in a single wide-angle photograph. He used the instrument to make a survey of all the galaxies in the cluster and used measurements of the Doppler shift of their spectra to determine their velocities. He then applied the virial theorem. A straightforward application of classical mechanics, the virial theorem relates the velocity of orbiting objects to the amount of gravitational force acting on them. Isaac Newton's theory tells us that gravitational force is proportional to the masses of the objects involved, so Zwicky was able to calculate the total mass of the Coma Cluster from his measured galactic velocities.
Zwicky also measured the total light output of all the cluster's galaxies, which contain about a trillion stars altogether. When he compared the ratio of the total light output to the mass of the Coma Cluster with a similar ratio for the nearby Kapteyn stellar system, he found the light output per unit mass for the cluster fell short of that from a single Kapteyn star by a factor of over 100. He reasoned that the Coma Cluster must contain a large amount of matter not accounted for by the light of the stars. He called it "dark matter."
Zwicky's measurements took place just after astronomers had realized that galaxies are very large groups of stars. It took some time for dark matter to become the subject of active research it is today. When Zwicky first observed the Coma Cluster, tests of Einstein's theory were just starting, the first cosmological measurements were taking place, and nuclear physicists were only beginning to develop the theories that would explain the Big Bang and supernovae. Since galaxies are complex, distant objects, it is not surprising that astronomers did not immediately begin to worry about "the dark matter problem."
By the early 1970s, technology, astronomy, and particle physics had advanced enough that the dark matter problem seemed more tractable. General relativity and nuclear physics had come together in the Big Bang theory of the early universe, and the detection of microwave photons from the time when the first atoms formed from free electrons and protons had put the theory on a solid footing. Larger telescopes and more precise and more sensitive light detectors made astronomical measurements quicker and better. Just as important, the emergence of affordable mini-computers allowed physics and astronomy departments to purchase their own high-performance computers for dedicated astronomical calculations. Every advance set the scene for a comprehensive study of dark matter, and two very important studies of dark matter soon appeared.
In 1973, Princeton University astronomers Jeremiah Ostriker and James Peebles used numerical simulation to study how galaxies evolve. Applying a technique called N-body simulation, they programmed 300 mass points into their computer to represent groups of stars in a galaxy rotating about a central point. Their simulated galaxy had more mass points, or stars, toward the center and fewer toward the edge. The simulation started by computing the gravitational force between each pair of mass points from Newton's law and working out how the mass points would move in a small interval of time. By repeating this calculation many times, Ostriker and Peebles were able to track the motion of all the mass points in the galaxy over a long period of time.
For a galaxy the size of the Milky Way (4x1020 meters), a mass point about halfway out the edge moves at about 200 kilometers per second and orbits the center in about 50 million years. Ostriker and Peebles found that in a time less than an orbital period, most of the mass points would collapse to a bar-shaped, dense concentration close to the center of the galaxy with only a few mass points at larger radii. This looked nothing like the elegant spiral or elliptical shapes we are used to seeing. However, if they added a static, uniform distribution of mass three to 10 times the size of the total mass of the mass points, they found a more recognizable structure would emerge. Ostriker and Peebles had solid numerical evidence that dark matter was necessary to form the types of galaxies we observe in our universe.
Fresh evidence from the Andromeda galaxy
At about the same time, astronomers Kent Ford and Vera Cooper Rubin at the Carnegie Institution of Washington began a detailed study of the motion of stars in the nearby galaxy of Andromeda. Galaxies are so large that even stars traveling at 200 kilometers per second appear stationary; astronomers must measure their Doppler shifts to obtain their velocities. However, early measurements of stellar velocities in different portions of Andromeda proved very difficult. Since the spectrometers used to measure the shift in frequency took a long time to accumulate enough light, observations of a given portion of Andromeda required several hours or even several nights of observing. Combining images from several observations was difficult and introduced errors into the measurement. However, new and more sensitive photon detectors developed in the early 1970s allowed much shorter measurement times and enabled measurements further out from the center of the galaxy.
Rubin and Ford measured the velocity of hydrogen gas clouds in and near the Andromeda galaxy using the new detectors. These hydrogen clouds orbit the galaxy much as stars orbit within the galaxy. Rubin and Ford expected to find that the hydrogen gas outside the visible edge of the galaxy would be moving slower than gas at the edge of the galaxy. This is what the virial theorem predicts if the mass in the galaxy is concentrated where the galaxy emits light. Instead, they found the opposite: the orbital velocity of the hydrogen clouds remained constant outside the visible edge of the galaxy. If the virial theorem is to be believed, there must be additional dark matter outside the visible edge of the galaxy. If Andromeda obeyed Newton's laws, Rubin reasoned, the galaxy must contain dark matter, in quantities that increased with increasing distance from the galactic center.
Alternative explanations of the Andromeda observations soon emerged. Theories of Modified Newtonian Dynamics (MOND), for example, aimed to explain the findings by modifying the gravitational interaction over galactic and larger distances. At very low accelerations, which correspond to galactic distances, the theories posit that the gravitational force varies inversely with the distance alone rather than the square of the distance. However, MOND would overturn Einstein's theory in an incredible way: General relativity is based on the simple idea of the equivalence principle. This states that there is no difference between gravitational mass (the mass that causes the gravitational force) and inertial mass (the mass that resists acceleration). There is no fundamental reason to expect these two masses to be the same, nor is there any reason to expect them to be different. But their equivalence forms the cornerstone of Einstein's general theory. MOND theories break that equivalence because they modify either gravity or inertia. If MOND were correct, a fundamental assumption underlying all of modern physics would be false.
2. Background from jwa.org/encyclopedia/article/rubin-vera-cooper
VERA COOPER RUBIN; 1928 – 2016 by Kristine Larsen
Vera Cooper Rubin has forever changed our fundamental view of the cosmos, from a universe dominated by starlight to one dominated by dark matter. Rubin was born on July 23, 1928, in Philadelphia, Pennsylvania, the younger of two daughters of electrical engineer Philip Cooper and his wife Rose (Applebaum). Philip Cooper encouraged his daughter’s interest in astronomy, taking her to amateur astronomy meetings after the family moved to Washington, D.C., and assisting in her first homemade telescope when she was fourteen.
Vera discovered early that women science students were not accepted at some universities. Her early experiences shaped her later work for women’s equality in the sciences, especially astronomy. Rubin received her B.A. from Vassar in 1948 and her M.A. from Cornell University in 1951, where she met and married Robert Rubin, a graduate student in physical chemistry. Her controversial master’s thesis examined the possibility of a bulk rotation in the universe by looking for “non-Hubble flow.” At that time, the redshifts (lengthening of light waves due to the motion of an object, such as a star or a galaxy) for only 109 galaxies had been obtained, yet her analysis seemed to show an extra, “sideways” motion of galaxies independent of the normal Hubble recession caused by the expansion of the universe. The paper got a cold reception and was rejected by both Astronomical Journal and Astrophysical Journal. Although Rubin later agreed that perhaps her data were too skimpy, her thesis was a factor in Gerald de Vaucouleur’s claim for evidence of the “Local Supercluster.”
Rubin’s doctoral work was conducted at Georgetown University under the auspices of George Gamow. Her thesis (1954) was one of the earliest works on the clustering of galaxies. She concluded that galaxies were not randomly distributed over the sky, but instead there was a definite clumping. Her results were not followed up by the scientific community, as the subject of large-scale structure was not studied seriously until the late 1970s.
From 1955 to 1965, Rubin rose from research associate to assistant professor at Georgetown, and from 1963 to 1964 she engaged in work on the rotation of galaxies with the famed husband-wife team of Geoffrey and Margaret Burbidge. In 1965, Rubin joined the staff of the Department of Terrestrial Magnetism of the Carnegie Institution of Washington, where she remains today. It was during this year that Rubin became the first woman to observe “legally” at Mount Palomar Observatory under her own name as a guest investigator.
In the early 1970s, Rubin renewed her interest in non-Hubble flow, and, with W. Kent Ford, she found evidence again for extra motion. The “Rubin-Ford effect” has been called spurious by some and well-established by others. Rubin is perhaps best-known for her work with Ford and others on the rotation curves of spiral galaxies, using newer technology to update the groundbreaking work of the Burbidges. Rubin found that spiral galaxies have “flat rotation curves.” Unlike our solar system, in which the majority of the matter is contained in the sun, and thus the planets follow Keplerian motion with Mercury having a much faster orbital velocity than Pluto, the luminous matter in spiral galaxies has a high orbital velocity out to the visible edge. This is usually explained as due to the fact that the bulk of the galaxy’s mass is not clustered at the center, where the visible bulge of the galaxy is, but there exists a halo of dark matter extending at least to the visible edge, if not farther. Thus, Rubin and her collaborators provided some of the first direct evidence for the existence of dark matter, verifying the earlier theoretical work of Jeremy Ostriker and James Peebles. Since 1978, Rubin has analyzed the spectra of over two hundred galaxies and found that nearly all contain copious amounts of dark matter.
Rubin holds four honorary doctorates, a 1993 Presidential National Medal of Science, the 1994 Dickson Prize in Science from Carnegie-Mellon University, and the 1994 Russell Lectureship Prize of the American Astronomical Society. In 1981, she became the second woman astronomer to be elected to the National Academy of Sciences. She served as associate editor of Astronomical Journal from 1972 to 1977 and of Astrophysical Journal Letters from 1977 to 1982. In addition to numerous scientific papers, she published Bright Galaxies, Dark Matter, a collection of less technical articles designed for the general public, in 1997.
The Rubins have four children: David M., Judith S., Karl C., and Allan M.—all of whom have Ph.D.s in the sciences, including daughter Judith S. Young, a noted astronomer in her own right.
On January 16, 2004, the National Academy of Sciences awarded Rubin its James Craig Watson Medal for “her seminal observations of dark matter in galaxies… and for generous mentoring of young astronomers, men and women.”
Remembering what it was like to be a lone woman staring at galaxies, Vera Rubin considers it a responsibility and a privilege to be a mentor. “It is well known,” she says, “that I am available twenty-four hours a day to women astronomers.”
SELECTED WORKS BY VERA RUBIN
Bright Galaxies, Dark Matter in Masters of Modern Physics Series (1997); “Extended Rotation Curves of High-Luminosity Spiral Galaxies. Vol. 4, Systematic Dynamical Properties, Sa to Sc,” with W. Kent Ford, Jr., and N. Thonnard. Astrophysical Journal Letters 225 (1978): L101–111; “Fluctuations in the Space Distribution of the Galaxies.” Proceedings of the National Academy of Sciences 40 (1954): 541–549; “Rotational Properties of 21 Sc Galaxies with a Large Range of Luminosities and Radii, from NGC 4605 (R = 4 kpc) to NGC 2885 (R = 122 kpc),” with W. Kent Ford, Jr., and N. Thonnard. Astrophysical Journal 238 (1980): 471–487; “Weighing the Universe: Dark Matter and Missing Mass.” In Bubbles, Voids and Bumps in Time: The New Cosmology, edited by James R. Cornell (1989); “Women’s Work.” Science 86 (July/August 1986): 58–65.
Bibliography
Bartusiak, Marcia. Through a Universe Darkly (1993), and “The Woman Who Spins the Stars.” Discover (October 1990): 88–94; Lightman, Alan, and Roberta Brawer. Origins (1990); Stille, Darlene R. Extraordinary Women Scientists (1995); Who’s Who in America 1996. Vol. 2 (1996); Yount, Lisa. Contemporary Women Scientists (1994)."
“Dark Matter” introduces the concept of Dark Matter by applying Newton’s Law of gravitation to estimate the speed of a star in a rotating galaxy as a function of the star’s distance from the center of a galaxy, discusses that the expected speed disagrees with Vera Rubin’s measurements and shows how to roughly bring in a distribution of Dark Matter into a new estimate of speed that agrees approximately with Rubin’s work. The makeup of Dark Matter is discussed and the potential role that the “Muon g-2” experiment at Fermi Lab might play in regards to Dark Matter makeup is alluded to. Andrew R. Ochadlick Jr. received a Ph.D. from the State University of New York at Albany (SUNYA) and is a career physicist with university, government and industry R&D experience and teaching experience at the undergraduate and graduate level.
https://www.youtube.com/watch?v=Raj1gTEd3VY
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Images: Vera Rubin, the astronomer who helped to discover about dark matter. The Coma Cluster, which provided the first evidence for dark matter. Source: © NASA, JPL-Caltech, SDSS, Leigh Jenkins, Ann Hornschemeier (Goddard Space Flight Center) et al.; : Observed and predicted rotation curves for the galaxy M33, also known as the "Triangulum Galaxy." Source: © M33 Image: NOAO, AURA, NSF, T. A. Rector.More info
1. Background from learner.org/courses/physics/unit/text.html?unit=10&secNum=2
Initial Evidence of Dark Matter
"Fritz Zwicky, an astronomer at the California Institute of Technology, stumbled across the gravitational effects of dark matter in the early 1930s while studying how galaxies move within the Coma Cluster. The Coma Cluster consists of approximately 1,000 galaxies spread over about two degrees on the sky—roughly the size of your thumb held at arm's length, and four times the size of the Sun and the Moon seen from Earth. Gravity binds the galaxies together into a cluster, known as a galaxy cluster. Unlike the gravitationally bound planets in our solar system, however, the galaxies do not orbit a central heavy object like the Sun and thus execute more complicated orbits.
To carry out his observations, Zwicky persuaded Caltech to build an 18-inch Schmidt telescope that could capture large numbers of galaxies in a single wide-angle photograph. He used the instrument to make a survey of all the galaxies in the cluster and used measurements of the Doppler shift of their spectra to determine their velocities. He then applied the virial theorem. A straightforward application of classical mechanics, the virial theorem relates the velocity of orbiting objects to the amount of gravitational force acting on them. Isaac Newton's theory tells us that gravitational force is proportional to the masses of the objects involved, so Zwicky was able to calculate the total mass of the Coma Cluster from his measured galactic velocities.
Zwicky also measured the total light output of all the cluster's galaxies, which contain about a trillion stars altogether. When he compared the ratio of the total light output to the mass of the Coma Cluster with a similar ratio for the nearby Kapteyn stellar system, he found the light output per unit mass for the cluster fell short of that from a single Kapteyn star by a factor of over 100. He reasoned that the Coma Cluster must contain a large amount of matter not accounted for by the light of the stars. He called it "dark matter."
Zwicky's measurements took place just after astronomers had realized that galaxies are very large groups of stars. It took some time for dark matter to become the subject of active research it is today. When Zwicky first observed the Coma Cluster, tests of Einstein's theory were just starting, the first cosmological measurements were taking place, and nuclear physicists were only beginning to develop the theories that would explain the Big Bang and supernovae. Since galaxies are complex, distant objects, it is not surprising that astronomers did not immediately begin to worry about "the dark matter problem."
By the early 1970s, technology, astronomy, and particle physics had advanced enough that the dark matter problem seemed more tractable. General relativity and nuclear physics had come together in the Big Bang theory of the early universe, and the detection of microwave photons from the time when the first atoms formed from free electrons and protons had put the theory on a solid footing. Larger telescopes and more precise and more sensitive light detectors made astronomical measurements quicker and better. Just as important, the emergence of affordable mini-computers allowed physics and astronomy departments to purchase their own high-performance computers for dedicated astronomical calculations. Every advance set the scene for a comprehensive study of dark matter, and two very important studies of dark matter soon appeared.
In 1973, Princeton University astronomers Jeremiah Ostriker and James Peebles used numerical simulation to study how galaxies evolve. Applying a technique called N-body simulation, they programmed 300 mass points into their computer to represent groups of stars in a galaxy rotating about a central point. Their simulated galaxy had more mass points, or stars, toward the center and fewer toward the edge. The simulation started by computing the gravitational force between each pair of mass points from Newton's law and working out how the mass points would move in a small interval of time. By repeating this calculation many times, Ostriker and Peebles were able to track the motion of all the mass points in the galaxy over a long period of time.
For a galaxy the size of the Milky Way (4x1020 meters), a mass point about halfway out the edge moves at about 200 kilometers per second and orbits the center in about 50 million years. Ostriker and Peebles found that in a time less than an orbital period, most of the mass points would collapse to a bar-shaped, dense concentration close to the center of the galaxy with only a few mass points at larger radii. This looked nothing like the elegant spiral or elliptical shapes we are used to seeing. However, if they added a static, uniform distribution of mass three to 10 times the size of the total mass of the mass points, they found a more recognizable structure would emerge. Ostriker and Peebles had solid numerical evidence that dark matter was necessary to form the types of galaxies we observe in our universe.
Fresh evidence from the Andromeda galaxy
At about the same time, astronomers Kent Ford and Vera Cooper Rubin at the Carnegie Institution of Washington began a detailed study of the motion of stars in the nearby galaxy of Andromeda. Galaxies are so large that even stars traveling at 200 kilometers per second appear stationary; astronomers must measure their Doppler shifts to obtain their velocities. However, early measurements of stellar velocities in different portions of Andromeda proved very difficult. Since the spectrometers used to measure the shift in frequency took a long time to accumulate enough light, observations of a given portion of Andromeda required several hours or even several nights of observing. Combining images from several observations was difficult and introduced errors into the measurement. However, new and more sensitive photon detectors developed in the early 1970s allowed much shorter measurement times and enabled measurements further out from the center of the galaxy.
Rubin and Ford measured the velocity of hydrogen gas clouds in and near the Andromeda galaxy using the new detectors. These hydrogen clouds orbit the galaxy much as stars orbit within the galaxy. Rubin and Ford expected to find that the hydrogen gas outside the visible edge of the galaxy would be moving slower than gas at the edge of the galaxy. This is what the virial theorem predicts if the mass in the galaxy is concentrated where the galaxy emits light. Instead, they found the opposite: the orbital velocity of the hydrogen clouds remained constant outside the visible edge of the galaxy. If the virial theorem is to be believed, there must be additional dark matter outside the visible edge of the galaxy. If Andromeda obeyed Newton's laws, Rubin reasoned, the galaxy must contain dark matter, in quantities that increased with increasing distance from the galactic center.
Alternative explanations of the Andromeda observations soon emerged. Theories of Modified Newtonian Dynamics (MOND), for example, aimed to explain the findings by modifying the gravitational interaction over galactic and larger distances. At very low accelerations, which correspond to galactic distances, the theories posit that the gravitational force varies inversely with the distance alone rather than the square of the distance. However, MOND would overturn Einstein's theory in an incredible way: General relativity is based on the simple idea of the equivalence principle. This states that there is no difference between gravitational mass (the mass that causes the gravitational force) and inertial mass (the mass that resists acceleration). There is no fundamental reason to expect these two masses to be the same, nor is there any reason to expect them to be different. But their equivalence forms the cornerstone of Einstein's general theory. MOND theories break that equivalence because they modify either gravity or inertia. If MOND were correct, a fundamental assumption underlying all of modern physics would be false.
2. Background from jwa.org/encyclopedia/article/rubin-vera-cooper
VERA COOPER RUBIN; 1928 – 2016 by Kristine Larsen
Vera Cooper Rubin has forever changed our fundamental view of the cosmos, from a universe dominated by starlight to one dominated by dark matter. Rubin was born on July 23, 1928, in Philadelphia, Pennsylvania, the younger of two daughters of electrical engineer Philip Cooper and his wife Rose (Applebaum). Philip Cooper encouraged his daughter’s interest in astronomy, taking her to amateur astronomy meetings after the family moved to Washington, D.C., and assisting in her first homemade telescope when she was fourteen.
Vera discovered early that women science students were not accepted at some universities. Her early experiences shaped her later work for women’s equality in the sciences, especially astronomy. Rubin received her B.A. from Vassar in 1948 and her M.A. from Cornell University in 1951, where she met and married Robert Rubin, a graduate student in physical chemistry. Her controversial master’s thesis examined the possibility of a bulk rotation in the universe by looking for “non-Hubble flow.” At that time, the redshifts (lengthening of light waves due to the motion of an object, such as a star or a galaxy) for only 109 galaxies had been obtained, yet her analysis seemed to show an extra, “sideways” motion of galaxies independent of the normal Hubble recession caused by the expansion of the universe. The paper got a cold reception and was rejected by both Astronomical Journal and Astrophysical Journal. Although Rubin later agreed that perhaps her data were too skimpy, her thesis was a factor in Gerald de Vaucouleur’s claim for evidence of the “Local Supercluster.”
Rubin’s doctoral work was conducted at Georgetown University under the auspices of George Gamow. Her thesis (1954) was one of the earliest works on the clustering of galaxies. She concluded that galaxies were not randomly distributed over the sky, but instead there was a definite clumping. Her results were not followed up by the scientific community, as the subject of large-scale structure was not studied seriously until the late 1970s.
From 1955 to 1965, Rubin rose from research associate to assistant professor at Georgetown, and from 1963 to 1964 she engaged in work on the rotation of galaxies with the famed husband-wife team of Geoffrey and Margaret Burbidge. In 1965, Rubin joined the staff of the Department of Terrestrial Magnetism of the Carnegie Institution of Washington, where she remains today. It was during this year that Rubin became the first woman to observe “legally” at Mount Palomar Observatory under her own name as a guest investigator.
In the early 1970s, Rubin renewed her interest in non-Hubble flow, and, with W. Kent Ford, she found evidence again for extra motion. The “Rubin-Ford effect” has been called spurious by some and well-established by others. Rubin is perhaps best-known for her work with Ford and others on the rotation curves of spiral galaxies, using newer technology to update the groundbreaking work of the Burbidges. Rubin found that spiral galaxies have “flat rotation curves.” Unlike our solar system, in which the majority of the matter is contained in the sun, and thus the planets follow Keplerian motion with Mercury having a much faster orbital velocity than Pluto, the luminous matter in spiral galaxies has a high orbital velocity out to the visible edge. This is usually explained as due to the fact that the bulk of the galaxy’s mass is not clustered at the center, where the visible bulge of the galaxy is, but there exists a halo of dark matter extending at least to the visible edge, if not farther. Thus, Rubin and her collaborators provided some of the first direct evidence for the existence of dark matter, verifying the earlier theoretical work of Jeremy Ostriker and James Peebles. Since 1978, Rubin has analyzed the spectra of over two hundred galaxies and found that nearly all contain copious amounts of dark matter.
Rubin holds four honorary doctorates, a 1993 Presidential National Medal of Science, the 1994 Dickson Prize in Science from Carnegie-Mellon University, and the 1994 Russell Lectureship Prize of the American Astronomical Society. In 1981, she became the second woman astronomer to be elected to the National Academy of Sciences. She served as associate editor of Astronomical Journal from 1972 to 1977 and of Astrophysical Journal Letters from 1977 to 1982. In addition to numerous scientific papers, she published Bright Galaxies, Dark Matter, a collection of less technical articles designed for the general public, in 1997.
The Rubins have four children: David M., Judith S., Karl C., and Allan M.—all of whom have Ph.D.s in the sciences, including daughter Judith S. Young, a noted astronomer in her own right.
On January 16, 2004, the National Academy of Sciences awarded Rubin its James Craig Watson Medal for “her seminal observations of dark matter in galaxies… and for generous mentoring of young astronomers, men and women.”
Remembering what it was like to be a lone woman staring at galaxies, Vera Rubin considers it a responsibility and a privilege to be a mentor. “It is well known,” she says, “that I am available twenty-four hours a day to women astronomers.”
SELECTED WORKS BY VERA RUBIN
Bright Galaxies, Dark Matter in Masters of Modern Physics Series (1997); “Extended Rotation Curves of High-Luminosity Spiral Galaxies. Vol. 4, Systematic Dynamical Properties, Sa to Sc,” with W. Kent Ford, Jr., and N. Thonnard. Astrophysical Journal Letters 225 (1978): L101–111; “Fluctuations in the Space Distribution of the Galaxies.” Proceedings of the National Academy of Sciences 40 (1954): 541–549; “Rotational Properties of 21 Sc Galaxies with a Large Range of Luminosities and Radii, from NGC 4605 (R = 4 kpc) to NGC 2885 (R = 122 kpc),” with W. Kent Ford, Jr., and N. Thonnard. Astrophysical Journal 238 (1980): 471–487; “Weighing the Universe: Dark Matter and Missing Mass.” In Bubbles, Voids and Bumps in Time: The New Cosmology, edited by James R. Cornell (1989); “Women’s Work.” Science 86 (July/August 1986): 58–65.
Bibliography
Bartusiak, Marcia. Through a Universe Darkly (1993), and “The Woman Who Spins the Stars.” Discover (October 1990): 88–94; Lightman, Alan, and Roberta Brawer. Origins (1990); Stille, Darlene R. Extraordinary Women Scientists (1995); Who’s Who in America 1996. Vol. 2 (1996); Yount, Lisa. Contemporary Women Scientists (1994)."
“Dark Matter” introduces the concept of Dark Matter by applying Newton’s Law of gravitation to estimate the speed of a star in a rotating galaxy as a function of the star’s distance from the center of a galaxy, discusses that the expected speed disagrees with Vera Rubin’s measurements and shows how to roughly bring in a distribution of Dark Matter into a new estimate of speed that agrees approximately with Rubin’s work. The makeup of Dark Matter is discussed and the potential role that the “Muon g-2” experiment at Fermi Lab might play in regards to Dark Matter makeup is alluded to. Andrew R. Ochadlick Jr. received a Ph.D. from the State University of New York at Albany (SUNYA) and is a career physicist with university, government and industry R&D experience and teaching experience at the undergraduate and graduate level.
https://www.youtube.com/watch?v=Raj1gTEd3VY
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Very interesting stuff.
I read an article in Scientific American years ago that predicted there might be an additional 11 dimensions. I think I'm beginning to see a correlation; about 10 times the mass than predicted (theoretically due to "dark matter"), and about 10 more dimensions than described by science. Could there be a connection?
I read an article in Scientific American years ago that predicted there might be an additional 11 dimensions. I think I'm beginning to see a correlation; about 10 times the mass than predicted (theoretically due to "dark matter"), and about 10 more dimensions than described by science. Could there be a connection?
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