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|June 24, 1957 65)(age
|Timothy C. Beers
| Purdue University
| Michigan State University
University of Notre Dame
|Dynamical Studies of Clusters of Galaxies (1983)
|Margaret J. Geller
Timothy C. Beers (born June 24, 1957) is an American astrophysicist. Beers teaches at the University of Notre Dame in the Department of Physics (2014–present), where he holds the Notre Dame Chair in Astrophysics. He is a co-founder of the Physics Frontier Center Joint Institute for Nuclear Astrophysics – Center for the Evolution of the Elements. Prior to coming to Notre Dame, Beers was Director of Kitt Peak National Observatory (2011-2014), and for 25 years was a professor in the Department of Physics and Astronomy at Michigan State University (1986-2011), retiring from that position as University Distinguished Professor.
Beers has published more than 425 refereed papers, and has received multiple Highly Cited Author awards. Beers is a Fellow of the American Physical Society, and was recognized with a Humboldt Senior Research award in 2009 by the Alexander von Humboldt Foundation of Germany. In 2017 he was presented a Distinguished Alumnus award from the Purdue University College of Science.
For decades, Beers has designed and executed large-scale surveys of stars in the Milky Way, efficiently sifting through literally millions of individual stars to find objects that have recorded the chemical history of the Universe in their atmospheres. These rare objects, known as metal-poor stars, are the most chemically primitive stars known, and are among the first generations of stars born in our galaxy, the Milky Way. They provide crucial information on the astrophysical nucleosynthesis sites of the chemical elements, and are powerful tracers of the assembly and evolution of large spiral galaxies.
Beers’ discoveries include: (1) The identification of the first metal-poor stars with measured abundances of Uranium, enabling the determination of a radioactive decay age limit on the Universe, (2) a class of stars known as carbon-enhanced metal-poor (CEMP) stars, a subset of which are thought to reflect the nucleosynthesis products of the very first stars in the Universe, and (3) The first large-scale chronographic (age) maps of the halo of the Milky Way, which astronomers can compare with simulations of the formation of the galaxy. In 2017, Beers and his graduate students were part of a team that identified the characteristic signature of the astrophysical r-process in the kilonova associated with a neutron star merger. This site is thought to be responsible for the production of over half of the elements in the periodic table heavier than iron.
Beers earned his PhD. in astronomy in 1983 from Harvard University. He also holds a master's degree in astronomy from Harvard University (1980), as well as bachelor's degrees of science in physics and in Metallurgical Engineering (1979), both from Purdue University.
A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of member stars. Their name is derived from Latin globulus. Globular clusters are occasionally known simply as "globulars".
A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when a white dwarf is triggered into runaway nuclear fusion. The original object, called the progenitor, either collapses to a neutron star or black hole, or is completely destroyed. The peak optical luminosity of a supernova can be comparable to that of an entire galaxy before fading over several weeks or months.
The Andromeda Galaxy, also known as Messier 31, M31, or NGC 224 and originally the Andromeda Nebula, is a barred spiral galaxy with the diameter of about 46.56 kiloparsecs approximately 2.5 million light-years from Earth and the nearest large galaxy to the Milky Way. The galaxy's name stems from the area of Earth's sky in which it appears, the constellation of Andromeda, which itself is named after the princess who was the wife of Perseus in Greek mythology.
During 1944, Walter Baade categorized groups of stars within the Milky Way into stellar populations. In the abstract of the article by Baade, he recognizes that Jan Oort originally conceived this type of classification in 1926:
The two types of stellar populations had been recognized among the stars of our own galaxy by Oort as early as 1926.
In nuclear astrophysics, the rapid neutron-capture process, also known as the r-process, is a set of nuclear reactions that is responsible for the creation of approximately half of the atomic nuclei heavier than iron, the "heavy elements", with the other half produced by the p-process and s-process. The r-process usually synthesizes the most neutron-rich stable isotopes of each heavy element. The r-process can typically synthesize the heaviest four isotopes of every heavy element, and the two heaviest isotopes, which are referred to as r-only nuclei, can be created via the r-process only. Abundance peaks for the r-process occur near mass numbers A = 82, A = 130 and A = 196.
In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word "metals" as a convenient short term for "all elements except hydrogen and helium". This word-use is distinct from the conventional chemical or physical definition of a metal as an electrically conducting solid. Stars and nebulae with relatively high abundances of heavier elements are called "metal-rich" in astrophysical terms, even though many of those elements are nonmetals in chemistry.
The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. The term Milky Way is a translation of the Latin via lactea, from the Greek γαλακτικός κύκλος, meaning "milky circle". From Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies.
HE 1523-0901 is the designation given to a red giant star in the Milky Way galaxy approximately 7500 light years from Earth. It is thought to be a second generation, Population II, or metal-poor, star ([Fe/H] = −2.95). The star was found in the sample of bright metal-poor halo stars from the Hamburg/ESO Survey by Anna Frebel and collaborators. The group's research was published in the May 10, 2007 issue of The Astrophysical Journal.
Knowledge of the location of Earth has been shaped by 400 years of telescopic observations, and has expanded radically since the start of the 20th century. Initially, Earth was believed to be the center of the Universe, which consisted only of those planets visible with the naked eye and an outlying sphere of fixed stars. After the acceptance of the heliocentric model in the 17th century, observations by William Herschel and others showed that the Sun lay within a vast, disc-shaped galaxy of stars. By the 20th century, observations of spiral nebulae revealed that the Milky Way galaxy was one of billions in an expanding universe, grouped into clusters and superclusters. By the end of the 20th century, the overall structure of the visible universe was becoming clearer, with superclusters forming into a vast web of filaments and voids. Superclusters, filaments and voids are the largest coherent structures in the Universe that we can observe. At still larger scales the Universe becomes homogeneous, meaning that all its parts have on average the same density, composition and structure.
Donald Delbert Clayton is an American astrophysicist whose most visible achievement was the prediction from nucleosynthesis theory that supernovae are intensely radioactive. That earned Clayton the NASA Exceptional Scientific Achievement Medal (1992) for “theoretical astrophysics related to the formation of (chemical) elements in the explosions of stars and to the observable products of these explosions”. Supernovae thereafter became the most important stellar events in astronomy owing to their profoundly radioactive nature. Not only did Clayton discover radioactive nucleosynthesis during explosive silicon burning in stars but he also predicted a new type of astronomy based on it, namely the associated gamma-ray line radiation emitted by matter ejected from supernovae. That paper was selected as one of the fifty most influential papers in astronomy during the twentieth century for the Centennial Volume of the American Astronomical Society. He gathered support from influential astronomers and physicists for a new NASA budget item for a gamma-ray-observatory satellite, achieving successful funding for Compton Gamma Ray Observatory. With his focus on radioactive supernova gas Clayton discovered a new chemical pathway causing carbon dust to condense there by a process that is activated by the radioactivity.
The metallicity distribution function is an important concept in stellar and galactic evolution. It is a curve of what proportion of stars have a particular metallicity of a population of stars such as in a cluster or galaxy.
James Michael Lattimer is a nuclear astrophysicist who works on the dense nuclear matter equation of state and neutron stars.
Carbon enhanced metal poor stars, usually referred to as CEMP stars, are a class of chemically peculiar star. CEMP stars have [C/Fe] > +1, which means compared to the Sun these stars have carbon enhanced at least ten times more than iron, and [Fe/H] < -1, meaning that iron is less than a tenth that in the Sun.
Daryl Haggard is an American-Canadian astronomer and Associate Professor of Physics in the Department of Physics at McGill University and the McGill Space Institute.
In astronomy, the lithium problem or lithium discrepancy refers to the discrepancy between the primordial abundance of lithium as inferred from observations of metal-poor halo stars in our galaxy and the amount that should theoretically exist due to Big Bang nucleosynthesis+WMAP cosmic baryon density predictions of the CMB. Namely, the most widely accepted models of the Big Bang suggest that three times as much primordial lithium, in particular lithium-7, should exist. This contrasts with the observed abundance of isotopes of hydrogen and helium that are consistent with predictions. The discrepancy is highlighted in a so-called "Schramm plot", named in honor of astrophysicist David Schramm, which depicts these primordial abundances as a function of cosmic baryon content from standard BBN predictions.
The [α/Fe] versus [Fe/H] diagram refers to the graph, commonly used in stellar and galactic astrophysics, which shows the logarithmic ratio number densities of diagnostic elements compared to the solar value. The x-axis shows the abundance of elements iron (Fe) vs. hydrogen (H), that is, [Fe/H]. The y-axis shows the combination of one or several of the alpha process elements compared to iron (Fe), that is, [α/Fe].
HD 222925 is a horizontal branch star about 1,470 light years away in the southern constellation Tucana. It is magnitude 9, far below naked-eye visibility. It is an Ap star, a type of chemically peculiar star with an over-abundance of certain metals in its spectrum.
James Wellington Truran Jr. was an American physicist, known for his research in nuclear astrophysics.
Ken'ichi Nomoto is a Japanese astrophysicist and astronomer, known for his research on stellar evolution, supernovae, and the origin of heavy elements.
Michael C. F. Wiescher is a German-American experimental nuclear physicist and astrophysicist, known for his laboratory research in nuclear physics connected with various astrophysical phenomena such as stellar evolution and explosion environments.