A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek galaxias (γαλαξίας), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. Galaxies, averaging an estimated 100 billion stars, range in size from dwarfs with less than a hundred million stars, to the largest galaxies known – supergiants with one hundred trillion stars, each orbiting its galaxy's center of mass. Most of the mass in a typical galaxy is in the form of dark matter, with only a few percent of that mass visible in the form of stars and nebulae. Supermassive black holes are a common feature at the centres of galaxies.
Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, meteoroids, asteroids, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, astronomy studies everything that originates beyond Earth's atmosphere. Cosmology is a branch of astronomy that studies the universe as a whole.
Sandra Moore Faber is an American astrophysicist known for her research on the evolution of galaxies. She is the University Professor of Astronomy and Astrophysics at the University of California, Santa Cruz, and works at the Lick Observatory. She has made discoveries linking the brightness of galaxies to the speed of stars within them and was the co-discoverer of the Faber–Jackson relation. Faber was also instrumental in designing the Keck telescopes in Hawaii.
Astrophysics is a science that employs the methods and principles of physics and chemistry in the study of astronomical objects and phenomena. As one of the founders of the discipline, James Keeler, said, Astrophysics "seeks to ascertain the nature of the heavenly bodies, rather than their positions or motions in space–what they are, rather than where they are." Among the subjects studied are the Sun, other stars, galaxies, extrasolar planets, the interstellar medium and the cosmic microwave background. Emissions from these objects are examined across all parts of the electromagnetic spectrum, and the properties examined include luminosity, density, temperature, and chemical composition. Because astrophysics is a very broad subject, astrophysicists apply concepts and methods from many disciplines of physics, including classical mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics.
Vera Florence Cooper Rubin was an American astronomer who pioneered work on galaxy rotation rates. She uncovered the discrepancy between the predicted and observed angular motion of galaxies by studying galactic rotation curves. By identifying the galaxy rotation problem, her work provided evidence for the existence of dark matter. These results were later confirmed over subsequent decades.
Messier 81 (also known as NGC 3031 or Bode's Galaxy) is a grand design spiral galaxy about 12 million light-years away in the constellation Ursa Major. It has a D25 isophotal diameter of 29.44 kiloparsecs (96,000 light-years). Because of its relative proximity to the Milky Way galaxy, large size, and active galactic nucleus (which harbors a 70 million M☉ supermassive black hole), Messier 81 has been studied extensively by professional astronomers. The galaxy's large size and relatively high brightness also makes it a popular target for amateur astronomers. In late February 2022, astronomers reported that M81 may be the source of FRB 20200120E, a repeating fast radio burst.
Robert Charles Kennicutt, Jr. FRS is an American astronomer. He is currently a professor at Texas A&M University. He is a former Plumian Professor of Astronomy at the Institute of Astronomy in the University of Cambridge. He was formerly Editor-in-Chief of the Astrophysical Journal (1999–2006) and became a co-editor of the Annual Review of Astronomy and Astrophysics as of 2021. His research interests include the structure and evolution of galaxies and star formation in galaxies.
Amy J. Barger is an American astronomer and Henrietta Leavitt Professor of Astronomy at the University of Wisconsin–Madison. She is considered a pioneer in combining data from multiple telescopes to monitor multiple wavelengths and in discovering distant galaxies and supermassive black holes, which are outside of the visible spectrum. Barger is an active member of the International Astronomical Union.
Robert P. Kirshner is an American astronomer, Chief Program Officer for Science for the Gordon and Betty Moore Foundation, and the Clownes Research Professor of Science at Harvard University. Kirshner has worked in several areas of astronomy including the physics of supernovae, supernova remnants, the large-scale structure of the cosmos, and the use of supernovae to measure the expansion of the universe.
Lisa Jennifer Kewley is an Australian Astrophysicist and current Director of the Center for Astrophysics | Harvard & Smithsonian. Previously, Kewley was Director of the ARC Centre of Excellence for All Sky Astrophysics in 3-D and ARC Laureate Fellow at the Australian National University College of Physical and Mathematical Sciences, where she was also a Professor. Specialising in galaxy evolution, she won the Annie Jump Cannon Award in Astronomy in 2005 for her studies of oxygen in galaxies, and the Newton Lacy Pierce Prize in Astronomy in 2008. In 2014 she was elected a fellow of the Australian Academy of Science. In 2020 she received the James Craig Watson Medal. In 2021 she was elected as an international member of the National Academy of Sciences. In 2022 she became the first female director of the Center for Astrophysics | Harvard & Smithsonian.
Nicholas Zabriskie "Nick" Scoville is the Francis L. Moseley Professor of Astronomy at Caltech.
Marc Postman is an American astronomer at the Space Telescope Science Institute in Baltimore, Maryland, United States. His research interests include observational studies of the formation and evolution of galaxies and large scale structure in the universe. His work focuses on determining, observationally, the relationships between galaxy-scale phenomena and the surrounding large-scale environment and matter distribution. His recent research includes characterizing the properties of brightest cluster galaxies and placing new constraints on the cosmic optical background.
Wendy Laurel Freedman is a Canadian-American astronomer, best known for her measurement of the Hubble constant, and as director of the Carnegie Observatories in Pasadena, California, and Las Campanas, Chile. She is now the John & Marion Sullivan University Professor of Astronomy and Astrophysics at the University of Chicago. Her principal research interests are in observational cosmology, focusing on measuring both the current and past expansion rates of the universe, and on characterizing the nature of dark energy.
Claudia Megan Urry is an American astrophysicist, who has served as the President of the American Astronomical Society, as chair of the Department of Physics at Yale University, and as part of the Hubble Space Telescope faculty. She is currently the Israel Munson Professor of Physics and Astronomy at Yale University and Director of the Yale Center for Astronomy and Astrophysics. Urry is notable not only for her contributions to astronomy and astrophysics, including work on black holes and multiwavelength surveys, but also for her work addressing sexism and sex equality in astronomy, science, and academia more generally.
Megan Donahue is an American astronomer who studies galaxies and galaxy clusters. She is a professor of physics and astrophysics at Michigan State University, and the president of the American Astronomical Society for the 2018–2020 term.
Haley Gomez MBE, FRAS, FLSW is a Welsh Professor of Astrophysics at Cardiff University. She studies the formation and evolution of cosmic dust using the Herschel Space Observatory. She is Deputy Head of the School of Physics and Astronomy. She was awarded an Order of the British Empire in the 2018 Queen’s Birthday Honour’s.
Marcia Jean Rieke is an American astronomer. She is a Regents' Professor of Astronomy and associate department head at the University of Arizona. Rieke is the Principal Investigator on the near-infrared camera (NIRCam) for the James Webb Space Telescope (JWST). She has also served as the deputy-Principal Investigator on the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) for the Hubble Space Telescope (HST), and as the co-investigator for the multiband imaging photometer on the Spitzer Space Telescope, where she also acted as an outreach coordinator and a member of the Science Working Group. Rieke was also involved with several infrared ground-based observatories, including the MMT Observatory in Arizona. She was vice chair for Program Prioritization of the Astro2010 Decadal Survey Committee, "New Worlds, New Horizons". Marcia Rieke is considered by many to be one of the "founding mothers" of infrared astronomy, along with Judith Pipher.
Jean L. Turner is an astrophysicist and distinguished professor in the Department of Physics and Astronomy at the University of California, Los Angeles. She was lead author on research and discovery of a particular star cluster in the dwarf galaxy NGC 5253, considered 'remarkable' for being an extremely dusty gas cloud and having highly efficient star formation.
Ann I. Zabludoff is an American astronomer and astrophysicist whose research has included galaxy clusters and the effects of galactic environments on star formation, and the use of gravitational lenses to study the formation and interaction of the earliest galaxies, including observations with the Magellan Telescopes and Hubble Space Telescope. She is a professor of astronomy, astrophysics, and cosmology at the University of Arizona.
Rosa Amelia González-Lópezlira is a Mexican astronomer specializing in galaxy formation and evolution, the age distribution of stars in different regions of galaxies, and the rotation rate of globular clusters in galaxies, including the discovery of an anomalously fast rotation rate in Messier 106. She is a researcher at the National Autonomous University of Mexico (UNAM), in the UNAM Institute of Radio Astronomy and Astrophysics.
