Alar Toomre | |
|---|---|
 1970 | |
| Born | 5 February 1937 |
| Alma mater | Massachusetts Institute of Technology University of Manchester |
| Scientific career | |
| Institutions | Massachusetts Institute of Technology Institute for Advanced Study |
Alar Toomre (born 5 February 1937, in Rakvere) is an American astronomer and mathematician. [1] [2] He is a professor of applied mathematics at the Massachusetts Institute of Technology. [3] Toomre's research is focused on the dynamics of galaxies. He is a 1984 MacArthur Fellow.
Following the Soviet occupation of Estonia in 1944, Toomre and his family fled to Germany; they emigrated to the United States in 1949. He received an undergraduate degree in Aeronautical Engineering and Physics from MIT in 1957 [2] [4] and then studied at the University of Manchester on a Marshall Scholarship where he obtained a Ph.D. in fluid mechanics. [5] [6]
Toomre returned to MIT to teach after completing his Ph.D. and remained there for two years. [5] After spending a year at the Institute for Advanced Study, [7] he returned again to MIT as part of the faculty, where he stayed. [5] Toomre was appointed an Associate Professor of Mathematics at MIT in 1965, and Professor in 1970. [7]
In 1964, Toomre devised a local gravitational stability criterion for differentially rotating disks. [8] It is known as the Toomre stability criterion, which is usually measured by a parameter denoted as Q. [9] The Q parameter measures the relative importance of vorticity and internal velocity dispersion (large values of which stabilise) versus the disk surface density (large values of which destabilise). The parameter is constructed so that Q<1 implies instability.
Toomre collaborated with Peter Goldreich in 1969 on the subject of polar wander, developing the theory of polar wander. [10] Whether true polar wander has been observed on earth, or apparent polar wander is accountable for all the observations of paleomagnetism remains a controversial issue. [11]
Toomre conducted the first computer simulations of galaxy mergers in the 1970s with his brother Jüri, an astrophysicist and solar physicist. [12] [13] Although the small number of particles in the simulations obscured many processes in galactic collisions, Toomre and Toomre were able to identify tidal tails in his simulations, similar to those seen in the Antennae Galaxies and the Mice. [14] [15] [16] The brothers attempted to reproduce specific galaxy mergers in their simulations, and it was their reproduction of the Antennae galaxies that gave them the greatest pleasure. [17] In 1977 Toomre suggested that elliptical galaxies are the remnants of the major mergers of spiral galaxies. [18] [19] He further showed that based on the local galaxy merger rate, over a Hubble time the observed number of elliptical galaxies are produced if the universe begins with only spiral galaxies. [20] This idea remained controversial and widely debated for some time. [21] [22]
From this work, the Toomre brothers identified the process of collision evolution as the Toomre sequence. [23] [24] The sequence begins with two well separated spiral galaxies and follows them (as for the Antennae) through collisional disruption until they settle into a single elliptical galaxy. [25]
In 1993, Toomre received the Dirk Brouwer Award which recognizes "outstanding contributions to the field of Dynamical Astronomy". [26] [27]
Toomre was one of the 1984 recipients of the MacArthur Fellowship, popularly known as the "Genius Grant". [1] [28]
In 1985, Toomre was elected a Fellow of the American Association for the Advancement of Science (AAAS). [29]
Toomre was the recipient of the Magellanic Premium award in 2014 for his work in numerical galaxy simulations during the 1960s. [30] Two years later, he was elected to the American Philosophical Society. [31]
The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have generated the variety of structures observed in nearby galaxies. Galaxy formation is hypothesized to occur from structure formation theories, as a result of tiny quantum fluctuations in the aftermath of the Big Bang. The simplest model in general agreement with observed phenomena is the Lambda-CDM model—that is, clustering and merging allows galaxies to accumulate mass, determining both their shape and structure. Hydrodynamics simulation, which simulates both baryons and dark matter, is widely used to study galaxy formation and evolution.
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 million stars, range in size from dwarfs with less than a thousand 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.
The Hubble sequence is a morphological classification scheme for galaxies published by Edwin Hubble in 1926. It is often colloquially known as the Hubble tuning-fork diagram because the shape in which it is traditionally represented resembles a tuning fork. It was invented by John Henry Reynolds and Sir James Jeans.
A lenticular galaxy is a type of galaxy intermediate between an elliptical and a spiral galaxy in galaxy morphological classification schemes. It contains a large-scale disc but does not have large-scale spiral arms. Lenticular galaxies are disc galaxies that have used up or lost most of their interstellar matter and therefore have very little ongoing star formation. They may, however, retain significant dust in their disks. As a result, they consist mainly of aging stars. Despite the morphological differences, lenticular and elliptical galaxies share common properties like spectral features and scaling relations. Both can be considered early-type galaxies that are passively evolving, at least in the local part of the Universe. Connecting the E galaxies with the S0 galaxies are the ES galaxies with intermediate-scale discs.
In astronomy, a galactic bulge is a tightly packed group of stars within a larger star formation. The term almost exclusively refers to the central group of stars found in most spiral galaxies. Bulges were historically thought to be elliptical galaxies that happened to have a disk of stars around them, but high-resolution images using the Hubble Space Telescope have revealed that many bulges lie at the heart of a spiral galaxy. It is now thought that there are at least two types of bulges: bulges that are like ellipticals and bulges that are like spiral galaxies.
The Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph), also known as the Sagittarius Dwarf Elliptical Galaxy, is an elliptical loop-shaped satellite galaxy of the Milky Way. It contains four globular clusters in its main body, with the brightest of them—NGC 6715 (M54)—being known well before the discovery of the galaxy itself in 1994. Sgr dSph is roughly 10,000 light-years in diameter, and is currently about 70,000 light-years from Earth, travelling in a polar orbit at a distance of about 50,000 light-years from the core of the Milky Way. In its looping, spiraling path, it has passed through the plane of the Milky Way several times in the past. In 2018 the Gaia project of the European Space Agency showed that Sgr dSph had caused perturbations in a set of stars near the Milky Way's core, causing unexpected rippling movements of the stars triggered when it moved through the Milky Way between 300 and 900 million years ago.
A starburst galaxy is one undergoing an exceptionally high rate of star formation, as compared to the long-term average rate of star formation in the galaxy, or the star formation rate observed in most other galaxies.
The Whirlpool Galaxy, also known as Messier 51a (M51a) or NGC 5194, is an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus. It lies in the constellation Canes Venatici, and was the first galaxy to be classified as a spiral galaxy. It is 7.22 megaparsecs away and 23.58 kiloparsecs (76,900 ly) in diameter.
Galaxy morphological classification is a system used by astronomers to divide galaxies into groups based on their visual appearance. There are several schemes in use by which galaxies can be classified according to their morphologies, the most famous being the Hubble sequence, devised by Edwin Hubble and later expanded by Gérard de Vaucouleurs and Allan Sandage. However, galaxy classification and morphology are now largely done using computational methods and physical morphology.
The Antennae Galaxies are a pair of interacting galaxies in the constellation Corvus. They are currently going through a starburst phase, in which the collision of clouds of gas and dust, with entangled magnetic fields, causes rapid star formation. They were discovered by William Herschel in 1785.
Interacting galaxies are galaxies whose gravitational fields result in a disturbance of one another. An example of a minor interaction is a satellite galaxy disturbing the primary galaxy's spiral arms. An example of a major interaction is a galactic collision, which may lead to a galaxy merger.
NGC 1316 is a lenticular galaxy about 60 million light-years away in the constellation Fornax. It is a radio galaxy and at 1400 MHz is the fourth-brightest radio source in the sky.
A Type Ia supernova is a type of supernova that occurs in binary systems in which one of the stars is a white dwarf. The other star can be anything from a giant star to an even smaller white dwarf.
The Eyes Galaxies are a pair of galaxies about 52 million light-years away in the constellation Virgo. The pair are members of the string of galaxies known as Markarian's Chain.
Arp 107 is a pair of interacting galaxies located about 450 million light-years away in the constellation Leo Minor. The galaxies are in the process of colliding and merging.
The Andromeda–Milky Way collision is a galactic collision predicted to occur in about 4.5 billion years between the two largest galaxies in the Local Group—the Milky Way and the Andromeda Galaxy. The stars involved are sufficiently far apart that it is improbable that any of them will individually collide, though some stars will be ejected.
Galaxy mergers can occur when two galaxies collide. They are the most violent type of galaxy interaction. The gravitational interactions between galaxies and the friction between the gas and dust have major effects on the galaxies involved, but the exact effects of such mergers depend on a wide variety of parameters such as collision angles, speeds, and relative size/composition, and are currently an extremely active area of research. Galaxy mergers are important because the merger rate is a fundamental measurement of galaxy evolution and also provides astronomers with clues about how galaxies grew into their current forms over long stretches of time.
A tidal tail is a thin, elongated region of stars and interstellar gas that extends into space from a galaxy. Tidal tails occur as a result of galactic tide forces between interacting galaxies. Examples of galaxies with tidal tails include the Tadpole Galaxy and the Mice Galaxies. Tidal forces can eject a significant amount of a galaxy's gas into the tail; within the Antennae Galaxies, for example, nearly half of the observed gaseous matter is found within the tail structures. Within those galaxies which have tidal tails, approximately 10% of the galaxy's stellar formation takes place in the tail. Overall, roughly 1% of all stellar formation in the known universe occurs within tidal tails.
Galaxy Zoo is a crowdsourced astronomy project which invites people to assist in the morphological classification of large numbers of galaxies. It is an example of citizen science as it enlists the help of members of the public to help in scientific research.
Galactic Bridges and Tails is a computer animation film created in 1972 by astrophysicists Alar Toomre and Juri Toomre. The brothers created the film as a teaching aid to accompany their 1972 landmark research paper of the same name, published in The Astrophysical Journal, which described galaxy collisions and galaxy mergers.
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