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Jaffe Profile
The Jaffe profile (or Jaffe model) is a mathematical function that is used to describe the distribution of mass or light in elliptical galaxies and the bulges of spiral galaxies. It was proposed by the astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, natural satellite, moons, comets and galaxy, g ... Walter Jaffe in 1983. Its usefulness derives from the fact that it accurately reproduces a de Vaucouleurs profile when projected onto the sky. The density in the Jaffe model is given by : \rho (r) = \left(\right)^ \left(1+\right)^. In this equation, \rho_0 and r_0 are parameters that can be varied to fit the observed density. Jaffe described how he arrived at his model: he formulawas derived heuristically from the observation that the brightness profiles of spherical galaxies seem to run as r^ and r^ in at least some ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Elliptical Galaxies
An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the four main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work ''The Realm of the Nebulae'', with their intermediate scale disks, a subset of the "early-type" galaxy population. Most elliptical galaxies are composed of older, low-mass stars, with a sparse interstellar medium and minimal star formation activity, and they tend to be surrounded by large numbers of globular clusters. Elliptical galaxies are believed to make up approximately 10–15% of galaxies in the Virgo Supercluster, and they are not the dominant type of galaxy in the universe overall. They are preferentially found close to the centers of galaxy clusters. Elliptical galaxies range in size from dwarf ellipticals with tens of millions of stars, to supergiants of over one hundred trillion stars that dominate their galaxy clusters. Originally, Ed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bulge (astronomy)
In astronomy, a galactic bulge (or simply 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 (see galactic spheroid). 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. Classical bulges Bulges that have properties similar to those of elliptical galaxies are often called "classical bulges" due to their similarity to the historic view of bulges. These bulges are composed primarily of stars that are older, Population II stars, and hence have a reddish hue (see stellar evolution). These stars are also in orbits that are essentially random co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spiral Galaxies
Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''Alt URL pp. 124–151) and, as such, form part of the . Most spiral galaxies consist of a flat, rotating containing s, gas and dust, and a central concentration of stars known as the |
Astronomer
An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, natural satellite, moons, comets and galaxy, galaxies – in either observational astronomy, observational (by analyzing the data) or theoretical astronomy. Examples of topics or fields astronomers study include planetary science, Sun, solar astronomy, the Star formation, origin or stellar evolution, evolution of stars, or the galaxy formation and evolution, formation of galaxies. A related but distinct subject is physical cosmology, which studies the Universe as a whole. Types Astronomers usually fall under either of two main types: observational astronomy, observational and theoretical astronomy, theoretical. Observational astronomers make direct observations of Astronomical object, celestial objects and analyze the data. In contrast, theoretical astronomers create and investigate C ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
De Vaucouleurs Profile
de Vaucouleurs's law, also known as the de Vaucouleurs profile or de Vaucouleurs model, describes how the surface brightness I of an elliptical galaxy varies as a function of apparent distance R from the center of the galaxy: : \ln I(R) = \ln I_ - k R^. By defining ''Re'' as the radius of the isophote containing half of the total luminosity of the galaxy, the half-light radius, de Vaucouleurs profile may be expressed as: : \ln I(R) = \ln I_ + 7.669 \left 1 - \left( \frac \right)^ \right or : I(R) = I_ e^ where ''Ie'' is the surface brightness at ''Re''. This can be confirmed by noting : \int^_0 I(r)2\pi r dr = \frac \int^_0 I(r)2\pi r dr . de Vaucouleurs model is a special case of Sersic's model, with a Sersic index of n=4. A number of (internal) density profiles that approximately reproduce de Vaucouleurs's law after projection onto the plane of the sky include Jaffe's model and Dehnen's model. The model is named after Gérard de Vaucouleurs Gérard Henri de Vauco ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lars Hernquist
Lars Hernquist (14 December 1954) is a theoretical astrophysicist and Mallinckrodt Professor of Astrophysics at the Center for Astrophysics Harvard & Smithsonian. He is best known for his research on dynamical processes in cosmology and galaxy formation/galaxy evolution. Career and research Hernquist's research involves the dynamics of galaxies and the effect of a merger driven model for galaxy evolution. He is a world expert in simulating mergers of galaxies to demonstrate the expected appearance and morphology of the resulting body. He defined the "Hernquist Profile", which is an analytic expression for the distribution of dark matter in galaxies. Hernquist's research is largely computational with one of the world's largest supercomputers accessible for his research. Awards Hernquist was awarded the 2020 Gruber Prize in Cosmology The Gruber Prize in Cosmology, established in 2000, is one of three prestigious international awards worth US$500,000 made by the Gruber Fo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
