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Encyclopedia > Seyfert galaxy

Seyfert galaxies are spiral or irregular galaxies containing an extremely bright nucleus, most likely caused by a supermassive black hole, that can sometimes outshine the surrounding galaxy. The light from the central nucleus varies in less than a year, which implies that the emitting region must be less than one light year across. They are named after the astronomer Carl Seyfert, who studied them extensively in the 1940s. They are a subclass of active galactic nuclei. A spiral galaxy is a type of galaxy in the Hubble sequence which is characterized by the following physical properties: Spiral Galaxy M74 presents a face-on view of its spiral arms. ... An irregular galaxy is a galaxy that does not fall into the Hubble classification for galaxies. ... This article is about a celestial body. ... Top: artists conception of a supermassive black hole drawing material from a nearby star. ... A light year, abbreviated ly, is the distance light travels in one year: roughly 9. ... An astronomer or astrophysicist is a scientist whose area of research is astronomy or astrophysics. ... Carl Keenan Seyfert (February 11, 1911 – June 13, 1960) was an American astronomer. ... // Events and trends The 1940s were dominated by World War II, the most destructive armed conflict in history. ... An active galaxy is a galaxy where a significant fraction of the energy output is not emitted by the normal components of a galaxy: stars, dust and interstellar gas. ...

The Circinus Galaxy, a Seyfert Type 2 spiral galaxy.
The Circinus Galaxy, a Seyfert Type 2 spiral galaxy.

Seyfert galaxies are characterized by extremely bright nuclei, and spectra which have very bright emission lines of hydrogen, helium, nitrogen, and oxygen. These emission lines exhibit strong Doppler broadening, which implies velocities from 500 to 4000 km/s, and are believed to originate in an accretion disk surrounding the central black hole. Each part of the accretion disk has a different velocity relative to our line of sight, and the faster the gas is rotating about the black hole, the broader the line will be. The narrow lines are believed to originate from the outer part of the disk where the rotational velocity is lower, while the broad lines originate closer to the black hole. This is confirmed by the fact that the narrow lines do not vary detectably, which implies that the emitting region is large, contrary to the broad lines which can vary on relatively short timescales. Seyfert galaxies also show strong emission in the radio, infrared, ultraviolet, and X-rays parts of the spectrum. Seyfert-type spiral galaxy in Circinus. ... Seyfert-type spiral galaxy in Circinus. ... Categories: Astronomy stubs | Circinus constellation | Spiral galaxies ... The electromagnetic spectrum encompasses all possible wavelengths of electromagnetic radiation. ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ... This article is about the chemical element oxygen. ... Sound waves emanating from an ambulance moving to the right. ... Velocity (symbol: v) is a vector measurement of the rate and direction of motion. ... An accretion disc (or accretion disk) is a structure formed by material falling into a gravitational source. ... Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. ... Ultraviolet (UV) radiation is electromagnetic radiation of a wavelength shorter than that of the visible region, but longer than that of soft X-rays. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... The electromagnetic spectrum encompasses all possible wavelengths of electromagnetic radiation. ...


Seyferts were first classified as Type 1 or 2, depending upon whether the spectra show both narrow and broad emission lines, or only narrow lines. They are now given a fractional classification depending upon the relative strengths of the narrow and broad components (e.g. Type 1.5 or Type 1.9). The narrow and broad components are believed to both originate from the accretion disk, but in Type 2 Seyferts it is believed that the broad component is obscured by dust and/or by our viewing angle on the galaxy. In some Type 2 Seyfert galaxies, the broad component can be observed in polarized light; it is believed that light from the broad-line region is scattered by a hot, gaseous halo surrounding the nucleus, allowing us to view it indirectly. This effect was first discovered by Antonucci and Miller in the Type 2 Seyfert NGC 1068. This article treats polarization in electrodynamics. ... In particle physics, scattering is a class of phenomena by which particles are deflected by collisions with other particles. ... Halo around the sun at the South Pole (NOAA) Halos are optical phenomena that appear near or around the Sun or Moon, and sometimes near other strong light sources such as street lights. ... The New General Catalogue (NGC) is the most well-known catalogue of deep sky objects in amateur astronomy. ...


  Results from FactBites:
 
Seyfert galaxy - definition of Seyfert galaxy in Encyclopedia (421 words)
Seyfert galaxies are spiral or irregular galaxies containing an extremely bright nucleus, most likely caused by a supermassive fl hole, that can sometimes outshine the surrounding galaxy.
Seyfert galaxies are characterized by extremely bright nuclei, and spectra which have very bright emission lines of hydrogen, helium, nitrogen, and oxygen.
In some Type 2 Seyfert galaxies, the broad component can be observed in polarized light; it is believed that light from the broad-line region is scattered by a hot, gaseous halo surrounding the nucleus, allowing us to view it indirectly.
  More results at FactBites »

 
 

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