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51-624: Seyfert is a surname, and may refer to: Carl Keenan Seyfert (1911–1960), United States astronomer Gabriele Seyfert (born 1948), German athlete in figure skating J. Michael Seyfert (born 1959), German Mexican documentary filmmaker, photographer Johann Caspar Seyfert (1697–1767), German music composer Johann Gottfried Seyfert  [ de ] (1731–1772), German music composer, son of Johann Caspar Seyfert R. Tracy Seyfert (born 1941), United States political figure from Pennsylvania Other uses [ edit ] Seyfert (crater) ,

102-480: A bright continuum and broad emission line nucleus. When the galaxy is viewed from the side, the nucleus is indirectly observed through reflection by gas and dust above and below the torus. This reflection causes the polarisation . In 1981, Donald Osterbrock introduced the notations Type 1.5, 1.8 and 1.9, where the subclasses are based on the optical appearance of the spectrum, with the numerically larger subclasses having weaker broad-line components relative to

153-727: A broad line emission region, but the line emitting region in LINERs has a lower density than in Seyferts. An example of such a galaxy is M104 in the Virgo constellation, also known as the Sombrero Galaxy . A galaxy that is both a LINER and a Type I Seyfert is NGC 7213 , a galaxy that is relatively close compared to other AGNs. Another very interesting subclass are the narrow line Type I galaxies (NLSy1), which have been subject to extensive research in recent years. They have much narrower lines than

204-471: A crater on the far side of Earth's Moon that is named after Carl Keenan Seyfert Seyfert Galaxy , a class of galaxies named after Carl Keenan Seyfert Seyfert's Sextet , a group of galaxies located in a cluster some 190 million light-years from Earth See also [ edit ] Seifert , surname Seiffert , surname Siefert , surname Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with

255-607: A fellow with the National Research Council . He stayed until 1942, studying a class of active galaxies now called Seyfert galaxies . In 1942 he returned to Cleveland, at Case Institute of Technology , where he taught navigation to military personnel and participated in secret military research. He also carried out some astronomical research at the Warner and Swasey Observatory of the Case Institute. In 1946 Seyfert joined

306-546: A few hundred galaxies distinguished by their very strong ultraviolet emission, with measurements on the position of some of them being improved in 1973 by other researchers. At the time, it was believed that 1% of spiral galaxies are Seyferts. By 1977, it was found that very few Seyfert galaxies are ellipticals, most of them being spiral or barred spiral galaxies. During the same time period, efforts have been made to gather spectrophotometric data for Seyfert galaxies. It became obvious that not all spectra from Seyfert galaxies look

357-427: A group of galaxies around NGC 6027 , now known as Seyfert's Sextet . He was an active innovator in instrumentation, being involved in new techniques such as the astronomical use of photomultiplier tubes and television techniques, and electronically controlled telescope drives. The lunar crater Seyfert is named in his honor (29.1N, 114.6E, 110 km diameter). The 24-inch (610 mm) telescope at Dyer Observatory

408-437: A high temperature corona near the black hole. Seyferts were first classified as Type I or II, depending on the emission lines shown by their spectra. The spectra of Type I Seyfert galaxies show broad lines that include both allowed lines, like H I, He I or He II and narrower forbidden lines, like O III. They show some narrower allowed lines as well, but even these narrow lines are much broader than

459-438: A paper on galaxies with bright nuclei that emit light with emission line spectra with characteristically broadened emission lines. The prototype example is Messier 77 (NGC 1068). It is this class of galaxies that is now known as Seyfert galaxies , in his honor. During his time at the Case Institute, he and Jason John Nassau obtained the first good color images of nebulae and stellar spectra. In 1951 he observed and described

510-518: A region 0.1–1 parsec across. The broad line emission region, R BLR , can be estimated from the time delay corresponding to the time taken by light to travel from the continuum source to the line-emitting gas. Type II Seyfert galaxies have the characteristic bright core, as well as appearing bright when viewed at infrared wavelengths. Their spectra contain narrow lines associated with forbidden transitions, and broader lines associated with allowed strong dipole or intercombination transitions. NGC 3147

561-746: A unification scheme is trying to explain why some AGN are radio loud while others are radio quiet. It has been suggested that these differences may be due to differences in the spin of the central black hole. Here are some examples of Seyfert galaxies: We derive the outward radiative force F rad as we do for stars assuming spherical symmetry: F rad = d p d t = 1 c d E d t = 1 c σ t L 4 π r 2 {\displaystyle F_{\textrm {rad}}={\frac {dp}{dt}}={\frac {1}{c}}{\frac {dE}{dt}}={\frac {1}{c}}\sigma _{t}{\frac {L}{4\pi r^{2}}}} where p

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612-418: Is considered the best candidate to be a true Type II Seyfert galaxy. In some Type II Seyfert galaxies, analysis with a technique called spectro-polarimetry (spectroscopy of polarised light component) revealed obscured Type I regions. In the case of NGC 1068 , nuclear light reflected off a dust cloud was measured, which led scientists to believe in the presence of an obscuring dust torus around

663-413: Is difficult to determine due to poor resolution of the galactic center. However, each part of the accretion disc has a different velocity relative to our line of sight, and the faster the gas is rotating around the black hole, the broader the emission line will be. Similarly, an illuminated disc wind also has a position-dependent velocity. The narrow lines are believed to originate from the outer part of

714-1860: Is momentum, t is time, c is the speed of light , E is energy, σ t is the Thomson cross-section and L is luminosity. The luminosity of the black hole must be less than the Eddington luminosity L Edd , i.e., L < L Edd {\displaystyle L<L_{\textrm {Edd}}} which is given when: F rad = F grav L = 4 π r 2 c σ t F rad = 4 π r 2 c σ t F grav = 4 π r 2 c σ t ⋅ G M BH m p r 2 = 4 π c G M BH m p σ t = 1.3 × 10 38 M BH M ⊙ e r g / s = 30000 M BH M ⊙ L ⊙ {\displaystyle {\begin{aligned}F_{\textrm {rad}}&=F_{\textrm {grav}}\\L&={\frac {4\pi r^{2}c}{\sigma _{t}}}F_{\text{rad}}={\frac {4\pi r^{2}c}{\sigma _{t}}}F_{\text{grav}}\\&={\frac {4\pi r^{2}c}{\sigma _{t}}}\cdot {\frac {GM_{\text{BH}}m_{p}}{r^{2}}}\\&={\frac {4\pi cGM_{\textrm {BH}}m_{p}}{\sigma _{t}}}\\&=1.3\times 10^{38}{\frac {M_{\textrm {BH}}}{M_{\odot }}}\,\mathrm {erg/s} \\&=30000{\frac {M_{\textrm {BH}}}{M_{\odot }}}L_{\odot }\end{aligned}}} where M ☉

765-446: Is the mass of the Sun and L ☉ is the solar luminosity. Therefore, given the observed luminosity (which would be less than the Eddington luminosity), an approximate lower limit for the mass of the central black hole at the center of an active galaxy can be estimated. This derivation is a widely used approximation; but when the actual geometry of accretion discs is taken into account, it

816-747: The Lick Observatory to look at the spectra of astronomical objects that were thought to be " spiral nebulae ". They noticed that NGC 1068 showed six bright emission lines , which was considered unusual as most objects observed showed an absorption spectrum corresponding to stars . In 1926, Edwin Hubble looked at the emission lines of NGC 1068 and two other such "nebulae" and classified them as extragalactic objects . In 1943, Carl Keenan Seyfert discovered more galaxies similar to NGC 1068 and reported that these galaxies have very bright stellar-like nuclei that produce broad emission lines. In 1944 Cygnus A

867-492: The Dyer Observatory was subsequently renamed "Carl Seyfert Memorial Drive" in his honor. A 1949 oil portrait of Seyfert by his wife Muriel Mussels Seyfert, who was a former Harvard computer , hangs in the Dyer Observatory. Carl Seyfert published many papers in the astronomical literature, on a wide variety of topics in stellar and galactic astronomy, as well as on observing methods and instrumentation. In 1943 he published

918-575: The Nashville community. As the result, the Arthur J. Dyer Observatory with its 24-inch (610 mm) reflector was completed in December 1953. Seyfert became director of the new observatory, a position he held until his death. Seyfert was also the local weatherman for WSM-TV, Nashville's NBC affiliate, during the 1950s. Seyfert died in an automobile accident in Nashville on June 13, 1960; a residential street near

969-501: The Universe, and their evolution puts constraints on cosmological models. Depending on the type, their luminosity varies over a timescale from a few hours to a few years. The two largest subclasses of active galaxies are quasars and Seyfert galaxies, the main difference between the two being the amount of radiation they emit. In a typical Seyfert galaxy, the nuclear source emits at visible wavelengths an amount of radiation comparable to that of

1020-401: The active galactic nucleus, where velocities are 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. Reverberation mapping is a technique which uses this variability to try to determine

1071-422: The active nuclei are obscured and only the colder outer regions located further away from the clouds' broad line emission region are seen. This theory is known as the "Unification scheme" of Seyfert galaxies. However, it is not yet clear if this hypothesis can explain all the observed differences between the two types. Type I Seyferts are very bright sources of ultraviolet light and X-rays in addition to

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1122-590: The best diagnostics for the composition of the surrounding material. Seen in visible light , most Seyfert galaxies look like normal spiral galaxies , but when studied under other wavelengths, it becomes clear that the luminosity of their cores is of comparable intensity to the luminosity of whole galaxies the size of the Milky Way . Seyfert galaxies are named after Carl Seyfert , who first described this class in 1943. Seyfert galaxies were first detected in 1908 by Edward A. Fath and Vesto Slipher , who were using

1173-460: The brightest representatives of this group. More recent surveys that count galaxies with low-luminosity and obscured Seyfert nuclei suggest that the Seyfert phenomenon is actually quite common, occurring in 16% ± 5% of galaxies; indeed, several dozen galaxies exhibiting the Seyfert phenomenon exist in the close vicinity (≈27 Mpc) of our own galaxy. Seyfert galaxies form a substantial fraction of

1224-487: The broad components of the lines are impossible to detect because of the angle we are at with respect to the galaxy. Specifically, in Type ;I Seyfert galaxies, we observe the central compact source more or less directly, therefore sampling the high velocity clouds in the broad line emission region moving around the supermassive black hole thought to be at the center of the galaxy. By contrast, in Type II Seyfert galaxies,

1275-591: The broad lines from classic Type I galaxies, steep hard and soft X-ray spectra and strong Fe[II] emission. Their properties suggest that NLSy1 galaxies are young AGNs with high accretion rates, suggesting a relatively small but growing central black hole mass. There are theories suggesting that NLSy1s are galaxies in an early stage of evolution, and links between them and ultraluminous infrared galaxies or Type II galaxies have been proposed. The majority of active galaxies are very distant and show large Doppler shifts . This suggests that active galaxies occurred in

1326-478: The central black hole. A lower limit to the mass of the central black hole can be calculated using the Eddington luminosity . This limit arises because light exhibits radiation pressure. Assume that a black hole is surrounded by a disc of luminous gas. Both the attractive gravitational force acting on electron-ion pairs in the disc and the repulsive force exerted by radiation pressure follow an inverse-square law. If

1377-426: The characteristic broad Hα emission line has rarely, if ever, disappeared. The origin of the differences between Type I and Type II Seyfert galaxies is not known yet. There are a few cases where galaxies have been identified as Type II only because the broad components of the spectral lines have been very hard to detect. It is believed by some that all Type II Seyferts are in fact Type I, where

1428-470: The different classes of AGNs as due to their different orientations with respect to the observational line of sight. Such models are called unified models. Unified models explain the difference between Type I and Type II galaxies as being the result of Type II galaxies being surrounded by obscuring toruses which prevent telescopes from seeing the broad line region. Quasars and blazars can be fit quite easily in this model. The main problem of such

1479-503: The distance to Seyfert galaxies and their age were limited since their nuclei vary in brightness over a time scale of a few years; therefore arguments involving distance to such galaxies and the constant speed of light cannot always be used to determine their age. In the same time period, research had been undertaken to survey, identify and catalogue galaxies, including Seyferts. Beginning in 1967, Benjamin Markarian published lists containing

1530-545: The duration of peak nuclear emissions is relatively short (> 10 years). In the 1960s and 1970s, research to further understand the properties of Seyfert galaxies was carried out. A few direct measurements of the actual sizes of Seyfert nuclei were taken, and it was established that the emission lines in NGC 1068 were produced in a region over a thousand light years in diameter. Controversy existed over whether Seyfert redshifts were of cosmological origin. Confirming estimates of

1581-401: The early Universe and, due to cosmic expansion , are receding away from the Milky Way at very high speeds. Quasars are the furthest active galaxies, some of them being observed at distances 12 billion light years away. Seyfert galaxies are much closer than quasars. Because light has a finite speed, looking across large distances in the Universe is equivalent to looking back in time. Therefore,

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1632-401: The electron transitions causing them are not forbidden but highly improbable. In some cases, the spectra show both broad and narrow permitted lines, which is why they are classified as an intermediate type between Type I and Type II, such as Type 1.5 Seyfert. The spectra of some of these galaxies have changed from Type 1.5 to Type II in a matter of a few years. However,

1683-432: The faculty of Vanderbilt University in Nashville, Tennessee. The astronomy program at Vanderbilt was very small at the time. The university had only a small observatory, equipped with a 6-inch (150 mm) refractor , and only a modest teaching program. Seyfert worked diligently to improve the teaching program and to raise funds to build a new observatory. Within a few years, he had obtained significant public support from

1734-493: The galaxies appearing in the Markarian catalog , a list of galaxies displaying an ultraviolet excess in their nuclei. An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a higher than normal luminosity over portions of the electromagnetic spectrum . A galaxy having an active nucleus is called an active galaxy. Active galactic nuclei are the most luminous sources of electromagnetic radiation in

1785-410: The gravitational force exerted by the black hole is less than the repulsive force due to radiation pressure, the disc will be blown away by radiation pressure. The emission lines seen on the spectrum of a Seyfert galaxy may come from the surface of the accretion disc itself, or may come from clouds of gas illuminated by the central engine in an ionization cone. The exact geometry of the emitting region

1836-405: The lines shown by normal galaxies. However, the spectra of Type II Seyfert galaxies show only narrow lines, both permitted and forbidden. Forbidden lines are spectral lines that occur due to electron transitions not normally allowed by the selection rules of quantum mechanics , but that still have a small probability of spontaneously occurring. The term "forbidden" is slightly misleading, as

1887-404: The location and morphology of the emitting region. This technique measures the structure and kinematics of the broad line emitting region by observing the changes in the emitted lines as a response to changes in the continuum. The use of reverberation mapping requires the assumption that the continuum originates in a single central source. For 35 AGN, reverberation mapping has been used to calculate

1938-450: The low-ionisation narrow-line emission radio galaxies (LINER), discovered in 1980. These galaxies have strong emission lines from weakly ionised or neutral atoms, while the emission lines from strongly ionised atoms are relatively weak by comparison. LINERs share a large amount of traits with low luminosity Seyferts. In fact, when seen in visible light, the global characteristics of their host galaxies are indistinguishable. Also, they both show

1989-413: The mass of the central black holes and the size of the broad line regions. In the few radio-loud Seyfert galaxies that have been observed, the radio emission is believed to represent synchrotron emission from the jet. The infrared emission is due to radiation in other bands being reprocessed by dust near the nucleus. The highest energy photons are believed to be created by inverse Compton scattering by

2040-459: The most intensely studied objects in astronomy , as they are thought to be powered by the same phenomena that occur in quasars, although they are closer and less luminous than quasars. These galaxies have supermassive black holes at their centers which are surrounded by accretion discs of in-falling material. The accretion discs are believed to be the source of the observed ultraviolet radiation. Ultraviolet emission and absorption lines provide

2091-733: The narrow lines. For example, Type 1.9 only shows a broad component in the Hα line, and not in higher order Balmer lines . In Type 1.8, very weak broad lines can be detected in the Hβ lines as well as Hα, even if they are very weak compared to the Hα. In Type 1.5, the strength of the Hα and Hβ lines are comparable. In addition to the Seyfert progression from Type I to Type II (including Type 1.2 to Type 1.9), there are other types of galaxies that are very similar to Seyferts or that can be considered as subclasses of them. Very similar to Seyferts are

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2142-410: The observation of active galactic nuclei at large distances and their scarcity in the nearby Universe suggests that they were much more common in the early Universe, implying that active galactic nuclei could be early stages of galactic evolution . This leads to the question about what would be the local (modern-day) counterparts of AGNs found at large redshifts. It has been proposed that NLSy1s could be

2193-487: The same, so they have been subclassified according to the characteristics of their emission spectra . A simple division into types I and II has been devised, with the classes depending on the relative width of their emission lines . It has been later noticed that some Seyfert nuclei show intermediate properties, resulting in their being further subclassified into types 1.2, 1.5, 1.8 and 1.9 (see Classification ). Early surveys for Seyfert galaxies were biased in counting only

2244-474: The small redshift counterparts of quasars found at large redshifts ( z > 4). The two have many similar properties, for example: high metallicities or similar pattern of emission lines (strong Fe [II], weak O [III]). Some observations suggest that AGN emission from the nucleus is not spherically symmetric and that the nucleus often shows axial symmetry, with radiation escaping in a conical region. Based on these observations, models have been devised to explain

2295-477: The study of ring nebulae. They had two children, daughter Gail Carol and son Carl Keenan Seyfert, Jr. In 1936 Seyfert joined the staff of the new McDonald Observatory in Texas, where he helped get the observatory started. He stayed until 1940, working with Daniel M. Popper on the properties of faint B stars and continuing his work on colors in spiral galaxies . In 1940 Seyfert went to Mount Wilson Observatory as

2346-514: The title Seyfert . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Seyfert&oldid=1089548319 " Categories : Disambiguation pages Disambiguation pages with surname-holder lists Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Carl Keenan Seyfert Seyfert

2397-497: The visible light coming from their cores. They have two sets of emission lines on their spectra: narrow lines with widths (measured in velocity units) of several hundred km/s, and broad lines with widths up to 10 km/s. The broad lines originate above the accretion disc of the supermassive black hole thought to power the galaxy, while the narrow lines occur beyond the broad line region of the accretion disc. Both emissions are caused by heavily ionised gas. The broad line emission arises in

2448-741: The whole galaxy's constituent stars, while in a quasar, the nuclear source is brighter than the constituent stars by at least a factor of 100. Seyfert galaxies have extremely bright nuclei, with luminosities ranging between 10 and 10 solar luminosities. Only about 5% of them are radio bright; their emissions are moderate in gamma rays and bright in X-rays. Their visible and infrared spectra show very bright emission lines of hydrogen , helium , nitrogen , and oxygen . These emission lines exhibit strong Doppler broadening , which implies velocities from 500 to 4,000 km/s (310 to 2,490 mi/s), and are believed to originate near an accretion disc surrounding

2499-557: Was born and raised in Cleveland, Ohio , then attended Harvard University , starting in 1929. He earned his B.S. and M.S. degrees in 1933, and his Ph.D. in astronomy in 1936. His thesis was "Studies of the External Galaxies", supervised by Harlow Shapley . The thesis dealt with colors and magnitudes of galaxies . In 1935 Seyfert married astronomer Muriel Elizabeth Mussels , who was a former Harvard computer who made contributions to

2550-522: Was detected at 160 MHz, and detection was confirmed in 1948 when it was established that it was a discrete source. Its double radio structure became apparent with the use of interferometry . In the next few years, other radio sources such as supernova remnants were discovered. By the end of the 1950s, more important characteristics of Seyfert galaxies were discovered, including the fact that their nuclei are extremely compact (< 100 pc, i.e. "unresolved"), have high mass (≈10 solar masses), and

2601-525: Was renamed after him. Seyfert galaxy Seyfert galaxies are one of the two largest groups of active galaxies , along with quasar host galaxies. They have quasar-like nuclei (very luminous sources of electromagnetic radiation that are outside of our own galaxy) with very high surface brightnesses whose spectra reveal strong, high- ionisation emission lines , but unlike quasars, their host galaxies are clearly detectable. Seyfert galaxies account for about 10% of all galaxies and are some of

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