Dorado is a constellation in the southern sky. It was named in the late 16th century and is now one of the 88 modern constellations. Its name refers to the dolphinfish (Coryphaena hippurus), which is known as dorado in Portuguese, although it has also been depicted as a swordfish. Dorado is notable for containing most of the Large Magellanic Cloud, the remainder being in the constellation Mensa. The South ecliptic pole also lies within this constellation.
Dorado shown in the Uranographia of Johann Bode under the name of Xiphias, the swordfish. Nubecula Major, above it, is better known as the Large Magellanic Cloud.
[http://www.ianridpath.com/startales/dorado.htm]
Even though the name Dorado is not Latin but Portuguese, astronomers give it the Latin genitive form Doradus when naming its stars; it is treated (like the adjacent asterism Argo Navis) as a feminine proper name of Greek origin ending in -ō (like Io or Callisto or Argo), which have a genitive ending -ūs.
Dorado was one of twelve constellations named by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman, and it first appeared on a 35-cm diameter celestial globe published in 1597 (or 1598) in Amsterdam by Plancius with Jodocus Hondius. Its first depiction in a celestial atlas was in Johann Bayer’s Uranometria of 1603 where it was also named Dorado. Dorado has been represented historically as a dolphinfish and a swordfish; the latter depiction is inaccurate. It has also been represented as a goldfish. The constellation was also known in the 17th and 18th century as Xiphias, the swordfish, first attested in Johannes Kepler’s edition of Tycho Brahe’s star list in the Rudolphine Tables of 1627. The name Dorado ultimately become dominant and was adopted by the IAU.
In Chinese astronomy, the stars of Dorado are located in two of Xu Guangqi’s Southern Asterisms (Jìnnánjíxīngōu): the White Patches Attached (Jiābái) and the Goldfish (Jīnyú).
Constellations of Reticulum and Dorado
[http://www.davidmalin.com/fujii/source/Dor.html]
Alpha Doradus is the brightest star in the southern constellation of Dorado. The distance to this system is about 169 light-years (52 parsecs).
This is a binary star system with an overall apparent visual magnitude that varies between 3.26 and 3.30, making it one of the brightest binary stars. The system consists of a subgiant star of spectral type B revolving around a giant star with spectral type A in an eccentric orbit with a period of about 12 years. The orbital separation varies from 2 astronomical units at periastron to 17.5 astronomical units at apastron. The primary, α Doradus A, is a chemically peculiar star whose atmosphere displays an abnormally high abundance of silicon, making this an Si star.
Alpha Doradus has an optical companion, CCDM J04340-5503C, located 77 arcseconds away along a position angle of 94°. It has no physical relation to the other two stars.
[https://en.wikipedia.org/wiki/Alpha_Doradus]
Beta Doradus is the second brightest star in the southern constellation of Dorado. It has an apparent visual magnitude of 3.63, making it visible to the naked eye from the southern hemisphere. Based upon parallax measurements with the Hubble Space Telescope, it is located at a distance of 1,040 light-years (320 parsecs) from Earth.
Beta Doradus is a Cepheid variable that regularly changes magnitude from a low of 4.05 to a high of 3.45 over a period of 9.842 days. The light curve of this magnitude change follows a regular saw-tooth pattern. During each radial pulsation cycle, the radius of the star varies by ±3.9 times the Sun’s radius around a mean of 67.8. Its spectral type and luminosity class are likewise variable, from F-type to G-type and from a supergiant to a bright giant.
Far ultraviolet emissions have been detected from this star with the Far Ultraviolet Spectroscopic Explorer, while X-ray emissions were detected with the XMM-Newton space telescope. The X-ray luminosity is about 1×10^29 erg/s and the emission varies with the pulsation period, suggesting a connection with the pulsation process. The peak X-ray emissions are in the 0.6–0.8 keV energy range, which occurs for plasmas with temperatures of 7–10 million K.
[https://en.wikipedia.org/wiki/Beta_Doradus]
Gamma Doradus is the third-brightest star in the constellation of Dorado. It has an apparent visual magnitude of approximately 4.25 and is a variable star, the type star of the class of Gamma Doradus variables. These stars, like γ Doradus, are pulsating variables which vary in brightness by less than a tenth of a magnitude owing to nonradial gravity wave oscillations. The magnitude of γ Doradus itself has been observed to have two sinusoidal variations with periods of approximately 17.6 and 18.2 hours. There is also some additional unexplained, apparently random fluctuation. [https://en.wikipedia.org/wiki/Gamma_Doradus]
Delta Doradus is a faint star in the Dorado constellation that becomes the Moon’s South Pole star once every 18.6 years. The pole star status changes periodically, because of the precession of the Moon’s rotational axis. When Delta Doradus is the pole star, it is better aligned than Earth’s Polaris (α Ursae Minoris), but much fainter.
[https://en.wikipedia.org/wiki/Delta_Doradus]
Zeta Doradus is a young star system that lies approximately 38 light-years away. The system consists of two widely separated stars, with the primary being bright enough to be observed with the naked eye but the secondary being much a much fainter star that requires telescopic equipment to be observed.
Zeta Doradus A is a bright, high proper motion star with a spectral type of F7V, meaning that it is a main sequence star that is hotter and brighter than the Sun. With an apparent magnitude of 4.82, it is approximately the eight brightest star in the constellation of Dorado.
Though it has been known that Zeta Doradus B is a nearby star since at least the Gliese Catalogue of Nearby Stars, the connection that it is a common proper motion companion to Zeta Doradus A was only made much more recently thanks to Hipparcos satellite data. The two stars form a wide binary, with a physical separation between the components of about 0.018 parsecs (0.06 light-years) which is approximately 12400 AU. This is comparable to the 15000 AU separation between Alpha Centauri AB and Proxima Centauri.
Both components of the system show considerable activity: the log R'HK of the stars are -4.373 and -4.575, respectively, whereas a star is ‘quiet’ when it has a Log R'HK of <-4.8. This indicates that the system is young; indeed, the estimated age for Zeta Doradus A is only 0.58 billion years, about an eighth of the solar age.
It is not unusual for a young star to possess a debris disk; Zeta Doradus A is no exception, as it has been found to have an infra-red excess indicative of a disk of small bodies like comets re-emitting absorbed light at a redder wavelength. For Zeta Doradus A, the dust disk has a luminosity of 6.0x10^−6 times the solar luminosity and a temperature of 91±12 Kelvin, indicating that it lies at a separation of several AU.
Stars of early spectral type (>F8) are often ignored by radial velocity (RV)-based planet searches due to issues with precision: their high temperature decreases the depth of their spectral lines and they tend to be fast rotators, which broadens their spectral lines. Still, it is still sometimes possible to reach levels of precision capable of the detection of planets in AF-type stars, so Zeta Doradus A was included in a sample early-type stars observed with HARPS. The star was found to be RV-stable to 17 m/s with internal uncertainties of 3 m/s, which indicates that the star does not have any close-in high mass companions, but does not preclude the presence of sub-Jovian mass planets.
[https://en.wikipedia.org/wiki/Zeta_Doradus]
S Doradus (also known as S Dor) is one of the brightest stars in the Large Magellanic Cloud (LMC), a satellite of the Milky Way. It is a Luminous Blue Variable and one of the most luminous stars known, but so far away that it is invisible to the naked eye:
[https://en.wikipedia.org/wiki/S_Doradus]
S Doradus (center). Image size: 5' × 5'
The brightest star in the Large Magellanic Cloud (LMC), one of the brightest stars known, and the prototype for the class of variable known as S Doradus stars (luminous blue variables). It lies in the young open cluster NGC 1910 on the northern rim of the LMC’s central bar.
S Doradus has a spectrum very similar to that of P Cygni, another variable of the same type. These stars are extremely massive (at least 60 solar masses) and luminous, using up their nuclear fuel so fast that their lifetimes can’t exceed a few million years; they will then explode as supernovae. The very high luminosity also results in an enormous radiation pressure at the star’s surface, which tends to blow away significant portions of the stellar mass by way of an intense stellar wind and, occasionally, in the form of an ejected gaseous shell. The light curve of S Doradus also points to a long period (40-year) eclipsing variable behavior.
Recent observations of S Dor have shown that its optical spectrum now resembles that of an F-type supergiant, with a rich complex of absorption lines. Despite nearly 50 years of spectroscopic monitoring, such a spectrum has never previously been seen for S Dor despite many occasions when the star was equally bright. Such F-type spectra have, however, been seen in other luminous blue variables, including Var B in M33 during a recent outburst, and in Eta Carina during an outburst in 1893. The singly ionized metal lines arise in a layer moving away from the star (toward us) at 50 km/s, consistent with the lines forming in a ‘pseudo photosphere’ originating in the stellar wind. The temperature suggested by the F-type spectrum is as cool as an LBV can get.
[http://www.daviddarling.info/encyclopedia/S/S_Doradus.html]
One of the many variable stars in Dorado is R Doradus. It is a red giant Mira variable star, although visually it appears more closely associated with the constellation Reticulum. Its distance from Earth is about 178 light-years. Having a uniform disk diameter of 0.057 ± 0.005 arcsec, it is currently believed to be the star with the largest apparent size as viewed from Earth (not counting our own Sun). The visible magnitude of R Doradus varies between 4.8 and 6.6, which makes it usually just visible to the naked eye. The estimated diameter of R Doradus is about 515 million km (3.46 AU) or about 370 times the diameter of the Sun. If placed at the center of the Solar System, the orbit of Mars and most of the main asteroid belt would be contained within the star:
[https://en.wikipedia.org/wiki/R_Doradus]
An international team of astronomers has used large telescopes in Chile and Australia to measure the biggest star in the sky. The star, designated R Doradus , is of the so-called red giant type and is located in the southern constellation of Dorado. Its apparent diameter (i.e., the size which the star appears to have when seen from the Earth) is larger than any other so far observed, except for the Sun. In particular, it exceeds by more than 30 % that of Betelgeuse , which for the past 75 years has held the title of star with the largest apparent size.
Measuring the sizes of stars is very difficult due to their enormous distances. For example, if our Sun were placed at the distance of the next closest star (four light-years away), it would have about the same apparent size as a DM 1 (or US quarter-dollar) coin placed at a distance of 500 km (about 0.01 arcsec). Even for the most powerful astronomical telescopes, it is a very challenging task to measure such small angles.
Ideally, the angular resolution of a telescope (its capability to resolve fine details in celestial sources) increases with its diameter. In practice, although ground-based optical telescopes now have diameters up to 10 meters, their actual resolution of visual light is that of a telescope of only about 20 centimeters aperture. This is because of the constant turbulence in the Earth’s atmosphere. This turbulence causes the stars to twinkle in a way which delights the poets but frustrates the astronomers, since it blurs the fine details of the images.
The first, and largest, star apart from the Sun to have its diameter measured was Betelgeuse, the brightest star in the constellation of Orion. Its angular diameter was found to be 0.044 arcsec by Albert Michelson and his team who used the Hooker telescope on Mt. Wilson in California in the early 1920s, pioneering interferometry techniques. Betelgeuse kept its title as the star with the largest apparent size for the next 75 years. This title has now been taken by R Doradus.
R Doradus is a variable star in the constellation of Dorado (the Swordfish), located in the far southern sky. At a distance of about 200 light years it is relatively nearby. R Doradus is a variable star with a period of about 338 days, changing its magnitude from approximately 4.8 at maximum (when it is visible with the unaided eye) to 6.6 at minimum (when it requires a small telescope).
In August 1993, the team of astronomers pointed the ESO 3.5-metre New Technology Telescope (NTT) towards R Doradus. For these observations, the NTT was covered with an opaque mask with seven holes arranged on a 3.3-metre diameter circle. Each of these holes had a diameter of 25 cm, which was smaller than the cells of turbulence in the atmosphere above. The main motivation for using the mask was to suppress the effects of the turbulence and in this way restore the full resolution capability of the NTT.
The seven light beams from a star were brought to interfere with each other at the telescope’s focus. Each pair of holes in the mask produced a fringe pattern in the image of the star, so at any moment there were 21 distinct fringe patterns. A camera in the focal plane recorded these fringes, their contrast being determined during subsequent computer analysis.
A star which is very far away will appear too small for its disk to be resolved by the telescope. All of the 21 fringes will then have approximately the same contrast. On the other hand, if the star is closer by and has a perceptible size, the contrast of the fringe patterns will be reduced for widely separate mask holes. By comparing the fringe contrast of the target star with that of a more distant, unresolved star, it is then possible to estimate the size of the target.
The present NTT observations were made at infrared wavelengths (1.25 microns) with the SHARP camera, developed by the Max-Planck Institut for Extraterrestrial Physics (Garching, Germany). Several hundred very short exposures of R Doradus were made, each lasting 0.1 second (this is short enough to freeze the 21 fringe patterns in each exposure). Immediately thereafter, a similar series of observations was made of an unresolved calibrator star (Gamma Reticuli). This procedure was repeated several times, producing thousands of images to be analyzed.
Additional observations were made in 1995 with the NTT as well as the 3.9-m Anglo-Australian Telescope at Siding Spring (Australia). These observations, and the application of different interferometric data analysis techniques to similar data sets, confirmed the results of the earlier ones.
The results clearly showed that R Doradus is extended, having an angular diameter of 0.057 +- 0.005 arcsec (assuming that the star appears as a uniform disk). This apparent size is 30% larger than Betelgeuse!
The bigger a star’s apparent diameter, the more easily it can be resolved. The surprise is therefore not only the large diameter of R Doradus, but also the fact that this was not discovered earlier.
Many of the larger stars were already measured by Albert Michelson and his team. The reason for the late discovery is most likely the southern latitude of R Doradus, which makes it inaccessible to the stellar interferometers predominantly located on the northern hemisphere. R Doradus is an inconspicuous star at visible wavelength but is one of the brightest in the sky in the infrared. This led Robert Wing (Ohio State University) to predict in 1971 that R Doradus should have a large angular size. Only now has this prediction been confirmed.
The NTT observations were made in the infrared. At first sight it may seem more sensible to observe at shorter, visible wavelengths because this would result in better angular resolution. However, measurements in the infrared - although more difficult to perform - result in a better estimate of the diameter of the underlying atmosphere (photosphere) of a star. The combination of a high-quality telescope and a high-quality infrared camera made this result possible.
R Doradus is approximately 200 light years away. The measured size implies that it has a physical diameter of 370 +- 50 times that of the Sun, or well over 515 million km! If R Doradus would be placed at the center of the Solar System, its surface would be outside of the orbit of Mars. Although even bigger stars are known- Betelgeuse for one- none appears as large in the sky because they are all at greater distances. The very large apparent size of R Doradus is due to the combination of its relative proximity and large physical size.
R Doradus has about the same mass as the Sun, but it is 6500 times brighter.
Although much more difficult, interferometry can also be done combining light from different telescopes. This has been successfully demonstrated by teams in France, UK and USA. As the telescopes can be some distance apart, the separation of the collecting apertures can be much increased, simulating a telescope with a diameter of a hundred meters, and the angular resolution can reach the level of the milli-arcsec.
This will be the case when the ESO Very Large Telescope Interferometer (VLTI) becomes operational some years from now. The VLTI is able to combine the light of four telescopes with 8.2-m diameter, and also from several smaller, movable auxiliary 1.8-m telescopes, at separations of up to 200 meters.
The VLTI will be a very powerful tool for studying small details in many astronomical objects. The team has already made observations of R Doradus with the Anglo-Australian Telescope which show the star to have structure on its surface, analogous to (but many times larger than) Sun spots. The VLTI would provide forty times more resolution, allowing such structures to be studied in incredible detail.
[https://www.eso.org/public/news/eso9706/]
HE 0437-5439
HE 0437-5439 is a massive, unbound hypervelocity star (HVS), also called HVS3. It is a main sequence B-type star located in the Dorado constellation. It was discovered in 2005 with the Kueyen 8.2-metre (320 in) telescope, which is part of the European Southern Observatory’s Very Large Telescope array. HE 0437-5439 is a young star, with an age of around 30 million years. The mass of the star is almost nine times greater than the mass of the Sun and the star is located 200,000 light years away in the direction of the Dorado constellation, 16 degrees northwest of the Large Magellanic Cloud (LMC) and further away than the LMC. The star appears to be receding at an extremely high velocity of 723 kilometers per second (449 mi/s), or 2,600,000 kilometers per hour (1,600,000 mph). At this speed, the star is no longer gravitationally bound and will leave the Milky Way galaxy system and escape into intergalactic space. It was thought to have originated in the LMC and been ejected from it soon after birth. This could happen if it originally was one of a pair of stars and if there is a supermassive black hole in the LMC.
In 2010 a study was published in which its proper motion was estimated using images from the Hubble Space Telescope from 2006 and 2009. This ruled out the possibility that the star came from the Large Magellanic Cloud, but was consistent with the hypothesis that it was ejected from the center of the Milky Way. Given its velocity, this would have occurred 100 million years ago. However, the star seems to be at most 20 million years old, which implies that it is a blue straggler, a star born from the merger of a binary star system, which was earlier ejected from the center of the Milky Way. In order for this to happen, there must have originally been a three-star system, or else there were two black holes and just the two stars.
Illustration of the proposed mechanism of ejection
Exact position of the star
Studies say that a triple-star system was traveling through the center of the Milky Way when it came too close to the galactic center (which is thought to have a giant black hole). One of the stars was captured by the black hole causing the other two to be ejected from the Milky Way, where they merged to form a hot blue star. The star is moving at a speed of 1,600,000 miles per hour (2,600,000 km/h), about three times faster than the Sun's orbital velocity around the galaxy’s center, and also faster than the galaxy’s escape velocity.
The star is about 200,000 light years from the galaxy’s center. Some doubt has surrounded the previous studies based on the speed and position of HE 0437-5439. The star would have to be at least 100 million years old to have traveled that distance from the galactic core, yet its mass and blue color indicate that it had burned only for 20 million years. These observations led to the explanation that it was part of a triple-star system consisting of two closely bound stars and one outer star. The black hole pulled the outer star away, which granted the star’s momentum to the tight binary system and boosted both stars to escape velocity from the galaxy. As the stars traveled away, they went into normal stellar evolution, with one of them becoming a red giant and engulfing the other and forming one giant star- a blue straggler.
In 2008, a team of astronomers found a match between the star's chemical composition and the characteristics of stars in the Large Magellanic Cloud. Support that the star originated in the LMC was strengthened because the star is only 65,000 light years away from the nearby galaxy. Later observations using the Hubble Space Telescope showed that the star originated from the Milky Way’s galactic center.
[https://en.wikipedia.org/wiki/HE_0437-5439]
A near infrared image of the R136 cluster, obtained at high resolution with the MAD adaptive optics instrument at ESO’s Very Large Telescope. R136a1 is resolved at the center with R136a2 close by, R136a3 below right, and R136b to the left.
RMC 136a1 (usually abbreviated to R136a1) is a Wolf–Rayet star located at the center of R136, the central condensation of stars of the large NGC 2070 open cluster in the Tarantula Nebula. It lies at a distance of about 50 kiloparsecs (163,000 light-years) in a neighboring galaxy known as the Large Magellanic Cloud. It has the highest mass and luminosity of any known star, at 315 M☉ and 8.7 million L☉, and is also one of the hottest at around 53,000 K.
In 1960, a group of astronomers working at the Radcliffe Observatory in Pretoria made systematic measurements of the brightness and spectra of bright stars in the Large Magellanic Cloud. Among the objects cataloged was RMC 136, (Radcliffe observatory Magellanic Cloud catalog number 136) the central ‘star’ of the Tarantula Nebula, which the observers concluded was probably a multiple star system. Subsequent observations showed that R136 was located in the middle of a giant region of ionized interstellar hydrogen known as an H II region that was a center of intense star formation in the immediate vicinity of the observed stars.
In 1979, ESO’s 3.6 m telescope was used to resolve R136 into three components; R136a, R136b, and R136c. The exact nature of R136a was unclear and a subject of intense discussion. Estimates that the brightness of the central region would require as many as 100 hot O class stars within half a parsec at the center of the cluster led to speculation that a star 3,000 times the mass of the Sun was the more likely explanation.
The first demonstration that R136a was a star cluster was provided by Weigelt and Beier in 1985. Using the speckle interferometry technique, R136a was shown to be made up of 8 stars within 1 arcsecond at the centre of the cluster, with R136a1 being the brightest.
Final confirmation of the nature of R136a came after the launch of the Hubble Space Telescope. Its Wide Field and Planetary Camera (WFPC) resolved R136a into at least 12 components and showed that R136 contained over 200 highly luminous stars. The more advanced WFPC2 allowed the study of 46 massive luminous stars within half a parsec of R136a and over 3,000 stars within a 4.7 parsec radius.
Sky position of R136a1 viewed from Argentina
In the night sky, R136 appears as a 10th magnitude object at the core of the NGC 2070 cluster embedded in the Tarantula Nebula in the Large Magellanic Cloud. It required a 3.6 meter telescope to detect R136a as a component of R136 in 1979, and resolving R136a to detect R136a1 requires a space telescope or sophisticated techniques such as adaptive optics or speckle interferometry.
South of about the 20th parallel south, the LMC is circumpolar, meaning that it can be seen (at least in part) all night every night of the year, weather permitting. In the Northern Hemisphere, it can be visible south of the 20th parallel north. This excludes North America (except southern Mexico), Europe, northern Africa and northern Asia.
The R136a system at the core of R136 is a dense luminous knot of stars containing at least 12 stars, the most prominent being R136a1, R136a2, and R136a3, all of which are extremely luminous and massive WN5h stars. R136a1 is separated from R136a2, the second brightest star in the cluster, by 5,000 AU.
R136 is located approximately 157,000 light-years away from Earth in the Large Magellanic Cloud, positioned on the south-east corner of the galaxy at the center of the Tarantula Nebula, also known as 30 Doradus. R136 itself is just the central condensation of the much larger NGC 2070 open cluster.
For such a distant star, R136a1 is relatively unobscured by interstellar dust. The reddening causes the visual brightness to be reduced by about 1.8 magnitudes, but only around 0.22 magnitudes in the near infrared.
The distance to R136a1 cannot be determined directly, but is assumed to be at the same distance as the Large Magellanic Cloud at around 50 kiloparsecs.
Although binary systems are very common among the most massive stars, R136a1 appears to be a single star as no evidence of a massive companion has been detected.
R136a1 is a high-luminosity WN5h star, placing it on the extreme top left corner of the Hertzsprung-Russell diagram. A Wolf–Rayet star is distinguished by the strong, broad emission lines in its spectrum. This includes ionized nitrogen, helium, carbon, oxygen and occasionally silicon, but with hydrogen lines usually weak or absent. A WN5 star is classified on the basis of ionized helium emission being considerably stronger than the neutral helium lines. The ‘h’ in the spectral type indicates significant hydrogen emission in the spectrum, and hydrogen is calculated to make up 40% of the surface abundance by mass.
WNh stars as a class are massive luminous stars still burning hydrogen at their cores. The emission spectrum is produced in a powerful dense stellar wind, and the enhanced levels of helium and nitrogen arise from convectional mixing of CNO cycle products to the surface.
R136a1 is the most massive star known, likely to be more than double the mass of Eta Carinae A, the Pistol Star, or the Peony Star. A recent analysis using BONNSAI to derive the age and mass by matching an evolutionary model to the observed parameters gives a current mass of 315 M☉, from an initial mass of 325 M☉.
R136a1 is undergoing extreme mass loss through a stellar wind reaching a velocity of 2,600 ± 150 km/s. This is caused by intense electromagnetic radiation from the very hot photosphere accelerating material away from the surface more strongly than gravity can retain it. Mass loss is largest for high luminosity stars with low surface gravity and enhanced levels of heavy elements in the photosphere. R136a1 loses 5.1×10^−5 M☉ (3.21×10^18 kg/s) per year, over a billion times more than the Sun, and is expected to have shed over 50 M☉ since its formation.
Left to right: a red dwarf, the Sun, a B-type main sequence star, and R136a1
At around 8,000,000 L☉, R136a1 is the most luminous star known, radiating more energy in five seconds than the Sun does in a year. If it replaced the Sun in the Solar System, it would outshine the Sun by 94,000 times (MV = −7.6) and would appear from Earth at magnitude -39. Its brightness at a distance of 10 parsecs, the absolute visual magnitude, is -7.6, three magnitudes brighter than Venus ever appears from Earth. Its brightness at the distance of the nearest star to Earth, Proxima Centauri (just over a parsec), would be about the same as the full Moon.
R136a1 supplies ~7% of the ionizing flux of the entire 30 Doradus region, as much as 70 O7 dwarf stars. Along with R136a2, a3, and c, it produces 43-46% of the Lyman continuum radiation of the whole R136 cluster.
Massive stars lie close to the Eddington limit, the luminosity at which the radiation pressure acting outwards at the surface of the star equals the force of the star's gravity pulling it inward. Above the Eddington limit, a star generates so much energy that its outer layers are rapidly thrown off. This effectively restricts stars from shining at higher luminosities for long periods. R136a1 is currently around 70% of its Eddington luminosity.
R136a1 has a surface temperature of over 50,000 K (49,700 °C; 89,500 °F), nearly ten times hotter than the Sun, and with peak radiation in the extreme ultraviolet.
R136a1 has a B-V index of about 0.03, which is a typical color for an F-type star. The ‘U-V’ colour from the HST WFPC2 336 nm and 555 nm filters is −1.28, more indicative of an extremely hot star. This variation of different color indices relative to a blackbody is the result of interstellar dust causing reddening and extinction.
A size comparison between R136a1 and the Sun
R136a1 is around thirty times the radius of the Sun (30 R☉; 21,000,000 km; 1⁄7 AU) which corresponds to a volume 27,000 times larger than the Sun.
R136a1 does not have a well-defined visible surface like the Earth or the Sun. The hydrostatic main body of the star is surrounded by a dense atmosphere being accelerated outwards into the stellar wind. An arbitrary point within this wind is defined as the surface for measuring the radius, and different authors may use different definitions. Stellar temperatures are typically quoted at the same depth so that the radius and temperature correspond to the luminosity.
R136a1’s dimensions are far smaller than the largest stars: red supergiants are several hundred to over a thousand R☉, tens of times larger than R136a1. Despite the large mass and modest dimensions, R136a1 has an average density around 1% of the Sun’s; at about 14 kg/m3, it is over 10 times denser than Earth’s atmosphere at sea level.
R136a1 is currently fusing hydrogen to helium, predominantly by the CNO cycle due to the high temperatures at the core. Despite the Wolf–Rayet spectral appearance, it is a young star. The emission spectrum is created by a dense stellar wind caused by the extreme luminosity, with the enhanced levels of helium and nitrogen being mixed from the core to the surface by strong convection. It is effectively a main sequence star.
The R136 cluster in a massive star forming region in the LMC
Models of star formation by accretion from molecular clouds predict an upper limit to the mass a star can achieve before its radiation prevents further accretion. The most simplistic accretion models at population I metallicities predict a limit as low as 40 M☉, but more complex theories allow masses several times higher. An empirical limit of around 150 M☉ has become widely accepted. R136a1 clearly exceeds all these limits, leading to development of new single star accretion models potentially removing the upper limit, and the potential for massive star formation by stellar mergers.
The future development of R136a1 is uncertain and there are no comparable stars to confirm predictions. The evolution of massive stars depends critically on the amount of mass they can lose, and various models give different results, none of which entirely match observations. Hydrogen fusion lasts for a little over two million years, and the star’s mass at the end is expected to be 70-80 M☉.
After core helium fusion starts, the remaining hydrogen in the atmosphere is rapidly lost and R136a1 will quickly contract to a hydrogen-free star and the luminosity will decrease. Wolf Rayet stars at this point are mostly helium and they lie on the Zero Age Helium Main Sequence (He-ZAMS), analogous to and parallel to the hydrogen-burning main sequence but at hotter temperatures.
During helium burning, carbon and oxygen will accumulate in the core and heavy mass loss continues. Towards the end of helium burning, core temperature increase and mass loss cause an increase in both luminosity and temperature, with the spectral type becoming WO. Several hundred thousand years will be spent fusing helium, but the final stages of heavier element burning take no more than a few thousand years. R136a1 will eventually shrink to a little over 50 M☉, with just half a M☉ of helium left surrounding the core.
Any star which produces a carbon-oxygen (C-O) core more massive than the maximum for a white dwarf (~1.4 M☉) will inevitably suffer core collapse. This usually happens when an iron core has been produced and fusion can no longer produce the energy required to prevent core collapse, although it can happen in other circumstances.
A C-O core between about 64 M☉ and 133 M☉ will become so hot that the gamma radiation will spontaneously produce electron-positron pairs and the sudden loss of energy in the core will cause it to collapse as a pair-instability supernova (PISN), sometimes called a pair-creation supernova (PCSN).
The type of any supernova explosion will be a type I since the star has no hydrogen, type Ic since it has almost no helium. The remnant from a type Ic core collapse supernova is either a neutron star or black hole, depending on the mass of the progenitor core. R136a1 will have a core far above the maximum mass of a neutron star, so a black hole is inevitable.
[https://en.wikipedia.org/wiki/R136a1]
WOH G64 is a red hypergiant star in the Large Magellanic Cloud satellite galaxy in the southern constellation of Dorado. It is 168,000 light years away from Earth and is one of the largest known stars, with a radius of 1,540 solar radii (1.07×10^9 km; 7.2 au), corresponding to a volume some 3.65 billion times bigger than the Sun. If placed at the center of the Solar System, the star’s surface would engulf Jupiter:
[https://en.wikipedia.org/wiki/WOH_G64]
Image: NASA, Spitzer Satellite, SAGE Team
For the first time, a team of astronomers has taken a close-up image of an individual dying supergiant star, WHO G64, in a neighboring galaxy, the Large Magellanic Cloud, about 160,000 light years distant. Researchers have been trying for decades to look closely at how aging stars lose a considerable amount of their mass before they go supernova. But this is difficult because of the great distances. However, by combining two 8.2m telescopes in Chile as an interferometer, they achieved the resolving power of a 60-m telescope. With this super-sharp view, they discovered that the dying supergiant star is developing a thick dust torus around it. They estimated that the star had an initial mass of about 25 times the mass of our sun. But now, the star is shedding material so rapidly that it has already lost 10 – 40% of its initial mass and is speeding toward its final fate as a supernova.
When a star becomes older, it ejects a huge amount of material and gets embedded in a thick envelope, in which a variety of molecules and dust form. Even with the world’s largest optical telescopes with 8 – 10m diameters, it is still difficult to take a close-up shot of aging stars closest to Earth, let alone those outside our own galaxy, the Milky Way.
Using two or more telescopes combined as an ‘interferometer’ provides a way to achieve much higher resolving power than an individual telescope alone. The ESO’s Very Large Telescope Interferometer (VLTI) in Chile is one of the largest interferometers, combining two or three 8.2m telescopes. A team of researchers at Max Planck Institute for Radio Astronomy (MPIfR) and the European Southern Observatory (ESO) these instruments at mid-infrared wavelengths, which is ideal for observing the thermal radiation from the dust envelope heated by the star.
Artist’s rendition of WOH G64
“For the first time we could take a close-up view of an individual star outside our Galaxy, and this is an important first step to understand how dying stars in other galaxies differ from their counterparts in our Milky Way”, says Keiichi Ohnaka at the MPIfR. “We discovered that the dying supergiant star WOH G64 is surrounded by a thick dust torus which sort of looks like a thick bagel by comparing it with detailed theoretical modeling.” The diameter of the supergiant star is as large as the orbit of Saturn in the solar system. The dimensions of the whole torus are considerably larger: the inner edge of the torus is at 120 AU, the total size of the torus reaches almost one light year.
In the next few thousand or ten thousand years, WHO G64 will explode as a supernova. Judging from its mass of WOH G64, it will become visible to the unaided eye in the southern hemisphere. The supernova explosion will blow away most of the mass of WOH G64, which will then be recycled as the building blocks for stars of the next generation.
[http://www.universetoday.com/14551/astronomers-image-dying-supergiant-star/]
Artist’s impression of the exoplanet Gliese 163 showing a thick water vapor atmosphere
[http://www.openexoplanetcatalogue.com/planet/Gliese%20163%20c/]
Gliese 163 is an M3.5V red dwarf located 49 light years (15.0pc) from the sun, in the constellation Dorado. Its coordinates in the night sky are RA 04h 9m 16s and Dec. -53°22'. It has a visual magnitude of 11.8 and an absolute magnitude of 10.9. Other stellar catalog names for it include HIP 19394 and LHS 188.
In September 2012, astronomers using the HARPS instrument announced the discovery of two planets orbiting Gliese 163. One planet, Gliese 163 c, with an orbital period of 26 days, and a minimum mass of 7.2 Earth masses, was considered potentially in the habitable zone, although hotter than Earth. A second planet, Gliese 163 b, was also announced, with a period of 1 day. It would be too hot to be considered habitable. Evidence was also found for a third planet orbiting further out than c and b. In June 2013, it was concluded that at least 3 planets orbit around the star with fourth planet being a possibility.
[https://en.wikipedia.org/wiki/Gliese_163]
VFTS 682 is a Wolf–Rayet star in the Large Magellanic Cloud. It is located over 29 parsecs (95 ly) north-east of the massive cluster R136 in the Tarantula Nebula.It is 150 times the mass of the sun and 3.2 million times more luminous which makes it one of the most massive and most luminous stars known:
[https://en.wikipedia.org/wiki/VFTS_682]
HD 37974. Artist concept of the stars, sun and planets not drawn to scale
HD 37974 (or R 126), formally RMC (Radcliffe observatory Magellanic Cloud) 126, is a massive luminous star with several unusual properties. It exhibits the B[e] phenomenon where forbidden emission lines appear in the spectrum due to extended circumstellar material. Its spectrum also shows normal (permitted) emission lines formed in denser material closer to the star, indicative of a power stellar wind. The spectra include silicate and polycyclic aromatic hydrocarbon (PAH) features that suggest a dusty disc.
The star itself is a hot supergiant thought to be seventy times more massive than the sun and over a million times more luminous. It has evolved away from the main sequence and is so luminous and large that it is losing material through its stellar wind over a billion times faster than the sun. It would lose more material than the sun contains in about 25,000 years.
The dust cloud around R126 is surprising because stars as massive as these were thought to be inhospitable to planet formation due to powerful stellar winds making it difficult for dust particles to condense. The nearby hypergiant HD 268835 shows similar features and is also likely to have a dusty disc, so R126 is not unique.
The disc extends outwards for 60 times the size of Pluto’s orbit around the sun, and probably contains as much material as the entire Kuiper Belt. It is unclear whether such a disc represents the first or last stages of the planet-forming process.
The brightness of R126 varies in an unpredictable way by around 0.6 magnitudes over timescales of tens to hundreds of days. The faster variations are characteristic of α Cygni variables, irregular pulsating supergiants. The slower variations are accompanied by changes in the colour of the star, with it being redder when it is visually brighter, typical of the S Doradus phases of Luminous Blue Variables.
[https://en.wikipedia.org/wiki/HD_37974]
White labels point to VFTS 682 and R 136. VFTS is short for VLT-FLAMES Tarantula Survey.
A team of astronomers using the ESO Very Large Telescope has taken a close look at the star VFTS 682. They determined that the star is 150 times the mass of the sun. Since very massive stars such as these have so far been found only in the crowded centers of star clusters, the exact mechanism for the formation of VFTS 682 remains a mystery.
This star resides in the Large Magellanic Cloud, a small satellite galaxy of our galaxy, the Milky Way. Astronomers studied VFTS 682 using the FLAMES instrument on the Very Large Telescope (VLT) of the European Southern Observatory (ESO). The team’s research is to appear in Astronomy and Astrophysics.
Joachim Bestenlehner, lead author of the study and a student at Armagh Observatory in Northern Ireland, said:
We were very surprised to find such a massive star on its own, and not in a rich star cluster. Its origin is mysterious.
Astronomers spotted VFTS 682 earlier, in a survey of the most brilliant stars in and around the Tarantula Nebula – situated 170,000 light-years away in the Large Magellanic Cloud (LMC). VFTS 682 lies in a stellar nursery, or huge region of gas, dust, and young stars. This particular location in space is said by astronomers to be the most active star-forming region in the Local Group of galaxies. (The local group consists of the Milky Way and Andromeda galaxies, as well as the Magellanic Clouds and many smaller galaxies.)
At first glance VFTS 682 was thought to be hot, young, and bright – and unremarkable. But the new study using the VLT has found that much of the star’s energy is being absorbed and scattered by dust clouds before it gets to Earth – so the star is more luminous than previously thought and is actually among the brightest stars known.
Red and infrared light emitted by the star can get through the dust, but the shorter-wavelength blue and green light is scattered more and lost. As a result, the star appears reddish, although if the view were unobstructed, it would shine a brilliant blue-white.
As well as being very bright, VFTS 682 is very hot, with a surface temperature of about 50,000 degrees Celsius. For comparison, the surface temperature of the sun is about 5500 degrees Celsius. Stars with these unusual properties may end their short lives not just as a supernova, as is normal for high-mass stars, but just possibly as an even more dramatic long-duration gamma-ray burst, the brightest type of explosion in the universe.
Although VFTS 682 seems now to be alone, it is not very far away from the very rich star cluster RMC 136 (often called R 136), which contains several similar “superstars.”
Paco Najarro, another member of the team, said:
The new results show that VFTS 682 is a near identical twin of one of the brightest superstars at the heart of the R 136 star cluster.
Is it possible that VFTS 682 formed there and was ejected? Such “runaway stars” are known, but all are much smaller than VFTS 682. It would be interesting to see how such a heavy star could be thrown from the cluster by gravitational interactions.
Jorick Vink, another member of the team, added:
It seems to be easier to form the biggest and brightest stars in rich star clusters. And although it may be possible, it is harder to understand how these brilliant beacons could form on their own. This makes VFTS 682 a really fascinating object.
[http://earthsky.org/space/a-brilliant-but-solitary-superstar]
Sanduleak -69° 202 (Sk -69° 202, also known as GSC 09162-00821) was a magnitude 12 blue supergiant star, originally charted by the Romanian-American astronomer Nicholas Sanduleak in 1970, located on the outskirts of the Tarantula Nebula in the Large Magellanic Cloud. It is notable as the progenitor of supernova 1987A. It is speculated that Sk -69° 202 may have been a luminous blue variable (LBV) in the recent past, although it was apparently a normal luminous supergiant at the time it exploded:
[https://en.wikipedia.org/wiki/Sanduleak_-69%C2%B0_202]
25th Anniversary of SN1987a
This February marks the 25th anniversary of the discovery of Supernova 1987A. A star, in the Tarantula Nebula within the Large Magellanic Cloud (LMC), called Sanduleak 69 202, exploded and became a supernova back on 24th February 1987. It is now 25 years since the light from this cosmic explosion first reached us here on Earth. The star itself actually exploded about 168,000 years before, of course, with the light taking that long to reach us.
SN1987A has become the most studied star remnant in history and has provided great insights into supernovae and their remnants. It was discovered by Ian Shelton and Oscar Duhalde at the Las Campanas Observatory in Chile on February 24, 1987, and within the same 24 hours independently by Albert Jones in New Zealand. On March 4-12, 1987 it was observed from space by Astron, the largest ultraviolet space telescope of that time. Hubble had yet to be launched.
On February 23rd, approximately three hours before the visible light from SN1987A reached the Earth, a burst of neutrinos was observed at separate neutrino observatories around the globe. This is likely due to neutrino emission (which occurs simultaneously with core collapse) preceding the emission of visible light (which occurs only after the shock wave reaches the stellar surface). This was the first time neutrinos emitted from a supernova had been observed directly, and marked the beginning of what is now ‘neutrino astronomy’.
The Supernova exploded in the Tarantula Nebula area near the edge of the Large Magellan Cloud- a satellite galaxy to our own. Even though its location in the LMC meant it was 10 times more distant than if it had been in our own Milky Way, it also meant that we had a relatively unobscured view of the supernova and its environment; there was never any ambiguity about its distance; and the fact that it lies so far south meant that observations could be done each night throughout the first year as it was always visible at some time during the night.
SN1987A was the brightest and closest supernova that has been seen since the invention of the telescope back in 1604. That supernova was called ‘Kepler’s Star’ and the supernova was in our own galaxy around 20,000 light years away. It was so bright that it outshone Venus and Jupiter and was even visible in daylight for 3 weeks back then. The only other one in our own galaxy was ‘Tycho’s Star’ seen in 1572 and also visible to the naked eye. There have only been a total of 8 naked eye supernova that are known.
The photograph shows the field around the site of the supernova in great detail, both before the supernova exploded (right) and about 10 days afterwards, when it was still brightening. The image of the star that exploded to create the supernova is elongated. This does not necessarily indicate any peculiarity or a close companion, rather it is the effect of stars being by chance aligned along the line of sight. Several other examples can be seen in this picture and other, different, blended images are seen in the photograph of the same field taken two weeks after the supernova appeared (left). The difference in image quality (‘seeing’) between these pictures is an effect of the Earth’s atmosphere which was much steadier when the plates used to make the pre-supernova picture were taken. Top left is NE. Width of each image is about 8 arc minutes.
[http://www.astronnewsroom.com/2012/02/25th-anniversary-of-sn1987a/]
SNR 0509-67.5 is a remnant from a supernova in the Large Magellanic Cloud (LMC). It was probably a type Ia supernova, as indicated by the detection in 2004 of the elements silicon and iron. Any surviving stars have not moved far from the site of the explosion. The supernova occurred about 400 years delayed in Earth’s time frame. However, researchers at the Space Telescope Science Institute in Baltimore, Md. have identified light from the supernova that was reflected off of interstellar dust, delaying its arrival at Earth by 400 years. This delay, called a light echo of the supernova explosion also allowed the astronomers to measure the spectral signature of the light from the explosion. By virtue of the color signature, astronomers were able to deduce it was a Type Ia supernova. Scientists have also observed the supernova remnant at X-ray and visible wavelengths, and studied a light echo that helps assess the energy involved in this unusually energetic supernova:
[https://en.wikipedia.org/wiki/SNR_0509-67.5]
SNR 0509-67.5: Supernova Bubble Resembles Holiday Ornament
SNR 0509-67.5 is another supernova remnant located in the Large Magellanic Cloud, a satellite galaxy to the Milky Way about 160,000 light years away. A new composite includes a Hubble image of the star field and gas that has been shocked by the expanding blast wave (pink). Chandra data (blue and green) show material in the center of the remnant that has been heated to millions of degrees.
This colorful creation was made by combining data from two of NASA’s Great Observatories. Optical data of SNR 0509-67.5 and its accompanying star field, taken with the Hubble Space Telescope, are composited with X-ray energies from the Chandra X-ray Observatory. The result shows soft green and blue hues of heated material from the X-ray data surrounded by the glowing pink optical shell which shows the ambient gas being shocked by the expanding blast wave from the supernova. Ripples in the shell’s appearance coincide with brighter areas of the X-ray data.
The Type 1a supernova that resulted in the creation of SNR 0509-67.5 occurred nearly 400 years ago for Earth viewers. The supernova remnant, and its progenitor star reside in the Large Magellanic Cloud (LMC), a small galaxy about 160,000 light-years from Earth. The bubble-shaped shroud of gas is 23 light-years across and is expanding at more than 11 million miles per hour (5,000 kilometers per second).
[http://chandra.harvard.edu/photo/2010/snr0509/]
Dorado contains part of the LMC (Large Magellanic Cloud):
[https://en.wikipedia.org/wiki/Large_Magellanic_Cloud]
The two Magellanic Clouds are two irregular dwarf galaxies visible from the southern hemisphere, which are members of the Local Group and are orbiting the Milky Way galaxy. The Large Magellanic Cloud and its neighbor and relative, the Small Magellanic Cloud, are conspicuous objects in the southern hemisphere, looking like separated pieces of the Milky Way to the naked eye. Roughly 21° apart in the night sky, the true distance between them is roughly 75,000 light-years. Until the discovery of the Sagittarius Dwarf Elliptical Galaxy in 1994, they were the closest known galaxies to our own (since 2003, the Canis Major Dwarf Galaxy was discovered to be closer still, and is now considered the actual nearest neighbor). The LMC lies about 160,000 light years away, while the SMC is around 200,000. The LMC is about twice the diameter of the SMC (14,000 ly and 7,000 ly respectively). For comparison, the Milky Way is about 100,000 ly across.
[https://en.wikipedia.org/wiki/Magellanic_Clouds]
Some celestial objects are only visible from Earth’s Southern Hemisphere, such as central portions of our Milky Way galaxy, left, plus the two Magellanic Clouds above and to the left of the observatory dome, as shown in this photo taken at Cerro Paranal in Chile’s Atacama Desert.
[https://www.nasa.gov/press/2013/july/nasas-sofia-investigates-the-southern-sky-from-new-zealand-1/#.V0y3e74rRWA]
A Large Magellanic Cloud Deep Field
Is this a spiral galaxy? No. Actually, it is the Large Magellanic Cloud (LMC), the largest satellite galaxy of our own Milky Way Galaxy. The LMC is classified as a dwarf irregular galaxy because of its normally chaotic appearance. In this deep and wide exposure, however, the full extent of the LMC becomes visible. Surprisingly, during longer exposures, the LMC begins to resemble a barred spiral galaxy. The Large Magellanic Cloud lies only about 180,000 light-years distant towards the constellation of Dorado. Spanning about 15,000 light-years, the LMC was the site of SN1987A, the brightest and closest supernova in modern times. Together with the Small Magellanic Cloud (SMC), the LMC can be seen in Earth’s southern hemisphere with the unaided eye.
[http://apod.nasa.gov/apod/ap080409.html]
Because Dorado contains part of the Large Magellanic Cloud, the constellation is rich in deep sky objects:
A HST image of a Star-forming region NGC 2080
NGC 2080 (The Ghost Head Nebula) is a star-forming region and emission nebula to the south of the 30 Doradus (Tarantula) nebula, in the southern constellation Dorado. It belongs to the Large Magellanic Cloud. NGC 2080 was discovered by John Frederick William Herschel in 1834. The Ghost Head Nebula has a diameter of 50 light-years and is named for the two distinct white patches it possesses, called the ‘eyes of the ghost.’ The western patch, called A1, has a bubble in the center which was created by the young, massive star it contains. The eastern patch, called A2, has several young stars in a newly formed cluster, but they are still obscured by their originating dust cloud. Because neither dust cloud has dissipated due to the stellar radiation, astronomers have deduced that both sets of stars formed within the past 10,000 years. These stars together have begun to create a bubble in the nebula with their outpourings of material, called stellar wind.
The presence of stars also greatly influences the color of the nebula. The western portion of the nebula has a dominant oxygen emission line because of a powerful star on the nebula's outskirts; this colors it green. The rest of the nebula’s outskirts have a red hue due to the ionization of hydrogen. Because both hydrogen and oxygen are ionized in the central region, which appears pale yellow; when hydrogen is energized enough to emit a second wavelength of light, it appears blue, as in the area surrounding A1 and A2.
NGC 2080 should not be confused with the Ghost Nebula (Sh2-136) or the Little Ghost Nebula (NGC 6369).
[https://en.wikipedia.org/wiki/NGC_2080]
The Tarantula Nebula is in the Large Magellanic Cloud, named for its spiderlike shape. It is also designated 30 Doradus, as it is visible to the naked eye as a slightly out-of-focus star. Larger than any nebula in the Milky Way at 1000 light-years in diameter, it is also brighter, because it is illuminated by the open star cluster NGC 2070, which has at its center the star cluster R136. The illuminating stars are supergiants:
The Tarantula Nebula
The Tarantula Nebula is more than a thousand light-years in diameter, a giant star forming region within nearby satellite galaxy the Large Magellanic Cloud, about 180 thousand light-years away. The largest, most violent star forming region known in the whole Local Group of galaxies, the cosmic arachnid sprawls across this spectacular composite view constructed with space- and ground-based image data. Within the Tarantula (NGC 2070), intense radiation, stellar winds and supernova shocks from the central young cluster of massive stars, cataloged as R136, energize the nebular glow and shape the spidery filaments. Around the Tarantula are other star forming regions with young star clusters, filaments, and blown-out bubble-shaped clouds In fact, the frame includes the site of the closest supernova in modern times, SN 1987A, at the lower right. The rich field of view spans about 1 degree or 2 full moons, in the southern constellation Dorado. But were the Tarantula Nebula closer, say 1,500 light-years distant like the local star forming Orion Nebula, it would take up half the sky.
[http://apod.nasa.gov/apod/ap160226.html]
N44 is a superbubble in the Large Magellanic Cloud that is 1,000 light-years wide. Its overall structure is shaped by the 40 hot stars towards its center. Within the superbubble of N44 is a smaller bubble catalogued as N44F. It is approximately 35 light-years in diameter and is shaped by an incredibly hot star at its center, which has a stellar wind speed of 7 million kilometers per hour. N44F also features dust columns with probable star formation hidden inside:
Huge Bubble in N44 Nebula
This image is part of the N44 super-bubble complex, a cloudy tempest dominated by a vast bubble about 325 by 250 light-years across. A cluster of massive stars inside the cavern has cleared away gas to form a distinctive mouth-shaped hollow shell. While astronomers do not agree on exactly how this bubble has evolved for up to the past 10 million years, they do know that the central cluster of massive stars is responsible for the cloud’s unusual appearance. It is likely that the explosive death of one or more of the cluster’s most massive and short-lived stars played a key role in the formation of the large bubble.
“This region is like a giant laboratory providing us with a glimpse into many unique phenomena,” said Sally Oey of the University of Michigan, who has studied this object extensively. “Observations from space have even revealed x-ray-emitting gas escaping from this super-bubble, and while this is expected, this is the only object of its kind where we have actually seen it happening.”
The Gemini data used to produce this image are being released to the astronomical community for further research and follow-up analysis. The image provides one of the most detailed views ever obtained of this relatively large region in the Large Magellanic Cloud, a satellite galaxy to the Milky Way, located some 150,000 light-years away and visible from the Southern Hemisphere. The images captured light of specific colors that reveal the compression of material and the presence of gases (primarily excited hydrogen gas and lesser amounts of oxygen and ‘shocked’ sulfur) in the cloud.
Multiple smaller bubbles appear in the image as bulbous growths clinging to the central super-bubble. Most of these regions were probably formed as part of the same process that shaped the central cluster. Their formation could also have been ‘sparked’ by compression as the central stars pushed the surrounding gas outward. Our view into this cavern could really be like looking through an elongated tube, which lends the object its monstrous mouth-like appearance.
The images used to produce the color composite were obtained with the Gemini Multi-object Spectrograph (GMOS) at the Gemini South Telescope on Cerro Pachón in Chile. The color image was produced by Travis Rector of the University of Alaska Anchorage and combines three single-color images to produce the image. H-alpha emission is rendered in violet, OIII (doubly ionized oxygen) emission in cyan, and SII emission in orange.
[http://www.wolaver.org/space/n44x.htm]
NGC 1566, commonly known as the Spanish Dancer, is an intermediate spiral galaxy in the constellation Dorado. It is the dominant member of the Dorado Group and also its brightest member. It is one of the brightest Seyfert galaxies in the sky. Its absolute luminosity is 3.7×10^10 L☉. It contains 1.4×10^10 M☉:
[https://en.wikipedia.org/wiki/NGC_1566]
Grand swirls
This new Hubble image shows NGC 1566, a beautiful galaxy located approximately 40 million light-years away in the constellation of Dorado (The Dolphinfish). NGC 1566 is an intermediate spiral galaxy, meaning that while it does not have a well-defined bar-shaped region of stars at its center- like barred spirals- it is not quite an unbarred spiral either (heic9902o).
The small but extremely bright nucleus of NGC 1566 is clearly visible in this image, a telltale sign of its membership of the Seyfert class of galaxies. The centers of such galaxies are very active and luminous, emitting strong bursts of radiation and potentially harboring supermassive black holes that are many millions of times the mass of the Sun.
NGC 1566 is not just any Seyfert galaxy; it is the second brightest Seyfert galaxy known. It is also the brightest and most dominant member of the Dorado Group, a loose concentration of galaxies that together comprise one of the richest galaxy groups of the southern hemisphere. This image highlights the beauty and awe-inspiring nature of this unique galaxy group, with NGC 1566 glittering and glowing, its bright nucleus framed by swirling and symmetrical lavender arms.
Distance: 40 million light years.
[https://www.spacetelescope.org/images/potw1422a/]
LEDA 89996, also known by its 2MASS designation 2MASS J04542829-6625280, is a spiral galaxy. It is located within the Dorado constellation and appears very close to the Large Magellanic Cloud. The galaxy was observed by the Hubble Telescope in 6 July 2015 and is similar in appearance to the Milky Way being spiral shaped with winding spiral arms. The darker patches between the arms is dust and gas. Lots of new stars form in this area making the spirals appear very bright:
[https://en.wikipedia.org/wiki/LEDA_89996]
Hubble Looks at Stunning Spiral
This little-known galaxy, officially named J04542829-6625280, but most often referred to as LEDA 89996, is a classic example of a spiral galaxy. The galaxy is much like our own galaxy, the Milky Way. The disk-shaped galaxy is seen face on, revealing the winding structure of the spiral arms. Dark patches in these spiral arms are in fact dust and gas- the raw materials for new stars. The many young stars that form in these regions make the spiral arms appear bright and bluish.
The galaxy sits in a vibrant area of the night sky within the constellation of Dorado (The Swordfish), and appears very close to the Large Magellanic Cloud — one of the satellite galaxies of the Milky Way.
[https://www.nasa.gov/image-feature/goddard/hubble-looks-at-leda-89996]
[https://en.wikipedia.org/wiki/Dorado]
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