Carina constellation is located in the southern sky. Its name means ‘keel’ (of a ship) in Latin. Carina is the 34th largest constellation in the sky, occupying an area of 494 square degrees. It lies in the second quadrant of the southern hemisphere (SQ2) and can be seen at latitudes between +20° and -90°. The neighboring constellations are Centaurus, Chamaeleon, Musca, Pictor, Puppis, Vela, and Volans. Carina belongs to the Heavenly Waters family of constellations, along with Columba, Delphinus, Equuleus, Eridanus, Piscis Austrinus, Puppis, Pyxis, and Vela.
[http://www.constellation-guide.com/constellation-list/carina-constellation/]
(Former) Constellation of Argo Navis
[http://www.davidmalin.com/fujii/source/afn1-05.html]
Johannes Hevelius’ Argo Navis from Uranographia (1690)
[http://chandra.harvard.edu/photo/constellations/carina.html]
Carina used to be a part of the constellation Argo Navis (‘the ship Argo’), created by the Greek astronomer Ptolemy in the 2nd century, before Argo Navis was divided into three constellations- Carina (the keel), Puppis (the stern) and Vela (the sails)- by Nicolas Louis de Lacaille in the 18th century. Argo Navis represented Argo, the ship on which Jason and the Argonauts sailed to retrieve the Golden Fleece. The constellation was also sometimes associated with the ship that carried Menelaus home after the Trojan War. Egyptians also identified the constellation with a ship, one that carried Osiris and Isis during the big flood.
[http://www.topastronomer.com/StarCharts/Constellations/Carina.php]
[http://astropixels.com/constellations/charts/Car.html]
Carina
[http://www.dibonsmith.com/car_con.htm]
An image of Canopus by Expedition 6
Canopus (Alpha Carinae) is the brightest star in the constellation of Carina, and the second brightest star in the night-time sky, after Sirius. Canopus’s visual magnitude is −0.72, and it has an absolute magnitude of −5.71. It is a bright giant of spectral type A9, so it is is essentially white when seen with the naked eye. It is located in the far southern sky, at a year 2000 declination of −52° 42′ and a right ascension of 06h 24.0m.
Its name is generally considered to originate from the mythological Canopus, who was a navigator for Menelaus, king of Sparta, on his quest to retrieve Helen of Troy after she was taken by Paris. Canopus was not visible to the ancient Greeks and Romans; it was, however, visible to the ancient Egyptians. Hence Aratus did not write of the star as it remained below the horizon, while Eratosthenes and Ptolemy- observing from Alexandria- did, calling it Kanōbos. The star traditionally marked the rudder of the ship Argo Navis.
Canopus was known to the ancient Mesopotamians and given the name NUN-ki and represented the city of Eridu in the Three Stars Each Babylonian star catalogues and later MUL.APIN around 1100 BC. Today, the star Sigma Sagittarii is known by the common name Nunki.
An Egyptian priestly poet in the time of Thutmose III mentions the star as Karbana, “the star which pours his light in a glance of fire, when he disperses the morning dew.”
In Indian Vedic literature, Agastya, the star Canopus, is said to be the ‘cleanser of waters’ and its rising coincides with the calming of the waters of the Indian Ocean. It is considered the son of Pulasthya, son of Brahma.
In medieval times Canopus was known as Suhel, from the Arabic name ‘suhayl’ for several bright stars. Its Greek name was revived during the Renaissance.
In Chinese traditional astronomy Canopus was called ‘the Old Man of the South Pole’ (‘Nanji Lǎorén’), and appears (albeit misplaced northwards) on the medieval Chinese star chart Dunhuang, despite not being visible from the then Chinese capital of Chang'an. The Chinese astronomer Yi Xing had journeyed south to chart Canopus and other far southern stars in 724 AD. However, it was already mentioned by Sima Qian in the second century BC, drawing on sources from the Warring States period, as the southern counterpart of Sirius.
The star Canopus (bottom center), as seen from the latitude of Key West, Florida
[http://oneminuteastronomer.com/2788/canopus-star-old-age/]
In the southern hemisphere, Canopus and Sirius are both visible high in the sky simultaneously, and reach the meridian just 21 minutes apart. Brighter than first magnitude, Canopus can be seen by naked eye already in the early twilight. Most visible in the southern hemisphere summer, Canopus culminates at midnight on December 27, and at 9PM on February 11. It is a circumpolar star when seen from points that have latitude south of 37°18' S; for example, Victoria and Tasmania, Australia; Auckland and south of it, New Zealand; Bahía Blanca, Argentina; and Valdivia, Chile and south of these cities in South America. Since Canopus is so far south in the sky, it never rises in mid- or far-northern latitudes; in theory the northern limit of visibility is latitude 37°18' north. This is just south of Athens, Richmond (USA), and San Francisco, and very close to Seville and Agrigento. It is almost exactly the latitude of Lick Observatory on Mt. Hamilton, California, from which it is readily visible because of the effects of elevation and atmospheric refraction, which add another degree to its apparent altitude. Under ideal conditions it has been spotted as far north as latitude 37°31' from the Pacific coast. Another northernmost record of visibility came from Mount Nemrut in Turkey, latitude 37°59'. It is more easily visible in places such as the Gulf Coast and Florida, and the island of Crete (Greece) where the best season for viewing it around 9 p.m. is during late January and early February.
Canopus has a B-V color index of +0.15 where 0 is a blue-white, indicating it is essentially white, although has been described as yellow-white. Its spectral type has been recorded as F0 and more recently A9. It has less yellow than Altair or Procyon, whose color indexes have been measured at 0.22 and 0.42 respectively. It may be that some observers have perceived it as yellow-tinged owing to its being located low in the sky and hence subject to atmospheric effects.
Before the launch of the Hipparcos satellite telescope, distance estimates for the star varied widely, from 96 light years to 1200 light years. Had the latter distance been correct, Canopus would have been one of the most luminous stars in our galaxy. Hipparcos established Canopus as lying 310 light years (96 parsecs) from our solar system; this is based on its 2007 parallax measurement of 10.43 ± 0.53 mas. The difficulty in measuring Canopus’ distance stemmed from its unusual nature. Canopus has an MK spectral type of A9 II, although it is sometimes treated as F0 Ib (Ib referring to ‘less luminous supergiant’) on account of its high luminosity, and such stars are rare and poorly understood; they are stars that can be either in the process of evolving to or away from red giant status. This in turn made it difficult to know how intrinsically bright Canopus is, and therefore how far away it might be. Direct measurement was the only way to solve the problem. Canopus is too far away for Earth-based parallax observations to be made, so the star’s distance was not known with certainty until the early 1990s.
The photospheric temperature of Canopus has been estimated at 7350 ± 30 K. Canopus is a strong source of X-rays, which are probably produced by its corona, magnetically heated to around 15 million K. The temperature has likely been stimulated by fast rotation combined with strong convection percolating through the star's outer layers. The star's surface temperature is too cool to account for the X-rays.
A comparison of our sun to Canopus
[http://earthsky.org/brightest-stars/few-know-the-second-brightest-star-canopus]
Infrared interferometry was used to calculate its angular diameter at 6.93 ± 0.15 mas. Combined with distance calculated by Hipparcos, this gives it a diameter of 71.4 ± 0.4 times that of the Sun. If it were placed at the centre of the Solar System, it would extend 90% of the way to the orbit of Mercury.
Canopus is the most intrinsically bright star within approximately 700 light years, and it has been the brightest star in Earth’s sky during three different epochs over the past four million years. Other stars appear brighter only during relatively temporary periods, during which they are passing the Solar System at a much closer distance than Canopus. About 90,000 years ago, Sirius moved close enough that it became brighter than Canopus, and that will remain the case for another 210,000 years. But in 480,000 years, Canopus will once again be the brightest, and will remain so for a period of about 510,000 years.
Canopus was previously claimed to be a member of the Scorpius-Centaurus Association, however it is not located near the subgroups of that association, and has not been included as a Sco-Cen member in kinematic studies that used Hipparcos astrometric data. At present, Canopus is not thought to be a member of any nearby young stellar groups.
In 2014, astronomer Eric Mamajek reported that an extremely magnetically active M dwarf (having strong coronal X-ray emission), situated 1.16 degrees south of Canopus, appears to share common proper motion with the bright star. The projected separation of the M dwarf (‘Canopus B’) is approximately 1.9 parsecs, however despite this large separation, it is still within the estimated tidal radius (2.9 parsecs) for the massive star Canopus.
[https://en.wikipedia.org/wiki/Canopus]
IC 2448 is an elliptical planetary nebula in the constellation of Carina. It lies near the bright star Beta Carinae, and the southern Carina can be explored in the months of autumn in the southern hemisphere.
[https://en.wikipedia.org/wiki/IC_2448]
Diamond cross
[https://en.wikipedia.org/wiki/Diamond_Cross]
Beta Carinae is the second brightest star in the constellation Carina and one of the brightest stars in the night sky, with apparent magnitude 1.68. It is the brightest star in the south polar asterism known as the Diamond Cross, marking the southwestern end of the asterism. Beta Carinae also has the traditional name Miaplacidus, meaning ‘placid waters.’ It lies near the planetary nebula IC 2448. Parallax measurements place it at a distance of 113.2 light-years (34.7 parsecs) from Earth.
Beta Carinae’s traditional name Miaplacidus made its debut on star maps in 1856 when the star atlas Geography of the Heavens, composed by Elijah Hinsdale Burritt, was published. The meaning and linguistic origin of the name remained an enigma for many decades, until William Higgins, a great scholar and expert on star names, surmised that the name Miaplacidus is apparently a bilingual combination of Arabic ‘miyāh’ for ‘waters’ and Latin placidus for ‘placid.’
The stellar classification of A1 III suggests this is an evolved giant star, although it has also been rated as an A2 IV subgiant star. It has an estimated age of 260 million years. This star does not show an excess emission of infrared radiation that might otherwise suggest the presence of a debris disk. It has about 3.5 times the Sun’s mass and has expanded to almost seven times the radius of the Sun. Presently it is radiating 288 times as much luminosity as the Sun from its outer envelope at an effective temperature of 8,866 K. Despite its enlarged girth, this star still shows a rapid rotation rate, with a projected rotational velocity of 146 km s−1.
[https://en.wikipedia.org/wiki/Beta_Carinae]
Illustration of the Avior system
Epsilon Carinae, also known by the name Avior, is the third brightest star in the constellation Carina. At apparent magnitude +1.86 it is one of the brightest stars in the night sky, but is not visible from the northern hemisphere.
Epsilon Carinae is a double star located roughly 560–660 light-years (170–200 parsecs) away from the Earth. Measurements during the Hipparcos mission give the pair an angular separation of 0.46 arcseconds with a difference in magnitude of 2.0. At their estimated distance, this angle is equivalent to a physical separation of around 4 Astronomical Units. This pair may form an eclipsing binary system with a period of 785 days (2.15 years), resulting in a magnitude change of 0.12 during each eclipse.
The primary component has an apparent visual magnitude of 2.2, which by itself would still make it the third brightest star in the constellation. It is an evolved giant star with a stellar classification of K0 III. However, examination of the ultraviolet flux from this star suggests it may instead be of spectral type K7. The fainter secondary companion has an apparent visual magnitude of 4.1, which, if it were a solitary star, would be bright enough to be seen with the naked eye. This is a hot, core hydrogen-fusing B-type main sequence star of spectral class B2 Vp. The secondary may itself have an orbiting stellar companion of spectral class F8.
The name Avior is not classical in origin. It was assigned to the star by HM Nautical Almanac Office in the late 1930s during the creation of The Air Almanac, a navigational almanac for the Royal Air Force. Of the fifty-seven navigation stars included in the new almanac, two had no classical names: Epsilon Carinae and Alpha Pavonis. The RAF insisted that all of the stars must have names, so new names were invented. Alpha Pavonis was named ‘Peacock,’ a translation of Pavo, whilst Epsilon Carinae was called ‘Avior.’
[https://en.wikipedia.org/wiki/Epsilon_Carinae]
The Southern Pleiades (also known as the Theta Carinae Cluster, Open Cluster IC 2602, or IC 2602) is an open cluster in the Carina constellation. It was discovered by Abbe Lacaille in 1751 from South Africa. The cluster is at a distance of about 479 light years away from Earth and can be seen with the naked eye.
[http://www.southernskyphoto.com/southern_sky/southern_pleiades_ic_2602.htm]
Theta Carinae marks the northeastern end of the Diamond Cross asterism, and with an apparent visual magnitude of 2.76, it is the brightest star in the open star cluster IC 2602. It is located at a distance of about 460 light-years (140 parsecs) from Earth.
The stellar classification of this star is B0.5 Vp, which indicates this is a B-type main sequence star that is generating energy at its core through the nuclear fusion of hydrogen. The ‘p’ suffix means it displays peculiar features in its spectrum, which have been observed in both the optical and ultraviolet band. This might be explained by a magnetic field, yet no such measurable field has been observed. Theta Carinae is actually a single-lined spectroscopic binary with a period of 2.2 days; the shortest known orbital period among massive stars. The close orbit means that a mass transfer between the two components may have occurred, which could explain the peculiarities of the spectrum.
The primary component in this system is a blue straggler, which is a type of star that is created by the interaction between two or more stars. Most likely the source of this mass transfer was the secondary member of the system, and what is now the primary star was probably once the secondary component. At an estimated age of 4 million years, this star is much younger than the age of the surrounding IC 2602 cluster, which is consistent with it being a straggler. At present the primary star has about 15 times the mass of the Sun and five times the Sun’s radius. It has an intensely hot outer envelope that is radiating more than 25,000 the Sun’s luminosity at an effective temperature of 31,000 K, giving it a blue-white glow. When the primary reaches the age of around 11 million years, it will expand to the point where it will begin to transfer part of its mass back to its companion. Little is known about this secondary component, but it may be an F-type star with a luminosity less than 1% of the primary.
[https://en.wikipedia.org/wiki/Theta_Carinae]
V382 Carinae
V382 Carinae, also known as x Carinae (x Car), is a yellow hypergiant in the constellation Carina. This is a G-type star with a mean apparent magnitude of +3.93, a variable star of low amplitude. A period of 556 days has been suggested, but it is not entirely regular. It is 8,900 light years from Earth and 700 times the size of our Sun.
This is the brightest yellow hypergiant in the night sky, easily visible to the naked eye and brighter than Rho Cassiopeiae although not visible from much of the northern hemisphere. The low infrared excess suggest that V382 Carinae may be cooling towards a red supergiant phase, less common than yellow hypergiants evolving towards hotter temperatures.
[https://en.wikipedia.org/wiki/V382_Carinae]
Eta Carinae: Our Neighboring Superstars
Eta Carinae is an intriguing double star system that contains one of the biggest and brightest stars in the Milky Way. X-rays from Eta Carinae give clues about the system, including how the winds from the stars interact. Astronomers have been observing Eta Carinae with Chandra since the telescope was launched in 1999.
The Eta Carinae star system does not lack for superlatives. Not only does it contain one of the biggest and brightest stars in our galaxy, weighing at least 90 times the mass of the Sun, it is also extremely volatile and is expected to have at least one supernova explosion in the future.
As one of the first objects observed by NASA’s Chandra X-ray Observatory after its launch some 15 years ago, this double star system continues to reveal new clues about its nature through the X-rays it generates.
Astronomers reported extremely volatile behavior from Eta Carinae in the 19th century, when it became very bright for two decades, outshining nearly every star in the entire sky. This event became known as the ‘Great Eruption.’ Data from modern telescopes reveal that Eta Carinae threw off about ten times the Sun’s mass during that time. Surprisingly, the star survived this tumultuous expulsion of material, adding ‘extremely hardy’ to its list of attributes.
Today, astronomers are trying to learn more about the two stars in the Eta Carinae system and how they interact with each other. The heavier of the two stars is quickly losing mass through wind streaming away from its surface at over a million miles per hour. While not the giant purge of the Great Eruption, this star is still losing mass at a very high rate that will add up to the Sun’s mass in about a millennium.
Though smaller than its partner, the companion star in Eta Carinae is also massive, weighing in at about 30 times the mass of the Sun. It is losing matter at a rate that is about a hundred times lower than its partner, but still a prodigious weight loss compared to most other stars. The companion star beats the bigger star in wind speed, with its wind clocking in almost ten times faster.
When these two speedy and powerful winds collide, they form a bow shock- similar to the sonic boom from a supersonic airplane- that then heats the gas between the stars. The temperature of the gas reaches about ten million degrees, producing X-rays that Chandra detects.
The Chandra image of Eta Carinae shows low energy X-rays in red, medium energy X-rays in green, and high energy X-rays in blue. Most of the emission comes from low and high energy X-rays. The blue point source is generated by the colliding winds, and the diffuse blue emission is produced when the material that was purged during the Great Eruption reflects these X-rays. The low energy X-rays further out show where the winds from the two stars, or perhaps material from the Great Eruption, are striking surrounding material. This surrounding material might consist of gas that was ejected before the Great Eruption.
An interesting feature of the Eta Carinae system is that the two stars travel around each other along highly elliptical paths during their five-and-a-half-year long orbit. Depending on where each star is on its oval-shaped trajectory, the distance between the two stars changes by a factor of twenty. These oval-shaped trajectories give astronomers a chance to study what happens to the winds from these stars when they collide at different distances from one another.
Throughout most of the system’s orbit, the X-rays are stronger at the apex, the region where the winds collide head-on. However, when the two stars are at their closest during their orbit (a point that astronomers call ‘periastron’), the X-ray emission dips unexpectedly.
To understand the cause of this dip, astronomers observed Eta Carinae with Chandra at periastron in early 2009. The results provided the first detailed picture of X-ray emission from the colliding winds in Eta Carinae. The study suggests that part of the reason for the dip at periastron is that X-rays from the apex are blocked by the dense wind from the more massive star in Eta Carinae, or perhaps by the surface of the star itself.
Another factor responsible for the X-ray dip is that the shock wave appears to be disrupted near periastron, possibly because of faster cooling of the gas due to increased density, and/or a decrease in the strength of the companion star’s wind because of extra ultraviolet radiation from the massive star reaching it. Researchers are hoping that Chandra observations of the latest periastron in August 2014 will help them determine the true explanation.
Distance Estimate: About 7,500 light years
[http://chandra.harvard.edu/photo/2014/etacar/index.html]
Snapshot of a shedding star
In this new Hubble image, the strikingly luminous star AG Carinae- otherwise known as HD 94910- takes centre stage. Found within the constellation of Carina in the southern sky, AG Carinae lies 20000 light-years away, nestled in the Milky Way.
AG Carinae is classified as a Luminous Blue Variable. These rare objects are massive evolved stars that will one day become Wolf-Rayet Stars- a class of stars that are tens of thousands to several million times as luminous as the Sun. They have evolved from main sequence stars that were twenty times the mass of the Sun.
Stars like AG Carinae lose their mass at a phenomenal rate. This loss of mass is due to powerful stellar winds with speeds of up to 7 million km/hour. These powerful winds are also responsible for the shroud of material visible in this image. The winds exert enormous pressure on the clouds of interstellar material expelled by the star and force them into this shape.
Despite HD 94910’s intense luminosity, it is not visible with the naked eye as much of its output is in the ultraviolet.
This image was taken with the Wide Field and Planetary Camera 2 (WFPC2), that was installed on Hubble during the Shuttle mission STS-61 and was Hubble’s workhorse for many years. It is worth noting that the bright glare at the centre of the image is not the star itself. The star is tiny at this scale and hidden within the saturated region. The white cross is also not an astronomical phenomenon but rather an effect of the telescope.
[https://www.spacetelescope.org/images/potw1439a/]
OGLE-TR-122b compared with Sun and Jupiter
[https://jumk.de/astronomie/special-stars/ogle-tr-122.shtml]
OGLE-TR-122 is a binary stellar system containing one of the smallest main-sequence stars whose radius has been measured. It was discovered when the Optical Gravitational Lensing Experiment (OGLE) survey observed the smaller star eclipsing the larger primary. The orbital period is approximately 7.3 days. The system’s primary is thought to resemble the Sun.
The smaller star, OGLE-TR-122B, is estimated to have a radius around 0.12 solar radii, or around 20% larger than Jupiter’s, and a mass of around 0.1 solar masses, or approximately 100 times Jupiter’s. This makes its average density approximately 50 times the Sun’s or over 80 times the density of water. OGLE-TR-122b’s mass is close to the lowest possible mass for a hydrogen-fusing star, estimated to be around 0.07 or 0.08 solar masses. The observed transit provides the first direct evidence for a star with a radius comparable to Jupiter’s.
[https://en.wikipedia.org/wiki/OGLE-TR-122]
Cluster and Starforming Region Westerlund 2
Located 20,000 light-years away in the constellation Carina, the young cluster and starforming region Westerlund 2 fills this cosmic scene. Captured with Hubble’s cameras in near-infrared and visible light, the stunning image is a celebration of the 25th anniversary of the launch of the Hubble Space Telescope on April 24, 1990. The cluster’s dense concentration of luminous, massive stars is about 10 light-years across. Strong winds and radiation from those massive young stars have sculpted and shaped the region’s gas and dust, into starforming pillars that point back to the central cluster. Red dots surrounding the bright stars are the cluster’s faint newborn stars, still within their natal gas and dust cocoons. But brighter blue stars scattered around are likely not in the Westerlund 2 cluster and instead lie in the foreground of the Hubble anniversary field of view.
[http://apod.nasa.gov/apod/ap150425.html]
Carina is known for its namesake nebula, NGC 3372, discovered by French astronomer Nicolas Louis de Lacaille in 1751, which contains several nebulae:
The Great Nebula in Carina
In one of the brightest parts of Milky Way lies a nebula where some of the oddest things occur. NGC 3372, known as the Great Nebula in Carina, is home to massive stars and changing nebulas. The Keyhole Nebula (NGC 3324), the bright structure just above the image center, houses several of these massive stars and has itself changed its appearance. The entire Carina Nebula spans over 300 light years and lies about 7,500 light-years away in the constellation of Carina. Eta Carinae, the most energetic star in the nebula, was one of the brightest stars in the sky in the 1830s, but then faded dramatically. Eta Carinae is the brightest star near the image center, just left of the Keyhole Nebula. While Eta Carinae itself maybe on the verge of a supernova explosion, X-ray images indicate that much of the Great Carina Nebula has been a veritable supernova factory.
[http://apod.nasa.gov/apod/ap160323.html]
The Carina Nebula overall is a colossal emission nebula that possesses vast star-forming regions; it has an overall magnitude of 8.0. It also has a massive apparent diameter, more than 2 degrees. Its central region is called the Keyhole Nebula, named in 1847 by John Herschel. The Keyhole is about seven light-years wide and is mostly made up of ionized hydrogen, with two major star-forming regions:
Eta and Keyhole in the Carina Nebula
South is toward the top in this colorful close-up view of the Great Carina Nebula (NGC 3372), famous star-forming region of the southern sky. Covering an area surrounding the dusty Keyhole Nebula (NGC 3324) near picture center, the image spans about 40 light-years within the larger Carina Nebula at an estimated distance of 7,500 light-years. Like the more northerly Orion Nebula, the bright Carina Nebula is easily visible to the naked-eye. But the dramatic colors in this telescopic picture are mapped colors, based on three exposures through narrow filters each intended to record the light emitted by specific atoms in the gaseous nebula. Sulfur is shown in blue, hydrogen in green and oxygen in red hues. The Carina Nebula is home to young, extremely massive stars, including the still enigmatic variable Eta Carinae, a star with well over 100 times the mass of the Sun. Highlighted by diffraction spikes, Eta is just above and right (east) of the Keyhole.
[http://apod.nasa.gov/apod/ap060316.html]
The Homunculus Nebula is a planetary nebula visible to the naked eye that is being ejected by the erratic luminous blue variable star Eta Carinae:
Astronomers Bring The Third Dimension To A Doomed Star's Outburst
A new shape model of the Homunculus Nebula reveals protrusions, trenches, holes and irregularities in its molecular hydrogen emission. The protrusions appear near a dust skirt seen at the nebula’s center in visible light (inset) but not found in this study, so they constitute different structures.
In the middle of the 19th century, the massive binary system Eta Carinae underwent an eruption that ejected at least 10 times the sun's mass and made it the second-brightest star in the sky. Now, a team of astronomers has used extensive new observations to create the first high-resolution 3-D model of the expanding cloud produced by this outburst.
“Our model indicates that this vast shell of gas and dust has a more complex origin than is generally assumed,” said Thomas Madura, a member of the study team. “For the first time, we see evidence suggesting that intense interactions between the stars in the central binary played a significant role in sculpting the nebula we see today.”
Eta Carinae lies about 7,500 light-years away in the southern constellation of Carina and is one of the most massive binary systems astronomers can study in detail. The smaller star is about 30 times the mass of the sun and may be as much as a million times more luminous. The primary star contains about 90 solar masses and emits 5 million times the sun's energy output. Both stars are fated to end their lives in spectacular supernova explosions.
Between 1838 and 1845, Eta Carinae underwent a period of unusual variability during which it briefly outshone Canopus, normally the second-brightest star. As a part of this event, which astronomers call the Great Eruption, a gaseous shell containing at least 10 and perhaps as much as 40 times the sun’s mass was shot into space. This material forms a twin-lobed dust-filled cloud known as the Homunculus Nebula, which is now about a light-year long and continues to expand at more than 1.3 million mph (2.1 million km/h).
Using the European Southern Observatory’s Very Large Telescope and its X-Shooter spectrograph over two nights in March 2012, the team imaged near-infrared, visible and ultraviolet wavelengths along 92 separate swaths across the nebula, making the most complete spectral map to date. The researchers have used the spatial and velocity information provided by this data to create the first high-resolution, fully 3-D model of the Homunculus Nebula. The new model contains none of the assumptions about the cloud’s symmetry found in previous studies.
Every 5.5 years, when their orbits carry them to their closest approach, called periastron, the immense and brilliant stars of Eta Carinae are only as far apart as the average distance between Mars and the sun. Both stars possess powerful gaseous outflows called stellar winds, which constantly interact but do so most dramatically during periastron, when the faster wind from the smaller star carves a tunnel through the denser wind of its companion. The opening angle of this cavity closely matches the length of the trenches (130 degrees) and the angle between the arm-like protrusions (110 degrees), indicating that the Homunculus likely continues to carry an impression from a periastron interaction around the time of the Great Eruption.
The new shape model confirms several features identified by previous studies, including pronounced holes located at the ends of each lobe and the absence of any extended molecular hydrogen emission from a dust skirt apparent in visible light near the center of the nebula. New features include curious arm-like protrusions emanating from each lobe near the dust skirt; vast, deep trenches curving along each lobe; and irregular divots on the side facing away from Earth.
[http://www.nasa.gov/content/goddard/astronomers-bring-the-third-dimension-to-a-doomed-stars-outburst]
Mystic Mountain Dust Pillars
It’s stars versus dust in the Carina Nebula and the stars are winning. More precisely, the energetic light and winds from massive newly formed stars are evaporating and dispersing the dusty stellar nurseries in which they formed. Located in the Carina Nebula and known informally as Mystic Mountain, these pillar's appearance is dominated by the dark dust even though it is composed mostly of clear hydrogen gas. Dust pillars such as these are actually much thinner than air and only appear as mountains due to relatively small amounts of opaque interstellar dust. About 7,500 light-years distant, the featured image was taken with the Hubble Space Telescope, digitally reprocessed by an industrious amateur, and highlights an interior region of Carina which spans about three light years. Within a few million years, the stars will likely win out completely and the entire dust mountain will be destroyed.
[http://apod.nasa.gov/apod/ap150415.html]
One noted galaxy cluster is 1E 0657-56, the Bullet Cluster, named for the shock wave seen in the intracluster medium, which resembles the shock wave of a supersonic bullet. The bow shock visible is thought to be due to the smaller galaxy cluster moving through the intracluster medium at a relative speed of 3000- 4000 kilometers per second to the larger cluster:
1E 0657-56: NASA Finds Direct Proof of Dark Matter
This composite image shows the galaxy cluster 1E 0657-56, also known as the ‘bullet cluster.’ This cluster was formed after the collision of two large clusters of galaxies, the most energetic event known in the universe since the Big Bang.
Hot gas detected by Chandra in X-rays is seen as two pink clumps in the image and contains most of the ‘normal,’ or baryonic, matter in the two clusters. The bullet-shaped clump on the right is the hot gas from one cluster, which passed through the hot gas from the other larger cluster during the collision. An optical image from Magellan and the Hubble Space Telescope shows the galaxies in orange and white. The blue areas in this image show where astronomers find most of the mass in the clusters. The concentration of mass is determined using the effect of so-called gravitational lensing, where light from the distant objects is distorted by intervening matter. Most of the matter in the clusters (blue) is clearly separate from the normal matter (pink), giving direct evidence that nearly all of the matter in the clusters is dark.
The hot gas in each cluster was slowed by a drag force, similar to air resistance, during the collision. In contrast, the dark matter was not slowed by the impact because it does not interact directly with itself or the gas except through gravity. Therefore, during the collision the dark matter clumps from the two clusters moved ahead of the hot gas, producing the separation of the dark and normal matter seen in the image. If hot gas was the most massive component in the clusters, as proposed by alternative theories of gravity, such an effect would not be seen. Instead, this result shows that dark matter is required.
Distance Estimate: About 3.8 billion light years
[http://chandra.harvard.edu/photo/2006/1e0657/index.html]
Carina contains the radiant of the Eta Carinids meteor shower, which peaks around January 21 each year.
[https://en.wikipedia.org/wiki/Carina_%28constellation%29]
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