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109-455: Eta Carinae ( η Carinae , abbreviated to η Car ), formerly known as Eta Argus , is a stellar system containing at least two stars with a combined luminosity greater than five million times that of the Sun, located around 7,500 light-years (2,300 parsecs ) distant in the constellation Carina . Previously a 4th-magnitude star, it brightened in 1837 to become brighter than Rigel , marking

218-417: A binary star , binary star system or physical double star . If there are no tidal effects, no perturbation from other forces, and no transfer of mass from one star to the other, such a system is stable, and both stars will trace out an elliptical orbit around the barycenter of the system indefinitely. (See Two-body problem ) . Examples of binary systems are Sirius , Procyon and Cygnus X-1 ,

327-599: A broad band of wavelengths) less affected. This shows a dramatic reduction in the ionisation level of the hydrogen for a short period in each cycle, coinciding with the spectroscopic events at other wavelengths. Eta Carinae is found within the Carina Nebula, a giant star-forming region in the Carina–Sagittarius Arm of the Milky Way . The nebula is a prominent naked-eye object in the southern skies showing

436-411: A close binary with a distant companion, with the other star(s) previously in the system ejected into interstellar space at high velocities. This dynamic may explain the runaway stars that might have been ejected during a collision of two binary star groups or a multiple system. This event is credited with ejecting AE Aurigae , Mu Columbae and 53 Arietis at above 200 km·s and has been traced to

545-456: A compact H II region at around 10,000 K. High resolution imaging shows the radio frequencies originating from a disk a few arcseconds in diameter, 10,000 astronomical units (AU) wide at the distance of Eta Carinae. The radio emission from Eta Carinae shows continuous variation in strength and distribution over a 5.5-year cycle. The H II and recombination lines vary very strongly, with continuum emission (electromagnetic radiation across

654-511: A complex mix of emission, reflection and dark nebulosity. Eta Carinae is known to be at the same distance as the Carina Nebula and its spectrum can be seen reflected off various star clouds in the nebula. The appearance of the Carina Nebula, and particularly of the Keyhole region, has changed significantly since it was described by John Herschel over 160 years ago. This is thought to be due to the reduction in ionising radiation from Eta Carinae since

763-411: A designation system, identifying the hierarchy within the system has the advantage that it makes identifying subsystems and computing their properties easier. However, it causes problems when new components are discovered at a level above or intermediate to the existing hierarchy. In this case, part of the hierarchy will shift inwards. Components which are found to be nonexistent, or are later reassigned to

872-883: A diagram multiplex if there is a node with more than two children , i.e. if the decomposition of some subsystem involves two or more orbits with comparable size. Because, as we have already seen for triple stars, this may be unstable, multiple stars are expected to be simplex , meaning that at each level there are exactly two children . Evans calls the number of levels in the diagram its hierarchy . Higher hierarchies are also possible. Most of these higher hierarchies either are stable or suffer from internal perturbations . Others consider complex multiple stars will in time theoretically disintegrate into less complex multiple stars, like more common observed triples or quadruples are possible. Trapezia are usually very young, unstable systems. These are thought to form in stellar nurseries, and quickly fragment into stable multiple stars, which in

981-540: A different subsystem, also cause problems. During the 24th General Assembly of the International Astronomical Union in 2000, the WMC scheme was endorsed and it was resolved by Commissions 5, 8, 26, 42, and 45 that it should be expanded into a usable uniform designation scheme. A sample of a catalog using the WMC scheme, covering half an hour of right ascension , was later prepared. The issue

1090-433: A fourth-magnitude star at approximately the correct position around 1595–1596, which was copied onto the celestial globes of Petrus Plancius and Jodocus Hondius and the 1603 Uranometria of Johann Bayer . Frederick de Houtman 's independent star catalogue from 1603 does not include Eta Carinae among the other 4th-magnitude stars in the region. The earliest firm record was made by Edmond Halley in 1677 when he recorded

1199-453: A hypergiant, V382 Carinae is a luminous star, with 212,000 times more luminosity than the Sun and over 480 times the Sun's size. Two bright Mira variable stars are in Carina: R Carinae and S Carinae ; both stars are red giants . R Carinae has a minimum magnitude of 10.0 and a maximum magnitude of 4.0. Its period is 309 days and it is 416 light-years from Earth. S Carinae is similar, with

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1308-416: A minimum magnitude of 10.0 and a maximum magnitude of 5.0. However, S Carinae has a shorter period—150 days, though it is much more distant at 1,300 light-years from Earth. Carina is home to several double stars and binary stars . Upsilon Carinae is a binary star with two blue-white-hued giant components, 1,600 light-years from Earth. The primary is of magnitude 3.0 and the secondary is of magnitude 6.0;

1417-922: A non-hierarchical system by this method, the same subsystem number will be used more than once; for example, a system with three visual components, A, B, and C, no two of which can be grouped into a subsystem, would have two subsystems numbered 1 denoting the two binaries AB and AC. In this case, if B and C were subsequently resolved into binaries, they would be given the subsystem numbers 12 and 13. The current nomenclature for double and multiple stars can cause confusion as binary stars discovered in different ways are given different designations (for example, discoverer designations for visual binary stars and variable star designations for eclipsing binary stars), and, worse, component letters may be assigned differently by different authors, so that, for example, one person's A can be another's C . Discussion starting in 1999 resulted in four proposed schemes to address this problem: For

1526-540: A number of absorption and emission features at various velocities relative to the central star. The 5.5-year orbital cycle produces strong spectral changes at periastron that are known as spectroscopic events. Certain wavelengths of radiation suffer eclipses, either due to actual occultation by one of the stars or due to passage within opaque portions of the complex stellar winds. Despite being ascribed to orbital rotation, these events vary significantly from cycle to cycle. These changes have become stronger since 2003 and it

1635-406: A number of more complicated arrangements. These arrangements can be organized by what Evans (1968) called mobile diagrams , which look similar to ornamental mobiles hung from the ceiling. Examples of hierarchical systems are given in the figure to the right ( Mobile diagrams ). Each level of the diagram illustrates the decomposition of the system into two or more systems with smaller size. Evans calls

1744-539: A similar way to a type IIn supernova . In the second half of the 20th century, much higher-resolution visual spectra became available. The spectrum continued to show complex and baffling features, with much of the energy from the central star being recycled into the infrared by surrounding dust, some reflection of light from the star from dense localised objects in the circumstellar material, but with obvious high-ionisation features indicative of very high temperatures. The line profiles are complex and variable, indicating

1853-456: A single set of Greek letters for the whole of Argo, and separate sets of Latin letter designations for each of the three sections. Therefore, Carina has the α, β and ε, Vela has γ and δ, Puppis has ζ, and so on. Carina contains Canopus , a white-hued supergiant that is the second-brightest star in the night sky at magnitude −0.72. Alpha Carinae, as Canopus is formally designated, is 313 light-years from Earth. Its traditional name comes from

1962-416: A single star. In these systems there is little interaction between the orbits and the stars' motion will continue to approximate stable Keplerian orbits around the system's center of mass, unlike the unstable trapezia systems or the even more complex dynamics of the large number of stars in star clusters and galaxies . In a physical triple star system, each star orbits the center of mass of

2071-588: A spectral type of B0Ieq. Direct spectral observations did not begin until after the Great Eruption, but light echoes from the eruption reflected from other parts of the Carina Nebula were detected using the U.S. National Optical Astronomy Observatory 's Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory . Analysis of the reflected spectra indicated the light was emitted when Eta Carinae had

2180-465: A system in which each subsystem in a mobile diagram is encoded by a sequence of digits. In the mobile diagram (d) above, for example, the widest system would be given the number 1, while the subsystem containing its primary component would be numbered 11 and the subsystem containing its secondary component would be numbered 12. Subsystems which would appear below this in the mobile diagram will be given numbers with three, four, or more digits. When describing

2289-487: Is circumpolar from locations on Earth south of latitude 30°S (for reference, the latitude of Johannesburg is 26°12′S), and is not visible north of about latitude 30°N , just south of Cairo , which is at a latitude of 30°2′N. The two main stars of the Eta Carinae system have an eccentric orbit with a period of 5.54 years. The primary is an extremely unusual star, similar to a luminous blue variable (LBV). It

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2398-427: Is a Cepheid variable noted for its brightness; it is the brightest Cepheid that is variable to the unaided eye. It is a yellow-hued supergiant star with a minimum magnitude of 4.2 and a maximum magnitude of 3.3; it has a period of 35.5 days. V382 Carinae is a yellow hypergiant , one of the rarest types of stars. It is a slow irregular variable , with a minimum magnitude of 4.05 and a maximum magnitude of 3.77. As

2507-407: Is a small number of stars that orbit each other, bound by gravitational attraction . A large group of stars bound by gravitation is generally called a star cluster or galaxy , although, broadly speaking, they are also star systems. Star systems are not to be confused with planetary systems , which include planets and similar bodies (such as comets ). A star system of two stars is known as

2616-566: Is also necessary to know the amount of interstellar extinction to the cluster and this can be difficult in regions such as the Carina Nebula. A distance of 7,330 light-years (2,250 parsecs) has been determined from the calibration of O-type star luminosities in Trumpler 16. After determining an abnormal reddening correction to the extinction, the distance to both Trumpler 14 and Trumpler 16 has been measured at 9,500 ± 1,000 light-years ( 2,900 ± 300 parsecs ). The known expansion rate of

2725-779: Is an optical multiple star Physical multiple stars are also commonly called multiple stars or multiple star systems . Most multiple star systems are triple stars . Systems with four or more components are less likely to occur. Multiple-star systems are called triple , ternary , or trinary if they contain 3 stars; quadruple or quaternary if they contain 4 stars; quintuple or quintenary with 5 stars; sextuple or sextenary with 6 stars; septuple or septenary with 7 stars; octuple or octenary with 8 stars. These systems are smaller than open star clusters , which have more complex dynamics and typically have from 100 to 1,000 stars. Most multiple star systems known are triple; for higher multiplicities,

2834-446: Is an example of a physical hierarchical triple system, which has an outer star orbiting an inner physical binary composed of two more red dwarf stars. Triple stars that are not all gravitationally bound might comprise a physical binary and an optical companion (such as Beta Cephei ) or, in rare cases, a purely optical triple star (such as Gamma Serpentis ). Hierarchical multiple star systems with more than three stars can produce

2943-515: Is another open cluster approximately of the same size, though it is more distant at 3,000 light-years from Earth. It is more loose and dim than NGC 2516, as its brightest stars are only 6th magnitude. The most prominent open cluster in Carina is IC 2602 , also called the "Southern Pleiades ". It contains Theta Carinae , along with several other stars visible to the unaided eye. In total, the cluster possesses approximately 60 stars. The Southern Pleiades

3052-502: Is assumed that the final line is from Fe very close to the green nebulium line now known to be from O. Photographic spectra from 1893 were described as similar to an F5 star, but with a few weak emission lines. Analysis to modern spectral standards suggests an early F  spectral type . By 1895 the spectrum again consisted mostly of strong emission lines, with the absorption lines present but largely obscured by emission. This spectral transition from F  supergiant to strong emission

3161-451: Is called a hierarchical system : the stars in the system can be divided into two smaller groups, each of which traverses a larger orbit around the system's center of mass . Each of these smaller groups must also be hierarchical, which means that they must be divided into smaller subgroups which themselves are hierarchical, and so on. Each level of the hierarchy can be treated as a two-body problem by considering close pairs as if they were

3270-491: Is called the Keyhole, or the Keyhole Nebula . This was described in 1847 by John Herschel , and likened to a keyhole by Emma Converse in 1873. The Keyhole is about seven light-years wide and is composed mostly of ionized hydrogen , with two major star-forming regions. 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 ,

3379-400: Is characteristic of novae , where ejected material initially radiates like a pseudo- photosphere and then the emission spectrum develops as it expands and thins. The emission line spectrum associated with dense stellar winds has persisted ever since the late 19th century. Individual lines show widely varying widths, profiles and Doppler shifts , often multiple velocity components within

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3488-444: Is considered a prime supernova candidate for the next several hundred thousand years because it has reached the end of its estimated million-year life span. NGC 2516 is an open cluster that is both quite large (approximately half a degree square) and bright, visible to the unaided eye. It is located 1,100 light-years from Earth and has approximately 80 stars, the brightest of which is a red giant star of magnitude 5.2. NGC 3114

3597-472: Is dominated by emission lines , usually broad although the higher excitation lines are overlaid by a narrow central component from dense ionised nebulosity, especially the Weigelt Blobs . Most lines show a P Cygni profile but with the absorption wing much weaker than the emission. The broad P Cygni lines are typical of strong stellar winds , with very weak absorption in this case because

3706-419: Is faster and stronger at high latitudes thought to be due to rapid rotation causing gravity brightening towards the poles. In contrast the spectrum shows a higher excitation temperature closer to the equatorial plane. By implication the outer envelope of Eta Carinae A is not strongly convective as that would prevent the gravity darkening . The current axis of rotation of the star does not appear to exactly match

3815-442: Is generally believed that long-term secular changes in the stellar winds or previously ejected material may be the culmination of a return to the state of the star before its Great Eruption. The ultraviolet spectrum of the Eta Carinae system shows many emission lines of ionised metals such as Fe II and Cr II , as well as Lyman α (Ly α ) and a continuum from a hot central source. The ionisation levels and continuum require

3924-530: Is heavily obscured by the Homunculus Nebula , which consists of material ejected from the primary during the Great Eruption. It is a member of the Trumpler 16 open cluster within the much larger Carina Nebula . Although unrelated to the star and nebula, the weak Eta Carinids meteor shower has a radiant very close to Eta Carinae. Eta Carinae was first recorded as a fourth-magnitude star in

4033-404: Is 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 3,000–4,000 kilometers per second to the larger cluster. Because this gravitational interaction has been ongoing for hundreds of millions of years,

4142-566: Is often mistaken for the Southern Cross, causing errors in astronavigation . Carina is known for its namesake nebula , NGC 3372, discovered by French astronomer Nicolas-Louis de Lacaille in 1751, which contains several nebulae . The Carina Nebula overall is an extended emission nebula approximately 8,000 light-years away and 300 light-years wide that includes vast star-forming regions . It has an overall magnitude of 8.0 and an apparent diameter of over 2 degrees. Its central region

4251-399: Is only known approximately, with a semi-major axis of 15–16 AU. The orbit is highly eccentric, e = 0.9. This means that the separation of the stars varies from around 1.6 AU, similar to the distance of Mars from the Sun, to 30 AU, similar to the distance of Neptune. Perhaps the most valuable use of an accurate orbit for a binary star system is to directly calculate the masses of

4360-407: Is particularly large for an open cluster, with a diameter of approximately one degree. Like IC 2602, NGC 3532 is visible to the unaided eye and is of comparable size. It possesses approximately 150 stars that are arranged in an unusual shape, approximating an ellipse with a dark central area. Several prominent orange giants are among the cluster's bright stars, of the 7th magnitude. Superimposed on

4469-438: Is still possible that it is not at the same distance as the cluster or that the parallax measurements have large systematic errors. The distances to star clusters can be estimated by using a Hertzsprung–Russell diagram or colour–colour diagram to calibrate the absolute magnitudes of the stars, for example fitting the main sequence or identifying features such as a horizontal branch , and hence their distance from Earth. It

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4578-408: Is the blue-white-hued Theta Carinae ; it is a magnitude 2.7 star 440 light-years from Earth. Theta Carinae is also the most prominent member of the cluster IC 2602 . Iota Carinae is a white-hued supergiant star of magnitude 2.2, 690 light-years from Earth. Eta Carinae is the most prominent variable star in Carina, with a mass of approximately 100 solar masses and 4 million times as bright as

4687-461: Is the brightest source in the night sky at mid-infrared wavelengths. Far infrared observations show a large mass of dust at 100–150 K, suggesting a total mass for the Homunculus of 20 solar masses ( M ☉ ) or more. This is much larger than previous estimates, and is all thought to have been ejected in a few years during the Great Eruption. Near-infrared observations can penetrate

4796-445: Is unclear whether Eta Carinae varied significantly in brightness over the next 50 years; there are occasional observations such as William Burchell 's at 4th magnitude in 1815, but it is uncertain whether these are just re-recordings of earlier observations. In 1827, Burchell specifically noted Eta Carinae's unusual brightness at 1st magnitude, and was the first to suspect that it varied in brightness. John Herschel , who

4905-634: The CNO cycle with some mixing to the surface. Perhaps the most striking feature is the rich Fe emission in both permitted and forbidden lines , with the forbidden lines arising from excitation of low density nebulosity around the star. The earliest analyses of the star's spectrum are descriptions of visual observations from 1869, of prominent emission lines "C, D, b, F and the principal green nitrogen line". Absorption lines are explicitly described as not being visible. The letters refer to Fraunhofer's spectral notation and correspond to H α , He, Fe, and H β . It

5014-612: The Cape of Good Hope indicated it peaked in brightness, surpassing Canopus, from 11 to 14 March 1843, then began to fade, then brightened to between the brightness of Alpha Centauri and Canopus between 24 and 28 March before fading once again. For much of 1844 the brightness was midway between Alpha Centauri and Beta Centauri , around magnitude +0.2, before brightening again at the end of the year. At its brightest in 1843 it likely reached an apparent magnitude of −0.8, then −1.0 in 1845. The peaks in 1827, 1838 and 1843 are likely to have occurred at

5123-680: The Hawaiian Ke Alii-o-kona-i-ka-lewa , "The Chief of the southern expanse" both attest to the star's prominence in the southern sky, while the Māori Atutahi , "First-light" or "Single-light", and the Tuamotu Te Tau-rari and Marere-te-tavahi , "He who stands alone". refer to the star's solitary nature. It was also called Kapae-poto ("Short horizon"), because it rarely sets from the vantage point of New Zealand, and Kauanga ("Solitary"), when it

5232-670: The Trapezium cluster in the Orion Nebula some two million years ago. The components of multiple stars can be specified by appending the suffixes A , B , C , etc., to the system's designation. Suffixes such as AB may be used to denote the pair consisting of A and B . The sequence of letters B , C , etc. may be assigned in order of separation from the component A . Components discovered close to an already known component may be assigned suffixes such as Aa , Ba , and so forth. A. A. Tokovinin's Multiple Star Catalogue uses

5341-495: The microwave band. It has been detected in the 21 cm H I line, but has been particularly closely studied in the millimetre and centimetre bands . Masing hydrogen recombination lines (from the combining of an electron and proton to form a hydrogen atom) have been detected in this range. The emission is concentrated in a small non-point source less than 4 arcseconds across and appears to be mainly free-free emission (thermal bremsstrahlung ) from ionised gas, consistent with

5450-589: The periastron passage—the point the two stars are closest together—of the binary orbit. From 1845 to 1856, the brightness decreased by around 0.1 magnitudes per year, but with possible rapid and large fluctuations. In their oral traditions, the Boorong clan of the Wergaia people of Lake Tyrrell , north-western Victoria, Australia, told of a reddish star they knew as Collowgullouric War / ˈ k ɒ l ə ɡ ʌ l ə r ɪ k ˈ w ɑːr / "Old Woman Crow",

5559-443: The 16th or 17th century. It became the second-brightest star in the sky in the mid-19th century, before fading below naked-eye visibility. During the second half of the 20th century, it slowly brightened to again become visible to the naked eye, and by 2014 was again a fourth-magnitude star. There is no reliable evidence of Eta Carinae being observed or recorded before the 17th century, although Dutch navigator Pieter Keyser described

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5668-655: The 4th Uhuru catalogue and 1044–59 in the HEAO-2 catalog. The earliest detection of X-rays in the Eta Carinae region was from the Terrier-Sandhawk rocket, followed by Ariel 5 , OSO 8 , and Uhuru sightings. More detailed observations were made with the Einstein Observatory , ROSAT X-ray telescope, Advanced Satellite for Cosmology and Astrophysics (ASCA), and Chandra X-ray Observatory . There are multiple sources at various wavelengths right across

5777-461: The Great Eruption. Prior to the Great Eruption the Eta Carinae system contributed up to 20% of the total ionising flux for the whole Carina Nebula, but that is now mostly blocked by the surrounding gas and dust. Eta Carinae lies within the scattered stars of the Trumpler 16 open cluster . All the other members are well below naked eye visibility, although WR 25 is another extremely massive luminous star. Trumpler 16 and its neighbour Trumpler 14 are

5886-554: The Homunculus Nebula provides an unusual geometric method for measuring its distance. Assuming that the two lobes of the nebula are symmetrical, the projection of the nebula onto the sky depends on its distance. Values of 2,300, 2,250 and 2,300 parsecs have been derived for the Homunculus, and Eta Carinae is clearly at the same distance. The Eta Carinae star system is currently one of the most massive stars that can be studied in great detail. Until recently Eta Carinae

5995-591: The Homunculus; and numerous condensations and arcs outside the main ring. All the high-energy emission associated with Eta Carinae varies during the orbital cycle. A spectroscopic minimum, or X-ray eclipse, occurred in July and August 2003, and similar events in 2009 and 2014 have been intensively observed. The highest-energy gamma rays above 100 MeV detected by AGILE show strong variability, while lower-energy gamma rays observed by Fermi show little variability. Radio emissions have been observed from Eta Carinae across

6104-512: The South (南方朱雀, Nán Fāng Zhū Què ). The rest of the stars were first classified by Xu Guanggi during the Ming dynasty , based on the knowledge acquired from western star charts, and placed among The Southern Asterisms (近南極星區, Jìnnánjíxīngōu ). Polynesian peoples had no name for the constellation in particular, though they had many names for Canopus. The Māori name Ariki ("High-born"), and

6213-490: The Sun. It was first discovered to be unusual in 1677, when its magnitude suddenly rose to 4, attracting the attention of Edmond Halley . Eta Carinae is inside NGC 3372, commonly called the Carina Nebula . It had a long outburst in 1827, when it brightened to magnitude 1, only fading to magnitude 1.5 in 1828. Its most prominent outburst made Eta Carinae the equal of Sirius ; it brightened to magnitude −1.5 in 1843. In

6322-525: The Trumpler 16 cluster are expected to be at a similar distance and are accessible to parallax. Gaia Data Release 2 has provided the parallax for many stars considered to be members of Trumpler 16, finding that the four hottest O-class stars in the region have very similar parallaxes with a mean value of 0.383 ± 0.017 milliarcseconds (mas), which translates to a distance of 2,600 ± 100 parsecs . This implies that Eta Carinae may be more distant than previously thought, and also more luminous, although it

6431-471: The alignment of the Homunculus. This may be due to interaction with Eta Carinae B which also modifies the observed stellar winds. The distance to Eta Carinae has been determined by several different methods, resulting in a widely accepted value of 2,330 parsecs (7,600 light-years), with a margin of error around 100 parsecs (330 light-years). The distance to Eta Carinae itself cannot be measured using parallax due to its surrounding nebulosity, but other stars in

6540-402: The apparent visual magnitude became brighter than magnitude 4.5. The brightness does not always vary consistently at different wavelengths, and does not always exactly follow the 5.5 year cycle. Radio, infrared and space-based observations have expanded coverage of Eta Carinae across all wavelengths and revealed ongoing changes in the spectral energy distribution . In July 2018, Eta Carinae

6649-430: The appearance of a 5,000  K G2-to-G5 supergiant, some 2,000 K cooler than expected from other supernova impostor events. Further light echo observations show that following the peak brightness of the Great Eruption the spectrum developed prominent P Cygni profiles and CN molecular bands, although this is likely from the material being ejected which may have been colliding with circumstellar material in

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6758-563: The central star is so heavily obscured. Electron scattering wings are present but relatively weak, indicating a clumpy wind. Hydrogen lines are present and strong, showing that Eta Carinae still retains much of its hydrogen envelope. He lines are much weaker than the hydrogen lines, and the absence of He lines provides an upper limit to the possible temperature of the primary star. N lines can be identified but are not strong, while carbon lines cannot be detected and oxygen lines are at best very weak, indicating core hydrogen burning via

6867-402: The central stars is absorbed by surrounding dust, then emitted as mid- and far infrared appropriate to the temperature of the dust. This allows almost the entire energy output of the system to be observed at wavelengths that are not strongly affected by interstellar extinction , leading to estimates of the luminosity that are more accurate than for other extremely luminous stars . Eta Carinae

6976-508: The central stars. An accidental resonance (where emission coincidentally has a suitable energy to pump the excited state) allows the Ly α emission to pump the Fe ions to certain pseudo-metastable states , creating a population inversion that allows the stimulated emission to take place. This effect is similar to the maser emission from dense pockets surrounding many cool supergiant stars, but

7085-468: The cluster is Chi Carinae , a yellow-white-hued star of magnitude 3.9, far more distant than NGC 3532. Carina also contains the naked-eye globular cluster NGC 2808 . Epsilon Carinae and Upsilon Carinae are double stars visible in small telescopes. One noted galaxy cluster is 1E 0657-56, the Bullet Cluster . At a distance of 4 billion light-years ( redshift 0.296), this galaxy cluster

7194-481: The colliding winds and partial "eclipses" of some spectroscopic features have constrained the possible orbits. The period of the orbit is accurately known at 5.539 years, although this has changed over time due to mass loss and accretion. Between the Great Eruption and the smaller 1890 eruption, the orbital period was apparently 5.52 years, while before the Great Eruption it may have been lower still, possibly between 4.8 and 5.4 years. The orbital separation

7303-401: The dark "V" dust lane of the nebula and appears distinctly orange and clearly non-stellar. High magnification will show the two orange lobes of a surrounding reflection nebula known as the Homunculus Nebula on either side of a bright central core. Variable star observers can compare its brightness with several 4th- and 5th-magnitude stars closely surrounding the nebula. Discovered in 1961,

7412-458: The decades following 1843 it appeared relatively placid, having a magnitude between 6.5 and 7.9. However, in 1998, it brightened again, though only to magnitude 5.0, a far less drastic outburst. Eta Carinae is a binary star , with a companion that has a period of 5.5 years; the two stars are surrounded by the Homunculus Nebula , which is composed of gas that was ejected in 1843. There are several less prominent variable stars in Carina. l Carinae

7521-458: The dust at high resolution to observe features that are completely obscured at visual wavelengths, although not the central stars themselves. The central region of the Homunculus contains a smaller Little Homunculus from the 1890 eruption, a butterfly of separate clumps and filaments from the two eruptions, and an elongated stellar wind region. Several X-ray and gamma ray sources have been detected around Eta Carinae, for example 4U 1037–60 in

7630-401: The end of March 1895 faded rapidly to about magnitude 7.5. Although there are only visual records of the 1890 eruption, it has been calculated that Eta Carinae was suffering 4.3 magnitudes of visual extinction due to the gas and dust ejected in the Great Eruption. An unobscured brightness would have been magnitude 1.5–1.9, significantly brighter than the historical magnitude. Despite this, it

7739-564: The existence of a source with a temperature at least 37,000 K. Certain Fe II UV lines are unusually strong. These originate in the Weigelt Blobs and are caused by a low-gain lasing effect. Ionised hydrogen between a blob and the central star generates intense Ly α emission which penetrates the blob. The blob contains atomic hydrogen with a small admixture of other elements, including iron photo-ionised by radiation from

7848-563: The first level of the hierarchy, lower-case letters (a, b, ...) for the second level, and numbers (1, 2, ...) for the third. Subsequent levels would use alternating lower-case letters and numbers, but no examples of this were found in the sample. Carina (constellation) Carina was once a part of Argo Navis , the great ship of the mythical Jason and the Argonauts who searched for the Golden Fleece . The constellation of Argo

7957-405: The high energy electromagnetic spectrum: hard X-rays and gamma rays within 1 light-month of the Eta Carinae; hard X-rays from a central region about 3 light-months wide; a distinct partial ring "horse-shoe" structure in low-energy X-rays 0.67 parsec (2.2 light-years) across corresponding to the main shockfront from the Great Eruption; diffuse X-ray emission across the whole area of

8066-439: The initial eruption, rather than shaped by or including previously ejected or interstellar material, although the scarcity of material near the equatorial plane allows some later stellar wind and ejected material to mix. Therefore, the mass of the lobes gives an accurate measure of the scale of the Great Eruption, with estimates ranging from 12–15  M ☉ up to as high as 45  M ☉ . The results show that

8175-402: The last of which probably consists of a star and a black hole . A multiple star system consists of two or more stars that appear from Earth to be close to one another in the sky. This may result from the stars actually being physically close and gravitationally bound to each other, in which case it is a physical multiple star, or this closeness may be merely apparent, in which case it

8284-418: The latter effect is much weaker at optical and UV wavelengths and Eta Carinae is the only clear instance detected of an ultraviolet astrophysical laser . A similar effect from pumping of metastable O I states by Ly β emission has also been confirmed as an astrophysical UV laser. Infrared observations of Eta Carinae have become increasingly important. The vast majority of the electromagnetic radiation from

8393-402: The material from the Great Eruption is strongly concentrated towards the poles; 75% of the mass and 90% of the kinetic energy were released above latitude 45°. A unique feature of the Homunculus is the ability to measure the spectrum of the central object at different latitudes by the reflected spectrum from different portions of the lobes. These clearly show a polar wind where the stellar wind

8502-406: The most massive visible star known. Eta Carinae is so massive that it has reached the theoretical upper limit for the mass of a star and is therefore unstable. It is known for its outbursts; in 1840 it briefly became one of the brightest stars in the sky due to a particularly massive outburst, which largely created the Homunculus Nebula. Because of this instability and history of outbursts, Eta Carinae

8611-421: The mythological Canopus , who was a navigator for Menelaus , king of Sparta. There are several other stars above magnitude 3 in Carina. Beta Carinae , traditionally called Miaplacidus, is a blue-white-hued star of magnitude 1.7, 111 light-years from Earth. Epsilon Carinae is an orange-hued giant star similarly bright to Miaplacidus at magnitude 1.9; it is 630 light-years from Earth. Another fairly bright star

8720-481: The number of known systems with a given multiplicity decreases exponentially with multiplicity. For example, in the 1999 revision of Tokovinin's catalog of physical multiple stars, 551 out of the 728 systems described are triple. However, because of suspected selection effects , the ability to interpret these statistics is very limited. Multiple-star systems can be divided into two main dynamical classes: or Most multiple-star systems are organized in what

8829-469: The orbital phase of the binary star system and that the photon index of the emission is similar to that derived through analysis of the γ-ray (gamma) spectrum. As a fourth-magnitude star, Eta Carinae is comfortably visible to the naked eye in all but the most light-polluted skies in inner-city areas according to the Bortle scale . Its brightness has varied over a wide range, from the second-brightest star in

8938-502: The process may eject components as galactic high-velocity stars . They are named after the multiple star system known as the Trapezium Cluster in the heart of the Orion Nebula . Such systems are not rare, and commonly appear close to or within bright nebulae . These stars have no standard hierarchical arrangements, but compete for stable orbits. This relationship is called interplay . Such stars eventually settle down to

9047-530: The purposes of using Latin letter designations three times over. Eta fell within the keel portion of the ship which was later to become the constellation Carina . It was not generally known as Eta Carinae until 1879, when the stars of Argo Navis were finally given the epithets of the daughter constellations in the Uranometria Argentina of Gould . Eta Carinae is too far south to be part of the mansion-based traditional Chinese astronomy , but it

9156-464: The rotation axis of the star, plus an equatorial "skirt", the whole being around 18 ″ long. Closer studies show many fine details: a Little Homunculus within the main nebula, probably formed by the 1890 eruption; a jet; fine streams and knots of material, especially noticeable in the skirt region; and three Weigelt Blobs—dense gas condensations very close to the star itself. The lobes of the Homunculus are considered to be formed almost entirely due to

9265-412: The same line. The spectral lines also show variation over time, most strongly with a 5.5-year period but also less dramatic changes over shorter and longer periods, as well as ongoing secular development of the entire spectrum. The spectrum of light reflected from the Weigelt Blobs , and assumed to originate mainly with the primary, is similar to the extreme P Cygni-type star HDE 316285 which has

9374-461: The same time there was a complete collapse of the X-ray emission presumed to originate in a colliding wind zone . The confirmation of a luminous binary companion greatly modified the understanding of the physical properties of the Eta Carinae system and its variability. A sudden doubling of brightness was observed in 1998–99 bringing it back to naked-eye visibility. During the 2014 spectroscopic event,

9483-467: The sky for a few days in the 19th century, to well below naked-eye visibility. Its location at around 60°S in the far southern celestial hemisphere means it cannot be seen by observers in Europe and much of North America. Located between Canopus and the Southern Cross, Eta Carinae is easily pinpointed as the brightest star within the large naked-eye Carina Nebula. In a telescope the "star" is framed within

9592-580: The smaller cluster is being destroyed and will eventually merge with the larger cluster. Carina contains the radiant of the Eta Carinids meteor shower, which peaks around January 21 each year. From China (especially northern China), the stars of Carina can barely be seen. The star Canopus (the south polar star in Chinese astronomy) was located by Chinese astronomers in the Vermilion Bird of

9701-421: The star itself may be revealed when dust from the great eruption finally clears. The binary nature of Eta Carinae is clearly established, although the components have not been directly observed and cannot even be clearly resolved spectroscopically due to scattering and re-excitation in the surrounding nebulosity. Periodic photometric and spectroscopic variations prompted the search for a companion, and modelling of

9810-587: The star simply as Sequens (i.e. "following" relative to another star) within a new constellation Robur Carolinum . His Catalogus Stellarum Australium was published in 1679. The star was also known by the Bayer designations Eta Roboris Caroli, Eta Argus or Eta Navis. In 1751 Nicolas-Louis de Lacaille gave the stars of Argo Navis and Robur Carolinum a single set of Greek letter Bayer designations within his constellation Argo, and designated three areas within Argo for

9919-428: The stars. This requires the dimensions and inclination of the orbit to be accurately known. The dimensions of Eta Carinae's orbit are only known approximately as the stars cannot be directly and separately observed. The inclination has been modelled at 130–145 degrees, but the orbit is still not known accurately enough to provide the masses of the two components. Stellar system A star system or stellar system

10028-405: The start of its so-called "Great Eruption". It became the second-brightest star in the sky between 11 and 14 March 1843 before fading well below naked-eye visibility after 1856. In a smaller eruption, it reached 6th magnitude in 1892 before fading again. It has brightened consistently since about 1940, becoming brighter than magnitude 4.5 by 2014. At declination −59° 41′ 04.26″, Eta Carinae

10137-400: The system. Usually, two of the stars form a close binary system , and the third orbits this pair at a distance much larger than that of the binary orbit. This arrangement is called hierarchical . The reason for this arrangement is that if the inner and outer orbits are comparable in size, the system may become dynamically unstable, leading to a star being ejected from the system. EZ Aquarii

10246-425: The time of discovery, which has been calculated as magnitude 3.3 on the modern scale. The handful of possible earlier sightings suggest that Eta Carinae was not significantly brighter than this for much of the 17th century. Further sporadic observations over the next 70 years show that Eta Carinae was probably around 3rd magnitude or fainter, until Lacaille reliably recorded it at 2nd magnitude in 1751. It

10355-752: The two components are distinguishable in a small amateur telescope. Two asterisms are prominent in Carina. The 'Diamond Cross' is composed of the stars Beta , Theta , Upsilon and Omega Carinae . The Diamond Cross is visible south of 20ºN latitude , and is larger but fainter than the Southern Cross in Crux . Flanking the Diamond Cross is the False cross , composed of four stars - two stars in Carina, Iota Carinae and Epsilon Carinae , and two stars in Vela, Kappa Velorum and Delta Velorum [ 3 ] - and

10464-501: The two dominant star clusters of the Carina OB1 association, an extended grouping of young luminous stars with a common motion through space. Eta Carinae is enclosed by, and lights up, the Homunculus Nebula , a small emission and reflection nebula composed mainly of gas ejected during the Great Eruption event in the mid-19th century, as well as dust that condensed from the debris. The nebula consists of two polar lobes aligned with

10573-409: The variations were first identified as having a 5.52-year period, later measured more accurately at 5.54 years, leading to the idea of a binary system. The binary theory was confirmed by observations of radio, optical and near-infrared radial velocity and line profile changes, referred to collectively as a spectroscopic event , at the predicted time of periastron passage in late 1997 and early 1998. At

10682-511: The weak Eta Carinids meteor shower has a radiant very close to Eta Carinae. Occurring from 14 to 28 January, the shower peaks around 21 January. Meteor showers are not associated with bodies outside the Solar System, making the proximity to Eta Carinae merely a coincidence. The strength and profile of the lines in the Eta Carinae spectrum are highly variable, but there are a number of consistent distinctive features. The spectrum

10791-599: The wife of War "Crow" ( Canopus ). In 2010, astronomers Duane Hamacher and David Frew from Macquarie University in Sydney showed that this was Eta Carinae during its Great Eruption in the 1840s. From 1857, the brightness decreased rapidly until it faded below naked-eye visibility by 1886. This has been calculated to be due to the condensation of dust in the ejected material surrounding the star, rather than to an intrinsic change in luminosity. A new brightening started in 1887, peaked at about magnitude 6.2 in 1892, then at

10900-587: Was brighter still on 2 January 1838, equivalent to Alpha Centauri , before fading slightly over the following three months. Herschel did not observe the star after this, but received correspondence from the Reverend W.S. Mackay in Calcutta, who wrote in 1843, "To my great surprise I observed this March last (1843), that the star Eta Argus had become a star of the first magnitude fully as bright as Canopus , and in colour and size very like Arcturus ." Observations at

11009-581: Was discussed again at the 25th General Assembly in 2003, and it was again resolved by commissions 5, 8, 26, 42, and 45, as well as the Working Group on Interferometry, that the WMC scheme should be expanded and further developed. The sample WMC is hierarchically organized; the hierarchy used is based on observed orbital periods or separations. Since it contains many visual double stars , which may be optical rather than physical, this hierarchy may be only apparent. It uses upper-case letters (A, B, ...) for

11118-468: Was in South Africa at the time, made a detailed series of accurate measurements in the 1830s showing that Eta Carinae consistently shone around magnitude 1.4 until November 1837. On the evening of 16 December 1837, Herschel was astonished to see that it had brightened to slightly outshine Rigel . This event marked the beginning of a roughly 18-year period known as the Great Eruption. Eta Carinae

11227-407: Was initially 150–250  M ☉ , of which it has already lost at least 30  M ☉ , and it is expected to explode as a supernova in the astronomically near future. This is the only star known to produce ultraviolet laser emission. The secondary star is hot and also highly luminous, probably of spectral class O , around 30–80 times as massive as the Sun. The system

11336-431: Was introduced in ancient Greece . However, due to the massive size of Argo Navis and the sheer number of stars that required separate designation, Nicolas-Louis de Lacaille divided Argo into three sections in 1763, including Carina (the hull or keel). In the 19th century, these three became established as separate constellations, and were formally included in the list of 88 modern IAU constellations in 1930. Lacaille kept

11445-595: Was mapped when the Southern Asterisms were created at the start of the 17th century. Together with s Carinae , λ Centauri and λ Muscae , Eta Carinae forms the asterism 海山 ( Sea and Mountain ). Eta Carinae has the names Tseen She (from the Chinese 天社 [Mandarin: tiānshè ] "Heaven's altar") and Foramen. It is also known as 海山二 ( Hǎi Shān èr , English: the Second Star of Sea and Mountain ). Halley gave an approximate apparent magnitude of 4 at

11554-464: Was reported to have the strongest colliding wind shock in the solar neighbourhood. Observations with the NuSTAR satellite gave much higher resolution data than the earlier Fermi Gamma-ray Space Telescope . Using direct focussing observations of the non-thermal source in the extremely hard X-ray band that is spatially coincident with the star, they showed that the source of non-thermal X-rays varies with

11663-420: Was similar to the first one, even almost matching its brightness, but not the amount of material expelled. Between 1900 and at least 1940, Eta Carinae appeared to have settled at a constant brightness of around magnitude 7.6, but in 1953 it was noted to have brightened again to magnitude 6.5. The brightening continued steadily, but with fairly regular variations of a few tenths of a magnitude. In 1996,

11772-530: Was the last star visible before sunrise. Carina is in the southern sky quite near the south celestial pole, making it never set (circumpolar) for most of the southern hemisphere. Due to precession of Earth's axis, by the year 4700 the south celestial pole will be in Carina. Three bright stars in Carina will come within 1 degree of the southern celestial pole and take turns as the southern pole star: Omega Carinae (mag 3.29) in 5600, Upsilon Carinae (mag 2.97) in 6700, and Iota Carinae (mag 2.21) in 7900. About 13,860 CE,

11881-474: Was thought to be the most massive single star, but the system's binary nature was proposed by the Brazilian astronomer Augusto Damineli in 1996 and confirmed in 2005. Both component stars are largely obscured by circumstellar material ejected from Eta Carinae A, and basic properties such as their temperatures and luminosities can only be inferred. Rapid changes to the stellar wind in the 21st century suggest that

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