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V838 Monocerotis

V838 Monocerotis and its light echo as imaged by the Hubble Space Telescope on December 17, 2002. A light echo is a phenomenon observed in Astronomy. Analogous to an echo of Sound, a Light echo is produced when a sudden flash or burst The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into Credit: NASA/ESA
Observation data
Epoch 2000. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program The European Space Agency ( ESA) established in 1975 is an intergovernmental organisation dedicated to the exploration of space, currently with 17 member In Astronomy, an epoch is a moment in time used as a reference for the Orbital elements of a Celestial body. 0
Constellation
(pronunciation)		 Monoceros
Right ascension 07h 04m 04. In common usage a constellation is a group of celestial bodies that are connected together in some arrangement typically stars to form a visible figure or picture Each culture has its own Constellations usually based on Mythology. Right ascension (abbrev RA; symbol α) is the Astronomical term for one of the two Coordinates of a point on the Celestial sphere 85s
Declination −03° 50′ 50. In Astronomy, declination (abbrev dec or δ) is one of the two coordinates of the Equatorial coordinate system, the other being either 1″
Apparent magnitude (V) 15. The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value 74
Other designations
Nova Monocerotis 2002, GSC 04822-00039
Database references
SIMBAD data

V838 Monocerotis (V838 Mon) is a variable star in the constellation Monoceros about 20,000 light years (6 kpc)[1] from the Sun. A star catalogue, or star catalog, is an Astronomical catalogue that lists Stars In Astronomy, many stars are referred to simply by catalogue For the missile mounting see Mistral missile SIMBAD (the S et of I dentifications M easurements and B ibliography for For the astronomical object see Variable star. Variable Star is a 2006 novel written by Spider Robinson A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth In common usage a constellation is a group of celestial bodies that are connected together in some arrangement typically stars to form a visible figure or picture Monoceros (məˈnɒsərəs Μονόκερος) is a faint Constellation in the Winter night sky surrounded by Orion to the west Gemini A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by History The first direct measurements of an object at interstellar distances were undertaken by German Astronomer Friedrich Wilhelm Bessel in 1838 The Sun (Sol is the Star at the center of the Solar System. The star experienced a major outburst in early 2002. See also 2002 (disambiguation Year 2002 ( MMII) was a Common year starting on Tuesday of the Gregorian calendar. Originally believed to be a typical nova eruption, it was then realized to be something completely different. A nova (pl novae or novas) is a Cataclysmic nuclear explosion caused by the accretion of hydrogen onto the surface of a White The reason for the outburst is still uncertain, but several theories have been put forward, including an eruption related to stellar death processes and a merger of a binary star or planets.

Contents

Outburst

On January 10, 2002, a previously unknown star was seen to brighten up in Monoceros, the Unicorn. Events 49 BC - Julius Caesar crosses the Rubicon, signaling the start of civil war. See also 2002 (disambiguation Year 2002 ( MMII) was a Common year starting on Tuesday of the Gregorian calendar. A unicorn (from Latin unus 'one' and cornu 'horn' is a Mythological creature. [2] Being a new variable star, it was designated V838 Monocerotis, the 838th variable star of Monoceros. The initial light curve resembled that of a nova, an eruption that occurs when enough hydrogen gas has accumulated on the surface of a white dwarf from its close binary companion. In Astronomy, a light curve is a graph of light intensity of a Celestial object or region as a function of time A nova (pl novae or novas) is a Cataclysmic nuclear explosion caused by the accretion of hydrogen onto the surface of a White Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 A white dwarf, also called a degenerate dwarf, is a small Star composed mostly of Electron-degenerate matter. A binary star is a Star system consisting of two Stars orbiting around their Center of mass. Therefore it was also designated Nova Monocerotis 2002. V838 Monocerotis reached maximum visual magnitude of 6. The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value 75 on February 6, 2002 after which it started to dim rapidly, as expected. Events 46 BC - Julius Caesar defeats the combined army of Pompeian followers and Numidians under Metellus Scipio See also 2002 (disambiguation Year 2002 ( MMII) was a Common year starting on Tuesday of the Gregorian calendar. However, in early March the star started to brighten again, this time mostly in infrared wavelengths. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Yet another brightening in infrared occurred in early April after which the star returned to near its original brightness before the eruption, magnitude 15. 6. The lightcurve produced by the eruption is unlike anything previously seen. [3]

The star brightened to about a million times solar luminosity[4] ensuring that at the time of maximum V838 Monocerotis was one of the most luminous stars in the Milky Way galaxy. Luminosity has different meanings in several different fields of science The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply The brightening was caused by a rapid expansion of the outer layers of the star. The star was observed using the Palomar Testbed Interferometer which provided a radius of 1,570 ± 400 times solar (comparable to Jupiter's orbital radius), confirming the earlier indirect calculations. The Palomar Testbed Interferometer is a near-IR long-baseline stellar Interferometer located at Palomar Observatory in north San Diego County. The Sun (Sol is the Star at the center of the Solar System. [5] The expansion took only a couple of months meaning the expansion speed was phenomenal. The laws of thermodynamics dictate that expanding gas cools. In Physics, thermodynamics (from the Greek θερμη therme meaning " Heat " and δυναμις dynamis meaning " Therefore the star became extremely cool and deep red. In fact, some astronomers argue that the spectra of the star resembled that of L-type brown dwarfs. Historically Astronomy was more concerned with the classification and description of phenomena in the sky while Astrophysics attempted to explain these phenomena A spectrum (plural spectra or spectrums) is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. Brown dwarfs are sub- stellar objects with a mass below that necessary to maintain Hydrogen -burning Nuclear fusion reactions in their cores as do stars If that is the case, V838 Monocerotis would be the first known L-type supergiant. In Astronomy, stellar classification is a classification of Stars based initially on photospheric temperature and its associated Spectral characteristics Supergiants are among the most massive Stars In the Hertzsprung-Russell diagram they occupy the top region of the diagram [6]

Other possibly similar events

There are a handful of outbursts that resemble the one which occurred on V838 Monocerotis. In 1988 a red star was detected erupting in the Andromeda Galaxy. The Andromeda Galaxy (ænˈdrɒmədə also known as Messier 31, M31, or NGC 224; often referred to as the Great Andromeda The star, designated M31-RV, reached the absolute bolometric magnitude of −9. In Astronomy, absolute magnitude (also known as absolute visual magnitude) is the Apparent magnitude an object would have if it were at a standard 95 at maximum (corresponding a luminosity of 7. 5 million times solar) before dimming beyond detectability. A similar eruption occurred in 1994 in the Milky Way (V4332 Sagittarii). [7]

Progenitor star

Some details are emerging on the nature of the star that experienced the outburst. Based on the light echo the eruption generated, the distance of the star was first measured to be 1,900 to 2,900 light years. A light echo is a phenomenon observed in Astronomy. Analogous to an echo of Sound, a Light echo is produced when a sudden flash or burst Combined with the apparent magnitude measured from pre-eruption photographs, it was thought to be an underluminous F-type dwarf not much unlike our Sun which posed a considerable enigma. In Astronomy, stellar classification is a classification of Stars based initially on photospheric temperature and its associated Spectral characteristics [8]

More accurate measurements gave a much larger distance, 20,000 light years (6 kpc). It appears that the star is considerably more massive and luminous than the Sun. The mass of the star is probably from 5 to 10 times solar,[9] and luminosity from 550 to 5,000 times solar. The original radius may have been about 5 times solar and temperature 4,700–30,000 K. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic [1] Needless to say, these values are very approximate. Munari et al. (2005) suggest that the progenitor star is in fact a very massive supergiant with a mass of about 65 times solar. They also conclude that the system may be only about 4 million years old. [10]

The spectrum of V838 Monocerotis reveals a companion, a hot blue B-type main sequence star probably not much different from the erupted star. In Astronomy, stellar classification is a classification of Stars based initially on photospheric temperature and its associated Spectral characteristics The main sequence is the name for a continuous and distinctive band of stars that appear on a plot of stellar color versus brightness [9] It is also possible that the erupted star was slightly less massive than the companion and only just entering the main sequence. [8]

Based on the photometric parallax of the companion, Munari et al. Parallax is an apparent displacement or difference of orientation of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between get a greater distance, 36,000 light years (10 kpc). [10]

Light echo

Images showing the expansion of the light echo. Credit: NASA/ESA.
Images showing the expansion of the light echo. Credit: NASA/ESA. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program The European Space Agency ( ESA) established in 1975 is an intergovernmental organisation dedicated to the exploration of space, currently with 17 member

Rapidly brightening objects like novae and supernovae are known to produce a phenomenon known as light echo. A supernova (plural supernovae or supernovas) is a stellar Explosion. A light echo is a phenomenon observed in Astronomy. Analogous to an echo of Sound, a Light echo is produced when a sudden flash or burst The light that travels directly from the object arrives first. If there are clouds of interstellar matter between the star and the observer, some light is reflected from the clouds. Because of the longer path, the reflected light arrives later producing a vision of expanding rings of light around the erupted object. In addition, the rings appear to travel faster than the speed of light. [3]

In the case of V838 Monocerotis, the light echo produced was unprecedented and is well documented in images taken by the Hubble Space Telescope. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into It is not yet clear if the surrounding nebulosity is associated with the star itself. If that is the case, they may have been produced by the star in earlier eruptions which would rule out several models that are based on single catastrophic events. [3] However, there is strong evidence that the V838 Monocerotis system is very young and still embedded in the nebula from which it formed. A nebula (from Latin: "mist" pl nebulae or nebulæ, with ligature or nebulas) is an Interstellar cloud of [4]

Interestingly, the first eruption occurred at shorter wavelengths (i. e. was bluer) and can be seen in the light echo: the outer border of the echo is bluish in the Hubble images. [3]

Models

So far several rather different explanations for the eruption of V838 Monocerotis have been published.

Atypical nova outburst

The outburst of V838 Monocerotis may be a nova eruption after all, albeit a very unusual one. However, this is very unlikely considering that the system includes a B-type star, and stars of this type are young and massive. There has not been enough time for a possible white dwarf to cool and accrete enough material to cause the eruption. [7]

Thermal pulse of a dying star

V838 Monocerotis may be a post-asymptotic giant branch star, on the verge of its death. The asymptotic giant branch is the region of the Hertzsprung-Russell diagram populated by evolving low to medium-mass Stars This is a period of Stellar evolution The nebulosity illuminated by the light echo may actually be shells of dust surrounding the star, created by the star during previous similar outbursts. The brightening may have been a so-called helium flash, where the core of a dying low-mass star suddenly ignites carbon fusion disrupting, but not destroying, the star. A helium flash is the sudden beginning of Helium fusion in the core of intermediate mass Stars of less than about 2 Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus Such an event is known to have occurred in Sakurai's Object. Sakurai's Object ( V4334 Sgr) in the Constellation of Sagittarius, an object discovered to behave as a "slow Nova " by Yukio Sakurai However, several pieces of evidence supports the argument that the dust is interstellar rather than centered around V838 Monoceros. A dying star that has lost its outer envelopes would be appropriately hot, but the evidence points to a young star instead. [9]

Thermonuclear event within a massive supergiant

According to some evidence, V838 Monocerotis may be a very massive supergiant. Supergiants are among the most massive Stars In the Hertzsprung-Russell diagram they occupy the top region of the diagram If that is the case, the outburst may have been a so-called carbon flash, a thermonuclear event where a shell in the star containing helium suddenly ignites and starts to fuse carbon. In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Very massive stars survive multiple such events, however they experience heavy mass loss (about half of the original mass is lost while in the main sequence) before settling as extremely hot Wolf-Rayet stars. The main sequence is the name for a continuous and distinctive band of stars that appear on a plot of stellar color versus brightness This theory may also explain the apparent dust shells around the star. V838 Monoceros is located in the approximate direction of the antigalactic centre and off from the disk of the Milky Way. Stellar birth is less active in outer galactic regions, and it is not clear how such a massive star can form there. Star Formation is the process by which dense parts of Molecular clouds collapse into a ball of plasma to form a Star. However, there are very young clusters like Ruprecht 44 and the 4 million years old NGC 1893 at a distance of ca. 7 kpc and 6 kpc, respectively. [10]

Mergeburst

The outburst may have been the result of a so-called mergeburst, the merger of two main sequence stars (or an 8 M☉ main sequence star and a 0. 3 M☉ pre-main sequence star). This model is strengthened by the apparent youth of the system and the fact that multiple stellar systems may be unstable. The less massive component may have been in a very eccentric orbit or deflected towards the massive one. Computer simulations have shown the merger model to be plausible. A computer simulation, a computer model or a computational model is a Computer program, or network of computers that attempts to simulate an The simulations also show that the inflated envelope would have come almost entirely from the smaller component. In addition, the merger model explains the multiple peaks in the light curve observed during the outburst. [4]

Planetary capture event

Perhaps the most intriguing possibility is that V838 Monocerotis may have swallowed its giant planets. A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is If one of the planets entered into the atmosphere of the star, the stellar atmosphere would have begun slowing down the planet. As the planet penetrated deeper into the atmosphere, friction would become stronger and kinetic energy would be released into the star more rapidly. The star's envelope would then warm up enough to trigger deuterium fusion, which would lead to rapid expansion. Deuterium, also called heavy hydrogen, is a Stable isotope of Hydrogen with a Natural abundance in the Oceans of Earth The later peaks may then have occurred when two other planets entered into the expanded envelope. The authors of this model calculate that every year about 0. 4 planetary capture events occur in Sun-like stars, whereas for massive stars like V838 Monocerotis the rate is ~0. 5–2. 5 events per year. [1]


See also

References

  1. ^ a b c Retter, A. Stellar evolution is the process by which a Star undergoes a sequence of radical changes during its lifetime ; Zhang, B. ; Siess, L. ; Levinson, A. (May 22, 2006). "The planets capture model of V838 Monocerotis: conclusions for the penetration depth of the planet/s". 1. Retrieved on 2006-08-10. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 612 BC - Killing of Sinsharishkun, King of Assyrian Empire
  2. ^ Brown, N. J. (January 10, 2002). IAU Circular No. 7785. Retrieved on 2006-08-10. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 612 BC - Killing of Sinsharishkun, King of Assyrian Empire
  3. ^ a b c d Bond, Howard E. ; Henden, Arne; Levay, Zoltan G. ; Panagia, Nino; Sparks, William B. ; Starrfield, Sumner; Wagner, R. Mark; Corradi, R. L. M. ; Munari, U. (March 27, 2003). "An energetic stellar outburst accompanied by circumstellar light echoes". Nature 422 (6930): 405–408. doi:10.1038/nature01508. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  4. ^ a b c Soker, N. ; Tylenda, R. (June 15, 2006). "Modelling V838 Monocerotis as a Mergeburst Object". 1.
  5. ^ Lane, B. F. ; Retter, A. ; Thompson, R. R. ; Eisner, J. A. (April, 2005). "Interferometric Observations of V838 Monocerotis". The Astrophysical Journal 622 (2): L137–L140. The American Astronomical Society. doi:10.1086/429619. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  6. ^ Evans, A. ; Geballe, T. R. ; Rushton, M. T. ; Smalley, B. ; van Loon, J. Th. ; Eyres, S. P. S. ; Tyne, V. H. (August, 2003). "V838 Mon: an L supergiant?". Monthly Notice of the Royal Astronomical Society 343 (3): 1054. Royal Astronomical Society. doi:10.1046/j.1365-8711.2003.06755.x. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  7. ^ a b Boschi, F. ; Munari, U. (May, 2004). "M 31-RV evolution and its alleged multi-outburst pattern". Astronomy & Astrophysics 418: 869–875. doi:10.1051/0004-6361:20035716. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  M31-RV - 0402313
  8. ^ a b Tylenda, R. (June 4, 2005). "Evolution of V838 Monocerotis during and after the 2002 eruption". Astronomy and Astrophysics 436 (3): 1009–1020. doi:10.1051/0004-6361:20052800. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  9. ^ a b c Tylenda, R. ; Soker, N. ; Szczerba, R. (October, 2005). "On the progenitor of V838 Monocerotis". Astronomy and Astrophysics 441 (3): 1099-1109. doi:10.1051/0004-6361:20042485. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  10. ^ a b c Munari, U. ; Munari, U. ; Henden, A. ; Vallenari, A. ; Bond, H. E. ; Corradi, R. L. M. ; Crause, L. ; Desidera, S. ; Giro, E. ; Marrese, P. M. ; Ragaini, S. ; Siviero, A. ; Sordo, R. ; Starrfield, S. ; Tomov, T. ; Villanova, S. ; Zwitter, T. ; Wagner, R. M. (May 2, 2005). "On the distance, reddening and progenitor of V838 Mon". Astronomy and Astrophysics 434 (3): 1107–1116. doi:10.1051/0004-6361:20041751. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  

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