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Sunday, May 20, 2018

Virgo

The constellation Virgo
[https://en.wikipedia.org/wiki/Virgo_(constellation)]

[https://www.iau.org/public/images/detail/vir/]

Virgo constellation lies in the southern sky. Its name means ‘virgin’ in Latin. It is one of the 12 zodiac constellations, first catalogued by the Greek astronomer Ptolemy in the 2nd century. It contains Spica, one of the brightest stars in the night sky. It also contains the autumn equinox point, which lies close to the star Beta Virginis. This is one of the two points in the sky (the other being in the constellation Pisces) where the celestial equator intersects with the ecliptic. Virgo is the second largest constellation in the sky. Virgo is the second largest constellation in the sky, occupying an area of 1294 square degrees. The only constellation larger in size is Hydra. It is located in the third quadrant of the southern hemisphere (SQ3) and can be seen at latitudes between +80° and -80°. The neighboring constellations are Boötes, Coma Berenices, Corvus, Crater, Hydra, Leo, Libra and Serpens Caput.
[http://www.constellation-guide.com/constellation-list/virgo-constellation/]

Virgo is the sixth astrological sign in the Zodiac and spans the 150-180th degree of the zodiac. Under the tropical zodiac, the Sun transits this area on average between August 23 and September 22, and under the sidereal zodiac, the sun transits the constellation of Virgo from September 17 to October 17. The symbol of the maiden is based on Astraea. In Greek mythology, she was the last immortal to abandon Earth at the end of the Silver Age, when the gods fled to Olympus- hence the sign’s association with Earth.
[https://en.wikipedia.org/wiki/Virgo_(astrology)]

Virgo depicted in the Atlas Coelestis of John Flamsteed (1729). In her right hand she carries a palm frond, while in her left hand she holds an ear of wheat marked by the bright star Spica.

Virgo was called by the Greeks Παρθένος (Parthenos), which is the name Ptolemy gave in the Almagest. She is usually identified as Dike, goddess of justice, who was daughter of Zeus and Themis; but she is also known as Astraeia, daughter of Astraeus (father of the stars) and Eos (goddess of the dawn). Virgo is depicted with wings, reminiscent of an angel, holding an ear of wheat in her left hand (the star Spica).

Dike features as the impartial observer in a moral tale depicting mankind’s declining standards. It was a favorites tale of Greek and Roman mythologists, and its themes still sound familiar today. Dike was supposed to have lived on Earth in the Golden Age of mankind, when Cronus ruled Olympus. It was a time of peace and happiness, a season of perennial spring when food grew without cultivation and humans never grew old. Men lived like the gods, not knowing work, sorrow, crime, or war. Dike moved among them, dispensing wisdom and justice.

Then, when Zeus overthrew his father Cronus on Olympus, the Silver Age began, inferior to the age that had just passed. In the Silver Age, Zeus shortened springtime and introduced the yearly cycle of seasons. Humans in this age became quarrelsome and ceased to honor the gods. Dike longed for the idyllic days gone by. She assembled the human race and spoke sternly to them for forsaking the ideals of their ancestors. ‘Worse is to come’, she warned them. Then she spread her wings and took refuge in the mountains, turning her back on mankind. Finally came the Ages of Bronze and Iron, when humans descended into violence, theft, and war. Unable to endure the sins of humanity any longer, Dike abandoned the Earth and flew up to heaven, where she sits to this day next to the constellation of Libra, which some see as the scales of justice.

In Chinese astronomy, northern Virgo was part of an area called Taiwei, a court or palace of the Emperor, where the Privy Council met in camera for administrative and legal discussions. This court, also known as the Supreme Palace Enclosure, included parts of Coma Berenices and Leo. Taiwei was not in itself a constellation but an area of sky in which events or characters with a common theme were depicted.
[http://www.ianridpath.com/startales/virgo.htm]

According to the Babylonian Mul.Apin, which dates from 1000-686 BCE, this constellation was known as ‘The Furrow,’ representing the goddess Shala’s ear of grain. One star in this constellation, Spica, retains this tradition as it is Latin for ‘ear of grain,’ one of the major products of the Mesopotamian furrow. The constellation was also known as ‘AB.SIN’ and ‘absinnu.’ For this reason the constellation became associated with fertility. According to Gavin White the figure of Virgo corresponds to two Babylonian constellations: the ‘Furrow’ in the eastern sector of Virgo and the ‘Frond of Erua’ in the western sector. The Frond of Erua was depicted as a goddess holding a palm-frond- a motif that still occasionally appears in much later depictions of Virgo.
[https://en.wikipedia.org/wiki/Virgo_(constellation)]

Constellation of Virgo (with Crater and Corvus)
[http://www.davidmalin.com/fujii/source/Vir.html]

The layout and major stars of the constellation Virgo [http://oneminuteastronomer.com/3642/constellation-virgo/]

Spica- Arcturus location

Alpha Virginis (Spica) is the brightest star in Virgo, and the 15th brightest star in the sky. It has an apparent magnitude of 1.04. The easiest way to find Spica in the sky is to follow the arc of the Big Dipper’s handle to Arcturus in the constellation Boötes and continue along the same line to Spica. The name Spica comes from the Latin ‘spīca virginis,’ which means ‘virgo’s ear of grain.’

Spica is classified as a blue giant of the spectral types B1 III-IV and B2 V, approximately 260 light years distant from the solar system. It is one of the nearest massive double stars to the solar system. The primary star is midway between the subgiant and giant stage of evolution (spectral class B1 III-IV) and about 12,100 times brighter than the Sun. This is one of the nearest stars sufficiently evolved and massive enough to explode as a Type II supernova. The secondary component is a main sequence star of the spectral type B2 V.

Beta Virginis (Zavijava) belongs to the spectral class F9 V, and is only 35.65 light years distant from the Sun. Even though it is designated beta, it is only the fifth brightest star in the constellation. The star’s traditional name, Zavijava, is derived from the Arabic ‘zāwiyat al-cawwa’, which means ‘the corner of the barking dog.’ It was also sometimes known as Alaraph.

Gamma Virginis (Porrima) is a binary star with a visual magnitude of 2.74. It is the second brightest star in the constellation, and is approximately 38.1 light years distant. Both stars in the Gamma Virginis system are of the spectral type F0V and have similar visual magnitudes, 3.65 and 3.56. The traditional name, Porrima, is the Latin name of two goddesses of prophecy, the Carmenae.

Delta Virginis (Auva) is a red giant belonging to the spectral class M3 III, approximately 198 light years distant. It has an apparent magnitude of 3.4 and can be seen without binoculars. It has a mass 1.4 times solar, but with a radius 48 times that of the Sun, it is about 468 times more luminous. The star’s traditional name, Auva or Minelauva, are derived from the Arabic ‘cawwa’, which means ‘barking (dog)’ or simply ‘the barker.’

Epsilon Virginis (Vindemiatrix) is the third brightest star in Virgo. It has a visual magnitude of 2.826, and is 109.6 light years distant. The star is a giant belonging to the spectral class G8 III. It is about 77 times more luminous than the Sun. The star’s name, derived from the Latin ‘vindēmiātrix,’ means ‘the grape gatherer’ or ‘the grape harvestress.’

Zeta Virginis (Heze) is a main sequence star of the spectral type A3 V. It has an apparent magnitude of 3.376, and is 74.1 light years distant. Zeta Virginis has twice the mass and radius of the Sun. It can be seen without binoculars. The origin of its traditional name, Heze, is unknown.

61 Virginis

61 Virginis is a yellow main sequence dwarf belonging to the spectral class G5V, approximately 27.9 light years distant. It is believed to be a disk star. It has a visual magnitude of 4.74. 61 Virginis is almost identical in composition to the Sun and slightly less massive. It rotates at the equator every 29 days. The star’s age is estimated at more than six billion years. It is the first well established yellow dwarf almost identical to the Sun with a potential Super Earth (extrasolar planet more massive than Earth, but considerably below the mass of the smaller gas giants- Uranus and Neptune- in the Solar System) in its orbit.
[http://www.constellation-guide.com/constellation-list/virgo-constellation/]

Artist’s impression of the planet Ross 128 b, with the star Ross 128 visible in the background

Ross 128 is a red dwarf in the constellation of Virgo, near β Virginis. The apparent magnitude of Ross 128 is 11.13, which is too faint to be seen with the unaided eye. The distance of this star from Earth is 10.89 light-years (3.34 parsecs), making it the twelfth closest stellar system to the Solar System. It was first cataloged in 1926 by American astronomer Frank Elmore Ross.

The planet Ross 128 b was discovered in July 2017 by the HARPS instrument at the La Silla Observatory in Chile, by measuring changes in radial velocity of the host star. Its existence was confirmed on 15 November 2017. It is the second-closest known Earth-size exoplanet, after Proxima b. As of 2017, it is the best candidate for a potentially habitable exoplanet, if it has an atmosphere and if it has the right chemical balance for life to thrive. It is calculated that Ross 128 b has a minimum mass of 1.35 times the Earth, and orbits 20 times closer to its star than Earth orbits the Sun, with a year (rotation period) lasting about 9.9 days. It intercepts only about 1.38 times more solar radiation than Earth, increasing the chance of retaining an atmosphere over a geological timescale.
[https://en.wikipedia.org/wiki/Ross_128]

Virgo constellation is the location of a large group of galaxies:

Virgo Cluster Galaxies

Well over a thousand galaxies are known members of the Virgo Cluster, the closest large cluster of galaxies to our own local group. In fact, the galaxy cluster is difficult to appreciate all at once because it covers such a large area on the sky. This careful wide-field mosaic of telescopic images clearly records the central region of the Virgo Cluster through faint foreground dust clouds lingering above the plane of our own Milky Way galaxy. The cluster’s dominant giant elliptical galaxy M87, is just below and to the left of the frame center. To the right of M87 is a string of galaxies known as Markarian’s Chain. A closer examination of the image will reveal many Virgo cluster member galaxies as small fuzzy patches. Sliding your cursor over the image will label the larger galaxies using NGC catalog designations. Galaxies are also shown with Messier catalog numbers, including M84, M86, and prominent colorful spirals M88, M90, and M91. On average, Virgo Cluster galaxies are measured to be about 48 million light-years away. The Virgo Cluster distance has been used to give an important determination of the Hubble Constant and the scale of the Universe.
[https://apod.nasa.gov/apod/ap150804.html]

Across the Virgo Galaxy Cluster lies a string of galaxies known as Markarian’s Chain:

Markarian’s Eyes

Across the heart of the Virgo Galaxy Cluster lies a string of galaxies known as Markarian’s Chain. Prominent in Markarian’s Chain are these two interacting galaxies, NGC 4438 (left) and NGC 4435- also known as The Eyes. About 50 million light-years away, the two galaxies appear to be about 100,000 light-years apart in this sharp close-up, but have likely approached to within an estimated 16,000 light-years of each other in their cosmic past. Gravitational tides from the close encounter have ripped away at their stars, gas, and dust. The more massive NGC 4438 managed to hold on to much of the material torn out in the collision, while material from the smaller NGC 4435 was more easily lost. The remarkably deep image of this crowded region of the universe also includes many more distant background galaxies.
[http://apod.nasa.gov/apod/ap070608.html]

Arp 286 is a triplet of interacting galaxies:

Arp 286: Trio in Virgo

A remarkable telescopic composition in yellow and blue, this scene features a trio of interacting galaxies almost 90 million light-years away, toward the constellation Virgo. On the right, two, spiky, foreground Milky Way stars echo the trio galaxy hues, a reminder that stars in our own galaxy are like those in the distant island universes. With sweeping spiral arms and obscuring dust lanes, NGC 5566 is enormous, about 150,000 light-years across. Just above it lies small, blue NGC 5569. Near center, the third galaxy, NGC 5560, is multicolored and apparently stretched and distorted by its interaction with NGC 5566. The galaxy trio is also included in Halton Arp’s 1966 Atlas of Peculiar Galaxies as Arp 286. Of course, such cosmic interactions are now appreciated as a common part of the evolution of galaxies.
[https://apod.nasa.gov/apod/ap160706.html]

The Sombrero Galaxy is a characteristic galaxy in the constellation Virgo, due to its shape:

Sombrero Galaxy

Why does the Sombrero Galaxy look like a hat? Reasons include the Sombrero’s unusually large and extended central bulge of stars, and dark prominent dust lanes that appear in a disk that we see nearly edge-on. Billions of old stars cause the diffuse glow of the extended central bulge. Close inspection of the bulge in the above photograph shows many points of light that are actually globular clusters.

The spectacular dust rings harbor many younger and brighter stars, and show intricate details astronomers don’t yet fully understand. The very center of the Sombrero is thought to house a large black hole. Fifty million-year-old light from the Sombrero Galaxy can be seen with a small telescope towards the constellation of Virgo.
[http://www.nasa.gov/multimedia/imagegallery/image_feature_283.html]

XJ1500+0154 is a super-massive black hole, located in the constellation Virgo:

XJ1500+0154: Black hole meal sets record for duration and size

A trio of X-ray observatories has captured a remarkable event in their data: a decade-long binge by a black hole almost two billion light years away. This discovery was made using data from NASA’s Chandra X-ray Observatory, Swift Observatory, and ESA’s XMM-Newton, as reported in our press release.

This artist’s illustration depicts what astronomers call a ‘tidal disruption event,’ or TDE. This is when an object, such as a star, wanders too close to a black hole and is destroyed by tidal forces generated from the black hole’s intense gravitational forces. During a TDE, some of the stellar debris is flung outward at high speeds, while the rest (shown as the red material in the illustration) becomes hotter as it falls toward the black hole, generating a distinct X-ray flare. A wind blowing away from this infalling material is shown in blue.

Among observed TDEs, this event involved either the most massive star to be completely ripped apart and devoured by a black hole or the first instance where a smaller star was completely ripped apart. The resulting X-ray source is known as XJ1500+154 and is located in a small galaxy about 1.8 billion light years from Earth. The optical image in the left inset shows this galaxy and a cross to mark the location of XJ1500+0154. This image reveals that XJ1500+0154 is found in the center of the galaxy, implying that the source likely originates from a supermassive black hole that resides there. The image on the right shows XJ1500+0154 in the Chandra image covering the same field.

The source was not detected in a Chandra observation on April 2, 2005, but was detected in an XMM-Newton observation on July 23, 2005, and reached peak brightness in a Chandra observation on June 5, 2008. These observations show that the source became at least 100 times brighter in X-rays. Since then, Chandra, Swift, and XMM-Newton have observed it multiple times.

The X-ray data also indicate that radiation from material surrounding this black hole has consistently surpassed the so-called Eddington limit, defined by a balance between the outward pressure of radiation from the hot gas and the inward pull of the gravity of the black hole.

This TDE may help answer the question as to how supermassive black holes in the early universe grow. If supermassive black holes can grow, from TDEs or other means, at rates above those corresponding to the Eddington limit, this could explain how supermassive black holes were able to reach masses about a billion times higher than the sun when the universe was only about a billion years old.
[http://chandra.harvard.edu/photo/2017/tidal/index.html]

Virgo is also home to the quasar 3C 273, which was the first quasar ever to be identified. With a magnitude of ~12.9 it is also the optically brightest quasar in the sky:
[https://en.wikipedia.org/wiki/3C_273]

NASA’s Hubble gets the best image of bright quasar 3C 273

This image from Hubble’s Wide Field and Planetary Camera 2 (WFPC2) is likely the best of ancient and brilliant quasar 3C 273, which resides in a giant elliptical galaxy in the constellation of Virgo (The Virgin). Its light has taken some 2.5 billion years to reach us. Despite this great distance, it is still one of the closest quasars to our home. It was the first quasar ever to be identified, and was discovered in the early 1960s by astronomer Allan Sandage.

The term quasar is an abbreviation of the phrase ‘quasi-stellar radio source,’ as they appear to be star-like on the sky. In fact, quasars are the intensely powerful centers of distant, active galaxies, powered by a huge disc of particles surrounding a supermassive black hole. As material from this disk falls inwards, some quasars, including 3C 273, have been observed to fire off super-fast jets into the surrounding space. In this picture, one of these jets appears as a cloudy streak, measuring some 200,000 light-years in length.

Quasars are capable of emitting hundreds or even thousands of times the entire energy output of our galaxy, making them some of the most luminous and energetic objects in the entire Universe. Of these very bright objects, 3C 273 is the brightest in our skies. If it was located 30 light-years from our own planet- roughly seven times the distance between Earth and Proxima Centauri, the nearest star to us after the sun- it would still appear as bright as the sun in the sky.
[https://www.nasa.gov/content/goddard/nasas-hubble-gets-the-best-image-of-bright-quasar-3c-273/#.V2RZOjUrRWA]




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