Ophiuchus is a large constellation located around the celestial equator. Its name is from the Greek ‘Ὀφιοῦχος,’ ‘serpent-bearer,’ and it is commonly represented as a man grasping the snake that is represented by the constellation Serpens. Ophiuchus was one of the 48 constellations listed by the 2nd-century astronomer Ptolemy. It was formerly referred to as Serpentarius and Anguitenens.
Ophiuchus is located between Aquila, Serpens and Hercules, northwest of the center of the Milky Way. The southern part lies between Scorpius to the west and Sagittarius to the east. In the northern hemisphere, it is best visible in summer. It is located opposite Orion in the sky. As Ophiuchus is depicted as a man grasping a serpent, the interposition of his body divides the snake constellation Serpens into two parts, Serpens Caput and Serpens Cauda, which are nonetheless counted as one constellation.
Ophiuchus straddles the equator but lies predominately to its south. However, Rasalhague, a fairly conspicuous star in its north, is circumpolar north of 78° north latitude. The constellation extends southward to −30° declination. Segments of the ecliptic that lie within Ophiuchus lie south of −20° declination. A determination of exactly where these stars are visible on Earth would depend on atmospheric refraction, the Novaya Zemlya effect, mountains and clouds.
In contrast to Orion, it is in the period November–January (summer in the Southern Hemisphere, winter in the Northern Hemisphere) when Ophiuchus is in the daytime sky and thus not visible at most latitudes. However for much of the Arctic Circle in the Northern Hemisphere’s winter months, the Sun is below the horizon even at midday. Stars (and thus parts of Ophiuchus, especially Rasalhague) are then visible at twilight for a few hours around local noon, low in the South. In the Northern Hemisphere’s spring and summer months, when Ophiuchus is normally visible in the night sky, the constellation is actually not visible, at those times and places in the Arctic when midnight sun obscures the stars. In countries close to the equator Ophiuchus appears overhead in June around midnight and in the October evening sky.
Ophiuchus is one of thirteen constellations that cross the ecliptic. It has therefore been called the ‘13th sign of the zodiac.’ However, this confuses sign with constellation. The signs of the zodiac are a twelve-fold division of the ecliptic, so that each sign spans 30° of celestial longitude, approximately the distance the Sun travels in a month, and (in the Western tradition) are aligned with the seasons so that the March equinox always falls on the boundary between Pisces and Aries.
Constellations, on the other hand, are unequal in size and are based on the positions of the stars. The constellations of the zodiac have only a loose association with the signs of the zodiac, and do not in general coincide with them. In Western astrology the constellation of Aquarius, for example, largely corresponds to the sign of Pisces. Similarly, the constellation of Ophiuchus occupies most (November 29 – December 18) of the sign of Sagittarius (November 23 – December 21). The differences are due to the fact that the time of year that the sun passes through a particular zodiac constellation’s position has slowly changed (because of the precession of the equinoxes) over the centuries from when the Greeks, Babylonians and the Dacians through Zamolxis originally developed the Zodiac.
18th century star map illustrating how the feet of Ophiuchus cross the ecliptic
[https://en.wikipedia.org/wiki/Ophiuchus_%28astrology%29]
There is no evidence of the constellation preceding the classical era, and in Babylonian astronomy, a ‘Sitting Gods’ constellation seems to have been located in the general area of Ophiuchus. However, Gavin White proposes that Ophiuchus may in fact be remotely descended from this Babylonian constellation, representing Nirah, a serpent-god who was sometimes depicted with his upper half human but with serpents for legs.
The earliest mention of the constellation is in Aratus, informed by the lost catalogue of Eudoxus of Cnidus (4th century BCE). To the ancient Greeks, the constellation represented the god Apollo struggling with a huge snake that guarded the Oracle of Delphi. Later myths identified Ophiuchus with Laocoön, the Trojan priest of Poseidon, who warned his fellow Trojans about the Trojan Horse and was later slain by a pair of sea serpents sent by the gods to punish him.
According to Roman era mythography, the figure represents the healer Asclepius, who learned the secrets of keeping death at bay after observing one serpent bringing another healing herbs. To prevent the entire human race from becoming immortal under Asclepius’ care, Jupiter killed him with a bolt of lightning, but later placed his image in the heavens to honor his good works.
In medieval Islamic astronomy (Azophi’s Uranometry, 10th century), the constellation was known as Al-Ḥawwaʾ ‘the snake-charmer.’
Aratus describes Ophiuchus as trampling on Scorpius with his feet. This is depicted in Renaissance to Early Modern star charts, beginning with Albrecht Dürer in 1515; in some depictions (such as that of Johannes Kepler, 1604), Scorpius also seems to threaten to sting Serpentarius in the foot. This is consistent with Azophi, who already included ψ Oph and ω Oph as the snake-charmer’s ‘left foot,’ and θ Oph and ο Oph as his ‘right foot,’ making Ophiuchus a zodiacal constellation at least as regards his feet. This arrangement has been taken as symbolic in later literature, and placed in relation to the words spoken by God to the serpent in the Garden of Eden.
[http://www.astralnewz.com/moonmanlunations/ophiuchus.html]
[http://astropixels.com/constellations/charts/Oph.html]
The brightest stars in Ophiuchus are:
Rasalhague (Alpha Ophiuchi) is the brightest star in Ophiuchus. It has an apparent visual magnitude of 2.07 and is approximately 48.6 light years distant from Earth. It is a binary star with an orbital period of 8.62 years. The primary component in the system is a white giant star with the stellar classification of A5 III. It has a mass 2.4 times that of the Sun. The companion is an orange main sequence dwarf with 85 percent of the Sun’s mass. It belongs to the stellar class K5-7 V. The brighter component is about 25 times more luminous than the Sun. It is a very fast spinner, with a projected rotational velocity of 240 km/s. As a result, it has an equatorial bulge that is about 20 percent larger than the polar radius, which gives Alpha Ophiuchi the shape of an oblate spheroid. The star’s traditional name, Rasalhague, is derived from the Arabic ‘raʾs al-ḥawwa,’ which means ‘the head of the serpent collector.’ The star marks Asclepius’ head.
Sabik (Eta Ophiuchi) is the second brightest star in the constellation. It has a combined visual magnitude of 2.43 and is approximately 88 light years distant from the Sun. It is a binary star that is not easy to resolve in smaller telescopes. The system is composed of two white main sequence dwarfs belonging to the spectral classes A1 V and A3 V. They have an orbital period of 87.58 years. The stars have apparent magnitudes of 3.05 and 3.27.
Zeta Ophiuchi is the third brightest star in Ophiuchus. It is an extremely large blue main sequence star with the stellar classification of O9.5 V. It has an apparent visual magnitude of 2.569 and is about 366 light years distant from the solar system. The star is classified as a Beta Cephei variable, a star that exhibits variations in brightness as a result of pulsation of its surface. Within the next few million years, the star will expand into a red supergiant and likely explode as a supernova, leaving behind a pulsar or neutron star. Zeta Ophiuchi has 8 times the Sun’s radius and more than 19 solar masses. It is a fast rotating star, spinning close to the velocity at which it could begin to break up. Its estimated rotational velocity may be 400 km/s. The star’s estimated age is only 3 million years:
Zeta Ophiuchi- runaway star plowing through space dust
The blue star near the center of this image is Zeta Ophiuchi. When seen in visible light it appears as a relatively dim red star surrounded by other dim stars and no dust. However, in this infrared image taken with NASA’s Wide-field Infrared Survey Explorer, or WISE, a completely different view emerges. Zeta Ophiuchi is actually a very massive, hot, bright blue star plowing its way through a large cloud of interstellar dust and gas.
Astronomers theorize that this stellar juggernaut was likely once part of a binary star system with an even more massive partner. It’s believed that when the partner exploded as a supernova, blasting away most of its mass, Zeta Ophiuchi was suddenly freed from its partner’s pull and shot away like a bullet moving 24 kilometers per second (54,000 miles per hour). Zeta Ophiuchi is about 20 times more massive and 65,000 times more luminous than the sun. If it weren’t surrounded by so much dust, it would be one of the brightest stars in the sky and appear blue to the eye. Like all stars with this kind of extreme mass and power, it subscribes to the ‘live fast, die young’ motto. It’s already about halfway through its very short 8-million-year lifespan. In comparison, the sun is roughly halfway through its 10-billion-year lifespan. While the sun will eventually become a quiet white dwarf, Zeta Ophiuchi, like its ex-partner, will ultimately die in a massive explosion called a supernova.
Perhaps the most interesting features in this image are related to the interstellar gas and dust that surrounds Zeta Ophiuchi. Off to the sides of the image and in the background are relatively calm clouds of dust, appearing green and wispy, slightly reminiscent of the northern lights. Near Zeta Ophiuchi, these clouds look quite different. The cloud in all directions around the star is brighter and redder, because the extreme amounts of ultraviolet radiation emitted by the star are heating the cloud, causing it to glow more brightly in the infrared than usual.
Even more striking, however, is the bright yellow curved feature directly above Zeta Ophiuchi. This is a magnificent example of a bow shock. In this image, the runaway star is flying from the lower right towards the upper left. As it does so, its very powerful stellar wind is pushing the gas and dust out of its way (the stellar wind extends far beyond the visible portion of the star, creating an invisible ‘bubble’ all around it). And directly in front of the star’s path the wind is compressing the gas together so much that it is glowing extremely brightly (in the infrared), creating a bow shock. It is akin to the effect you might see when a boat pushes a wave in front it as it moves through the water. This feature is completely hidden in visible light. Infrared images like this one from WISE shed an entirely new light on the region.
The colors used in this image represent specific wavelengths of infrared light. Blue and cyan (blue-green) represent light emitted at wavelengths of 3.4 and 4.6 microns, which is predominantly from stars. Green and red represent light from 12 and 22 microns, respectively, which is mostly emitted by dust.
[https://www.nasa.gov/mission_pages/WISE/multimedia/gallery/pia13455.html]
Yed Prior (Delta Ophiuchi) is a red giant with the stellar classification of M0.5 III. It is the fourth brightest star in the constellation. It has an apparent visual magnitude of 2.75 and is approximately 171 light years distant from the Sun. It forms an optical double with the star Epsilon Ophiuchi, or Yed Posterior. The word ‘yed’ comes from Arabic and means ‘the hand.’ The two stars mark the left hand of the Serpent Bearer, which holds the head of the serpent. Delta Ophiuchi has a mass 1.5 times that of the Sun and a radius about 59 times solar. It is a suspected variable star with possible variations in magnitude by 0.03.
Celbalrai (Beta Ophiuchi) is an orange giant star belonging to the spectral class K2 III. It is the fifth brightest star in the constellation. It has a visual magnitude that ranges from 2.75 to 2.77 and is 81.8 light years distant from Earth. The star’s traditional name, Celbalrai (and variants Cheleb and Kelb Alrai) comes from the Arabic ‘kalb al-rā‘ī,’ which means ‘the shepherd dog.’ Celbalrai has 113 percent of the Sun’s mass and a radius 12.42 times solar. The star is 63.4 times more luminous than the Sun. It has an unconfirmed planetary companion in its orbit.
Kappa Ophiuchi is another suspected variable star in Ophiuchus. It is an orange giant with the stellar classification of K2 III. It has a mean apparent magnitude of 3.20 and is 91.5 light years distant from the Sun. Kappa Ophiuchi has 119 percent of the Sun’s mass and 11 times the solar radius. It is 46 times more luminous than the Sun.
Yed Posterior (Epsilon Ophiuchi) is a yellow giant star belonging to the spectral class G9.5 IIIb. It has a visual magnitude of 3.220 and is 106.4 light years distant from the solar system. It is 1.85 times more massive than the Sun and has a radius 10.39 times solar. The star is 54 times more luminous than the Sun. Its estimated age is about a billion years.
[http://www.constellation-guide.com/constellation-list/ophiuchus-constellation/]
Theta Ophiuchi
[https://it.wikipedia.org/wiki/Theta_Ophiuchi]
Theta Ophiuchi is a multiple star system in the equatorial constellation of Ophiuchus. It lies on the ‘right foot’ of the serpent-bearer, and is only a little to the southwest of the Kepler’s Star, the nova of 1604. This star has an apparent visual magnitude of +3.26, making it readily visible to the naked eye. It is located at a distance of roughly 436 light-years (134 parsecs) from Earth.
Theta Ophiuchi appears to be a triple star system. The brightest component is a spectroscopic binary with an orbital period of 56.71 days and an eccentricity of 0.17. The tertiary component is 5.5 magnitude star with a stellar classification of B5. It is located at an angular separation of 0.15 arcseconds from the binary pair. This system is a proper motion member of the Upper Scorpius sub-group in the Scorpius-Centaurus OB association, the nearest such co-moving association of massive stars to the Sun.
The primary component of this system is a variable star of the Beta Cephei type with a short period of just 3h 22m.[ It has nearly nine times the mass of the Sun and more than six times the Sun’s radius. Although only 21 million years old, it has begun to evolve away from the main sequence and has become a subgiant star with a stellar classification of B2 IV. This massive star is radiating around 5,000 times the luminosity of the Sun from its outer atmosphere at an effective temperature of about 22,260 K, giving it the blue-white hue of a B-type star.
[https://en.wikipedia.org/wiki/Theta_Ophiuchi]
The location of Barnard’s Star, ca. 2006 (south is up)
Barnard’s Star is a very-low-mass red dwarf about six light-years away from Earth in the constellation of Ophiuchus. It is the fourth-closest known individual star to the Sun (after the three components of the Alpha Centauri system) and the closest star in the Northern Hemisphere. Despite its proximity, at a dim apparent magnitude of about nine, it is not visible with the unaided eye; it is much brighter in the infrared than it is in visible light.
The star is named after the American astronomer E. E. Barnard. He was not the first to observe the star, but in 1916 he measured its proper motion (which is a function of its close proximity to earth, and not of its actual space velocity) as 10.3 arcseconds per year, which remains the largest proper motion of any star relative to the Sun.
Barnard’s Star is among the most studied red dwarfs because of its proximity and favorable location for observation near the celestial equator. Although Barnard’s Star is an ancient star, it still experiences star flare events, one being observed in 1998. Although the presence of small terrestrial planets around Barnard’s Star remains a possibility, earlier claims of large gas giants were refuted in the mid-1970s.
[https://en.wikipedia.org/wiki/Barnard%27s_Star]
[https://commons.wikimedia.org/wiki/File:70_Ophiuchi_sky.jpg]
70 Ophiuchi is a binary star system located 16.6 light years away from the Earth. It is in the constellation Ophiuchus. At magnitude 4 it appears as a dim star visible to the unaided eye away from city lights.
The primary star is a yellow-orange main sequence dwarf BY Draconis variable of spectral type K0, and the secondary star is an orange main sequence dwarf of spectral type K4. The two stars orbit each other at an average distance of 23.2 AUs.
This star system was first cataloged by William Herschel in the late 18th century in his study of binary stars. Herschel proved that this system is a gravitationally bound binary system where the two stars orbit around a common center of mass. This was an important contribution to the proof that Newton’s law of universal gravitation applied to objects beyond the solar system.
The negative results of past studies does not completely rule out the possibility of planets. In 2006 a McDonald Observatory team has set limits to the presence of one or more planets around 70 Ophiuchi with masses between 0.46 and 12.8 Jupiter masses and average separations spanning between 0.05 and 5.2 AU.
[https://en.wikipedia.org/wiki/70_Ophiuchi]
Nu Ophiuchi and its brown dwarf companion Nu Ophiuchi b
Nu Ophiuchi is a star in the equatorial constellation of Ophiuchus. The apparent visual magnitude is +3.3, making it one of the brighter members of this constellation. It is sometimes called by the name Sinistra, meaning left side in Latin. Based upon parallax measurements made during the Hipparcos mission, this star is located about 151 light-years (46 parsecs) from Earth.
Nu Ophiuchi has about three times the mass of the Sun and is roughly 330 million years old. The spectrum of the star matches a stellar classification of K0 IIIa, indicating it is a giant star that has exhausted the supply of hydrogen at its core and evolved away from the main sequence of stars like the Sun. Unusually, it displays an anomalously low abundance of cyanogen for a star of its type. The star’s outer envelope has expanded to around 14 times the Sun’s radius and now radiates 123 times as much luminosity of the Sun. This energy is being emitted from its outer envelope at an effective temperature of 4,928 K, giving it the cool, orange hue of a K-type star.
This is not a binary star system in the sense of having a gravitationally-bound stellar companion. However, in early 2004, a brown dwarf companion Nu Ophiuchi b was discovered. This sub-stellar companion has at least 21.9 times the mass of Jupiter and takes 536 days (1.47 years) to complete an orbit. A second brown dwarf companion was discovered in 2010, orbiting further from the star with a period of 3,169 days (8.68 years). These have been confirmed in 2012.
[https://en.wikipedia.org/wiki/Nu_Ophiuchi]
Rho Ophiuchi is a multiple star system in the constellation Ophiuchus. It consists of at least two blue subgiants, ρ Oph A and ρ Oph B, both of which are of class B. ρ Oph AB is a visual binary, and the sky-projected distance between ρ Oph A and ρ Oph B is 3.1" (or 344 AU at the 111 pc distance of ρ Oph AB).
Two to three other blue subgiants, ρ Oph C and ρ Oph DE, are found to be related to the star system, with sky-projected distances to ρ Oph AB of ~ 17,000 and ~ 19,000 AU, respectively. ρ Oph C and ρ Oph D are also of class B.
The apparent brightness of the star system has been dimmed by about 2 magnitudes, as a result of interstellar extinction, due to its location within the Ophiuchus cloud. The star system, ρ Oph AB, is located about 360 light years away:
[https://en.wikipedia.org/wiki/Rho_Ophiuchi]
Rho Ophiuchi wide field
The clouds surrounding the star system Rho Ophiuchi compose one of the closest star forming regions. Rho Ophiuchi itself is a binary star system visible in the light-colored region on the image right. The star system, located only 400 light years away, is distinguished by its colorful surroundings, which include a red emission nebula and numerous light and dark brown dust lanes. Near the upper right of the Rho Ophiuchi molecular cloud system is the yellow star Antares, while a distant but coincidently-superposed globular cluster of stars, M4, is visible between Antares and the red emission nebula. Near the image bottom lies IC 4592, the Blue Horsehead nebula. The blue glow that surrounds the Blue Horsehead’s eye- and other stars around the image- is a reflection nebula composed of fine dust. On the above image left is a geometrically angled reflection nebula cataloged as Sharpless 1. Here, the bright star near the dust vortex creates the light of surrounding reflection nebula. Although most of these features are visible through a small telescope pointed toward the constellations of Ophiuchus, Scorpius, and Sagittarius, the only way to see the intricate details of the dust swirls, as featured above, is to use a long exposure camera.
[https://apod.nasa.gov/apod/ap140727.html]
Explosions from White Dwarf Star RS Oph
Spectacular explosions keep occurring in the binary star system named RS Ophiuchi. Every 20 years or so, the red giant star dumps enough hydrogen gas onto its companion white dwarf star to set off a brilliant thermonuclear explosion on the white dwarf's surface. At about 2,000 light years distant, the resulting nova explosions cause the RS Oph system to brighten up by a huge factor and become visible to the unaided eye. The red giant star is depicted on the right of the above drawing, while the white dwarf is at the center of the bright accretion disk on the left. As the stars orbit each other, a stream of gas moves from the giant star to the white dwarf. Astronomers speculate that at some time in the next 100,000 years, enough matter will have accumulated on the white dwarf to push it over the Chandrasekhar Limit, causing a much more powerful and final explosion known as a supernova.
[https://apod.nasa.gov/apod/ap060726.html]
[http://www.gdnordley.com/_files/TCAFM_Science.html]
36 Ophiuchi is a triple star system 19.5 light years from Earth, in the constellation Ophiuchus. The primary and secondary stars are nearly identical orange main sequence dwarves of spectral type K2/K1; the tertiary star is an orange main sequence dwarf of spectral type K5.
Star C is separated from the A-B pair by 700 arc seconds, compared to a minimum of 4.6 arcsec for A-B, so its effect on the movements of the A-B pair is small. A and B have active chromospheres.
The McDonald Observatory team has set limits to the presence of one or more planets around 36 Ophiuchi A with masses between 0.13 and 5.4 Jupiter masses and average separations spanning between 0.05 and 5.2 astronomical units, although beyond 1.5 AU orbits are inherently unstable around either 36 Ophiuchi A or 36 Ophiuchi B.
[https://en.wikipedia.org/wiki/36_Ophiuchi]
The sky area in the constellation of Ophiuchus near the red dwarf star Wolf 1061
[http://www.drewexmachina.com/2015/12/19/habitable-planet-reality-check-wolf-1061/]
Wolf 1061 (also known as HIP 80824 and V2306 Ophiuchi) is an M class red dwarf star located about 13.8 light years away in the constellation Ophiuchus. It is the 36th closest known star system to the Sun and has a relatively high proper motion of 1.2 seconds of arc per year. Like many red dwarfs, it most likely has a long rotation period of more than 100 days, although it is difficult to measure accurately. Wolf 1061 is very stable and most likely does not have any significant activity such as sunspots or flares. It also does not have any unusual spectroscopic features. The star was first cataloged in 1919 by German astronomer Max Wolf when he published a list of dim stars that had high proper motions. Wolf 1061’s name originates from this list. The star has a stellar rotation period of 89.3±1.8 days. A seven years study found no evidence of photometric transits and confirms the radial velocity signals are not due to stellar activity. The Habitable Zone estimate for the system, lies between 0.11-0.21 AU and 0.09–0.23 AU.
In December 2015, a team of astronomers from the University of New South Wales announced the discovery of three planets orbiting Wolf 1061. The planets were detected by analyzing 10 years of observations of the Wolf 1061 system by the HARPS spectrograph at La Silla Observatory in Chile. The team used archive radial velocity measurements of the star’s spectrum in the HARPS data and, along with 8 years of photometry from the All Sky Automated Survey, discovered two definite planets with orbital periods of around 4.9 and 17.9 days and a very likely third with a period of 67.3 days.
All three planets have masses low enough that they are likely to be rocky planets similar to the inner planets of the Solar System although their actual sizes and densities are currently unknown. However, this information could be determined if the planets happen to transit in front of Wolf 1061 when viewed from Earth. Because all three planets orbit close to the star and have short orbital periods, there is a chance that this will occur.
One of the planets, Wolf 1061 c, is a super-Earth located near the inner edge of the star’s habitable zone, which extends from approximately 0.073 to 0.190 AU. It is one of the closest known potentially habitable planet to Earth after Proxima b. The next planet out, Wolf 1061 d, could be marginally habitable depending on its atmosphere’s composition as it orbits just beyond the habitable zone.
[https://en.wikipedia.org/wiki/Wolf_1061]
Gliese 1214 (GJ 1214) is a dim M4.5 red dwarf in the constellation Ophiuchus with an apparent magnitude of 14.7. It is located at a distance of approximately 47 light years from Earth. It is about one-fifth as large as the Sun with a surface temperature estimated to be 3000 K (2730 °C; 4940 °F). Its luminosity is only 0.003% that of the Sun.
In mid-December 2009, a team of astronomers announced the discovery of a companion extrasolar planet, Gliese 1214 b, potentially composed largely of water and having the mass and diameter of a super-Earth.
[https://en.wikipedia.org/wiki/Gliese_1214]
RS Ophiuchi is a recurrent nova system approximately 5,000 light-years away in the constellation Ophiuchus. In its quiet phase it has an apparent magnitude of about 12.5. It has been observed to erupt in 1898, 1933, 1958, 1967, 1985, and 2006 and reached about magnitude 5 on average. A further two eruptions, in 1907 and 1945, have been inferred from archival data. The recurrent nova is produced by a white dwarf star and a red giant in a binary system. About every 20 years, enough material from the red giant builds up on the surface of the white dwarf to produce a thermonuclear explosion. The white dwarf orbits close to the red giant, with an accretion disc concentrating the overflowing atmosphere of the red giant onto the white dwarf:
[https://en.wikipedia.org/wiki/RS_Ophiuchi]
Near θ Ophiuchi is located Kepler’s Supernova. The supernova was first observed on 9 October 1604. Johannes Kepler saw it first on 16 October and studied it so extensively that the supernova subsequently took his name:
Kepler’s Supernova remnant: Was Kepler’s Supernova unusually powerful?
In 1604, a new star appeared in the night sky that was much brighter than Jupiter and dimmed over several weeks. This event was witnessed by sky watchers including the famous astronomer Johannes Kepler. Centuries later, the debris from this exploded star is known as the Kepler supernova remnant.
Astronomers have long studied the Kepler supernova remnant and tried to determine exactly what happened when the star exploded to create it. New analysis of a long observation from NASA’s Chandra X-ray Observatory is providing more clues. This analysis suggests that the supernova explosion was not only more powerful, but might have also occurred at a greater distance, than previously thought.
This image shows the Chandra data derived from more than 8 days worth of observing time. The X-rays are shown in five colors from lower to higher energies: red, yellow, green, blue, and purple. These various X-ray slices were then combined with an optical image from the Digitized Sky Survey (light yellow and blue), showing stars in the field.
Previous analysis of this Chandra image has determined that the stellar explosion that created Kepler was what astronomers call a ‘Type Ia’ supernova. This class of supernovas occurs when a white dwarf gains mass, either by pulling gas off a companion star or merging with another white dwarf, until it becomes unstable and is destroyed by a thermonuclear explosion.
Unlike other well-known Type Ia supernovas and their remnants, Kepler’s debris field is being strongly shaped by what it is running into. More specifically, most Type Ia supernova remnants are very symmetrical, but the Kepler remnant is asymmetrical with a bright arc of X-ray emission in its northern region. This indicates the expanding ball of debris from the supernova explosion is plowing into the gas and dust around the now-dead star.
The bright X-ray arc can be explained in two ways. In one model, the pre-supernova star and its companion were moving through the interstellar gas and losing mass at a significant rate via a wind, creating a bow shock wave similar to that of a boat moving through water. Another possibility is that the X-ray arc is caused by debris from the supernova expanding into an interstellar cloud of gradually increasing density.
In either model, the X-ray spectrum - that is, the amount of X-rays produced at different energies- reveals the presence of a large amount of iron, and indicates an explosion more energetic than the average Type Ia supernova. Additionally, to explain the observed X-ray spectrum in this model, a small cavity must have been cleared out around the star before it exploded. Such a cavity, which would have a diameter less than a tenth that of the remnant’s current size, might have been produced by a fast, dense outflow from the surface of the white dwarf before it exploded, as predicted by some models of Type Ia supernovas.
The wind and bow shock model described above requires that the Kepler supernova remnant is located at a distance of more than 23,000 light years. In the latter alternative, the gas into which the remnant is expanding has higher density than average, and the distance of the remnant from the earth is between about 16,000 and 20,000 light years. Both alternatives give greater distances than the commonly used value of 13,000 light years.
Evidence for an unusually powerful Type Ia supernova has previously been observed in another remnant with Chandra and an optical telescope. These results were independently verified by subsequent observations of light from the original supernova explosion that bounced off gas clouds, a phenomenon called light echoes. This other remnant is located in the Large Magellanic Cloud, a small galaxy about 160,000 light years from Earth, making it much farther away than Kepler and therefore more difficult to study.
[http://chandra.harvard.edu/photo/2012/kepler/]
Messier 10 with amateur telescope
Ophiuchus contains several star clusters, such as IC 4665, NGC 6633, M9, M10, M12, M14, M19, M62, and M107, as well as the nebula IC 4603-4604.
Messier 10 or M10 (also designated NGC 6254) is a globular cluster of stars in Ophiuchus. The object was discovered by the French astronomer Charles Messier on May 29, 1764, who cataloged it as number 10 in his catalogue and described it as a “nebula without stars.” In 1774, German astronomer Johann Elert Bode likewise called it a “nebulous patch without stars; very pale.” Using larger instrumentation, German-born astronomer William Herschel was able to resolve the cluster into its individual members. He described it as a “beautiful cluster of extremely compressed stars.” The first to estimate the distance to the cluster was Harlow Shapley, although his derivation of 33,000 light years was much further than the modern value.
The tidal radius of M10 is 19.3 arcminutes, which is about two-thirds of the apparent diameter of the Moon. Viewed through medium-sized telescopes it appears about half that size (8–9 arcminutes), as its bright core is only 35 light-years across. It has a core radius of 48 arcseconds and a half-mass radius of 147 arcseconds (2.5 arcminutes). M10 has a spatial diameter of 83 light-years and is estimated to be 14,300 light-years away from Earth.
In terms of the abundance of elements other than hydrogen and helium, what astronomers term the metallicity, Messier 10 is moderately metal-poor. The abundance of iron is only 3.5% of the abundance found at the surface of the Sun. The cluster shows evidence of being enriched by the elements generated through the s-process in massive stars and Type II supernovae. It shows little evidence of enrichment by Type 1a supernovae.
Because binary stars are, on average, more massive than normal stars, the binaries tend to migrate toward the center of the cluster. The fraction of binary stars in the core region is about 14%. This proportion decreases with increasing radius to about 1.5% in the outlying regions of the cluster. Correspondingly, the core region contains a concentration of interaction-formed blue straggler stars, most of which formed 2–5 billion years ago. The density of stars in the core region is about 3.8 solar masses per cubic parsec. Four variable stars have been discovered in this cluster.
The cluster is currently located about 5 kiloparsecs (16 kly) from the Galactic Center. It completes an orbit around the Milky Way galaxy about every 140 million years, during which it crosses the plane of the galactic disk every 53 million years. Its rosette orbit has an eccentricity of 0.21.
[https://en.wikipedia.org/wiki/Messier_10]
Little Ghost Nebula is a planetary nebula in the constellation Ophiuchus. It was discovered by William Herschel. Round and planet-shaped, the nebula is also relatively faint. Planetary nebulae are not related to planets at all, but instead are created at the end of a sun-like star’s life as its outer layers expand into space while the star’s core shrinks to become a white dwarf. The transformed white dwarf star, seen near the center, radiates strongly at ultraviolet wavelengths and powers the expanding nebula’s glow. The nebula’s main ring structure is about a light-year across and the glow from ionized oxygen, hydrogen, and nitrogen atoms are colored blue, green, and red respectively:
[https://en.wikipedia.org/wiki/Little_Ghost_Nebula]
NGC 6369, a cosmic ghost
Known to amateur astronomers as the ‘Little Ghost Nebula,’ because it appears as a small, ghostly cloud surrounding a faint dying star, NGC 6369 lies in the direction of the constellation Ophiuchus. The NASA/ESA Hubble Space Telescope took this image of the planetary nebula NGC 6369, at a distance estimated to be between about 2000 and 5000 light-years from Earth.
When a star with a mass similar to that of our own Sun nears the end of its lifetime, it expands in size to become a ‘red giant.’ The red-giant stage ends when the star expels its outer layers into space, producing a faintly glowing nebula. Astronomers call such an object a planetary nebula, because its round shape resembles that of a planet when viewed with a small telescope.
The Hubble photograph of NGC 6369, captured with the Wide Field Planetary Camera 2 (WFPC2) in 2002, reveals remarkable details of the ejection process that are not visible from ground-based telescopes because of the blurring produced by the Earth’s atmosphere.
The remnant stellar core in the center is now sending out a flood of ultraviolet (UV) light into the surrounding gas. The prominent blue-green ring, nearly a light-year in diameter, marks the location where the energetic UV light has stripped electrons off of atoms in the gas. This process is called ionization. In the redder gas at larger distances from the star, where the UV light is less intense, the ionization process is less advanced. Even farther outside the main body of the nebula, one can see fainter wisps of gas that were lost from the star at the beginning of the ejection process.
This color image has been produced by combining WFPC2 pictures taken through filters that isolate light emitted by three different chemical elements with different degrees of ionization. The doughnut-shaped blue-green ring represents light from ionized oxygen atoms that have lost two electrons (blue) and from hydrogen atoms that have lost their single electrons (green). Red marks emission from nitrogen atoms that have lost only one electron. Our own Sun may eject a similar nebula, but not for another 5000 million years.
The gas will expand away from the star at about 15 miles per second, dissipating into interstellar space after some 10 000 years. After that, the remnant stellar member in the center will gradually cool off for millions of years as a tiny white dwarf star, and eventually wink out.
[http://www.esa.int/Our_Activities/Space_Science/Exploring_space/Little_Ghost_Nebula_NGC_6369]
The unusual galaxy merger remnant and starburst galaxy NGC 6240 is also in Ophiuchus. At a distance of 400 million light-years, this ‘butterfly-shaped’ galaxy has two supermassive black holes 3,000 light-years apart. Confirmation of the fact that both nuclei contain black holes was obtained by spectra from the Chandra X-ray Observatory. Astronomers estimate that the black holes will merge in another billion years. NGC 6240 also has an unusually high rate of star formation, classifying it as a starburst galaxy. This is likely due to the heat generated by the orbiting black holes and the aftermath of the collision:
Hubble revisits tangled NGC 6240
Not all galaxies are neatly shaped, as this new NASA/ESA Hubble Space Telescope image of NGC 6240 clearly demonstrates. Hubble previously released an image of this galaxy back in 2008, but the knotted region, shown here in a pinky-red hue at the center of the galaxies, was only revealed in these new observations from Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys.
NGC 6240 lies 400 million light-years away in the constellation of Ophiuchus (The Serpent Holder). This galaxy has an elongated shape with branching wisps, loops and tails. This mess of gas, dust and stars bears more than a passing resemblance to a butterfly and a lobster.
This bizarrely-shaped galaxy did not begin its life looking like this; its distorted appearance is a result of a galactic merger that occurred when two galaxies drifted too close to one another. This merger sparked bursts of new star formation and triggered many hot young stars to explode as supernovae. A new supernova, not visible in this image was discovered in this galaxy in 2013, named SN 2013dc.
At the center of NGC 6240 an even more interesting phenomenon is taking place. When the two galaxies came together, their central black holes did so, too. There are two supermassive black holes within this jumble, spiraling closer and closer to one another. They are currently only some 3,000 light-years apart, incredibly close given that the galaxy itself spans 300,000 light-years. This proximity secures their fate as they are now too close to escape each other and will soon form a single immense black hole.
[https://www.nasa.gov/image-feature/goddard/hubble-revisits-tangled-ngc-6240]
Barnard 68 is a large dark nebula, located 410 light-years from Earth. Despite its diameter of 0.4 light-years, Barnard 68 only has twice the mass of the Sun, making it both very diffuse and very cold, with a temperature of about 16 Kelvins. Though it is currently stable, Barnard 68 will eventually collapse, inciting the process of star formation. One unusual feature of Barnard 68 is its vibrations, which have a period of 250,000 years. Astronomers speculate that this phenomenon is caused by the shock wave from a supernova:
Secrets of a Dark Cloud
Astronomers at ESO have recently been ‘Seeing the Light through the Dark!’ Some months ago, the ESO Very Large Telescope (VLT) observed a classical dark globule, Barnard 68 (B68) , in front of a dense star field in the Milky Way band. CCD images were obtained in various visual wavebands with the FORS1 multi-mode instrument at the 8.2-m VLT ANTU (UT1). They were combined into a color photo.
This dark cloud is situated at a distance of about 500 light-years (160 pc) towards the southern constellation Ophiuchus (The Serpent-holder). The VLT photo shows it as a compact, opaque and rather sharply defined object, the central parts of which are so dense that they completely block out the light from the stars behind.
It is known that clouds like B68 at some moment begin to contract and subsequently transform themselves into normal, hydrogen-burning stars. But how exactly does this happen? And what is going on just now inside B68? Is it currently at the beginning of the contraction phase or have stars already been formed? How dense and heavy is it really?
Answers to some of these basic questions are now being provided by new and unique observations in the infrared part of the spectrum with the SOFI multi-mode instrument at the ESO 3.5-m New Technology Telescope (NTT) at La Silla. For the first time, it has been possible to look right through even the most opaque regions of such an object and learn what is inside in unsurpassed detail.
The new near-infrared imaging observations were taken with the SOFI multi-mode instrument at the NTT on La Silla during a spell of excellent observing conditions in March 1999. The measured seeing was about 0.6 arcsec during several hours while these exposures were being made.
SOFI (Son OF ISAAC) is a scaled-down copy of ISAAC, the major VLT instrument that has already produced spectacular observations. SOFI is a unique instrument for the study of extended objects like B68 because of its very sensitive infrared detector and unrivalled large field-of-view.
About 200 exposures (each lasting about 10 sec) were made in each of the H- and Ks-bands to reach as faint objects as possible; less time was spent in the shorter wavelength J-band. They were then added to produce three frames that form the basis for the subsequent study and which were used to produce the images shown here.
Dark clouds are dark because they contain myriads of submicron-sized solid particles- the interstellar dust grains. They also harbor many different species of molecules. They are responsible for the obscuration of light at visible wavelengths. The images and video provide a very direct illustration of the dependence of this obscuration on the wavelength (astronomers speak about ‘dust extinction’): it is higher at shorter wavelengths than at longer ones.
The new data are unique in the sense that it allows astronomers, for the first time, to see through the very center of a dense molecular cloud, into the cold regions where stars like our Sun will form. We know this because a large number of background stars, not related to the cloud, are seen through the central, most dense regions of B68 in the Ks-image at 2.16 µm.
Dark clouds are the coolest objects in the known Universe with temperatures around -263 °C, just ten degrees above the absolute zero. They are the nurseries of stars and planets. To understand them is to understand the processes that took place when the Solar System was formed about 4,500 million years ago.
Unfortunately, because they are mostly composed of molecular hydrogen (H 2) and also because they are so cold, 99% of a molecular cloud's mass is virtually undetectable by means of direct observations.
A traditional way to study such clouds is by means of observations with radio-telescopes of rare molecules (such as CO, CS and NH 3) that ‘trace’ the molecular hydrogen. However, the analysis of such data is rarely straightforward and a clear and unambiguous interpretation is frequently impossible.
Thanks to the recent advent of improved infrared technology, incorporated into SOFI, it will now become possible to study molecular clouds in a more direct way, as illustrated here. By means of careful measurements of the change of color of background stars seen through a molecular cloud (cf. the ‘reddening’ of the stars near the center of the first image), astronomers can chart the distribution of matter inside these clouds.
The new SOFI observations of B68 allow such measurements to be done for the first time through the central, densest regions of a molecular cloud. These unique data provide astronomers with important clues on how a dark cloud transforms itself into stars.
Through careful measurements of the color of the background stars that are seen through the cloud, it is now possible to determine the total amount of obscuration at the center of the cloud. It turns out to be no less than 35 magnitudes in the V-band at wavelength 0.55 µm. This number corresponds to a dimming of the starlight of a factor of no less than 10^14!
If, in a thought experiment, a sheet of dust with this high degree of obscuration were placed in front of the Sun, there would be eternal darkness on the Earth. Our central star would then shine with magnitude 9 only, i.e. it would be about 15 times too faint to be observable with the naked eye!
An analysis of the map of obscuration shows the detailed distribution of dust within the cloud. The densest part is somewhat to the west (right) of the geometrical center of B68 . It looks as if two smaller areas (to the lower left, i.e. southeast of the center) are detaching themselves from the rest of the cloud.
The small-scale structure of B68 seems to be very smooth and homogeneous. The SOFI observations rule out the presence of ‘clumpy’ structures inside the cloud, on nearly all scales.
The new data clearly show that B68 is now in the very early phase of collapse, on its way towards star formation . The duration of such a stage is relatively short, of the order of 100,000 years, and to catch a cloud in this phase is likely to be a rare occurrence. If the collapse had been going on for a little longer, it would not have been possible to see through this cloud today, since the obscuration would then have been much higher, of the order of hundreds of magnitudes.
Moreover, the observed distribution of matter inside B68 provides us a first glimpse of how nature begins to form stars. These outstanding observations will now be used to test current theories of proto-stellar collapse.
The total mass of the dust in B68 can be determined quite accurately from the obscuration map by adding over the entire area of the cloud. It comes to about 0.03 solar mass. If the gas-to-dust ratio in B68 is what is normally assumed, about 100, then the total mass of this cloud is about 3 solar masses. Accordingly, only a few stars will eventually form in this cloud.
After this first, impressive demonstration of what is now possible in this exciting research field with top-class astronomical instruments, other clouds will be studied in the near future, with SOFI and ISAAC. With more data from more clouds, it will soon be possible to comprehend their elusive nature in much greater detail and to characterize the fundamental mechanisms that trigger star formation.
[https://www.eso.org/public/news/eso9934/]
The Snake Nebula (also known as Barnard 72) is a dark nebula in the Ophiuchus constellation. It is a small but readily apparent S-shaped dust lane that snakes out in front of the Milky Way star clouds from the north-north-west edge of the bowl of the Pipe Nebula. Its thickness runs between 2′ and 3′ and runs around 6′ in the north-west / south-east orientation. A good view in a 4" to 6" telescope requires clear dark skies. It is part of the much larger Dark Horse Nebula. To the right side of the Snake Nebula is found Barnard 68:
Snake in the Dark
Dark nebulae snake across a gorgeous expanse of stars in this wide-field view toward the pronounceable constellation Ophiuchus and the center of our Milky Way Galaxy. In fact, the central S-shape seen here is well known as the Snake Nebula. It is also listed as Barnard 72 (B72), one of 182 dark markings of the sky cataloged in the early 20th century by astronomer E. E. Barnard. Unlike bright emission nebulae and star clusters, Barnard’s nebulae are interstellar dark clouds of obscuring gas and dust. Their shapes are visible in cosmic silhouette only because they lie in the foreground along the line of sight to rich star fields and glowing stellar nurseries near the plane of our Galaxy. Many of Barnard’s dark nebulae are themselves likely sites of future star formation. Barnard 72 is a few light years across and about 650 light years away.
[http://apod.nasa.gov/apod/ap050521.html]
[https://en.wikipedia.org/wiki/Ophiuchus]
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