Aquila

Aquila constellation is located in the northern sky, near the celestial equator. The constellation’s name means ‘eagle’ in Latin. Aquila is the 22nd biggest star constellation in the sky, occupying an area of 652 square degrees in the fourth quadrant of the northern hemisphere (NQ4). It can be seen at latitudes between +90° and -75°. The neighboring constellations are Aquarius, Capricornus, Delphinus, Hercules, Ophiuchus, Sagitta, Sagittarius, Scutum, and Serpens Cauda. [http://www.constellation-guide.com/constellation-list/aquila-constellation/]

The constellation is best seen in the summer as it is located along the Milky Way. The alpha star, Altair, is a vertex of the Summer Triangle asterism. It is the brightest star in this constellation with a magnitude of 0.76, and it is one of the closest naked-eye stars to Earth at a distance of 17 light-years. Its name is Arabic for ‘flying eagle.’

Johannes Hevelius’ Aquila from Uranographia (1690)

[http://chandra.harvard.edu/photo/constellations/aquila.html]

Aquila represents an eagle, the thunderbird of the Greeks. There are several explanations for the presence of this eagle in the sky. In Greek and Roman mythology, the eagle was the bird of Zeus, carrying (and retrieving) the thunderbolts which the wrathful god hurled at his enemies. But the eagle was involved in love as well as war.

According to one story, Aquila is the eagle that snatched up the beautiful Trojan boy Ganymede, son of King Tros, to become the cup-bearer of the gods on Olympus. Authorities such as the Roman poet Ovid say that Zeus turned himself into an eagle, whereas others say that the eagle was simply sent by Zeus. Ganymede himself is represented by the neighbouring constellation of Aquarius, and star charts show Aquila swooping down towards Aquarius. Germanicus Caesar says that the eagle is guarding the arrow of Eros (neighbouring Sagitta) which made Zeus love-struck.

The constellations of the eagle and the swan are linked in an account by Hyginus. Zeus fell in love with the goddess Nemesis but, when she resisted his advances, he turned himself into a swan and had Aphrodite pretend to pursue him in the form of an eagle. Nemesis gave refuge to the escaping swan, only to find herself in the embrace of Zeus. To commemorate this successful trick, Zeus placed the images of swan and eagle in the sky as the constellations Cygnus and Aquila.

[http://www.ianridpath.com/startales/aquila.htm]

The constellation was also known as Vultur Volans (the flying vulture) to the Romans, not to be confused with Vultur Cadens which was their name for Lyra.

The Greek Aquila is probably based on the Babylonian constellation of the Eagle (MUL.A.MUSHEN), which is located in the same area as the Greek constellation.

In the Chinese love story of Qi Xi, Niu Lang (Altair) and his two children (β and γ Aquilae) are separated forever from their wife and mother Zhi Nu (Vega) who is on the far side of the river, the Milky Way.

In Hinduism, the constellation Aquila is identified with the half-eagle half-human deity Garuda.

Also, there were several different Polynesian equivalents to Aquila as a whole. The Maori people named Altair ‘Poutu-te-rangi,’ ‘Pillar of the Sky,’ because of its important position in their cosmology. It was used differently in different Maori calendars, being the star of February and March in one version and March and April in the other. Altair was also the star that ruled the annual sweet potato harvest.

Looking east once the sky is dark in August, the Summer Triangle is an obvious sight.

[http://www.slate.com/blogs/bad_astronomy/2015/06/27/vega_deneb_altair_up_close_and_personal.html]

[http://astropixels.com/constellations/charts/Aql.html]

Altair (Alpha Aquilae) is the brightest star in the constellation Aquila and the twelfth brightest star in the night sky. It is an A-type main sequence star with an apparent visual magnitude of 0.77. It has approximately 1.8 times the mass of the Sun and 11 times its luminosity. It is 16.7 light-years (5.13 parsecs) from Earth and is one of the closest stars visible to the naked eye. Along with Beta Aquilae and Gamma Aquilae, it forms the well-known line of stars sometimes referred to as the Family of Aquila or Shaft of Aquila. It is also one of the vertices of the Summer Triangle (the other two vertices are marked by Deneb and Vega). The name Altair has been used since medieval times and it is an abbreviation of the Arabic phrase ‘al-nesr al-ṭā’ir,’ ‘the flying eagle.’

[https://en.wikipedia.org/wiki/Altair]

Position of Tarazed relative to Altair (center)

Gamma Aquilae has the traditional name Tarazed. This star has an apparent visual magnitude of 2.712, so it is readily visible to the naked eye at night. It is at a distance of 395 light-years (121 parsecs) from Earth.

Gamma Aquilae is a relatively young star with an age of about 100 million years. Nevertheless, it has reached a stage of its evolution where it has consumed the hydrogen at its core and expanded into what is termed a bright giant star, with a stellar classification of K3 II. The star is now burning helium into carbon in its core. After it has finished generating energy through nuclear fusion, Gamma Aquilae will become a white dwarf.

The traditional name Tarazed may derive from Persian ‘šāhin tarāzu,’ ‘the beam of the scale,’ referring to an asterism of the Scale, α, β and γ Aquillae.

[https://en.wikipedia.org/wiki/Gamma_Aquilae]

Beta Aquilae has the traditional name Alshain from the Perso-Arabic term ‘aš-šāhīn,’ ‘the (peregrine) falcon,’ perhaps by folk etymology from the Persian ‘šāhīn tarāzū’ (or possibly ‘šāhīn tara zed’), the Persian name for the asterism α, β and γ Aquilae.

This star has magnitude 3.71 and is of spectral class G8IV. It is approximately 44.7 light years from Earth. It has a 12th magnitude optical companion, β Aquilae B, which is 13 arcseconds away in the sky.
[https://en.wikipedia.org/wiki/Beta_Aquilae]

Delta Aquilae is a binary star system. It has an apparent visual magnitude of 3.4 and is located about 50.6 light-years (15.5 parsecs) from Earth. The system is an astrometric binary where the two components orbit each other with a period of 3.422 years and an eccentricity of about 0.36. This is a type of binary star system where the presence of the secondary component is revealed by its gravitational perturbation of the primary. The individual components have not been resolved with a telescope.

The primary component, Delta Aquilae A, is a subgiant star with a stellar classification of F0 IV, where the luminosity class of IV indicates it is in the process of exhausting the supply of hydrogen at its core and evolving into a giant star. The mass of the star is 65% greater than the Sun and it has expanded to more than double the Sun’s radius. It is radiating around 7-8 times the luminosity of the Sun from its outer atmosphere at an effective temperature of 7,016 K, giving it the yellow-white hue of an F-type star. Delta Aquilae A is a Delta Scuti variable that exhibits variations in luminosity caused by pulsations in its outer envelope.

The secondary component, Delta Aquilae B, is a smaller star with about 67% of the Sun’s mass and an estimated 61% of the radius of the Sun. It may be a K-type star.

This star is sometimes called by the name Denebokab, meaning the tail of eagle in Arabic. In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated ‘Djenubi Menkib al Nesr,’ which was translated into Latin as Australior Humerus Vulturis, meaning the southern shoulder of the eagle.

[https://en.wikipedia.org/wiki/Delta_Aquilae]

Epsilon Aquilae is a binary star with an apparent visual magnitude of 4.02 and is visible to the naked eye. It lies at a distance of approximately 155 light-years (48 parsecs) from Earth. It has the traditional name Deneb el Okab, from an Arabic term ‘ðanab al-cuqāb,’ meaning ‘the tail of the eagle.’ It is more precisely called Deneb el Okab Borealis, because is situated to the north of Zeta Aquilae, which can therefore be called Deneb el Okab Australis.

The pair orbit each other over a period of 1,271 days (3.5 years) with an eccentricity of 0.27. The primary component of this system is an evolved giant star with a stellar classification of K1 III. It has more than double the mass of the Sun and has expanded to ten times the Sun’s radius. It shines with 54-fold the Sun’s luminosity, which is being radiated from its outer envelope at an effective temperature of 4,760 K. At this heat, it glows with the orange-hue of a K-type star.

[https://en.wikipedia.org/wiki/Epsilon_Aquilae]

Zeta Aquilae is a double star with the traditional name Deneb el Okab (Deneb el Okab Australis), which shares with ε Aquilae (Deneb el Okab Borealis). As a third magnitude star, Zeta Aquilae is readily visible with the naked eye. It is at a distance of approximately 83 light-years (25 parsecs) from Earth.

Zeta Aquilae has a stellar classification of A0 Vn, with the luminosity class ‘V’ indicating is a main sequence star that is generating energy through the nuclear fusion of hydrogen at its core. It has more than double the mass and twice the radius of the Sun, and is radiating more than 39 times the Sun’s luminosity. The effective temperature of the star’s outer envelope is about 9620 K, which gives it the white hue typical of A-type stars. The estimated age of this star is 50–150 million years.

This star has two 12th magnitude companions at angular separations of 6.5 and 158.6 arcseconds.

[https://en.wikipedia.org/wiki/Zeta_Aquilae]

Eta Aquilae is a multiple star, and it was once part of the former constellation Antinous. It has an apparent visual magnitude of 3.87 and is located at a distance of roughly 1,382 light-years (424 parsecs).

The η Aquilae system contains at least two stars, probably three. The primary star η Aql A is by far the brightest and dominates the spectrum. An ultraviolet excess in the spectral energy distribution suggest the presence of a faint hot companion, η Aql B, which has been given a spectral type of B8.9 V.

A companion has been resolved visually 0.66" distant, but measurements give this a spectral type of F1 -F5. It seems likely that the hot star detected in the spectrum is closer and unresolved. The resolved companion has not been shown to be physically associated, but it is estimated that it would have a period of nearly a thousand years. Measurements with the HST fine guidance sensors show variations likely to be due to orbital motion on a scale of two years, so η Aql would appear to be a triple system.

η Aquilae A is a Cepheid variable star, discovered by Edward Pigott in 1784. Its apparent magnitude ranges from 3.5 to 4.3 over a period of 7.176641 days. Along with Delta Cephei, Zeta Geminorum and Beta Doradus, it is one of the most prominent naked eye Cepheids; that is, both the star itself and the variation in its brightness can be distinguished with the naked eye. Some other Cepheids such as Polaris are bright but have only a very small variation in brightness.

At the relatively young age of 26 million years, this massive star has burned through the hydrogen fuel at its core and evolved into a supergiant, giving it a baseline stellar classification of F6 Ibv. The periodic pulsations of this star actually cause the stellar class to vary between (F6.5–G2)Ib over the course of each cycle.

Compared to the Sun, Eta Aquilae has around 9 times the mass, roughly 66 times the radius, and is radiating 11,474 times as much luminosity. This energy is being emitted from the outer envelope at an effective temperature of 6,000 K, giving it the yellow-white hued glow of an F-type star. The radius of the star varies by 4.59 × 106 km (0.007 solar radii) over the course of a pulsation cycle.

[https://en.wikipedia.org/wiki/Eta_Aquilae]

Theta Aquilae is a binary star with a combined apparent visual magnitude of 3.26, making it the fourth brightest member of the constellation.

Theta Aquilae is a double-lined spectroscopic binary, which indicates that the individual components have not been viewed through a telescope; instead, what can be viewed is their combined spectrum with the individual absorption line features shifting back and forth over the course of an orbit because of the Doppler effect. Their orbit has a period of 17.1 days with a large orbital eccentricity is 0.60. At the estimated distance of this system, the angular separation of 3.2 milliarcseconds corresponds to a physical separation of only about 0.24–0.28 Astronomical Units.

Both stars have a matching stellar classification of B9.5 III, indicating that they are massive, B-type giant stars that have exhausted the supply of hydrogen at their cores and evolved away from the main sequence of stars like the Sun.

In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated ‘Thanih Ras al Akab,’ which was translated into Latin as Secunda Capitis Vulturis, meaning the second (star) of eagle’s head.

In Chinese, ‘Tiān Fú,’ meaning Celestial Drumstick, refers to an asterism consisting of θ Aquilae, 62 Aquilae, 58 Aquilae and η Aquilae. Consequently, θ Aquilae itself is known as ‘Tiān Fú yī,’ ‘the First Star of Celestial Drumstrick.’

[https://en.wikipedia.org/wiki/Theta_Aquilae]

Lambda Aquilae is a star with the traditional name Al Thalimain, which it shares with ι Aquilae. The name is derived from the Arabic ‘al-thalīmain,’ ‘the two ostriches.’ Lambda Aquilae is more precisely Al Thalimain Prior. It has an apparent visual magnitude of 3.43, which is bright enough to be seen with the naked eye. It is at a distance of about 125 light-years (38 parsecs) from Earth.

Lambda Aquilae is a main sequence star with a stellar classification of B9Vn, which means that, like the Sun, it is generating energy at its core through the nuclear fusion of hydrogen. It is more massive than the Sun, with about three times its mass, and radiates about 55 times the Sun’s luminosity from its outer envelope at a higher effective temperature of 11,780 K. This temperature gives Lambda Aquilae the blue-white hue that is a characteristic of B-type stars. Lambda Aquilae has an age of about 160 million years.

This star lies about 5° from the galactic plane and about 30° from the line of sight to the Galactic Center. This region of the sky is crowded with other objects along the line of sight, with at least 55 located within 10 arcseconds of the star. Examination of the star shows no companions. Despite this, it is suspected of being a spectroscopic binary star. That is, it may have an orbiting companion whose presence is revealed by displacements in the absorption lines in the spectrum caused by the Doppler effect.

[https://en.wikipedia.org/wiki/Lambda_Aquilae]

Iota Aquilae has the traditional name Al Thalimain (Al Thalimain Posterior), which it shares with λ Aquilae (Al Thalimain Prior). With an apparent visual magnitude of 4.364, this star is bright enough to be seen with the naked eye. It is located at a distance of around 390 light-years (120 parsecs) from Earth. At that distance, the visual magnitude of the star is diminished by 0.15 from extinction caused by intervening gas and dust.

Although Iota Aquilae is listed in star catalogues as a giant star, calculations of its dimension show that in reality it is a main-sequence star. It has nearly five times the mass of the Sun and five to six times the Sun's radius. It is emitting 851 times the luminosity of the Sun from its outer atmosphere at an effective temperature of 14,552 K, giving it the blue-white hue of a B-type star. Even though it is only around 100 million years old, it has already spent 91% of its allotted lifetime on the main sequence.

[https://en.wikipedia.org/wiki/Iota_Aquilae]

CoRoT-2a: Star Blasts Planet With X-rays

This graphic contains an image and illustration of a nearby star, named CoRoT-2a, which has a planet in close orbit around it. The separation between the star and planet is only about 3 percent of the distance between the Earth and the Sun, causing some exotic effects not seen in our solar system.

The planet-hosting star is located in the center of the image. Data from NASA’s Chandra X-ray Observatory are shown in purple, along with optical and infrared data from the Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes (PROMPT) and the Two Micron All Sky Survey (2MASS). CoRoT-2a is surrounded by a purple glow showing that it is an X-ray source.

This star is pummeling its companion planet- not visible in this image- with a barrage of X-rays a hundred thousand times more intense than the Earth receives from the Sun. Data from Chandra suggest that high-energy radiation from CoRoT-2a is evaporating about 5 million tons of matter from the nearby planet every second, giving insight into the difficult survival path for some planets. The artist’s representation shows the material, in blue, being stripped off the planet.

The Chandra observations provide evidence that CoRoT-2a is a very active star, with bright X-ray emission produced by powerful, turbulent magnetic fields. This magnetic activity is represented by the prominences and eruptions on the surface of the star in the illustration.

Such strong activity is usually found in much younger stars and may be caused by the proximity of the planet. The planet may be speeding up the star's rotation, causing its magnetic fields to remain active longer than expected. Support for this idea comes from observations of a likely companion star to CoRoT-2a that orbits at a distance about a thousand times greater than the distance between the Earth and the Sun. This star is visible in the image as the faint, nearby star located below and to the right of CoRoT-2a. It is also shown as the bright background star in the illustration. This star is not detected in X-rays, perhaps because it does not have a close-in planet like CoRoT-2b to cause it to stay active.

The planet, CoRoT-2b, was discovered by the French Space Agency’s Convection, Rotation and planetary Transits (CoRoT) satellite in 2008. It is located about 880 light years from Earth and has a mass about 3 time that of Jupiter.

[http://chandra.harvard.edu/photo/2011/corot/]

Two major novae have been observed in Aquila: the first one was in 389 BC and was recorded as being as bright as Venus; the other (Nova Aquilae 1918) briefly shone brighter than Altair, the brightest star in Aquila:

V603 Aquilae = Nova Aquilae 1918

[http://asd.gsfc.nasa.gov/Koji.Mukai/iphome/systems/v603aql.html]

V603 Aquilae (or Nova Aquilae 1918) was a bright nova occurring in the constellation Aquila in 1918. It is a binary system, comprising a white dwarf and donor low-mass star in close orbit to the point of being only semidetached. The white dwarf sucks matter off its companion onto its accretion disk and surface until the excess material is blown off in a thermonuclear event. This material then forms an expanding shell, which eventually thins out and disappears.

First seen by Zygmunt Laskowski, a medical professor and amateur astronomer, and then confirmed on the night of 8 June 1918 by the professional astronomer Grace Cook, Nova Aquilae reached a peak magnitude of −0.5; it was the brightest nova recorded in the era of the telescope. It was brighter than all stars except for Sirius and Canopus. Tycho’s and Kepler’s supernovae were brighter, but both occurred before the invention of the telescope. Originally a star system with a magnitude of 11.43, it took twelve days to fade three magnitudes and then 18.6 years to fade to quiescence.

The star system has settled to an average apparent magnitude of 11.4 since the 1940s, fading by around 1/100 of a magnitude per decade. Spectroscopic analysis conducted by Arenas and colleagues indicated the system consisted of a white dwarf of about 1.2 times as massive as the sun, with an accretion disk, and a companion star with about 20% of the Sun’s mass. This second star is most likely a red dwarf. The two stars orbit each other approximately every 3 hours 20 minutes.

[https://en.wikipedia.org/wiki/V603_Aquilae]

W49B: Rare Explosion May Have Created Our Galaxy’s Youngest Black Hole

W49B is a highly distorted supernova remnant, produced by a rare type of explosion. Instead of radiating out symmetrically, W49B’s exploding star shot more material out from its poles versus from its equator. There is evidence that W49B left behind a black hole- not a neutron star like most other supernovas. If confirmed, W49B would be the most recent black hole formed in our Galaxy.

The image combines X-rays from NASA’s Chandra X-ray Observatory in blue and green, radio data from the NSF’s Very Large Array in pink, and infrared data from Caltech's Palomar Observatory in yellow.

The remnant, called W49B, is about a thousand years old, as seen from Earth, and is at a distance of about 26,000 light years away.

The supernova explosions that destroy massive stars are generally symmetrical, with the stellar material blasting away more or less evenly in all directions. However, in the W49B supernova, material near the poles of the doomed rotating star was ejected at a much higher speed than material emanating from its equator. Jets shooting away from the star’s poles mainly shaped the supernova explosion and its aftermath.

By tracing the distribution and amounts of different elements in the stellar debris field, researchers were able to compare the Chandra data to theoretical models of how a star explodes. For example, they found iron in only half of the remnant while other elements such as sulfur and silicon were spread throughout. This matches predictions for an asymmetric explosion. Also, W49B is much more barrel-shaped than most other remnants in X-rays and several other wavelengths, pointing to an unusual demise for this star.

The authors also examined what sort of compact object the supernova explosion left behind. Most of the time, massive stars that collapse into supernovas leave a dense spinning core called a neutron star. Astronomers can often detect these neutron stars through their X-ray or radio pulses, although sometimes an X-ray source is seen without pulsations. A careful search of the Chandra data revealed no evidence for a neutron star, implying an even more exotic object might have formed in the explosion, that is, a black hole.

This may be the youngest black hole formed in the Milky Way galaxy, with an age of only about a thousand years, as viewed from Earth (i.e., not including the light travel time). A well-known example of a supernova remnant in our Galaxy that likely contains a black hole is SS433. This remnant is thought to have an age between 17,000 and 21,000 years, as seen from Earth, making it much older than W49B.

[http://chandra.harvard.edu/photo/2013/w49b/index.html]

Because of Aquila’s location along the line of our galaxy, many clusters and nebulae are found within its borders, but they are dim and there are few galaxies. Some of the most interesting planetary nebulae in Aquila are the following:

Cosmic Bubble NGC 6781

Stars such as our Sun do not contain enough mass to finish their lives in the glorious explosions known as supernovae. However, they are still able to salute their imminent demise into dense, Earth-sized embers called white dwarfs by first expelling colourful shells of gas known as planetary nebulae. This misnomer comes from the similarity in appearance of these spherical mass expulsions to giant planets when seen through small telescopes.

NGC 6781 is a nice representative of these cosmic bubbles. The planetary nebula lies a few thousand light-years away towards the constellation of Aquila (the Eagle) and is approximately two light-years across. Within NGC 6781, shells of gas blown off from the faint, but very hot, central star’s surface expand out into space. These shells shine under the harsh ultraviolet radiation from the progenitor star in intricate and beautiful patterns. The central star will steadily cool down and darken, eventually disappearing from view into cosmic oblivion.

This image was captured with the ESO Faint Object Spectrograph and Camera (EFOSC2) through three wide band filters (B, V, R) and two narrow-band ones (H-alpha, OIII). EFOSC2 is attached to the 3.6-metre telescope at ESO’s La Silla Observatory in Chile. EFOSC2 has a field of view of 4.1 x 4.1 arcminutes.

[https://www.eso.org/public/usa/images/ngc6781-potw/]

NGC 6751: The Glowing Eye Nebula

Planetary nebulae can look simple, round, and planet-like in small telescopes. But images from the orbiting Hubble Space Telescope have become well known for showing these fluorescent gas shrouds of dying Sun-like stars to possess a staggering variety of detailed symmetries and shapes. This composite color Hubble image of NGC 6751, the Glowing Eye Nebula, is a beautiful example of a classic planetary nebula with complex features. It was selected in April of 2000 to commemorate the tenth anniversary of Hubble in orbit, but was reprocessed recently by an amateur as part of the Hubble Legacy program. Winds and radiation from the intensely hot central star (140,000 degrees Celsius) have apparently created the nebula’s streamer-like features. The nebula’s actual diameter is approximately 0.8 light-years or about 600 times the size of our Solar System. NGC 6751 is 6,500 light-years distant in the high-flying constellation of the Eagle (Aquila).

[http://apod.nasa.gov/apod/ap130313.html]

NASA/ESA Hubble Space Telescope image of NGC 6741

NGC 6741, also known as the Phantom Streak Nebula, is located about 7000 light-years away in the constellation of Aquila. NGC 6741 is classed as a planetary nebula, though no planets are responsible for this billowy cloud. Although fairly bright, this object appears very small though a typical telescope and was missed by early surveyors of the skies and only spotted in 1882 by Edward Charles Pickering.

[https://en.wikipedia.org/wiki/NGC_6741]

NGC 6709

[https://en.wikipedia.org/wiki/NGC_6709]

NGC 6709 is one of Aquila’s open clusters. This is a loose open cluster containing approximately 40 stars, which range in magnitude from 9 to 11. It is approximately 3000 light-years from Earth. It has an overall magnitude of 6.7 and is approximately 9100 light-years from Earth. NGC 6709 appears in a rich Milky Way star field and is classified as a Shapley class d and Trumpler class III 2 m cluster. These designations mean that it does not have many stars, is loose, does not show greater concentration at the center, and has a moderate range of star magnitudes.

Aquila also holds some extragalactic objects. One of them is what may be the largest single mass concentration of galaxies in the Universe known, the Hercules- Corona Borealis Great Wall. It was discovered in November 2013 and has the size of 10 billion light years. It is the biggest and the most massive structure in the Universe known.

Another structure is the Galactic halo which Chandra satellite observed in the direction of Aquila:

Galactic Halo: Milky Way is Surrounded by Huge Halo of Hot Gas

Chandra has provided evidence that our Milky Way Galaxy is embedded in an enormous halo of hot gas that extends for hundreds of thousands of light years. The mass of the halo is estimated to be comparable to the mass of all the stars in the Milky Way galaxy. If the size and mass of this gas halo is confirmed, it could be the solution to the ‘missing-baryon’ (dark matter) problem for the Galaxy.

This artist’s illustration shows an enormous halo of hot gas (in blue) around the Milky Way galaxy. Also shown, to the lower left of the Milky Way, are the Small and Large Magellanic Clouds, two small neighboring galaxies. The halo of gas is shown with a radius of about 300,000 light years, although it may extend significantly further.

Data from NASA’s Chandra X-ray Observatory was used to estimate that the mass of the halo is comparable to the mass of all the stars in the Milky Way galaxy. If the size and mass of this gas halo is confirmed, it could be the solution to the ‘missing-baryon’ problem for the Galaxy.

In a recent study, a team of five astronomers used data from Chandra, ESA’s XMM-Newton, and Japan’s Suzaku satellite to set limits on the temperature, extent and mass of the hot gas halo. Chandra observed eight bright X-ray sources located far beyond the Galaxy at distances of hundreds of millions of light years. The data revealed that X-rays from these distant sources are selectively absorbed by oxygen ions in the vicinity of the Galaxy. The nature of the absorption allowed the scientists to determine that the temperature of the absorbing halo is between 1 million and 2.5 million Kelvins.

Other studies have shown that the Milky Way and other galaxies are embedded in warm gas, with temperatures between 100,000 and one million degrees, and there have been indications that a hotter component with a temperature greater than a million degrees is also present. This new research provides evidence that the mass in the hot gas halo enveloping the Milky Way is much greater than that of the warm gas.

[http://chandra.harvard.edu/photo/2012/halo/index.html]

[https://en.wikipedia.org/wiki/Aquila_%28constellation%29]

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