M31: The Andromeda Galaxy (APOD 2009 May 10)

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http://apod.nasa.gov/apod/ap090510.html
http://antwrp.gsfc.nasa.gov/apod/ap080913.html

<<HVC 127-41-330 is a high velocity cloud. The three numbers that compose its name indicate, respectively, the galactic longitude and latitude, and velocity towards Earth in km/s. It is 20,000 light years in diameter and is located 2.3 million light years from Earth, between M31 and M33.This cloud of neutral hydrogen (detectable via 21 cm H-I emissions), unlike other HVCs shows a rotational component and dark matter. 80% of the mass of the cloud is dark matter. It is also the first HVC discovered not associated with the Milky Way galaxy or subgroup (subcluster).


Astronomer Josh Simon considers it a candidate for being a dark galaxy.
With its rotation, it may be a very low density dwarf galaxy of unused hydrogen
(no stars), a remnant of the formation of the Local Group.>>

[kovil]

Art, I am consistently impressed with your skills at gathering varying data together from multitudinously diverse sources. Bravo again !

"The true nature of M31 began to become clear in 1923. In that year Edwin Hubble, using the just completed 100 inch Hooker telescope at the Mount Wilson observatory, made his monumental discovery of Cepheid Variable stars in M31 and in one stroke forever changed the astronomical paradigm of the universe as we knew it. Appropriately interpreting the cepheid data, Hubble was the first to appreciate the faint nebula in Andromeda as an "island universe", an immense galaxy in its own right, similar to our Milky Way."

"M31 has the distinction of being the nearest of all spirals at a distance of 2.5 million light years. Its disk, tilted toward Earth by some 13 degrees, exposes the grandeur of its spiral structure and star systems to telescopic exploration."

"M31, along with its near twin, the Milky Way, represent the two dominant giant galaxies of our Local Group which consists of some 40 members. M31 and the Milky Way are actually moving toward each other and a close encounter or even a full collision may be in store for both galaxies in several billion years. Studies of globular clusters in M31 have revealed at least 4 different subpopulations . . ."

"As far back as 1974 astronomers noted a curious asymmetry to the nucleus of M31. It wasn't until 1995 that the Hubble Space Telescope with its great precision, was able to resolve the light of the nucleus into two separate structures. The two light sources of the double nucleus are separated by a miniscule 0.49 arcseconds (6 light years), a distance difficult or impossible to resolve with earth based telescopes. HST images resolved two brightness peaks which were named P1 and P2. Further investigation showed that the optically dimmer P2 was very close to the true center of the galaxy. The brighter P1 is slightly off center creating the illusion of an asymmetric nucleus in ground based images. Recent HST observations have identified a rotating disk of more than 400 blue stars orbiting the true nucleus. The disk is only one light year in diameter and its stars have a remarkable orbital velocity of 2.2 million miles per hour (600 miles per second), . . . The brighter light source P1 is artifactual and has its basis in the eccentricity of the rotating circumnuclear stellar disk. It seems that the appearance of the two extremes of the ellipsoidal orbit creates an illusion of a second bright region towards our line of site. Several other galaxies are known which possess a true double nucleus . . ."

For my own part I can't stand the insertion of 'fringe science' clap-trap assumptions about black holes etc, so I edited out those massively assumptive presumptions of such fictious things, and left the real data. Not being allowed here to post a better explanation of what is going on at the core of the Andromeda Galaxy due to the religious/political rules of the APOD posting boards, Good Morning !

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<<The Andromeda Galaxy is the nearest spiral galaxy to our own, the Milky Way. Andromeda is the largest galaxy of the Local Group. The 2006 observations by the Spitzer Space Telescope revealed that M31 contains one trillion stars, greatly exceeding the number of stars in our own galaxy. [However,] a study released by the Harvard-Smithsonian Center for Astrophysics on January 5, 2009 concluded that Andromeda and the Milky Way are about equal in size and mass.

The earliest recorded observation of the Andromeda Galaxy was in 964 CE by the Persian astronomer, Abd al-Rahman al-Sufi (Azophi), who described it as a "small cloud" in his Book of Fixed Stars. The first description of the object based on telescopic observation was given by Simon Marius in 1612.

Charles Messier catalogued it as object M31 in 1764 and incorrectly credited Marius as the discoverer, unaware of Al Sufi's earlier work:

http://apod.nasa.gov/apod/ap090510.html

• Jules Verne » All Around the Moon » Chapter 5
  
  "Ether, friend Michael, is an elastic gas consisting of imponderable
  atoms, which, as we are told by works on molecular physics, are, in
  proportion to their size, as far apart as the celestial bodies are from
  each other in space. This distance is less than the 1/3000000 x 1/1000',
  or the one trillionth of a foot. The vibrations of the molecules of this
  ether produce the sensations of light and heat, by making 430 trillions
  of undulations per second, each undulation being hardly more than the
  one ten-millionth of an inch in width."
  
  "trillions per second! ten-millionths of an inch in width!" cried Ardan.
  "These oscillations have been very neatly counted and ticketed, and
  checked off! Ah, friend Barbican," continued the Frenchman, shaking his
  head, "these numbers are just tremendous guesses, frightening the ear
  but revealing nothing to the intelligence."
  
  "To get ideas, however, we must calculate--"
  
  "No, no!" interrupted Ardan: "not calculate, but compare. A trillion
  tells you nothing--Comparison, everything. For instance, you say, the
  volume of _Uranus_ is 76 times greater than the Earth's; _Saturn's_ 900
  times greater; _Jupiter's_ 1300 times greater; the Sun's 1300 thousand
  times greater--You may tell me all that till I'm tired hearing it, and I
  shall still be almost as ignorant as ever. For my part I prefer to be
  told one of those simple comparisons that I find in the old almanacs:
  The Sun is a globe two feet in diameter; _Jupiter_, a good sized orange;
  _Saturn_, a smaller orange; _Neptune_, a plum; _Uranus_, a good sized
  cherry; the Earth, a pea; _Venus_, also a pea but somewhat smaller;
  _Mars_, a large pin's head; _Mercury_, a mustard seed; _Juno_,
  _Ceres_, _Vesta_, _Pallas_, and the other asteroids so many grains
  of sand. Be told something like that, and you have got at least the tail
  of an idea!"

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one trillion: <<Used to denote a basketball player who has played one minute without recording any other statistic. The term takes its name from its appearance in a box score, as it reads as one followed by twelve zeros – the conventional American rendering of "one trillion." Notable "trillionaires" include Mark Titus at Ohio State.

[aristarchusinexile]

The photo seems to be reversed from a previous photo I've seen here.

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Explanation: In an effort to find out true ages of stars in neighboring Andromeda galaxy's halo, astronomers stared into the galaxy giant with the new Advanced Camera for Surveys through the Hubble Space Telescope. The resulting exposure of over three days, shown above, is the deepest exposure in visible light ever taken, although shorter in duration than the multi-wavelength effort toward the Hubble Deep Field. The final image illuminated not only Andromeda (M31) but the distant universe. Andromeda's halo stars turned out to be have a wider range of ages than our Milky Way's halo stars, likely indicating more encounters with small neighboring galaxies. Visible on the above left is one of Andromeda's
globular star clusters.

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Explanation: Just like our own Milky Way Galaxy, the nearest major galaxy M31 has many star systems spewing high energy radiation. High energy X-radiation is visible to certain satellites in Earth orbit such as ROSAT - which took the above picture. The X-ray sources in M31 occur in globular clusters, the spiral arms, and near the galaxy's center. Probably most of these sources are accretion disk binary star systems. M31 has more X-ray sources near its center than our Galaxy, and the reason for this is currently unknown.

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Explanation: A big beautiful spiral galaxy 2 million light-years away, Andromeda (M31) has long been touted as an analog to the Milky Way, a distant mirror of our own galaxy. The popular 1960s British sci-fi series, A For Andromeda, even postulated that it was home to another technological civilization that communicated with us. Using the newly unleashed observing power of the orbiting Chandra X-ray telescope, astronomers have now imaged the center of our near-twin island universe, finding evidence for an object so bizarre it would have impressed many 60s science fiction writers (and readers). Like the Milky Way, Andromeda's galactic center appears to harbor an X-ray source characteristic of a black hole of a million or more solar masses. Seen above, the false-color X-ray picture shows a number of X-ray sources, likely X-ray binary stars, within Andromeda's central region as yellowish dots. The blue source located right at the galaxy's center is coincident with the position of the suspected massive black hole. While the X-rays are produced as material falls into the black hole and heats up, estimates from the X-ray data show Andromeda's central source to be surprisingly cool - only a million degrees or so compared to the tens of millions of degrees indicated for Andromeda's X-ray binaries.

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Explanation: Elliptical galaxies are known for their old, red stars. But is this old elliptical up to new tricks? In recent years, the centers of elliptical galaxies have been found to emit unexpectedly high amounts of blue and ultraviolet light. Most blue light from spiral galaxies originates from massive young hot stars, in contrast to the red light from the old cool stars thought to compose ellipticals. In the above recently released, false-color photograph by the Hubble Space Telescope, the center of nearby dwarf elliptical M32 has actually been resolved and does indeed show thousands of bright blue stars. The answer is probably that these blue stars are also old and glow blue, reaching relatively high temperatures by the advanced process of fusing helium, rather than hydrogen, in their cores. M32 appears in many pictures as the companion galaxy to the massive Andromeda Galaxy (M31).

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Explanation: The center of M31 is twice as unusual as previously thought. In 1991 the Planetary Camera then onboard the Hubble Space Telescope pointed toward the center of our Milky Way's closest major galactic neighbor: Andromeda (M31). To everyone's surprise, M31's nucleus showed a double structure. The nuclear hot-spots are quite close together when considering Galactic distances: M31 is about 150,000 light years across while the above shows only the central 30 light-years. Subsequent ground-based observations have led to speculation that indeed two nuclei exist, are moving with respect to each other, that one nucleus is slowly tidally disrupting the other, and that one nucleus may be the remains of smaller galaxy "eaten" by M31. The nuclei of many galaxies, including M31, are known to be quite violent places, and the existence of massive black holes are frequently postulated to explain them.

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