Andromeda

© Robert Gendler,

Astroimaging Gallery

(Used with permission)

Larger mosaic (more).

Andromeda is the

largest member of

the Local Group of

galaxies, which

includes the Milky

Way and its satellite

galaxies. Andromeda's

own satellites include

M32, at center left, and

M110, at lower right

(more from APOD).

Breaking News

On June 11, 2012, astronomers working with the National Science Foundation's Green Bank Telescope (GBT) confirmed the 2004 finding of hydrogen gas streaming between Andromeda and the Triangulum Galaxy. The position and relatively velocity properties of six dense clumps within the gas stream indicate that the two galaxies may have passed relatively close billions of years ago. As a result, their immense gravity attracted and drew out gas from each other that appears as a connecting stream made of tenuous "tidal trails" (NRAO press release).

Bill Saxton, AUI, NRAO, NSF

Larger and jumbo illustrations.

A bridge of hydrogen gas connecting

the Andromeda and Triangulm galaxies

suggests that the two had a near miss

in the distant past (more).

On May 31, 2012, astronomers using NASA's Hubble Space Telescope announced "findings [that] are statistically consistent with a head-on collision" between the Andromeda Galaxy and our own Milky Way in about four billion years. Their computer simulations show that it will take an additional two billion years after the first encounter for the two galaxies to completely merge and be reshaped by gravitational interactions into a single elliptical galaxy. Moreover, Andromeda has a satellite, the Triangulum Galaxy. (M33), which will also join in the collision and perhaps later merge with Andromeda-Milky Way, with a a small chance that Triangulum will hit the Milky Way first.

Z. Levay, R. van der Marel, A. Mellinger;

STScI, ESA, NASA

Larger and jumbo illustrations.

New data and simulations suggest

that Andromeda and the Milky Way

will collide in about four billion

years (more).

While the two spiral galaxies will merge into a single elliptical, stars inside each galaxy are so far apart that they will not collide with each other, but many stars will be thrown into different orbits around the new joint galactic center. The astronomers' simulations show that it is likely our Sun, Sol, will be flung into a region of the Milky Way much further from the galactic core than it is today, but Earth and its Solar System are in no danger of being destroyed. (NASA Hubble news release).

A Large Spiral Galaxy

Wider and possibly brighter than our own Milky Way, the Andromeda Galaxy was once thought to be the dominant member of the Local Group of galaxies. Although it is Milky Way's nearest large galactic neighbor, this large spiral galaxy (type Sb with two arms) lies around 2.52 ± 0.14 million light-years (ly) from the Solar System (Ribas et al, 2005). It can be found in (0:40:27+40:40:12, J2000; and 0:42:44.3+41:16:9.4, ICRS 2000) Constellation Andromeda, the Chained Maiden. It is located northwest of Mu and Beta Andromedae (Mirach); west of Nu Andromedae; northeast of Theta and Sigma Andromedae; north of Pi, Delta, and Epsilon Andromedae; and south of Theta and Omega Cassiopeiae. Andromeda can be seen by Human eyes from Earth without a telescope as a "little cloud" (see Akira Fujii's photo to better relate the galaxy's location to the brightest stars of Constellation Andromeda).

© Jason Ware,

www.galaxyphoto.com

(Used with permission)

Larger image (more).

Andromeda has a bright

yellowish nucleus, dark

winding dustlanes, and

bluish spiral arms and

star clusters (more

from APOD).

Andromeda has a bright disk that is now believed to span as much as 228,000 ly in width (Chapman et al, 2005). In 2005, astronomers announced that Andromeda's disk actally extends far further out, so that the disk spans at least 260,000 light-years -- almost twice the size of the bright disk seen in photographs (Ibata et al, 2005). The outer disk emits nearly 10 percent of the galaxy's total light and may be comprised of metal-poor stars stripped from smaller galaxies that strayed too close. On January 7, 2007, a team of astronomers announced the discovery of low-metallicity, red giant stars up to some 500,000 light-years from Andromeda's core which suggests that the galaxy is much larger than originally thought, so that Andromeda's luminous halo may actually overlap with that of the Milky Way (BBC News -- more below).

WISE, UCLA,

CalTech, JPL, NASA

Larger and jumbo

infrared images.

In this 2010 infrared image,

dust heated by newborn,

massive stars are depicted

in yellow and red, which

trace out the spiral arms,

while mature stars are

colored blue (more).

In the venerable Star Names: Their Lore and Meaning, Richard Hinckley Allen noted that: "... the Great Nebula, the Queen of the Nebulae, ..., is said to have been known as far back as A.D. 905; was described by [Abd-al-Rahman] Al Sufi as the Little Cloud before 986; and appeared on a Dutch star-map of 1500." According to Robert Burnham, Jr. (1931-93): "The first hint of the true nature of the Andromeda Galaxy came late in 1923 when several [C]epheid variable stars were identified in the system [by Edwin Powell Hubble (1889-1953) who thus] ... definitively established the great spiral as an extra-galactic object ...."The galaxy is frequently referred to as M31 because it was the 31st object in the Messier Catalogue of diffuse objects that Charles Messier (1730-1817) found not to be comets. Subsequently, the "nebula" was also designated as NGC 224 by John Louis Emil Dreyer (1852-1926) in his New General Catalogue (NGC) of Nebulae and Clusters of Stars, which was first published in 1887 and later supplemented with Index Catalogue (IC) I in 1895 and IC II in 1907.

Bill Schoening, Vanessa Harvey,

REU program, NOAO/AURA/NSF

Larger red, green, and blue composite image.

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