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Andromeda's coat of many colours

ESA's fleet of space telescopes has captured the nearby Andromeda Galaxy, also known as M31, in different wavelengths. Most of these wavelengths are invisible to the eye and each shows a different aspect of the galaxy's nature.
Visible light, as seen by optical ground-based telescopes and our eyes, reveals the various stars that shine in the Andromeda Galaxy, yet it is just one small part of the full spectrum of electromagnetic radiation. There are many different wavelengths that are invisible to us but which are revealed by ESA's orbiting telescopes.

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Astronomers identify thick disc of older stars in nearby Andromeda galaxy

An international team of astronomers has identified for the first time a thick stellar disc in the Andromeda galaxy, the nearest large spiral galaxy to our own Milky Way.
The discovery of the thick disc, a major result from a five-year investigation, will help astronomers better understand the processes involved in the formation and evolution of large spiral galaxies like ours, according to the team, which includes UCLA research astronomer Michael Rich and colleagues from Europe and Australia.

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Andromeda Is Getting Closer to The Milky Way

Andromeda, large galaxies are known to be a neighbour of our galaxy is a cannibal space. Until now grow big like this, he has been eating other galaxies that flew too close to him. Interestingly, the Andromeda is now getting closer. As is known, Andromeda and our galaxy, the Milky Way, are the two giant galaxies in its environment. Andromeda is the nearest giant galaxy. The distance is only about 2.5 million light years. A light year alone is about 9.4 trillion miles. As reported by MSNBC, February 1, 2011, the Milky Way and Andromeda approaching each other with a speed of about 120 kilometres per second and will crash.
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Star Clusters in M31
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Title: Star Clusters in M31: II. Old Cluster Metallicities and Ages from Hectospec Data
Authors: Nelson Caldwell (CfA), Ricardo Schiavon (Gemini), Heather Morrison (Case), James A. Rose (UNC), Paul Harding (Case)

We present new high signal-to-noise spectroscopic data on the M31 globular cluster system, obtained with the Hectospec multifibre spectrograph on the 6.5m MMT. More than 300 clusters have been observed at a resolution of 5A. The primary focus of this paper is the determination of mean cluster metallicities, ages and reddenings. Metallicities were estimated using a calibration of Lick indices with [Fe/H] provided by Galactic GCs. The metallicity distribution is not generally bimodal, in strong distinction with the bimodal Galactic globular distribution. Rather, the M31 distribution shows a broad peak, centered at [Fe/H]=-1, suggesting that the cluster systems of M31 and the Milky Way had different formation histories. Ages for clusters with [Fe/H] > -1 were determined using the automatic stellar population analysis program EZ_Ages. We find no evidence for massive clusters in M31 with intermediate ages. Moreover, we find that the mean ages of the old GCs are remarkably constant over about a decade in metallicity (-0.95 < [Fe/H] < 0.0).

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This mosaic of the Andromeda spiral galaxy highlights explosive stars in its interior, and cooler, dusty stars forming in its many rings. The image is a combination of observations from the Herschel Space Observatory taken in infrared light (seen in orange hues), and the XMM-Newton telescope captured in X-rays (seen in blues). NASA plays a role in both of these European Space Agency-led missions.
Herschel provides a detailed look at the cool clouds of star birth that line the galaxy's five concentric rings. Massive young stars are heating blankets of dust that surround them, causing them to glow in the longer-wavelength infrared light, known as far-infrared, that Herschel sees.
In contrast, XMM-Newton is capturing what happens at the end of the lives of massive stars. It shows the high-energy X-rays that come from, among other objects, supernova explosions and massive dead stars rotating around companions. These X-ray sources are clustered in the center of the galaxy, where the most massive stars tend to form.

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M31*
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Title: The Murmur of The Hidden Monster: Chandra's Decadal View of The Super-massive Black Hole in M31
Authors: Zhiyuan Li, Michael R. Garcia, William R. Forman, Christine Jones, Ralph P. Kraft, Dharam V. Lal (CfA), Stephen S. Murray (CfA/JHU), Q. Daniel Wang (UMass)
(Version v2)

The Andromeda galaxy (M31) hosts a central super-massive black hole (SMBH), known as M31*, which is remarkable for its mass (~10^8 solar masses) and extreme radiative quiescence. Over the past decade, the Chandra X-ray observatory has pointed to the center of M31 ~100 times and accumulated a total exposure of ~900 ks. Based on these observations, we present an X-ray study of a highly variable source that we associate with M31* based on positional coincidence. We find that M31* remained in a quiescent state from late 1999 to 2005, exhibiting an average 0.5-8 keV luminosity \lesssim 10^{36}ergs~s^{-1}, or only ~10^{-10} of its Eddington luminosity. We report the discovery of an outburst that occurred on January 6, 2006, during which M31* radiated at ~4.3 x 10^{37}ergs~s^{-1}. After the outburst, M31* entered a more active state that apparently lasts to the present, which is characterised by frequent flux variability around an average luminosity of ~4.8 x 10^{36}ergs~s^{-1}. These flux variations are similar to the X-ray flares found in the SMBH of our Galaxy (Sgr A*), making M31* the second SMBH known to exhibit recurrent flares. Future coordinated X-ray/radio observations will provide useful constraints on the physical origin of the flaring emission and help rule out a possible stellar origin of the X-ray source.

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Birth and death within Andromeda

The great life cycle of stars, from the moment they switch on to the point they destroy themselves, is caught in a new view of the Andromeda Galaxy.
This picture, released to the BBC, combines the power of Europe's Herschel and XMM-Newton space telescopes.
Herschel is sensitive to infrared light and sees the cold clouds of gas and dust where stars are forming.
XMM-Newton, on the other hand, sees X-rays, a signature of the violent cosmos and the death throes of stars.

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Andromeda 'born in a collision'

The nearest spiral galaxy to the Milky Way - Andromeda - was born when two smaller galaxies collided, say astronomers.
An international team conducted a computer simulation of how Andromeda evolved over time.

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French astronomers have used a computer model to show that the Andromeda Galaxy may have gotten its current shape due to a huge collision with a smaller galaxy.

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UCL space scientists have brought Andromeda Galaxy, the most distant object visible to the naked eye, into focus with the highest-ever resolution ultraviolet image of this most famous external galaxy.
The image - the most detailed ever taken of Andromeda in the ultraviolet - was made up of a 330 individual images in three ultraviolet colours, showing approximately 20,000 sources. The ultraviolet picks out the spiral arms where hot young stars are being born.

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