Time Travel Research Center
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Andromeda Galaxy (M31) and Neighbors
Size: 2.1 degrees
2.6 x 3.9
2.5 million light years
RA (Jnow): 0h 42m 36s
Dec (Jnow): +41 degrees 16' 38"
Position Angle: +74 degrees
The Great Andromeda Galaxy is the most prominent member of our local
group, which includes the large and small Magellanic Clouds, M33 (Pinwheel
Galaxy), and the neighboring elliptical galaxies M110 and M32, seen
above at 5 o'clock and 10 o'clock (just off center), respectively. This
image represents a total 9.7 hours of exposure and is comprised of data
from Luminance, Ha, and RGB filters (details below). The Ha signal is
particularly interesting, since it highlights the bright HII regions
most prominent in the outer galactic arms. HII emission in galaxies is
most often due to excitation of surrounding hydrogen gas by UV
irradiation emitted by newly-formed, young stars. That's why we see so
much HII emission in our own galaxy in regions such as the Orion Nebula
and in Cygnus, for instance. Notice how the HII emission in the above
image corresponds to regions of blue star formation, best seen in this
higher resolution crop. The southwestern arm in the lower left contains
a particularly active region of new star formation referred to as NGC
206, shown in this image by Rob Gendler. In my image, notice the
absence of prominent HII emission in the two elliptical galaxies, M110
and M32, which contain old stars and lack regions of new star formation
(it is possible that HII regions exist in these galaxies as well but are
simply below the level of resolution in this image).
M31, like most large spirals, is thought to contain a large, central
black hole that consumes gas and nearby stars at a prodigious rate. The
radiation emitted in the vicinity of black holes (due to extreme heating
of matter as it flows into the region) compresses surrounding gas and
most likely triggers a new wave of star formation in a disk surrounding
the galactic center. In this regard, there is a rotating disk of about
400 blue stars that formed 200 million years ago and is rotating
around the galactic center at an orbital velocity of 2.2 million miles
per hour (the details may be found in Rob Gendler's excellent
description of the M31 nucleus). Given the proximity of these star to
the intense radiation emitted from the central black hole, it would be
impossible for life as we know it to evolve around such stars. It is
predictable that we exist in an outer arm of a spiral galaxy, where
conditions are more favorable for life to evolve (i.e., the galactic
habitable zone). Perhaps intelligent lifeforms are pondering the same
things about us, as they gaze at the Milky Way from their vantage point
in one of the outer arms of M31.
At a dark site, M31 is a naked eye object, although for city and
suburban dwellers it's almost impossible to view without a telescope. The
central portion glows slightly yellow as a result of older stars,
whereas the periphery has a characteristic bluish hue due to a
predominance of younger stars. Please check out the higher resolution
links for more detail, especially in the HII regions.
Date: August 13, 2007: Luminance; August 19, September 6, 7: RGB and
Scope: Takahashi FSQ106 at f5 on the Takahashi NJP Mount.
Autoguider: SBIG ST-402 with e-finder.
Camera: STL11K -20C.
Filters: Astronomiks LRGB set (50mm unmounted); Baader 7nm Ha filter
Exposures: Luminance- 45 x 4'; Red- 12
x 6'; Green- 15 x 5'; Blue- 12 x 8'; Ha- 8x 20'. Total exposure 9.7
Conditions: Temperature varied on each
night- generally 55-70 degrees F average. Some nights were marked by
intermittent clouds, requiring several nights of exposure to obtain the
best frames for processing.
Post-processing: Calibrated, aligned, and Sigma Clip combined in Maxim,
followed by DDP in ImagesPlus (IP). Further processing in Photoshop CS
(16 bit format). The Ha signal was combined with the red channel using
the lighten mode in Photoshop.
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