The Great Andromeda Galaxy (M31) and Neighbors
Size: 2.1 degrees
FOV: 2.6 x 3.9 degrees
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
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.
central portion glows slightly yellow as a result of older stars,
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 Ha.
FSQ106 at f5 on the Takahashi NJP
Autoguider: SBIG ST-402 with
Camera: STL11K -20C.
LRGB set (50mm unmounted); Baader 7nm
Ha filter (50mm unmounted).
Exposures: Luminance- 45 x 4';
Red- 12 x 6'; Green- 15 x 5'; Blue- 12 x 8';
Ha- 8x 20'. Total
exposure 9.7 hours.
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
Calibrated, aligned, and Sigma Clip combined
in Maxim, followed
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.
note: Graphics on this website may not be reproduced without
Back to Galaxies