Spiral Galaxies

Spiral galaxies consist of ca. 100 to 200 billion stars and interstelllar gas. These components are arranged in a thin disk with an extent of about 100000 light years. The stars and the gas rotate about a gravitational centre, with a rotation period of about 250 million years. The salient spiral structure of the stars and the gas components is caused by so-called density waves, which propagate about the galaxy centre, thereby compressing the gas along the spiral arms. Within these compression zones new stars are formed out of the condensed gas, their bright light highlighting the spiral arms.

NGC 5457 (M 101)
Maksutov-Newton, Canon 1100Da, 14.1 hours

M 101, about 25 million ly distant, is surrounded by copious dwarf galaxies. One of these, NGC 5477, is visible in this image east (to the left) of the main galaxy, whereas all others are outside of the field shown here. They orbit the main galaxy over a period of between 1 and 3 billion years, which also leads to the somewhat bizarre spiral structure of this galaxy.

NGC 628 (M74)
Maksutov-Newton, Canon 1100Da, 17.2 hours

This 25 million ly distant galaxy exhibits are rather symmetric spiral structure, which in view of its rather isolated position is not a surprise.

NGC 4321 (M100)
Maksutov-Newton, Canon 1100Da, 6.0 hours

The spiral galaxy M 100, 55 million ly distant, is also a member of the Virgo Cluster and is located at the periphery of the cluster towards us. One can see a number of other spiral galaxies (NGC 4312, NGC 4322, NGC 4328, IC 783) in its immediate surroundings, which are contained in the field shown here. NGC 4312, visible at the bottom of the image is the brightest of the satellite galaxies. In contrast those galaxies located close to the centre of the galaxy cluster, peripheral spirals still possess a lot of interstellar gas as they have not been diving through the centre of the galaxy cluster so far where they would get rid of much of their gas because of the strong ram pressure exerted on them there.

NGC 6946 + star cluster NGC 6939
Maksutov-Newton, Canon 1100Da, 11.0 hours

Here we see a classical spiral galaxy with a somewhat irregular spiral structure, located at a distance of 20 million ly. Because of its proximity to the Galactic plane (b = -11°) the galaxy is reddened. In particular the blue part of the light  is absorbed by the interstellar matter (gas and dust) on its way through the Milky-Way plane so that the galaxy appears yellowish compared to those that are further away from the Milky-Way band. To the north-west of NGC6946, one can easily make out the open star cluster NGC6939, which is only about 6000 ly away from us..

NGC 6946 + NGC 6939
Evostar 72, Canon 1100Da, 6.2 hours

Here we see a larger field. Inspection of this image in a dark room disclosess quite a few dark patches. These are not defects in the camera sensor, but reflect in fact locations in which there is significantly more dust blocking the light of the stars.

IC 342
Maksutov-Newton, Canon 1100Da, 7.3 hours

Similar to NGC 6946, also this galaxy, located at a distance of about 8 million ly, lies close to the Galactic plane (b = + 11°). It is rather similar to NGC 6946, with the spiral structure more regular though.

NGC 4736 (M 94)
Maksutov-Newton, Canon 1100Da, 17.4 hours

This galaxy, 15 million ly away from us, consists of a very bright central region in which intense star formation is going on. This region connects to a dimmer part in which star formation has essentially ceased. Still further out one recognizes a gleaming ring, which is also structureless. Its orientation is markedly different from that of the inner regions, with a conspicuous gap between this outer ring and the next inner one. What we see here is a resonance phenomenon, which developed over billions of years, owing the complex dynamics of such a stellar system.

NGC 224 (M 31)
Evostar 72, Canon 1100Da, 6.9 hours

This nearby galaxy (distance 2.5 million ly) is rather similar to our Milky Way. Apart from the bright nuclear region, two elliptical satellite galaxies, M 32 (NGC 221) below and NGC 205 above catch the eye. The educated eye will easily see the Andromeda Nebula - given a dark sky (e.g. in the Eifel) - without a binocular. A binocular provides a really pretty view of these 200 billion suns!

NGC 224 (M 31)
Maksutov-Newton, Canon 1100Da, 4.3 hours

Mosaic of two images taken with the larger focal length.

(NGC 598 (M 33)
Maksutov-Newton, Canon 1100Da, 35,9 hours

One of our neighbouring galaxies is the smaller spiral galaxy M 33 at a distance of 2.8 million ly. Its spiral arms are less pronounced because this galaxy possesses too little mass to produce density waves, which form strong spiral arms. The galaxy is featured by a number of large HII regions, i.e. regions of ionised gas. These are by far larger than the Orion Nebula. In these regions, the interstellar gas is ionised by newly formed massive and very hot stars. The most conspicuous regions are NGC 604 in the north-east of the galaxy, and NGC 595 located a bit north-west of its centre. Finding this relatively faint object with a good binocular needs a bit of patience...

NGC598 (M 33)
Evostar 72, Canon 1100Da, 9.9 hours

Wide-field image of M 33.

NGC 2403
Maksutov-Newton, Canon 1100Da, 5.8 hours

This galaxy can be considered as a 'twin' of M 33. It has rather similar properties: less pronounced, 'flocculant' spiral arms, which also here is due to its relatively small mass. The galaxy is also characterized by numerous prominent HII regions. In spite of the rather different distances (NGC 2403: 8 million ly; M 33: 2.8 million ly) the close similarity is evident at first glance, also because of the roughly similar inclination angles (about 60°).

NGC 925
Maksutov-Newton, Canon 1100Da, 15.5 hours

NGC 925 Is a late-type galaxy, and a little bit more massive than the Large Magellanic Cloud. However, it possesses spiral structure, indicating the action of density waves. It is 30 million ly away from us.

NGC 5055 (M 63)
Maksutov-Newton, Canon 1100Da, 18.1 hours

This galaxy, located 30 million ly away from us, is featured by a conspicuous dust lane running through the galaxy disc. It is most likely caused by a dwarf galaxy, which has penetrated M 63, whereby it was disrupted, with luminous parts of it remaining visible a little bit south of the bright foreground star to the west of the galaxy.

NGC 2903
Maksutov-Newton, Canon 1100Da, 7.6 hours

Even though this galaxy, 30 million ly away, lacks any neighbouring galaxy in its surroundings, it possesses very pronounced spiral arms, indicating the action of density waves. Its centre is crossed by bar structure, which also hints at resonance phenomena in the gravitational field of the galaxy.

NGC 4258 (M106)
Maksutov-Newton, Canon 1100Da, 13.2 hours

NGC 4258 alias M 106 is a remarkable spiral galaxy. It hosts a supermassive Black Hole (several tens of million solar masses) in its centre, which produces jets consisting of very energetic particles, the impact of which can be seen in certain spectral regimes (radio, optical in the Hα line, X-rays). These effects are hardly visible in normal optical images as the one shown here. However, one can see that the central region of this galaxy is characterized by intense star formation.

NGC 4826 (M 64)
Maksutov-Newton, Canon 1100Da, 10.7 hours

The galaxy NGC 4826, also called 'Black-Eye Galaxy', is rather conspicuous because of its kidney-shaped dust region in the centre, while the outer range of the galaxy appears in rather blue light. The blue colour hints at the formation of large numbers of young, massive and hence very hot stars. The peculiar dust structure in the centre is most likely the result of the infall of a dusty dwarf galaxy. This is corroborated by counter-rotation that has been found in that central region. This 'meal', which is ongoing since about a billion years, is hence a very 'dry' one.

NGC 7331
Maksutov-Newton, Canon 1100Da, 19.8 hours

The galaxy NGC 7331 is about 35 million light years distant. It is the biggest within a group, with three other group members visible to the east, viz. (top to bottom) NGC 7336, NGC 7335, and NGC 7337.

NGC 253
Maksutov-Newton, Canon 1100Da, 75 minutes

The central region of this about 11 million ly distant galaxy is featured by extremely strong star formation, whereby many more stars are formed out of the interstellar gas per unit time than in the whole Milky Way galaxy. Taking the image of this 'starburst galaxy' was not easy: as it is located at a very low declination (-25°) trees had to be cropped and good weather with a transparent atmosphere have to be waited for.

NGC 891
Maksutov-Newton, Canon 1100Da, 12.5 hours

NGC 891, located at a distance of 30 million ly, possesses a lot of dust, which dims the light of the disc and makes it appear in a somewhat yellowish colour. One can clearly make out dark vertical structures emanating from the disc and reaching out into the galaxy halo. This material (dust and gas) is ejected through the pressure induced by supernova explosions in the disc.

NGC 5907
Maksutov-Newton, Canon 1100Da, 7.1 hours

This galaxy, 50 million ly distant, is also seen edge-on. Also here, vertical dust structures can be seen reaching out of the galactic plane.

NGC 4565
Maksutov-Newton, Canon 1100Da, 4.0 hours

NGC 4565, located at a distance of 30 million ly, is a prototypical example of a galaxy seen exactly edge-on. Close inspection reveals a multitude of dark structures, which emanate from the disc in a vertical direction. This material (gust and gas) is pushed out of the disc perpendicular to it by supernova explosions and stellar winds. In the lower right a smaller galaxy is also visible.

NGC 4631
Maksutov-Newton, Canon 1100Da, 5.0 hours

NGC 4631 is about 30 million light years distant. It exhibits intense star formation, which is also responsible for its conspicuous blue colour. It shows a lot of dust along its plane, which forms pronounced vertical structures that emanate from the disc. This material (dust and gas) is mainly ejected by the pressure of supernova explosions within the disc. The small elliptical galaxy NGC 4627 (seen immediately above it) appears to be structureless as it lacks recent star formation. Its interstellar gas has been almost completely converted into stars.

NGC 7640
Maksutov-Newton, Canon 1100Da, 10.1 hours

The rather poorly studied galaxy NGC 7640 is nearly 30 million ly distant. Because of its proximity to the Galactic plane (b = - 19°) it is not very conspicuous. It is a barred spiral, viewed nearl edge-on.