M33/NGC598, The Pinwheel Galaxy in the Triangulum
[Image of the Triangulum Galaxy, M33]
We have chosen to write about the Triangulum Galaxy, because we have imaged it on our own with an Apogee CCD camera (Equipment: Optical data : 5 " APO Meade f = 1140 mm - mounted PB on a 16 " SCT). In this report we want to include a bit history and then a lot of comparing with other objects. For instance the Andromeda Galaxy which is not far away from the Triangulum Galaxy.
At the image it is possible to see many nebulas in the galaxy.
Nebulas are the most obvious of the presence of matter in interstellar space. Several hundred can be counted in our own galaxy, as well as in several neighbouring galaxies. In our system, they are distributed in the neighbourhood of the galactic disk, where most of the interstellar matter is congregated. Nebulas demonstrate in various ways the action of stars, at different stages of their evolution, on the surrounding diffuse matter. Generally speaking, these effects are greatest at the beginning and at the end of a stars life. Four types of nebulas are distinguished: 1. Regions of ionised hydrogen, often called H II regions
2. Reflection nebulas
3. Planetary nebulas
4. Supernova remnants
These nebulas exist of cosmic gas. At the nebulas stars are being born and this also where they die.
Nebulas are only visual when they are blocking of the light of some stars.
Emissions nebulas:
These nebulas are is very colourful, and they shine like neon when their light is increased by the radiation energy from the stars in them.
When you closer at these nebulas, you might see the luminous gas, and maybe see the green and red colours. But normally it is only the red colour (hydrogen)
Generally about the Triangulum Galaxy
The Triangulum Galaxy is one of our neighbour galaxies, and its common name is M33. Messier object number 33 (M33) is a nearby galaxy and a part of the Local Group of Galaxies and Clusters. (more about that later on in this report).
The Triangulum Galaxy is also called Messier 33, which is a bit strange because it was probably originally discovered by Giovanni Batista Hodierna (1597-1660) before 1654. In 1764, which is more than 100 years later, Charles Messier rediscovered it independently, though, from Hodierna and catalogued it in the Messier catalogue.
M33 is also catalogued under in the following catalogues:
• The Messier Catalogue: M 33
• New General Catalogue of nebulae and clusters of stars: NGC 598
• Catalogue of Principal Galaxies: PGC 5818
• Morphological Catalogue of Galaxies: MCG5-4-69
• Catalogue of Galaxies and Clusters of Galaxies: CGCG 502-110
• Uppsala General Catalogue of galaxies: UGC 1117
• And probably many more...
The Triangulum Galaxy, M 33 is located on the northern hemisphere with the coordinates
RA.: 01h33m50s
Dec.: +30°39'37"

The reason for calling this galaxy the Triangulum Galaxy is not that some Grecian Goddess or Hero were named Triangulum, but because it is situated in the star constellation called the Triangulum. The star constellation “The Triangulum” consists of the following three stars:

ALP tri   (Alpha)  (RA: 01h53m04s, Dec: +29°34'46")
BET tri   (Beta)  (RA: 02h09m32s, Dec: +34°59'15")
GAM tri   (Gamma)  (RA: 02h17m18s, Dec: +33°50'50")
The Triangulum Star Constellation
As you can see at the illustration at the previous page the galaxy itself is not placed within the Triangulum, but it is placed inside the constellation boundaries which goes a lot further away from the star constellation itself.
How to find the Triangulum Galaxy
The galaxy in the Triangulum is located at the right border of the star constellation: the Triangulum. It is only visible at the northern hemisphere, but it is possible to see it with the naked eye if you have very good eagle eyes and if the sky is very clear. To find it you have to find the Andromeda Galaxy (M31), which is usually pretty luminous, and the two bright stars "beneath" it in the constellation Andromeda. If you take the distance from M 31 to the second star (Mirach) and add the distance to the line of the three objects (M31 – MU And – Mirach), you will find the Triangulum Galaxy, M33.
How to find the M33
"Technical info" about the Triangulum Galaxy
This galaxy has a mass of 25 billion solar masses and a diameter of 50,000 lightyears which is not that much in comparison with the Andromeda Galaxy which is 200,000 ly wide.
When we look at our image we are able to see both the older and younger stars. The old ones are yellow, and the youngest are blue and smaller than the others. At the centre there is a very bright nucleus which is red in colour caused by H(alfpha)-emmision (emission from ionised hydrogen). This nucleus is only about 5,000 parsecs in diameter which is very small.
Long spiral arms full of stars and nebulas are then visible from the nucleus and out. The arms are twisted counter-clockwise, and at the end of one of the arms a nebula is located that is particularly bright. It is the NGC 604. This is an area which is extremely active, which means that there is a production of new stars. See images below.
The NGC604 in the M33
[Image of NGC 604 in M33]
The structure of the Pinwheel Galaxy is pretty complicated because it has a north-south asymmetry. The southern part of the galaxy turns at 15-20 kilometres per second slower than the northern part. This asymmetry is probably not due to an excess of mass of the northern part, because no asymmetry has been noted in the Photometric Profile nor in the distribution of neutral hydrogen. The asymmetry could be caused by the bulge if the latter was slightly displaced with respect to the centre of the disc. Such displacements are often noted in barred spirals but could not be directly verified for the bulges. The asymmetry of the Triangulum Galaxy also appears in the hydrogen regions. Their excitation is stronger in the northern spiral arms than in the southern. This could result from two things:
1. A difference of chemical abundances between the two parts of the galaxy.
2. A difference in the effective temperatures of the stars which ionise the gas of the hydrogen regions. This leads us to the classification of galaxies.
Classification of galaxies
To be able to compare different galaxies in type and appearance Edwin Powell Hubble made a scheme (called the Hubble Scheme) for all Messier objects:
Hubble divided all galaxies into 4 main-categories: • Spiral galaxies
• Lenticular galaxies
• Elliptical galaxies
• Irregular galaxies
Spiral galaxies:
Spiral galaxies are in general large discs with a luminous centre that also is the mass centre of the galaxy. M33 is a spiral galaxy, and it is obvious that it has a centre even though it is not that big. This leads us to the subclasses of the spiral galaxies:
Spiral galaxies with conspicuous bulges are given the suffix a. If a galaxy is dominated by the nucleus and the arms are rather faint in comparison with the core, the galaxy is given the suffix b. For instance the Andromeda Galaxy is a Sb-galaxy (see image later on in the report). If a galaxy is dominated by its arms the galaxy is given the suffix c, and if the nucleus is almost missing or very faint it is given d. The Triangulum Galaxy is therefore a bit hard to categorise because it has a faint nucleus but not a very faint nucleus. Some scientist therefore makes it a Scd, which is a combination of the two categories, and other scientists agree that it is a Sc. This is very hard to determine, but in reality it doesn’t really matter which category a galaxy is a part of, unless you want to find it in a catalogue.
Another possibility for a galaxy is to be a barred galaxy, e.g. the M91:
The NGC604 in the M33
[Image of M91]
Those kinds of galaxies are classified with a SB, and then they can have the same extensions as the “normal” spiral galaxies.
Lenticular galaxies:
These galaxies are usually old spiral galaxies, and therefore they classified S0. They do have the appearance of usual spiral galaxies with the disc, but they don’t have any nucleus, and those galaxies consist only of old stars.
Elliptical galaxies:
Like spiral galaxies look like discs elliptical galaxies have their own appearance: they look like footballs (American football). But because they have this “free” kind of structure lenticular galaxies are often confused with these elliptical galaxies. The elliptical galaxies are classified with an E and then a number from 0 to 9, where 0 is total circular and 9 is very elliptical. An example is the M32 that is a neighbour galaxy to the Andromeda Galaxy (see also our image of M31, where M32 is visible just underneath M31). M32 is an E2:
The elliptical galaxy, M32
[Image of M32]
Irregular galaxies:
Irregular galaxies are as the name says galaxies that do not fit into the Hubble Scheme. This is galaxies which has been interacting (or more likely: are interacting) with other larger galaxies. A good example of this is M51, which is “sucking” the life out of NGC 5195:
M51's companion; NGC 5195
[Image of M51 and its companion NGC 5195]
Those galaxies are classified with the prefix: Ir.
Comparison between the Andromeda Galaxy (M31) and the Triangulum Galaxy (M33):
To compare these two galaxies you have to know something about them, of course. Therefore we have begun this comparison by taking pictures of both M33 and M31. M33 is shown earlier on in this report, but before comparing the two galaxies we will just comment the image of M31:
The Andromeda Galaxy
[Image of the Andromeda Galaxy, M31]
This is an image taken over several nights with this result. The total exposure is 19500 seconds luminosity. We have not yet had the whether to make colour images, and therefore the image is still in black/white. This image is one of our deepest and it is possible to see objects down to 21,7th magnitude. This also means that the amount of details on the Andromeda Galaxy is very high which leads to that the structure of the galaxy is visible.
In comparison the two galaxies are very different; not only in classification, where M31 is a Sb galaxy and M33 is a Sc, but also in size. The Andromeda Galaxy is about 200,000 ly wide and the Triangulum Galaxy is only about 50,000 ly wide. But M31 is not only wider, it is also heavier than M33, and therefore the M33 is slowly being sucked towards the bigger Andromeda Galaxy during to mass attraction between the two objects.
The velocity of the two galaxies have been measured and determined.
The Pinwheel Galaxy in Triangulum has a velocity towards our solar system of 179 +/- 3 km/sec. Due to our solar systems movement around the Milky Way nucleus M33 is only approaching us (the entire galaxy) with a velocity of 24 km/sec.
We now know how fast it is coming towards us and the distance to the galaxy, and now we can calculate when it is going to hit us:
Distance: 2.7 · 10 6 ly = 2.7 · 10 6 ly · 9.4608 · 10 12 km/ly = 2.554 · 10 19 km
Velocity: 24 km/sec.
Armageddon: 2.554 · 10 19 km : 24 km/sec = 1.0643 · 10 18 sec = 3.375 · 10 10 years
With this result we clearly see that we are not in danger for the many years to come – at least not from M33!
Litterature: • Information
   Source: Students for the Exploration and Development of Space (SEDS):
• Information about Messier Object 33
   Source: Students for the Exploration and Development of Space (SEDS):
• Information about galaxies and the universe
   Authors: Johannes Andersen, Leif Hansen and Birgitta Nordström:
   Galakser og kosmologi (Book in danish)
• Information about galaxies and the universe
   Publisher: Gyldendal
   Gyldendals store stjerne håndbog og himmelguide (Books in danish)
Our own images:
Our own images are obtainable at http://www.amtsgym-sdbg.dk/as. The following images were used: • Image of M33, The Triangulum Galaxy
   Info: Total exposure: 3.7 hours (9600 sec L, 500 sec R, 1200 sec G, 1900 sec B)
•Image of M31, The Andromeda Galaxy (black and white)
   Info: Total exposure: 5.4 hours (19500 sec L so far)
•Illustrations of the Triangulum Region
   Info: The backgroundimage is a screenshot from Desktop Universe 1.02.
Other images:
• Image of NGC 604, Giant Diffuse Nebula and star forming region in M33
   Source: Students for the Exploration and Development of Space (SEDS):
• Image of M91, Barred spiral galaxy in Coma Berenices
   Source: Students for the Exploration and Development of Space (SEDS):
• Image of M32, Elliptical galaxy in Andromeda
   Source: Students for the Exploration and Development of Space (SEDS):
• Image of NGC 5195 (M51’s companion), Irregular galaxy in Canes Venatici
   Source: Students for the Exploration and Development of Space (SEDS):
This report was written by:
Christian Hedeager Clausen, age: 18.
Jeppe Overbeck Petersen, age: 18.
Fie Buus, age: 17.
Teacher: Mogens Winther
Amtsgymnasiet in Sonderborg
Grundtvigsallé 86
DK - 6400 Sonderborg