Galaxies

Our galaxy is thought to be shaped like a bar galaxy. This picture is from NASA if you want to read more about this.

Our galaxy may also have gas arms (without stars) according to Australian astronomers, that stretch out from the arms containing stars in them.

How Stuff Works discusses the halo in a way I am familiar with.

The halo exists outside the boundary formed by the almost 2 dimensional milky way galaxy at this scale. How stuff works also mention globular clusters of stars that are dotted around the galaxy, these stars have no gas apparently. If you ever get a astronomy program, try a fly-by of the galaxy, these globular clusters remind me of single stars (in fly-by mode; page 6 when viewed on November 2008), but they are in fact made up of a huge number of stars in reality.

Apart from globular clusters our galaxy has and is colliding with mini-galaxies and will eventually collide with the Andromeda spiral galaxy:

• http://en.wikipedia.org/wiki/Milky_Way

• http://www.space.com/scienceastronomy/060227_mm_milky_way_tour.html

• http://csep10.phys.utk.edu/astr162/lect/galaxies/colliding.html

• http://www.nasa.gov/audience/forstudents/9-12/features/F_When_Galaxies_Collide.html

The Halo is quite interesting because it is made up of hot gas, dark matter (apparently) and of cause photons of electromagnetic radiation (on earth we see this radiation (a small part of it) as light). While how it works does not state this directly, we can infer this from the fact that hot gas will at minimum give off infrared radiation. However the hot gas spoken of here could be of much higher temperatures.

The classical galactic structure is:

• Galactic Disk

  • Nucleus

  • bulge

  • spiral arms

• Halo

The magnetic fields of our galaxy are part of a structure we can not easily see and yet it does have a large amount of energy stored in it due simply to its' large scale.

The milky ways magnetic fields can trap high energy particles despite being weak when compared to our own solar systems magnetic field strength. For example: cosmic rays rotate around the Milky Way with the gas and stars. While I would expect these trapped particles to emit synchrotron radiation, I can not find any supporting work for this assumption.

"Total magnetic field strengths can be determined from the intensity of total synchrotron emission, assuming energy balance (equipartition) between magnetic fields and cosmic rays. This assumption seems valid on large spatial and time scales, but deviations probably occur on local scales in galaxies. The typical average equipartition strength for spiral galaxies is about 10 μG (microGauss) or 1 nT (nanoTesla). For comparison, the Earth's magnetic field has an average strength of about 0.5 G or 50 μT. Radio-faint galaxies like M 31 (Fig.3) and M 33, our Milky Way's neighbours, have weaker fields (about 5 μG), while gas-rich galaxies with high star-formation rates, like M 51 (Fig.1), M 83 and NGC 6946 (Fig.2), have 15 μG on average. In prominent spiral arms the total equipartition field can be up to 30 μG strong, in regions where also cold gas and dust are concentrated. The strongest total equipartition fields (50-100 μG) were found in starburst galaxies, like M 82 and the "Antennae", and in nuclear starburst regions, like in the centers of NGC 1097 and other barred galaxies. "

This quote (above) from www.scholarpedia.org indicates that synchrotron emission does occur in the weak magnetic fields formed on a galactic scale. Below; slide 28 also shows synchrotron radiation does exist because of the Milky Ways magnetic fields.

"Slide 28 Following subtraction of the dipole anisotropy and components of the detected emission arising from dust (thermal emission), hot gas (free-free emission), and charged particles interacting with magnetic fields (synchrotron emission) in the Milky Way Galaxy, the cosmic microwave background (CMB) anisotropy can be seen."

Still, such maps are hard to understand (at least for me) but in combination it would seem that magnetic fields in the galaxy and in the galactic arms do produce synchrotron radiation. This might indicate that charge is flowing around the galactic arms.

Does the huge galactic field simply form part of a circuit?

Further this magnetic field can focus a supernova into a flash light like pattern increasing its power out to further distances then previously thought. This means that distant super nova explosions previously thought harmless can be a threat to the earth.

However now that we believe that the galaxy is a bar galaxy type, this classical structure may be changed eventually. It is beginning to look very likely that a super massive black hole exists in the centre of our galaxy. It was originally thought that all black holes evaporated if they happened to have formed during the big bang, however scientist now feel that some black holes (containing exotic sub particles I believe) may have survived the big bang, could one of these surviving black holes be the youngster that eventually make the black hole in the centre of our galaxy (who knows).

The galaxy itself if one of many. Apparently if we zoomed back and looked at all the galaxies in the universe they would seem to form clouds that resemble strings that border spaces that appear empty (some say these spaces have dark matter in them, while other say that dark matter and matter are intertwined.).

This picture is from http://www.atlasoftheuniverse.com , the site has some really cool pictures and you can zoom in and out of them.

Dark Matter

Why is dark matter important when considering a galaxy

Dark matter probably help form our galaxy and hold it together and it will play a part in how our galaxy behaves in the long run.

I also have questions that remain to be answered about "what happens when the galaxy expands and matter and dark matter becomes more dispersed?" but those answers will no doubt have to wait until the true answers on what dark matter is are answered.

What is it?

Dark matter is a recent discovery, it causes all sorts of new theories to exist. Examples are that it is dark matter that holds our galaxies together. Dark matter was influential in the formation of galaxies and so forth.

The exact nature of dark matter is currently under investigation. This investigation might also include the new CERN particle accelerator and resultant discoveries.

The risks of examining the universe!

Note: CERN does have some detractors saying that it will trigger the end of the universe or send a mini-black hole to the centre of the earth that will eventually devour the earth. This particular question

Dark matter may also alter theories to how our universe might end

There has also been some alternative discussions about the thought that matter may one day simply evaporate. Could dark matter also be part of what holds atoms together on the atomic scale. So far this idea seems unlikely since dark matter is probably left over antimatter that had a higher then expected survival rate then originally expected.

a variation of matter disappearing (and not related to the previous discussion) is of black holes swallowing all matter and then dissolving away. However, I believe that dark matter will add a very interesting twist to this story in the near future as science advances and begins to understand what dark matter is.

Keep a look out for further news on Dark matter and fundamental particles

The discussion of dark matter will certainly be interesting and worth the effort to keep track of if you are interested in galactic structures or exotic forms of subatomic particles.

Incidentally, this matter of subatomic particles is also being investigated by particle accelerators such as CERN as mentioned above.

Solar System orbital's

Classical models of our solar system have been rocked by a number of discoveries, these include bodies about the size of Pluto. This has caused a renaming of orbital body party that will probably last for some time and cause many discoverers much joy or pain. For what is the latest news on this I like to look up http://www.nineplanets.org/ if only for the reason that the URL seems to make more sense then others.

One thing of interest is to take a careful look at new moons discovered and any new rings discovered around planets.

One of the early surprises of the name changes was Pluto being given dwarf planet status instead of planetary status. This means there are only 8 planets.

Eris (larger then Pluto) and Ceres are two other dwarf planets. Some sites say there are two additional  minor planets: Haumea and Makemake.

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