Milky Way and Its Satellites
Our Milky Way galaxy has structure: a central bar and several arms. Our galaxy has a number of satellites: smaller galaxies and globular clusters. This mix interacts as a system. We have only a limited understanding of this system.
The following is a rough description of this system. Cosmologists must understand its details to make valid predictions in our galaxy's system. That basis is also needed to make valid predictions for another spiral galaxy like ours.
These numbers are estimates from Wikipedia.
The region of space with the Milky Way has many unknowns. From on or near Earth we are observing from within one of the spiral arms. Much of the galaxy and much of the universe is obscured by gas and dust as well as so many stars.
It is literally impossible to know what cannot be seen, even with different wavelengths of light.
Overview of our system (MW=Milky Way):
a) MW disk diameter = 150–200 kly (46–61 kpc)
b) MW disk thickness = about 2 kly (0.6 kpc)
c) MW arms = 2 major arms and several minor arms or spurs; these arms are loose structures of stars, gas, dust.
d) MW stars = between 100 - 400 billion (many are binaries)
there are roughly 8 distinct types of stars
e) MW globular clusters = about 150 (each has > 10^5 stars)
f) MW satellite galaxies > 50
There are 59 small galaxies confirmed to be within 420 kiloparsecs (1.4 million light-years) of the Milky Way, but not all of them are necessarily in orbit, and some may themselves be in orbit of other satellite galaxies. The only ones visible to the naked eye are the LMC and SMC.
LMC has 10 billion stars and 60 globular clusters; SMC has 100 million stars.
The complexity of our Milky Way system is quite impressive. Many critical details remain imprecise or unknown.
High resolution data are required but astronomers have been accumulating suitable data for not so many years.
The Yerkes Observatory would become the world's largest refracting telescope (102 cm) at the time in 1897, [and] is still the largest of its kind used for astronomy.
The Hale Telescope at 60" or 1.524m began in 1908.
The Hale Telescope at 200" or 5.08m began in 1948.
British Astronomer Sir Bernard Lovell made plans to build a large radio telescope in the 1950's. His vision was to build a huge 250-foot (76 meters) diameter dish radio telescope that could be aimed at any point in the sky. [It] was finally built in the summer of 1957 at Jodrell Bank in the UK.
The Arecibo Observatory, a 1000' or 305m radio telescope, was completed in 1963.
In 1990, NASA and ESA co-operated to build and deploy the Hubble Space Telescope. Although not the first space telescope, Hubble has is one of the largest and most flexible.
Since its deployment into low earth orbit, it has taken part in many vital research projects and PR for the field of astronomy in general. Liberated from the distortion of Earth's atmosphere (and limited background light), Hubble can provide very clear images of the stars and planets unparalleled from Earth.
The telescope consists of a 2.4-meter mirror and a suite of other instruments to observe near UV, visible light and near IR spectra. Hubble should be able to stay in service well into the 2030's.
We have been getting high resolution data for roughly a century and have found stars take millions of years for only one non-elliptical orbit in our spiral galaxy. Much time is required for observations at a scale beyond our solar system.
Beyond what can be seen our galaxy has a magnetic field and each star has an electric field.
It should not be a surprise we are currently unable to precisely predict the motion of individual stars in a complex galaxy like ours.
It is disappointing many accept the claim there is dark matter causing a failed prediction. The model must be improved not excused with a fiction. Dark matter is just the label for an excuse; it is not real.
The LHC is wasting time and resources looking for dark matter.
Hubble and Chandra are investigating dark matter. One of the stated goals of the Webb telescope is pursuing dark matter. It cannot be found simply because it does not exist.
What a terrible waste when we could be learning about the real universe.
The claim we can accurately predict the motions of stars in a distant galaxy (where dark matter is supposedly real) is just laughable.
There is so much to learn in the universe and yet many are convinced we must pursue a dark distraction instead.
The next daunting challenge in the future, after understanding our system, is understanding all the main galaxy types. The others are not as close as ours (the one we are in); those will have less critical details.
The main types:
a) elliptical - a huge sphere of stars but loosely held with no structure; or a very large globular cluster
M87 has > trillion stars [and 12000 globular clusters]. At least one elliptical is in every galaxy cluster. Ellipticals often have globular clusters.
b) spiral - arms spiral from around the core and its halo
c) barred spiral - the core is a bar and the arms spiral away from the bar's two ends; our Milky Way is this type.
d) lenticular- the core and halo look like a spiral but there are no arms, just a dust plane; alternately: like an elliptical with a dust plane.
e) ring - the core looks like an elliptical at the center of a ring structure with stars, dust, and gas but there is nothing between the core and ring; these are rare
f) irregular - the shape is close to none of the a-e above
The required resolution to individual stars is not yet possible for many galaxies.
All these galaxy types are observed in distant galaxy clusters, the domain of supposed dark energy (another mistake causing yet another distraction)
After all dark stuff is dropped by everyone, cosmology can make substantial progress toward its goal of understanding the real universe.
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