The Solar System is located at the spiral arms of our Galaxy is called the Milky Way. It is basically made of the galactic dick, globular clusters and the halo. Scattered below and above the disk are the globular clusters. They are randomly scattered and they orbit in elliptical orbits. They have little or no gas in them and contain older stars than in the disk. The halo is the dim region that surrounds the whole galaxy. Now, the location of the Solar System is in the galactic disk’s spiral arm. There are six spiral arms arising from the galactic center but our solar system is specifically located in the inner edge of a spiral arm known as Orion arm.
Evidences of the existence of a suppermassive black hole at the center of our Galaxy, the Milky Way
General assumption
A suppermassive black hole is believed to be at the center of our Galaxy. This center is normally called the galactic center. Astronomers believe that there could be black holes at the centers of most galaxies and even our own Galaxy, the Milky Way could not an exception. The suppermassive back hole at the center of our Galaxy, as the name suggests is believed to be very large and thought to be between a million and a billion times more than a typical stellar black hole.
Escape velocity
Sagittarius A *
The mass of this black hole could be millions times larger than our sun. A careful measurement of stellar motions around a point, say radio source in the middle, shows a black hole larger than our sun four million times. This source is called the Sagittarius A *
Existence of Quasars
Astronomers never had a concrete strong evidence for many years that suppermassive black holes really existed. The only indirect evidence was the existence of quasars in remote active galaxies. The indirect evidence was founded on the observation of the variability of time scale and the energy output of quasars. Considering the energy output of our sun, it was established that quasars could emit more than a trillion times more of this energy from a region that could be of the size of our Solar system. It was thus concluded that it could only be a massive black hole; through conversion energy to light that could be able to produce such enormous amounts of energy.
Gravitational effect near the galactic center
Gravitational effect of objects close to a black hole is the only observation to detect a black hole. A star, some years ago, was found orbiting close to the center of our galaxy, the Milky Way, where a suppermassive black hole is suspected to exist. In the pursuit to confirm and establish more evidence for this black hole, a second star ought to be observed too. Finally, a conclusive proof was confirmed that a suppermassive black hole is in the center of our Galaxy when astronomer and Physicist Andrea Ghez and her team found a second star even with a shorter orbit orbiting close to the center of our Galaxy. This could only be possible with a black hole in the center with huge gravitational pool capable to draw the star near.
Orbital velocities near the galactic center. Direct evidence however has been ascertained over the recent past for the existence of a suppermassive black hole in our Galaxy center. This evidence was founded on the observation of materials orbiting around the center our Galaxy. The observation confirmed high orbital velocities of stars and gases orbiting around the galactic center. The only way this acceleration could be explained is only by a massive object possessing overwhelmingly strong gravitational field which could be contained in a small space. This indeed could be a suppermassive black hole at the galactic center.
Cosmological collapsing
The formation of black holes is uncertain and even Astronomers are not sure how they are formed. As studied by astronomers, the collapse of massive stars is the genesis of stellar black holes and it has been suggested too that the genesis of the suppermassive black hole at the center of our Galaxy could be the collapse of massive clouds of gas during the early stages of formation. Also it has been suggested by scientists that the formation of this black hole could be due to stellar black holes consuming enormous amount of material and grow to a suppermasive black hole over millions of years. Emerging of a cluster of stellar black holes could also result to a suppermassive black hole. Astronomers generally believe that both active galactic nuclei and galactic jets are due to accretion of much material into the suppermassive black hole regardless of mechanism of formation.
The direct effect of Spiral Density Waves
Spiral density waves are directly responsible for Grand design Spirals.
The best explanation for the grand design spirals is by the Density wave theory. Creation of Spiral arms according to this theory is when the density waves turn around a galaxy at a speed different from the one of the stars and dusts around the galactic disk. Though the location of the stars in the spiral region may not be constant, they are normally clumped in dense regions due to the gravitational field effect of the dense material. They are pulled by gravity towards the dense material when they get nearer the spiral arm and they are slowed from exiting as they travel in the arm. As a result, dense material is caused to clump in the dense region referred to grand design spirals.
The reason why some galaxies in the Local Group exhibit blueshifted spectral lines and why this blueshifts are not a violation of the Hubble law.
Because of the mutual gravitational attraction between the galaxies, they also have their own motions relative to each other. Thus in relation to nearer galaxies, the speed of Hubble flow is small in contrast with these intrinsic velocities. That is why some Galaxies in the Local Group are actually approaching us and they exhibit blueshifted instead of redshifted spectral lines.
A hypothesis to test a sky object suspected to be a quasar
Observation of Quasars with naked eyes can be quite difficult but not impossible. This is because the basic brightness of quasars in the sky can hardly be more than brightness of magnitude 13. Therefore it is hard for them to be seen by an amateur telescope. In fact, most quasars are fainter in a hundreds of times. We can use CCD camera, a telescope with a clock drive and some software so that we can observe quasars and there motion properties as the best approach to test the hypothesis of a suspected quasar in the sky. Thus we shall be able to track properly the proper motion and annual parallax of faint stars which are light years away.
The demonstration of this crucial experiment demonstrates quasars having significant proper motion given that they are stars within our Galaxy. The average brightness of quasars has been described to be directly proportional to their nearness to the earth.
In conclusion, CCD cameras and small telescopes can be used to properly track quasars’ proper motion. Also by using infra-red or optical spectroscopy, we could find the intrinsic variability of the object.
The differences between the Doppler Redshift and Cosmological Redshift
General introduction on how redshifts could occur
Redshift, according to astrophysics could occur if electromagnetic radiations like light that is moving away from an observer is increased in wavelength or could be shifted to the red end of the spectrum. Increased wavelength is a direct inference of redder end of spectrum regardless of whether the radiations are within the visible spectrum equivalent to lower photon energy and lower frequency according to the quantum and wave theories of light respectively. Whenever the light source moves away from the observer, a redshift could occur.
The causal difference on the manner of the two redshifts
Apparent change in pitches of sounds like that of a siren and sound wave frequencies emitted by speeding machinery like vehicles caused the Doppler effect while Cosmological redshift is majorly due to expansion of the universe with light sources sufficiently distant by at least a million years away and the redshifts correspond to the rate of increase of distance away from the earth.
The emitting object behavior and its effect on the redshifts
Emitting object’s relative velocity is the most important factor in a Doppler shift. The light wavelength that is received cannot be affected by what happens to the emitting object. But for the cosmological redshift, what happens to the emitting object is important since it expands with the rest of the universe. In general, the measure of the total ‘stretching’ undergone by the universe between the time between emitting and receiving of light is what we reefer are Cosmological redshift.
Relative difference between the observe and emitted wavelengths
For cosmological redshifts with relative difference between the observed and emitted wavelengths less than 0.01, there could be additional Doppler Shifts. This additional redshifts are caused by peculiar motions of Galaxies relative to one another. This causes a wide scatter from the standard Hubble law. This resultant situation is well illustrated by the Expanding Rubber Sheet universe. This is a common analogy in cosmology in description of expansion of space. To illustrate this analogy, we take two objects. One is to be represented by a bearing and the other by spacetime. The spacetime representation is by a stretched rubber sheet. Doppler Effect is caused by rolling the ball across the sheet to create peculiar motions. The cosmological redshift unlike the Doppler redshifts occur when the ball bearings are struck to the sheet and the she sheet is stretched.
Reliance on local and recessional velocities
Doppler redshifts depend on local velocity while the Cosmological redshift depends on the recessional velocity due to the expansion of the universe.
Mathematical difference
Sometimes the expression, "Doppler redshift" instead of "cosmological redshift" especially in the modern literature especially in the description of the redshift galaxies which are dominated by the expansion of spacetime. But it is clear that the relativistic Doppler equation cannot be used to determine the Cosmological redshift which is principally characterized by special relativity. Thus the two redshifts are mathematically different.
Distance from the local center of mass
Distant galaxies could be seen blueshifted instead of being redshifted if the universe was contracting. This blueshift could be proportional to their distance amount. For regular special motions, both Cosmological and Doppler redshifts could be mixed up but cosmological redshifts are easily distinguishable and only important for distant Galaxies. Cosmological redshifts could only be seen unambiguous at distances of about a hundreds of Megaparsecs. Ordinary Doppler shifts from galaxian motion relative to the local center of mass can be comparable to the cosmological effect at nearer distances.
The effect of the universe expanding forever on the Cosmic Microwave Background radiations.
If we assume that the Universe will expand foe ever, then I think that either the microwave background radiations will be beyond our horizon or may cool approaching the absolute zero since they will be undetectable. There have been several theories brought forward to explain about the expansion and contraction of space but it seems like the big crunch is not inevitable.
This discovery paved a way for Astrophysicists to bin studying how they could use the properties of the Cosmic Microwave Background radiations to study how the universe was like long time ago. The radiations contained information on how matter was distributed even over ten billion years ago according to the Big bang theory when the universe was 500,000 year old only.
The background radiations were generated by the collision of photons with other particles constantly which have been described to have been of temperature of more than 3000 C. at the time of this collision, both the stars and the galaxies are thought not to have been formed.
It has been observed by Astrophysicists that after formation, the universe began to expand continuously. The astronomers also believe that galaxies once uses to be overlying each other but have moved apart over billions of years due to the universe expansion. Now, as the universe expanded, the background radiations cooled enough that atoms were formed by the combination of the electrons and the nuclei. The atoms formed were neutral electrically the photons of the background radiations never collided with them anymore.
The astronomers say that there were slight variations in the universe density after the formation of the first atoms which grew into the density variations we see today as illustrate by galaxies and clusters. Then, an exciting possibility was realized by the scientists that measurement of temperature variations of the background radiations in different regions of the sky could give the density variation of the earlier universe.
Talking about the fate of the Cosmic Background Microwave Radiations, assuming the universe would expand forever then, their distance away from the earth could be increasing too. Of cause the radiations will not expand too nor do the photons come further apart. Also say that these radiations could actually get red-shifted into a radio spectrum and beyond. In fact, there is no upper limit of the wavelength of light but according to me; there could be a practical limit for detectable wavelengths. In conclusion, despite all this hypotheses, according to temperature the Cosmic Background Microwave Radiations could approach but not reach zero as the universe expands infinitely.
The force of nature that formed second
The strong forces are said to have formed second.
The fundamental forces of nature in our present Universe are indeed distinct and they have different characteristics. This was not so in the earlier universe as thought by Astrophysicists. There is a hypothesis of scientists that the weak, electromagnetic and strong forces were unified into a single force in the earlier universe when temperatures were very high compared to today. The forces are thought to have separated from each other when the temperatures dropped possibly due to the universe expansion. According to the hypothesis, the strong forces separated first. Subsequently again, still at lower temperatures, the electromagnetic and weak forces separated. As a result of this, there were left four distinct forces that are seen in our current universe. The process of the separation of these forces of nature is called spontaneous symmetry breaking.
The stellar spectral most likely to have a planet on which advance life exists
Stellar habitability factors include luminosity, stability and lifespan. The G-star class is the one that hosts life it is ours. It has abundance of elements and low variability in brightness. It is also different from many stellar systems which in fact, have only one star in them. Spectral type O, B and A are too quick for advanced life to develop. Spectral m is a dwarf type of a stellar spectral, along with other problems due to its sheer number of longevity, is likely to tidally lock planets within its habitable zone.
Works cited
Exploring our Solar System - Crabtree Publishing:
<http://www.crabtreebooks.com/download/tg/9781427102096.pdf>
< http://igpg.gravity.psu.edu/archives/thesis/2000/dan.pdf>
Physical properties and environments of nearby galaxies
< http://cosmo.nyu.edu/blanton/nearby_preprint.pdf>
WMAP's Introduction to Cosmology - Wilkinson Microwave
< http://map.gsfc.nasa.gov/universe/WMAP_Universe.pdf>
Review 3 - Tufts Institute of Cosmology
< http://cosmos.phy.tufts.edu/~zirbel/ast21/tests/Review3.doc>
Cosmology; the history and fate of the universe
< http://astro.ucsc.edu/~sdmurray/AY5/FateOfUniverse.pdf>
Cosmology; the history and fate of the universe
< http://astro.ucsc.edu/~sdmurray/AY5/FateOfUniverse.pdf>
Extraterrestrial Life – Beyond Our Expectations?
< http://www.univie.ac.at/EPH/exolife/workshop_prog.pdf>
