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Friday, 29 March 2013

The evolution of Spiral Galaxies in the observable universe – Author’s views


    * Authors are_:
Mr. Rupak Bhattacharya-Bsc(cal), Msc(JU), of residences 7/51Purbapalli, Sodepur, Dist 24 Parganas(north) Kol-110,West Bengal, India**ProfessorPranab kumar Bhattacharya- MD(cal), FIC Path(Ind), Professor and HOD of Pathology convener in-charge of DCP and DLT course of WBUHS, , Calcutta school of Tropical Medicine, 108, CR Avenue, KOlkata-73 , West Bengal, India, Ex- Professor and HOD  Ophthalmic pathology, RIO KOl-73, Ex professor of Pathology WBUHS and EX Add. Professor IPGME&R KOl-20 W.B, India** Miss Upasana Bhattacharya – only daughter of Professor Pranab Kumar Bhattacharya of mahamaya Apartment Mahamyatala, Garia kol-84 *Mr.RitwikBhattacharya, *Miss Rupsa Bhattacharya-,* Mr Soumyak Bhattacharya BHM(cal) MSC(student) PUSHA, New Delhi, all of residence   7/51 Purbapalli, Sodepur, Dist 24 parganas(north) ,Kolkata-110,WestBengal, India*** Mrs. Dalia Mukherjee BA(hons) Cal, Swamiji Road, South Habra, 24 Parganas(north) West Bengal, India*** Mrs Dalia Mukherjee BA(hons) Cal cutta university, ***Miss Oaindrila Mukherjee- BA(hons) Student Cal Univ, ***Mr Debasis Mukherjee BSC(cal)  ,Swamiji Road, South Habra, 24 Parganas(north), West Bengal, India           

 There are about 1018 million of galaxies in the Universe, and there exist vast empty 3D dimensional space-time is between them. How much distance from one galaxy to another? "Cephids" can be used as a distant indicator to about 10 million light years, which is equivalent to 4 million persec. These galaxies are distributed through out the Universe. Galaxies are of different type and configu­rations. Some are spiral galaxies, some are non-spiral galaxies Amongst all the galaxies in the Universe, a small minority of the galaxies are spiral galaxies i.e. disc shaped galaxies (some are again of thin disc and some are of thick disc). There are non spiral galaxies also and most of the galaxies in the Universe are of non spiral (without disc) and majority of them are elliptical galaxies and rare verities are lenticular galaxies. Our "Milky way" is the local group of spiral galaxies. It is our home galaxy. Our Milky way galaxy is a spiral galaxy – a massive and a big galaxy at least 250 billions of solar mass MO and is a disk like of a diameter 100,000 light years. The light at its speed cross from one end to another end takes almost one lack years. It consists beside trillions numbers of stars contain also 1022 planets and thousands of clusters of nebulae (nebulae are of various types like diffuse nebulae, planetary nebulae, supernova remnants, and dark nebulae), supernovas and globular clusters.  The mass of the Milky way is probably in between 750 billion & one trillions of solar mass. Milky way is a spial galaxy of Hubble Sb or Sc type. So Milky Way has pronounced disk component exhibiting the spiral structure and a prominent nuclear region, which is a part of a notable buldge/ halo component. Milky way galaxy belongs to local group, a smaller group of three large and over 30 small galaxies and second largest galaxy in the universe. Milky way galaxy contain many clusters of galaxies. They are 1) Mosiac of Milky way extending from  Saggittarius galaxy to  Cassiopeia Galaxy. 2 Ophiuchus galaxy and 2 globular clusters 3)Theta Ophiuchi 4) Scorpius & saggituris galaxy 5) Serpens 6) starclouds in Sagittarius  7) Sagittarius M8 8) Aquita & Sagittarius M69) Western Aquita 10) Gamma Cygni galaxy 11) Alpha cygni galaxy and so many. The milky way appears to be brightest in the direction of Sagittarius where the galactic center lies. Relative to the celestial equator, the Milky Way passes as far north as the constellation of Cassiopeia and as far south as the constellation of Crux. This reflex the fact that the earth axis of rotation is highly inclined to the normal to the galactic plane The galactic disk of milky way has a diameter of about 100,000 light years, The distance from our Sun to the galactic center of our Milky way is about 27,7000 light years. The center of our galaxy is one of the highest infra Red sources of sky. It is about thousands time brighter in the infrared then in radio wave length. Infra red observation show that the center of our Milky Way is orbiting very rapidly. The center of Milky way is not visible at optical wave length because it is hidden behind numerous clouds of star gas and dusts. However we can view the center of Milky Way at infrared sources as infrared can easily penetrate gas and dusts. The Milky Way contain over 200 billions numbers of stars more massive then our sun. The amount of mass inside suns orbiting only around galactic center is 9.0x1016M0. The stars in the galactic disk rotate around galaxy’s center, which is suspected to harbor a super massive black hole. There are believed to be four-mazor spiral arm and at least two smaller arms, which all start at the galaxy’s center. They are named as follows 1) Norma arms 2) Scutum arm 3) Sagittarius arm 4) Orion arm 5) Pursues arm 6) outer arm. The distance between the local arm to the next arm’ Peruses arm” is about 65,000 light years. Each spiral arm describes a logthermic spiral. The disk is surrounded by halo of old stars and globular clusters. Our sun is located at an extreme distance of the disk. The disk of the milky way has four spiral arms that we described a little ago. The disk is approximately 300 Pc thick and 30KPc in diameter. It is made up of predominantly of Population I star [see star formation] which tends to be blue stars and reasonably spanning an age range between a million and ten billions years old. The buldge at the center of Milky Way is a flattened spheroid of dimension of 1KPc /6KPc. This is a high density region with population II stars which tends towards red and are very old stars about 10 billions years old. The halo, which is a spherical region surround the disk .It, has low density of old stars mainly in form of globular clusters [each globular clusters consist of stars between 10,000- 1lack]. The halo is believed to be composed of mainly cold dark matter 9CDM) which may extend beyond the edge of the disk. The local group of galaxies is probably millions of light years away from our A.G.N.
When Did the First Cosmic Structures Form as galaxy? Quasars are probably the first cosmic structure probably formed in our cosmos . Quasars are  most distant and distinct objects that astronomers have been able to directly detect. Because of their intrinsic brightness, the most distant quasars are seen at a time when the universe was one tenth of its present age, roughly a billion years after the Big Bang moment . However, astronomers believe that some objects must have formed earlier than quasars, because the ambient gas in the universe is observed to be ionized at a relatively early time, presumably due to ionizing radiation from a population of early objects. Since ionized gas can interact with cosmic microwave background photons, WMAP observations help to elucidate the nature of the ionized gas and the objects that caused the ionization. Since light travels at a finite speed, distant objects are seen as they existed in the past. We see the Sun not as it is now, but how it was just eight minutes ago. (The  so the Sun which we see at a moment time today is eight light minutes away from the Earth). We see the nearby stars as they were several years ago. We see Andromeda, the nearest spiral galaxy as it was roughly 2.5 million years ago how it was . Thus, the most distant objects that we see are the oldest objects that we can directly detect.
 What is Quasars?

Quasars are the most distant distinct objects that astronomers have been able to detect. In a region smaller than our solar system, a quasar  in fact emits more & more light than our total entire Milky Way galaxy emits light.  Can you imagine that ?   But Quasars are again believed to be super massive black holes, whose masses exceed that of a million Suns, and whose pull is swallowing gas and stars from their host galaxies. Then black holes also emits light. They do shine brightly by converting the gravitational energy of the in falling Astronomers and physicists are not till date certain what objects ionized the gas(Mixed dark matter oe WIMP) in the early universe nor do they know at what time this ionization occurred. Some speculate that an early generation of massive stars ionized the gas. Others speculate that most galaxies contain super massive black holes and that the formation of these super massive black holes illuminated the early universe. When Was then Gas Ionized is our question ? While observations of quasars enable astronomers to infer that the gas was ionized within the first billion years of the universe, we need to observe something more distant than quasars to learn when the gas was first ionized: the cosmic microwave background radiation. Since the cosmic microwave background photons were emitted roughly 380,000 years after the Big Bang, much earlier than the photons from quasars, their properties tell us about the subsequent evolutionary history of the universe. Microwave photons move freely through neutral gas, but they scatter off of ionized gas. This scattering reduces the amplitude of fluctuations in the temperature of the cosmic microwave background and produces new "polarized" microwave background fluctuations.

material into light. The most distant quasars are seen at a time when the universe was one tenth its present age, roughly a billion years after the Big Bang

What Ionized the Gas in the Early Universe? Scattered light is often polarized. On a bright day, we see not only sunlight directly from the Sun, but also light that scatters off of dust in the air. This scattered light, or "glare", is polarized and can thus be filtered out by a good pair of polarized sunglasses. Similarly, scattered cosmic microwave background photons are polarized by scattering off of free electrons in the early universe. WMAP is designed to detect polarized photons. In principal, their properties reveal the number of free electrons in the early universe and the ionization history of the universe. This enables astronomers to infer that the first objects in the universe capable of ionizing the gas formed at about 200 million years after the Big Bang. We hope that the time history of the ionization will help determine the nature of these first objects

How the spiral gala­xies were formed? Before formation of the galaxies, there were pre galactic clouds which is consisted of gaseous substance. Sir James Jeans first proposed that when the same density perturbation exist in the homogenous gas clouds and when clouds exceeds a certain limit, the cloud suffer an instability. As a result the cloud begins to collapse. The Jeans critical mass (Mj) was described as follows.

       MJ=1023(T/U)3/2-1/2p gm
[Where "P" is the density, "T" is the Tempe­rature and fl is the mean molecular weight of cloud. ]

The pre galactic gaseous mass were above the critical mass and as a result this pre galactic gaseous clouds collapsed owing to density perturbation. The mass of discrete such clouds was about 1014-1015 MO which is typical for the mass of super cluster in the present Universe. Now the fragmentation process carried on within the super clusters. The denser central region of the collapsing gas cloud collapsed more rapidly than the outer region and became more and more dense. Ultimately it became so compact that instability set in and it was fragmented in pieces. Each individual fragment continued to collapse and was re fragmented and the process went on until star formation set in. Thus Super clusters collapsed and frag­mented resulting cluster of galaxies which in course of time again fragmented into galaxies. -If further fragmentation would continue, one would star clusters from where baby stars generated. If we observe today at high galactic latitude, we can see hydrogen clouds .concentrated in a thin layer around the galactic plane, which is moving with a very fast velocity about 5 Km S-I. There are several such gaseous clouds with very high velocity up to 200 Km S-I. The distributions of gases are extremely uneven. It is concen­trated in clouds (dark matters) of different sizes. This cloud matter are probably still in extra galactic system or even in the proto­galactic system. Now, the spiral galaxy system evolution resulted when the protogalactic gasses or clouds detached itself from the surrounding Universe. They then gained angular momen­tum, at the moment of their detachment. There was a minimum radius for the "cell" bellow which it no longer contained the nece­ssary angular momentum. For our spiral galaxy "Milky way" the minimum radius reached, suppose at the time "t" when the radius of the Universe "p" was about 1/25th of the present radius Ro. And that was the time when the "Cell" spiral galaxy had a large amount of angular momentum. There was of course radial stream momentum as well as transverse stream momentum in the ­cell. All these momentum resulted initiation of rotation. The angular momentum in the "Cell" containing cloud gasses gave spiral galaxy due to the collapse of the part of the gas, (Fig-I) It happened probably at the time of about 109 years, a little shorter then the age of the Universe 1010 years (1000 billion years). The radial stream force should diminish the Universe expansion locally. They will not in 'general eliminate it entirely and so the spiral galaxy will expand some time. But it will also collapse again, due to angular momentum in about again 109 years beyond the present time. Now the question remain to us if the galaxies would be formed where the velocity gradient happened to be favorable for spiral galaxies, then there may be many other areas where no such function was possible. So then, in those areas, we should have direct evidence of inter galactic matter. There must be considerable quantities of C D M matter in the local group galaxies, besides that they concentrated in galaxy. The "Milky way" galaxy is such a spiral arm galaxy. The spiral arm structure of our galaxy can be traced by radio wave -demonstration of interstellar hydrogen at a wave length 21 cm where neutral hydrogen is used as a tracer element to delineate the spiral arm and the galactic disks, in which gasses are largely concentrated. By these study, the position of various concentration of. Hydrogen, which can be seen in each line of sign are indicatated by filled circles. A series of small open circles correspond to a broad peak on the profile indicate a spiral arm. There are significant differences in the neutral hydrogen distribution on the two side of the galaxy. In the outer region, the peaks of the spiral arm are less pronounced on the southern side of the galaxy then they are on the northern side. This galaxy shows multi armed structure. The arm shows geometrical trailing tendency clock wise. The neutral hydrogen is confined mostly in the thin layer in the galactic disc.
 The Active galactic neucleus (AGN) like other spiral galaxies, is the central region of our galaxy. What is present at the center?

It is yet a great puzzle to us. There are many theories. A bright quarser! A black hole! A neutron star! Or globular clusters! The concept that the center of our galaxy might explode with the violence of a bright quarsar, by "Lorry Niven" in his book "Ring World" (Gollancz publishers-1970). Accor­ding to him, this galaxy will turn into a quarsar, and once, the blast of light, electro­magnetic radiations and very high energy particles will reach to us. Since, we orbit round the center of our galaxy, at a distance of about 10 Kilo Persec, then it is however possible that the nucleus of our galaxy had already exploded in the past 30,000 years and we have not yet know about it. The light from such an explosion along with cosmic ray particles will take much long time to reach to us. And if this happened in reality in past time, then the blast particles from the quarser at the center of our galaxy, as soon as will reach to us, will destroy the total civilization. It may happen on any day, any time. The center region of our galaxy, like the central region of other spiral galaxies contain globular clusters. However the feature is consistent with the elliptical galaxies "Spheri­cal type". These globular cluster contain the oldest stars of the galaxy, and their formation was clearly related to the formation of the first component of our galaxy as we have told early, Then one question appears to us "is it the fact that all the galaxies forming, at initial phase were elliptical one? and then under gravitational influence of central retarded core, some of them turned into spiral galaxies? Then another question appears to us, where from the material came for formation of disc of the spiral galaxy?

 How could these globular clusters form at AGN? The another big question!

The Conventional view is that they were produced by collapse of greater region of self gravita­ting gasses that became spiral galaxy as we have shown in above picture (Fig. 1). And if we take the concept of globular clusters at our AGN, there remains no possibility of explosion of our AGN. like that of a "quarser" or "Sey fert galaxies". These bright globular clusters were formed at the earliest stage of the deve­lopment of our galaxy, and these globular clusters are brightest at a distance 30,000 light years. (It is the distance of ours, from galactic center, at some direction). Each globular clusters were formed of tens of thousands of stars, and more than few hundred globular clusters are associated with AGN of our "Milky Way”. The most exciting theory is "Black hole" at the center of our spiral galaxy. Where from the black holes came in center? Then black holes has to be originated in the birth time of the galaxy or in the "Big Bang" time, or the black holes grew from the globular cluster? The x-ray sources have now been identified with globular clusters, and this has encouraged the speculation that there might be a massive black holes like "SgRA" at our galactic nucleus. The Globular clusters show no sign of exploding like "Sey fert" galaxies, or quarsers and may stay retarded for ever as simple massive black hole or perhaps they burst their bounds very soon after the "Big Bang" in the galaxy and settled down into a long life of respectability as quiet collapsed objects. Our spiral galaxy has a dark halo extend­ing 50 KPC to 100 KPC at its center. The shape of the halo is unknown. The gamma ray observatory (GRO) satellite found distri­bution of γ-ray on the sky and the γ ray burst was isotropic. The source of the gamma ray is non solar origin and is either in an extended galactic halo or at cosmological distance. So the most conservative approach is to assume that the halo at the center of our galaxy is of old population of type II accreting neutron stars and thus the halo emits y ray bursts. The distribution of neutron stars have an isotropic distribution in the galactic center. Our galaxy have spiral arms. Successful efforts to trace the spiral structure of our galaxy began in 1940s. Spectroscopic studies show that spiral arms themselves are made of mainly neutral hydrogen gasses and young hot stars. Measuring directly the concentration of hydrogen gas by its emission at 21 cm wave length. Our spiral arms show to contain huge concentration of hydrogen gasses. Other method of tracing the spiral structure is (1) tracing the young stars (0 and B stars). They are so common in our spiral structure, as if they are lighting the path of the spiral structure, like street lamps lighting a twisted road. (2) Co line luminosity of the spiral structure. Hydrogen mass of the galaxy can be calculated from the co line luminosity of a galaxy accordingly MH2/L’co = (4u/3π G)1/2(n (H2)1/2Tb), where (4μ/3μG)1/2 =2.1 MΘ (K. KmS-1Pc2)-1cm3/2K and n (H2) is the hydrogen density (P Solomon-Nature vol. 356, P. 318-19, 1992). Our galaxy contain trillions of stars.
Our galaxy has a spin rota­tion. Every spiral galaxies does rotate. Elliptical galaxies do not rotate very much. Our "Milky Way" is a very slow rotating galaxy. It rotates in its spiral arm "a few cm", once in every 10 million years. Where from the rotation came? Who set the spiral galaxies to rotate? It is the Soviet Astronomer V.A. Ambartsumian, who gave a theory that gala­xies are formed by a process of ejection from the parent galaxies, by a violent outbursts from the galactic nuclei, he told that spiral galaxies form in pairs, and that when two nuclei from one cosmic gusher to become the new pair of spirals, they split up with opposite rotation, relative to each other due to equal and opposite amount of angular momen­tum. So in that case there must be a link material or link bridge between the two spiral galaxy and each spiral galaxy must contain its companion galaxy. The "Whirlpool galaxy" M51 with its companion is the classical example of such a theory of Ambartsumian. Actually M 51 first revealed the astronomers about the existence of other spiral galaxies in the Universe. It has a very clear, beautiful spiral pattern, with bright young stars, edged by a lane of dark material, sweeping out from the center in two opposite arms. This M 61 has a bridge material which extends from one of the spiral arm to its companion galaxy, small and bright, made of same kind of materials. The spiral arm of M51 is radio spiral, and two strong spiral arms running along the inner edge of the spiral pattern of bright young (0 & B stars) stars. The spiral arm contain great quantities of neutral hydrogen gas, like ours "Milky way". The radio evidence also clearly reveals that lane of hydrogen gasses extended across the bridge to its companion galaxy. This compa­nion galaxy makes the end of one of the two major spiral arms. But the difficulties of Ambartsumian theory is that our galaxy and majority of spiral galaxies has no companion galaxy like M51
Our spiral galaxy is not any thing new or special in the Universe. Besides our "Milky way", there are at least 63 spiral galaxies (Catalogued so far) known, who have velo­cities 800 Kms.l. Spiral structures has also variability, some are tightly wound, others are open spirals. IRAS study has detected a spiral galaxy with a distant red shift Z=2.286. It is IRAS 10214+4724 galaxy with most intrinsically luminous objects in the universe α=1014LΘ (LΘ=Solar luminosity) The total mass of neutral molecular hydro­gen in the IRAS 10214+4724 is 2-6 X 1011 M0. This mass is compatible to total mass of a large spiral galaxy. "Co luminosity is recent technique to estimate the H2 mass in the spiral galaxy, and IRAS 10214+4724 galaxy has a Co luminosity at least 20 times than that of local group galaxy. Its hydrogen mass is roughly equal to total mass of large spiral galaxy like the "Milky way" (P.M. Solomon ­Nature vol 356, 26th March P. 318-19, 1992). 90% of the galaxy contain stars and 10% gasses (The total agglomeration of molecular gas in Milky way is 106-107 M0).

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 Tribute & Acknowledgement- To our late parent diseased late Mr. Bholanath Bhattacharya FCA(India) SAS(India) and  late Mrs Bani Bhattacharya House wife of their residence 7/51 Purbapalli, Po-Sodepur, Dist 24 parganas (north) , Kolkata-110,WestBengal, India,  for their initial teaching  for us about the universe, Big Bang galaxy stars and the eternity 
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Sd/ Professor Pranab Kumar Bhattacharya WBMES