Large Scale Structure Of The Universe - Galaxy Maps & Filaments
The spreading of galaxies is much more irregular and rugged per volume of space , fluctuations almost reaching more than 100% even though the cosmic microwave background radiation (CMBR) shows a uniform distribution of the radiation in the early Universe. The sky survey maps of the galaxies show narrow long thin spatial filaments connecting the collections of small and large galaxies and separated by voids that span billions of kilometers in the almost spherical form.
FIGURE-1: Galaxies Filaments
The above image is the effort of several years of meticulous observations of galaxies. The further most spread of galaxies in the Universe , the entangled connections between clusters , filaments and voids is what is the larg-scale structure of the Universe.
It should not astound you that galaxies are grouped together (clustered). Intially there were density fluctuations in the early Universe at the time of the BigBang. This has been proved by the spreading of the Cosmic Microwave Background Radiation (CMBR) across the Universe. These density fluctuations exerted gravitational forces on the surroundings, pulling the matter together. This gravitational differences across the Universe led to more and more pulling of the matter and the gravity of these lumps of matter grew tremendously and let the formation of the galaxies that we see today.
Though the detection of clusters of galaxies is predicted, their huge expanse has astonished the physicists. Regular galaxies are generally 200 million light-years across and one very too big screen-like structure - the Great Wall - has spreaded over across the Universe along a length of half a billion light-years across. What astounded the scientists is that even this large size , when compared to the scale that was measured by the COBE satellite, lesser than a tenth of that. On the whole, the expanses and the spacings (farawayness) involved in the large-scale structure of the Universe extends over from a factor of a million , from the typical sizes of the galaxies , to the size of the CMBR anisotropy scales measured by the COBE satellite. This collection of measurements provides us a very clear picture of the BigBang density dissimilarities across a wide range of scales. The degree of density fluctuations in the early Universe on different size scales and their consequent growth in the influence of gravity are very important clues to the characteristic and magnitude of dark matter in the Universe.
Physicists are seriously involved now in mapping the Universe now. The recent advancements in light detectors has facilitated the measuring of redshifts hastily , even using the moderate-sized telescopes. Physicists discovered only 2,700 galaxies in 1976 with the measured redshifts. But currently there are 1,00,000 such galaxies. Scientists are expecting more and more of the galaxies to be discovered in the coming years. This aspect of astronomy has been going on so seriously now.
One principal ask is how large the galaxies should be before they have to appear uniform?. Any observatory located on the ground can see only a tiny fraction of the sky. There are three requirements to reach the best-possible-degree of uniformity required over the entire sky. First, single independent scrutinies should cover as much sky as possible. Secondly, The studies have to be standardized so as to be knitted together with other individual studies. Thirdly, it is important that only satellites above the Earth should conduct the homogeneous entire-sky surveys (satellites like the Infrared Astronomy Satellite(IRAS)).
The coming generations of surveys have to produce outputs spanning over to 3 billion light-years which is approximately 20% of the radius of the visible Universe. Galaxies cluster together over extraordinarily large range of scales and this galaxy clustering can be collated with the CMBR anisotropy maps without any extra-computation. This should show us how the initial density dissimilarities in the early Universe from the era of CMBR emission (the era of photon decoupling) have led to the present day galxy structures. This information provides the physicists with the requisite evidences about the characteristics and the magnitude of dark matter in the Universe.
These six cubes show the simulated distribution of galaxies at redshifts 9, 7, 5, 3, 2, and 1, with the corresponding cosmic ages shown. As the universe expands, the density of galaxies within each cube decreases, from more than half a million at top left to about 80 at lower right. Each cube is about 100 million light-years across. Galaxies assembled along vast strands of gas separated by large voids, a foam-like structure echoed in the present-day universe on large cosmic scales.
Credit: NASA's Goddard Space Flight Center/F. Reddy and Z. Zhai, Y. Wang (IPAC) and A. Benson (Carnegie Observatories)
Galaxies clusters , with sizes in the range of 3 million light-years and mass of 1015 Suns, are very important to our understanding of the structure. Physicists have learned that galactic cores are solid and compact enough to act as gravitational lenses , that most of the ordinary (baryonic) matter inside them is being in the form of hot gas, not galaxies, that dark matter makes up nearly 80 percent of their total mass, and that they show a considerable amount of substructure when examined at high spatial resolution. The teemingness of clusters and their complete intrinsic structure are predicted by models to be sensitive to assumptions about properties of the dark matter and the total amount of matter in the Universe. Only the most high-processing parallel supercomputers can sufficiently represent the dynamical processes of the gravity and gas-dust at sufficient resolution to model clusters.
An even more difficult problem is addressing how the galaxies originated. Earlier the galaxy formation was thought to be a regular process not as important but now the cosmologists think that galaxy formation is the smallest bit in the total phenomenon of the structure formation. Galaxy formation is terribly complex because it entails the extensive physics of gas clouds , not merely the simple pulling of gravity. For example, to precipitate into a forming galaxy, gas has to turn into a cool dust first, which has to do with the emission of radiation. The cooled-off gas then forms into stars. The final-stage (near death) stars in turn chuck out energy and gas back into the gas source (reservoir) of the galaxy via supernova explosions. All along this period of time, gas clouds are clashing and pushing each other around through shock waves and gas pressure. A galaxy is a compounded system of immense complexity.
The above image is the effort of several years of meticulous observations of galaxies. The further most spread of galaxies in the Universe , the entangled connections between clusters , filaments and voids is what is the larg-scale structure of the Universe.
It should not astound you that galaxies are grouped together (clustered). Intially there were density fluctuations in the early Universe at the time of the BigBang. This has been proved by the spreading of the Cosmic Microwave Background Radiation (CMBR) across the Universe. These density fluctuations exerted gravitational forces on the surroundings, pulling the matter together. This gravitational differences across the Universe led to more and more pulling of the matter and the gravity of these lumps of matter grew tremendously and let the formation of the galaxies that we see today.
Though the detection of clusters of galaxies is predicted, their huge expanse has astonished the physicists. Regular galaxies are generally 200 million light-years across and one very too big screen-like structure - the Great Wall - has spreaded over across the Universe along a length of half a billion light-years across. What astounded the scientists is that even this large size , when compared to the scale that was measured by the COBE satellite, lesser than a tenth of that. On the whole, the expanses and the spacings (farawayness) involved in the large-scale structure of the Universe extends over from a factor of a million , from the typical sizes of the galaxies , to the size of the CMBR anisotropy scales measured by the COBE satellite. This collection of measurements provides us a very clear picture of the BigBang density dissimilarities across a wide range of scales. The degree of density fluctuations in the early Universe on different size scales and their consequent growth in the influence of gravity are very important clues to the characteristic and magnitude of dark matter in the Universe.
Using Hubble's Law For Mapping The Galaxies
The mapping of galaxies calls for the knowledge of the faraway position of each galaxy from the Earth. One approach to get this position of each galaxy is to apply the Hubble's law for the expanding Universe. Hubble noticed that the speed at which two galaxies pull away from each other is corresponding to their distance from each other. Reordering this equation gives an approximation of the distance from the measured velocity. The speed at which a galaxy is pulling away from us is calculated by gauging the shift to redder colors of spectral characteristics in its spectrum, ( a "Red shift" is equivalent to how the Dopler shift happens in case of sound waves when the source of the sound is going away from us). The red shift is in proportion to the velocity of the galaxy and correspondingly , according to the Hubble's law - the distance of the galaxy is in proportion to its velocity.Physicists are seriously involved now in mapping the Universe now. The recent advancements in light detectors has facilitated the measuring of redshifts hastily , even using the moderate-sized telescopes. Physicists discovered only 2,700 galaxies in 1976 with the measured redshifts. But currently there are 1,00,000 such galaxies. Scientists are expecting more and more of the galaxies to be discovered in the coming years. This aspect of astronomy has been going on so seriously now.
The Significance Of Homogeneous Galaxy Investigations
What we need as a first and foremost step to perform a redshift survey is to collect together a listing of galaxy positions and their refulgences in the sky. Conventionally, such listings are composed out of the photographic surveys done in the visible light. Physicists have come to know that even small mistakes in the listing of target galaxies will have a considerable effect on the final map which has led to more focus on finding out the galaxies in a better and innovative ways. Three basic approaches are being researched now. Intense surveys of the entire sky are being carried out in the visible light with the use of exceptionally acute detectors (which are the charge-coupled devices, CCDs) that can find out constitutionally shadowy galaxies which have only dim brightness on the surface and remote galaxies. Carrying on the near-infrared surveys on the sky calibrated at 2-micron wavelength facilitated for the fist time the observation of the dipping down close to the plane of our own galaxy whose dust and clouds makes almost 35 percent of the sky invisible in the visible light. As a drastic new approach, satellites doing the X-ray surveys allow for one more additional means of plotting of galaxy clusters.One principal ask is how large the galaxies should be before they have to appear uniform?. Any observatory located on the ground can see only a tiny fraction of the sky. There are three requirements to reach the best-possible-degree of uniformity required over the entire sky. First, single independent scrutinies should cover as much sky as possible. Secondly, The studies have to be standardized so as to be knitted together with other individual studies. Thirdly, it is important that only satellites above the Earth should conduct the homogeneous entire-sky surveys (satellites like the Infrared Astronomy Satellite(IRAS)).
The coming generations of surveys have to produce outputs spanning over to 3 billion light-years which is approximately 20% of the radius of the visible Universe. Galaxies cluster together over extraordinarily large range of scales and this galaxy clustering can be collated with the CMBR anisotropy maps without any extra-computation. This should show us how the initial density dissimilarities in the early Universe from the era of CMBR emission (the era of photon decoupling) have led to the present day galxy structures. This information provides the physicists with the requisite evidences about the characteristics and the magnitude of dark matter in the Universe.
Theoretical Modeling Of The Large-Scale Structure
Modeling of the observer galaxy distribution has been very successful in the recent times. Most of this modeling has been carried out on the largest available supercomputers. The models commonly espouse the evolution of a large nebula of the Universe. Phsicists have performed the calculations with random initial fluctuations which are statistically anticipated for different cosmological parameters and different types of dark matter.The supercomputer numerically solves the equations controlling the gravitational coupling and other physical processes. The fluctuations starting from small amplitudes, become progressively larger, which is expected from the representation of the gravitational instability. Physicists then compare the calculated results to the observed characteristics of large-scale structure in the universe.These six cubes show the simulated distribution of galaxies at redshifts 9, 7, 5, 3, 2, and 1, with the corresponding cosmic ages shown. As the universe expands, the density of galaxies within each cube decreases, from more than half a million at top left to about 80 at lower right. Each cube is about 100 million light-years across. Galaxies assembled along vast strands of gas separated by large voids, a foam-like structure echoed in the present-day universe on large cosmic scales.
Credit: NASA's Goddard Space Flight Center/F. Reddy and Z. Zhai, Y. Wang (IPAC) and A. Benson (Carnegie Observatories)
Galaxies clusters , with sizes in the range of 3 million light-years and mass of 1015 Suns, are very important to our understanding of the structure. Physicists have learned that galactic cores are solid and compact enough to act as gravitational lenses , that most of the ordinary (baryonic) matter inside them is being in the form of hot gas, not galaxies, that dark matter makes up nearly 80 percent of their total mass, and that they show a considerable amount of substructure when examined at high spatial resolution. The teemingness of clusters and their complete intrinsic structure are predicted by models to be sensitive to assumptions about properties of the dark matter and the total amount of matter in the Universe. Only the most high-processing parallel supercomputers can sufficiently represent the dynamical processes of the gravity and gas-dust at sufficient resolution to model clusters.
An even more difficult problem is addressing how the galaxies originated. Earlier the galaxy formation was thought to be a regular process not as important but now the cosmologists think that galaxy formation is the smallest bit in the total phenomenon of the structure formation. Galaxy formation is terribly complex because it entails the extensive physics of gas clouds , not merely the simple pulling of gravity. For example, to precipitate into a forming galaxy, gas has to turn into a cool dust first, which has to do with the emission of radiation. The cooled-off gas then forms into stars. The final-stage (near death) stars in turn chuck out energy and gas back into the gas source (reservoir) of the galaxy via supernova explosions. All along this period of time, gas clouds are clashing and pushing each other around through shock waves and gas pressure. A galaxy is a compounded system of immense complexity.