Astronomical objects - Essay Example

Topic: Astronomical Objects Sara Peters Section: The Rise of Modern Science SCI110 INTRODUCTION: One of the most impressive achievements of science is the development of a quite detailed understanding of the physical properties of the Universe, even at its earliest stages. Astronomy and Cosmology is a fundamental part of our natural sciences today. Through close interaction with other disciplines, above all with mathematics and physics, it is been expanding, which on one hand triggers from knowledge, and then on the other profits from them. The great majority of astronomical objects are characterized by large masses and enormous energies. These generally cause matter to exist under extreme conditions of temperature and density, which, even today still lie well beyond what can be realized in a physicals laboratory. The various forms of matter that is encountered away from the Earth, at great distances is being studied as an area of interest. In current astrophysical cosmology there is some interesting and more or less generally accepted observational facts. Thus, in any active-galactic-nucleus phenomenon massive central objects like black holes, tachyons, neutrinos, WIMPS etc are expected to be common, and they are surrounded in a variety of scales, by gas clouds commonly termed circumnuclear gas, with liner a dimensions of a few ten kilo space. All these and few other astronomical objects and their current position in the study of cosmology is being discussed in this thesis. Neutron Stars: Neutron stars are highly compact stellar objects with masses 1-2 M (where M is the mass of the sun), and radii of order 10km. They are produced in the cores of stars that at the end of their evolution undergo gravitational collapse and subsequent supernova explosion. Neutron stars contain 10^57 baryons, primarily in the form of the densest matter in the universe, with central density approaching a magnitude beyond nuclear matter density. The ever-growing body of observational data on neutron stars, gathered with a wide variety of detectors from radio to gamma-ray, provides increasingly stringent constraints on theories of their constitution. Precision radio and optical timing measurements show that pulsars have remarkable long-term timing stability, and thus the neutron stars forming them must have reasonably thick rigid crusts anchoring stable magnetic fields. Despite substantial work over the past half century, the nature of matter at the extreme densities in the cores of neutron stars remains uncertain. A better understanding of the possible states of matter in neutron stars interiors can also enable the world of cosmology to infer whether an independent family of denser quark stars, composed essentially of quark matters can exist (Rowan, 1996). Strings: Strings are extended objects with an intrinsic tension (energy per unit l length). Recent years have seen a radically different approach to the problem of quantum gravity this has led to a different idea of the possible structure of the quantum gravity theory. One of the most exciting ideas is that the fundamental entities upon which quantum operations must be performed are not point-like but are one dimensional. Such objects are usually known as strings, or more often super strings. In the last decades string theory has become a promised candidate for the underlying theory of the fundamental interactions of nature. However, even though lots of progress has been done it has not been yet possible to confront it with real physics. One possibility to achieve this is through cosmology by studying the cosmological implications of string theory. On the other hand string theory would provide an alternative to answer the basic questions that standard cosmology currently faces, such as the initial singularity, dimensionality of space time, cosmological constant, horizon and flatness problem and the origin of density perturbations in the cosmic microwave background. All these reasons suggest, that cosmology and strings complement each other in several ways, giving rise to string cosmology. A rigorous way to understand string cosmology is by studying the time dependent backgrounds in string theory, unfortunately this is a hard task due to cosmological singularities that arise in this context, and still much work has to be done. On the other hand, a good approximation can be done by studying the adiabatic evolution of time dependent backgrounds in string theory. In this direction lot of work has been done where a low energy effective approach is made. Winding states and T-dualities are intrinsic features of string theory and playa fundamental role in the B&V model, which main objectives are the solution to the cosmological singularity problem and the dimensionality of space time. Pulsars: The discovery many years ago of the remarkable objects which came to be known as pulsars and their identification as neutron stars, fulfilled a prediction made many years earlier. Pulsars, rapidly rotating highly magnetized neutron stars, have many exciting applications in physics and astronomy. After nearly 40 years, since the original discovery, pulsar research has great vitality, making major contributions to fields ranging from ultra-dense matter physics to relativistic gravity, cosmology and stellar evolution. The outstanding observational characteristic of pulsars is the pulsed emission and its precise periodicity. Pulsars are relatively weak radio sources. The shape and amplitude of individual pulses is very variable. This shows that the pulses are emitted in a dynamic and rapidly varying environment. However, if one adds a few hundred pulses synchronously with the pulsar period, the resulting mean pulse profile is remarkably stable and has a characteristic shape for each pulsar Over 550 pulsars are now known, almost all detected at radio frequencies. Their pulse periods range from 1.5ms to several seconds. Most pulsars are single neutron stars but, in an important subset, the pulsar is in a binary orbit with a companion star. Observations have revealed a wealth of detail about the structure and evolution of pulsars and the pulse-emission process, giving new insight into the behavior of matter in the presence of extreme gravitational and electromagnetic fields. Pulsars have unique properties which make them nearly ideal probes for a wide range of physical studies. Supernovas: Supernovas are stars that explode spewing out heavier elements that are important to galaxy evolution, and the existence of life. An examination of the facts discloses that galactic magnetic fields in the spiral arms and the molecular clouds they push is partly responsible for causing supernovas. Large, really massive stars face a far more catastrophic end of life. After they have used up the bulk of their hydrogen fuel, gravity sets in motion an irreversible process. The stars core collapses and the temperature rises so rapidly that a tremendous explosion ensues, during which the star can reach up to 100 million times its original brightness. The resultant release of energy scatters what is left of the stars mass several light years into space at velocities of thousand of kilometers per second. This is what is known as supernova (Peter, 2003). Supernovas appear to leave behind gaseous nebulas and pulsars. A helical field (synchrotron) causes a rapid variation of accelerated electrons in a strong magnetic field. Field dynamics are quite evident in supernova phenomenon. The overwhelming majority of spiral galaxies for which supernovas have been discovered are viewed almost pole on. Supernovas occur mostly in rich star-clusters and are located at the bottom of vertical chimney-like or steep-sided pit structures that are embedded in the equatorial gas and dust layers. Quasars: Quasars are ultra luminous objects and are another enigmatic class of objects. Because they appear point-like in optical photographs these objects were called Quasi-stellar objects abbreviated later on to Quasars. The most striking characteristic feature of quasars are their large red shifts. The most distant quasar known at the present time has a red shift of z= 6.42. These objects are very useful for probing gas and dust in the early universe. Hence the search for quasars at higher and higher red shift is an important area of study. Quasars emit enormous amount of radiation in the far infrared region. The study of this radiation should provide valuable information on dust. The spectra of quasars are dominated by both emissions and absorption lines. The study of emission lines of quasars provides information on the physical state and chemical composition of the gas and dust close to quasars. On the other hand the study of absorption lines with increasing red shift samples the intervening gas and dust material at larger and larger distances. Therefore the study of elemental abundances from quasars should help in tracing the environment of heavy metals in the universe from early times to the present time. Black holes: A stellar - mass black - hole is the end result of the core collapse of a high - mass (greater than 10 solar mass) star. It is an object from which no light can escape within a certain distance. Although space behaves strangely very close to a black hole, at astronomical distances, the black hole's only effect is gravitational. A black hole occurs according to Oppenheimer if the relative density of mass - energy becomes too great for any form of energy, as that of matter or light, to be able to escape the gravitational field in which it is contained. Black holes arise because gravity affects the way light waves travel through space. The existence of stellar mass black holes, and of super-massive black holes at the center of most, if not all, galaxies is supported by an abundance of evidence. There is little doubt that such objects exist as described the general theory of relativity. Only recently has it been possible to detect intermediate mass black holes and the evidence for them are slighter but growing. The current picture is that in the center of galaxies, and of global clusters, stellar mass black holes merge and grow to super massive black holes and intermediate mass black holes respectively. Magnestars: Recent observations of soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars are providing evidence for the existence of magnetars, a class of neutron stars with surface magnetic fields exceeding the critical field of 4.4 X 10 * 13 gauss. Magnetars are the first astrophysical sources believed to derive their primary radiation power from magnetic energy, which substantially exceeds their rotational energy. In addition, the physics of supercritical magnetic fields operates in a more exotic realm than even that of normal pulsars. The discovery of long periods and high period derivatives in soft gamma-ray repeaters over the past year strongly suggest that SGRs are magnetars. The origin of the strong magnetic field in compact stars, especially neutron stars, have been an open problem. Recent discovery of magnetars seems to renew this problem. Conservation of the magnetic flux during the collapse of a main sequence star has been a nave idea to understand the magnetic filed in neutron stars. WIMPS: WIMPS is an acronym for weakly interacting massive particles. Since, the 1980s they have been the standard cold dark matter (CDM) candidate. The primary motivation for including such objects comes from the theory of structure formation that suggests the existence of CDM. Super symmetric extensions of the standard model of particle physics (invented to solve problems unrelated to dark matter) predict the existence of such particles. The fact that they have not yet been seen at accelerators suggest that they must have a very minute mass. The particles would have been thermally produced in the early Universe yielding a cosmological abundance inversely proportional to their annihilation cross - section. Super symmetric models contains many free parameters yielding relic densities within a few orders of magnitude on either side of the critical density. Today, wimps would be expected to inhabit the halos of spiral galaxies like our own. From the galactic rotation velocity, one can estimate the local density to be about 0.3 Ge V cm. Goodman and Witten suggested that these wimps could be detected via the observation of nuclei recoiling from wimp- nucleus elastic scatters. Galactic wimps with masses in the GeV range have kinetic energies in the keV range so we can also expect nuclei recoils on the keV range. The rate is proportional to the elastic wimp-nucleus scattering cross-section which depends up on the parameters of the particle physics model. Wimps scatters can be observe with "calorimetric techniques". Unfortunately, it is difficult to distinguish wimp events from events due to the beta or gamma radioactivity. Statistically, a signal from wimps can be isolated through the expected 5 % seasonal modulation of the event rate. This modulation is due to the fact that while the Solar System moves through the (isotropic) wimp gas, the Earth's motion around the Sun alternately adds or subtracts from the wimp detectors velocity. Neutrinos: Discoveries involving neutrinos are reshaping the foundations of our understanding of nature. The detections of neutrinos coming from the sun and from an exploding star and discoveries from underground experiments of the past decades were recognized by the 2002 Nobel Prize in Physics (Peter, 2003). Neutrinos certainly exist in large numbers (roughly one billion for every photon) and they can contribute a huge mass to the matter. High energy neutrinos are unique messengers of some of the most extreme processes occurring throughout the universe. Unlike high energy photons, high-energy neutrinos are not absorbed as they traverse the universe. Also, unlike charged particles such as protons and nuclei, neutrinos are not deflected by magnetic fields, and thus they point directly back to their sources. These unique properties of the neutrinos make possible the discovery of new astrophysical systems and new physical processes through the detection of neutrinos with high level of energies, this is as high as the current terrestrial accelerators reach, to much higher energies. Tachyons: Historically tachyons were described as particles which travel faster than light. This idea was first proposed by professor Arnold Sommerfeld. The name Tachyon was coined by Gerald Feinberg. This name derives from the Greek tachys, meaning swift. These particles have an imaginary mass and the velocity. The special theory of relativity only says that a particle cannot be accelerated to the speed of light and beyond. There could still be particles having speed exceeding. Actually tachyons do appear in conventional quantum field theories as well. The existence of a tachyon in a scalar field has a local maximum at the origin. In order for the theory to be sensible at least in perturbation theory, the potential must also have a (local) minimum. Typically whenever the potential in a scalar field theory has more than one extremum non-trivial classical solutions can be created which depend on one or more spatial directions. A cornerstone in special relativity is that no particular matter can be accelerated beyond c, no physical effect can be propagated faster than c, and no signal can be transmitted faster than c. It is an experimental fact that no particle has been found traveling at superluminal speed, but a name for such particles has been invented, tachyons. Special relativity does not forbid tachyons, but if they exist they cannot be retarded to speeds below c. In this sense the speed of light constitutes a two - way barrier: an upper limit for ordinary matter and a lower limit for tachyons. Antimatter: Matter made of particles with identical mass and spin as those of ordinary matter, but with opposite charge and quantum properties. Antimatter has the same properties of regular matter except that it has the opposite electrical charge (Jayant, 2002). Astronomical observations indicate that there is not much antimatter (that is antiprotons, antineutrons, positrons, etc) in the Universe. For examples, if sizeable amount of antimatter is present in the galaxy, it would be disclosed by powerful explosions as a result of matter-antimatter annihilation. In our vicinity there is a strong preponderance of matter over antimatter, and it is normally assumed that this is true for the universe as a whole, as a result of initial conditions. Some cosmologists, especially Alfven and Omnes, have argued that there are equal amounts of matter and antimatter in the universe, but that they remain specially segregated. The encounter of lumps of matter and antimatter (whole galaxies or clusters perhaps) would yield enormous amounts of annihilation energy. While annihilation occurs, pions are produced, which decay to give gamma rays. A peak in the gamma ray back ground would be expected at 100 MeV, but this is not observed. Cosmic-ray and gamma-ray data exclude the possibility of large amounts of anti-matter from the solar system, the Galaxy, the Local Group, galaxy clusters and the intergalactic medium (if any exists).Grand unified theories offer the possibility of explaining the excess of matter over antimatter which appears to prevail in the universe at the present epoch. CONCLUSION: Study of astronomical objects enables one to examine physical theories of the nature of the universe that range far beyond the conditions that we can experience here on Earth. Astronomical research is 'alive' and can only develop with the applications of physical laws, theories and data. A general aim of natural scientific research is to recognize and understand in a comprehensive way our material world with its phenomenon, inner relationships and obedience to the laws of the nature, and its evolutionary processes. These efforts come, on the one hand under the aspect of the practical and useful application of science for society, but also have a considerable spiritual component, and thus enable one to form a factually based conception of the universe. There is the further question of why extra-galactic objects should be moving apart at speeds increasing with distance. This leads to difficult and disputed problems in modern cosmology, where it is quite usual to pile unverified assumptions on top of one another in order to see what may emerge. Great hopes are entertained from the help which the newer science of radio- astronomy is now giving so abundantly, and it is most unfortunate that man-made interference is becoming such a factor in limiting its potentiality. REFERENCES: Coles Peter & Lucchin Francesco, 2002: Cosmology: The Origin and Evolution of Cosmic Structure, John Wiley & Sons Publishers Jayant Vishnu Narilkar, 2002: An Introduction to Cosmology, Cambridge University Press. Jedicke Peter, 2003: Cosmology: Exploring the Universe, The Creative Company Publishers Jerzy Plebaski, Andrzej Krasinski, 2006: An Introduction to General Relativity and Cosmology, Cambridge University Press. Michael Rowan, 1996: Cosmology, Oxford University Press Read More