Current research in astronomy embraces a range of problems related to the peculiarities of different celestial bodies and ways in which better knowledge of astronomical phenomena can help humans in various spheres. This paper will explore two important areas of research. The first is an attempt to explain the truncation of stellar discs with the application of the magnetic hypothesis. The second is a more general problem related to the ongoing research aiming to define the age of the universe.
Truncation of stellar discs
The paper prepared by a team of researchers from University de Granada in Spain attempts to test the viability of the magnetic hypothesis in the explanation of the truncation of stellar discs. In their mind, the formation of the stellar disc is influenced by three forces including magnetic and gravitational forces, inwards, and centrifugal forces. The sudden suppression of the magnetic force at the time when the new disc is formed is accompanied by insufficient gravitational force that cannot retain the disc at the same place. As a result, the disc is bound to shift into intergalactic space from its galactocentric orbit. The scientists predicted that their observations would demonstrate this discrepancy between the actual and the galactocentric radii which they called “truncation radius”.
The researchers do not limit themselves to the magnetic hypothesis and explore other plausible explanations as well. Thus, Kennicut in 1989 advanced the theory that seeks to explain the pause in the disk formation beyond a certain radius R through the presence of a ‘critical gas density’ (Battaner et al. 2002:2). Alternatively, Larson and Gunn explain the same process through the slow accretion of intergalactic matter, a process that is still ongoing albeit at a very slow pace. Finally, the truncation of stellar discs can be explained through tidal influences.
The research presents calculations that allow for the interaction of two centripetal forces in the process of disk formation, including gravitational and magnetic forces on the one hand and centrifugal forces on the other hand. After computing the central mass potential and exponential gas potential, they arrive at the decoupling time that proves to be very short, pointing to the possibility of an instantaneous transition from a magnetically driven disc to a proto-star.
As a result of investigation, researchers discard theories of ‘critical gas density’ and tidal interactions. They do not rule out Larson’s theory of slow disc formation and certainly insist that the magnetic theory is a viable explanation of the truncation of stellar discs. The magnetic hypothesis of rotation curves, the research suggests, provides a successful framework for predicting the truncation radius of the disc.
The Age of the Universe
It has long been known that the Universe is constantly expanding, and this expansion may be occurring at a quicker pace now. This idea was first advanced by Edwin Hubble who conducted his studies in Pasadena, California, and found out that the distance from the Milky Way galaxies determines the speed at which galaxies are moving away from each other. This theory conformed to the mathematical formula for the development of the universe advanced by Albert Einstein.
Hubble’s discovery led to the appearance of the Hubble constant that “determines the size of the observable universe and provides constraints on competing models of the evolution of the universe” (Freeman 2003). Determination of the accurate value of this constant still remains a challenge although recent years saw great progress in the measurement precision. The Carnegie Observatories in Pasadena, California, purchased the Hubble Space Telescope in order to measure the distance and velocity of different galaxies.
The main goal of the Hubble Key Project was to compare results obtained from two independent methods in order to determine the Hubble constant with a lower degree of uncertainty. The new telescope was used for measurement of Cepheid distances to galaxies. The next step was “to determine the Hubble constant by applying the Cepheid calibration to several methods for measuring distances further out in the Hubble expansion” (Freeman 2003).
It should be noted that in Einstein’a equation for the development of the universe there was a cosmological constant that the great physicist later regarded as “his greatest blunder” (Freeman 2003). This element of the equation denied any expansion of the universe. The studies of the Californian astronomers suggest that Einstein may have been right after all as it stands for the so-called ‘dark energy’. Freeman believes that if Hubble constant it taken to equal 70, “with matter contributing one-third and dark energy providing approximately two-thirds of the overall mass plus energy density”, the age of the universe can be pinpointed at around 13 billion years (Freeman 2003). This number corresponds to the data received from the age that was obtained from the examination of globular clusters. Although dark energy was at first met with scepticism by the scholarly community, greater investigation may confirm the existence of this type of matter.
The ongoing astronomic research is highly diverse in the range of explored topics. The determination of the age of the universe is a conventional area, an assignment with which scholars have been struggling for decades. However, the Hubble Key Project allows one to glance at the problem from a new angle, applying a combination of methods in order to make the resulting number more valid. The study may finally provide a more or less certain answer to the question “How old is the universe?”
The research going on at the University of Granada is focused on a more specific problem of truncation of the star discs. Scientists test a variety of theories to explore their usefulness in explanation of this truncation. The magnetic hypothesis is believed to be the most promising, which is confirmed by the mathematical modelling.
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Bibliography Battaner, E., Florido, E. and J. Jimenez-Vicente. “The truncation of stellar discs: The magnetic hypothesis.” 19 March 2002. Universidad de Granada, Astronomy & Astrophysics 388, 213–218 (2002)DOI: 10.1051/0004-6361:20020423c ESO. 25 Dec. 05 <http://www.ugr.es/local/battaner/papers/truncteorico.pdf> Freedman, Wendy L. “On the Age of the Universe.” Daedalus 132.1 (2003): 122+.