Elliptical galaxies must contain about five times as much mass in dark matter as the amount present in stars and gas. The conclusion: there is not enough mass in the stars and gas to provide the necessary gravity. Chandra and other X-ray telescopes can be used to measure the hot gas pressure, and observations with optical telescopes can be used to determine the mass of the stars. The pressure of the hot gas is balanced with the gravitational pull of all the mass in a galaxy. Large elliptical galaxies have extended atmospheres of hot gas which appear to be in equilibrium. Many subsequent studies confirmed this discovery, and the general picture that has emerged is that of a disk of stars and gas embedded in a large, spherical halo of dark matter. Pioneering work by Vera Rubin and her colleagues showed that, much to their surprise, the required mass of many spiral galaxies is much larger than the observed mass of all the visible stars and gas. In a similar way, astronomers can calculate the mass of a galaxy by measuring the acceleration of clouds orbiting on the outer edges of a galaxy. X-ray surface brightness fluctuations in the core (650 × 650 kpc) region of the Coma cluster are analysed using XMM. * Cloud of dark matter containing most of the mass of Galaxy. For now we can only state that in Coma, radio bubbles are a possible source of X-ray surface brightness fluctuations, although there exists no compelling evidence that this mechanism is really important for Coma. Unlike the case of Uranus, where the gravity of Neptune adds a fraction of a percent to the gravitational force acting of Uranus, the extra force needed in the cases described below is several hundred percent! It is no exaggeration to say that solving the dark matter problem will require a profound change in our understanding of the universe. Today, astronomers are faced with a similar, though much more severe, problem. The solution turned out to be Einstein's theory of general of relativity, which modified Newton's theory. In contrast, the attempt to explain the anomalies in the motion of Mercury as due to the existence of a new planet, called Vulcan, did not succeed. This procedure is still the primary method used to discover planets orbiting stars.Ī similar line of reasoning led to the detection in 1862, of the faint white dwarf Sirius B in orbit around the bright star Sirius. Thoracic surgeons as well as physicians need to be aware of this rare anomaly.For example, the anomalous motion of Uranus led astronomers to suggest that an unseen planet existed, and a few years later, in 1846, Neptune was discovered. Lung tumours, pneumothorax, extralobar pulmonary sequestration has been reported to occur in azygos lobe. Clinical importance of azygos lobe is that it may be confused with a bulla or abscess, a pulmonary nodule and a consolidated azygos lobe may mimick like a lung mass. Azygos lobe is formed due to penetration of right posterior cardinal vein, one of the precursors of azygos vein into the apex of the lung instead of normal migration over it during embryogenesis. But it’s not a true accessory lobe as it does not have its own bronchus and does not correspond to a specific bronchopulmonary segment. Azygos lobe is a very rare but normal anatomic variant of right upper lobe seen in only 0.4% of population radiologically and in 1% specimen during anatomical dissection. Azygos lobe has been reported in both the lungs. In 1877, azygos lobe was first described by Heinrich Wrisberg. Computed tomogram of thorax showing patch of consolidation in right upper lobe (blue arrow) adjacent to azygos lobe (brown arrow).
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