The term NUCLEOSYNTHESIS means the creation of new elements in nuclear reactions. Before we can consider how the present-day mix of elements may have come into being, we need to look at the various processes that could have contributed. It used to be sup¬posed that the Universe has always had the composition we observe today, […]
There are only two basic ways in which abundances, or the relative quantities of each clement in the Universe, may be determined: the direct chemical analysis of samples, and deduction from analysis of absorption and emission-line spectra. We include here the parts of the spectrum outside the visible range, because some of the most exciting […]
The discovery of the chemical composition of every type of astronomical body, from our planet Earth, through planets, stars and interstellar gas, to distant galaxies is a major occupation of astrophysicists in our own time. Since nuclear science realized the dream of the alchemist, to transmute the elements from one to another, we have come […]
In a close binary system, the stars are near enough to transfer matter from one to the other. Mass-flux rates of up to about a millionth of a solar mass per year have been observed by optical astronomers. A compact object in a close binary system can, therefore, receive enough matter to power it as […]
X-rays are associated with high-energy phenomena. The Sun emits most of its radiation at frequencies corresponding to visible light and has an effective surface temperature of about 5800 K. X-ray photons are roughly a thousand times more energetic than the photons of ordinary light, and so to produce X-rays we need either temperatures of several […]
If black holes are really objects from which no light, nor anything else, can escape, how can we detect their presence ? There are three main possibilities which we take in turn. First, there is the discovery by the Cambridge astrophysicist Stephen Hawking that black holes are not completely black. Matter antimatter pairs of particles […]
Two questions arise when discussing the astronomical consequences of the possibility of the existence of black holes .Where would we expect to find them, and how would we detect them ? To form a black hole we need to find places in the Universe which are much denser than their surroundings. The matter in the […]
In 1798 Laplace, in his book the ‘Exposition of the system of the world’, stated the following theorem: a luminous body in the Universe of the same density as the Earth, whose diameter is 250 times larger than the Sun, can, by its attractive power, prevent its light rays from reaching us. Consequently, he continued, […]
An important parameter to measure is the mass of a neutron star. This can best be determined in the same manner as for ordinary stars, by the observation of a binary system that contains a neutron star. To get the masses unambiguously we really need an eclipsing, double-lined binary, in which both components give us […]
The possibility that the degeneracy pressure of neutrons might stabilize a self gravitating object was first noted in the 1930s by T. L.D. Landau and F.Zwicky. W.Baade and F.Zwicky emphasized that they might exist as the stellar remnant of a supernova explosion, interest in neutron stars was aroused by the discovery of X-ray stars in […]