Since the first soft X-ray and EUV studies of hot DA white dwarfs it has been apparent that the fluxes of white dwarfs in these wavelength ranges are significantly lower than predicted (e.g. Kahn et al. 1984; Petre, Shipman & Canizares 1986; Jordan et al. 1987; Paerels & Heise 1989...
Where are newly formed stars found in a spiral galaxy? What information can be derived from the color of a star? What is found between the inner and outer planets? What is stellar nucleosynthesis? What are white dwarf stars made of?
the element composition of the interstellar medium that formed the Sun about 4.57 Gyr ago. The reason that we can identify the surface abundances of stars with the composition of the gas out of which they formed is due to the fact that nuclear transformations take place only in the central ...
" he wasn't speaking metaphorically. As Sagan said in the TV series "Cosmos," many of the elements in our bodies - "the nitrogen in our DNA, the calcium in our teeth, the iron in our blood" - were forged in the interiors of stars, in a process called stellar nucleosynthesis (element...
Schemes for explaining the presence of technetium (probably Tc-99 with a half-life of 200,000 years) and the presence of niobium (formed by decay of Zr-93 with a half-life of 1,500,000 years) are discussed. The importance of radioactive decay of technetium from an excited nuclear state...
less abundant than hydrogen, or in other words, for every 100,000 H atoms you will find one Fe atom in the universe. Answer questions 3 to 5 after finishing the rest of the lab. 1. How big is the probability that an element is Helium?
Equilibrium meant that both protons and neutrons were present in large numbers. The universe expanded and cooled, to ~1010Kelvin. At this temperature the nuclear chemistry changed and no more neutrons were formed. Free neutrons have a half life of 617 seconds. Once they stopped being produced [...
This is an important clue to determining the evolutionary pathways of HdC and RCB stars, for which two models have been proposed: the double degenerate (white dwarf (WD) merger), and the final helium-shell flash (FF). No overproduction of 18O is expected in the FF scenario. However, ...
When a supernova occurs, the star’s core collapses, crushing protons and neutrons together into neutrons. If the mass of a collapsing star is low enough—about four to eight times that of the sun—a neutron star is formed. In 2017, it was discovered that when these dense neutron stars ...
Chemistry of heavy elements in the Dark Ages Context. Primordial molecules were formed during the Dark Ages, i.e. the time between recombination and reionization in the earlyUniverse. They were the co... P.,Vonlanthen,T.,... - 《Astronomy & Astrophysics》 被引量: 17发表: 2009年 Evoluti...