Timeline[ edit ] Periodic table showing the cosmogenic origin of each element. Elements from carbon up to sulfur may be made in small stars by the alpha process. Elements beyond iron are made in large stars with slow neutron capture s-processfollowed by expulsion to space in gas ejections see planetary nebulae. Elements heavier than iron may be made in neutron star mergers or supernovae after the r-processinvolving a dense burst of neutrons and rapid capture by the element.
Print Last August 17, at 8: Eastern time, Earth received a message from deep space that solved — perhaps — a decades-old puzzle. The message began as a subtle quiver in the fabric of space, a gravitational wave. It grew to a cosmic cacophony that included gamma rays, radio waves and visible light.
It all emanated from a galaxy roughly million light-years away, Nucleosynthesis of heavy elements the dense cores of two long-dead stars collided. In the debris from the crash, some of the heaviest atoms in the cosmos, such as gold, platinum and uranium, were born.
For over 60 years, scientists had debated where such elements came from. Some physicists favored supernovas, the violent explosions of massive stars.
Others suspected that heavy elements might be generated in the explosive collisions of superdense neutron stars, remnants of supernovas. But no direct conclusive evidence had been available to settle the question. Thanks to the August gravitational wave signal, though, astronomers could train a full array of instruments on the collision site.
Their data now confirm that precious heavy metals and heavier radioactive atoms emerged from the neutron star smashup. The unimaginably high temperatures of the Big Bang gifted the cosmos with hydrogen and helium plus a dash of lithium by fusing together primordial protons.
Further fusion reactions in the cores of the first stars forged heavier elements, such as the carbon and oxygen needed for life. But stellar fusion can produce elements no heavier than iron, atomic number 26 on the periodic table.
Stars are in the business of producing energy to radiate into space, which fusion accomplishes nicely.
But fusing nuclei heavier than iron consumes energy, rather than releasing it. Populating the rest of the periodic table — the dozens of elements with atomic numbers higher than iron — requires a different strategy. Fortunately, there are neutrons.
They are electrically neutral and so can slip into a nucleus easily. And they possess a secret weapon — the ability to transform into protons. A nucleus capturing a neutron can then emit an electron, turning the neutron into a proton, and thereby raise the atomic number — creating a new, heavier element.
Neutron by neutron This neutron capture process can proceed slowly or rapidly. Neutrons enter the nucleus much more slowly than they can create protons. The s-process takes place over thousands of years in the bloated interiors of aging stars.
The rest of the periodic table, including its heaviest members, relies on rapid neutron capture: If the s-process resembles the gradual carving of a canyon by a trickle of water, then the r-process is like the rupture of a dam wiping out a village.
In the r-process, a tsunami of neutrons overwhelms the atoms, penetrating them faster than the rate of changing into protons. While physicists struggled to understand the dizzying variety of ways that new nuclei could be created, astronomers searched the cosmos for a site that could produce the necessary torrent of neutrons.
Evidence from existing stars suggested that elements born in the r-process must come from a single type of source.
Every star that harbors r-process elements — including the sun — has them in the same relative amounts. But the more theorists pursued that possibility, the less likely the supernova explanation seemed. A rare source for rare elements In astrophysicists Eugene Symbalisty and David Schramm suggested that collisions between neutron stars might work.
Suspected to exist in the s and first detected in the s, neutron stars betrayed their presence by emitting regular pulses of radiation, earning the designation of pulsar.Of supernova products, the iron-family elements are the most abundant, and the universe is far richer in "Fe than in the other heavy elements.
The reaction Bi(n,-y)21i(a)Pb (21OBi has an a-decay half-life of d) terminates the reaction chain of the slow process of neutron capture.
by neutrino heating, and r-process nucleosynthesis in the neutrino-driven wind of the newly formed neutron star, respectively, as suggested by current computer simulations. In the upper parts of the ﬁgures the dynamical state. Big Bang nucleosynthesis produced no elements heavier than lithium.
To do that you need stars, which means waiting around for at least billion years. we are all made of stars. More than ninety per cent of the universe is composed of hydrogen and helium. Both elements have been around since shortly after the beginning of the universe. We present nucleosynthesis results form calculations that follow the evolution of massive stars from their birth on the main sequence through their explosion as supernovae.
Such nucleosynthesis predictions have been extensively tested with respect to nuclear uncertainties due to masses far from stability, beta decays, ssion barriers, and . The lightest elements (hydrogen, helium, deuterium, lithium) were produced in the Big Bang nucleosynthesis.
According to the Big Bang theory, the temperatures in the early universe were so high that fusion reactions could take place.