19 Stars as the Cooking Pots for Heavy Nuclei
147
Fig. 19.4 Illustration of a binary neutron star merger. Source: Wikipedia.org
has been emerging in favor of another scenario where a rich neutron source is
a binary neutron star merger. Such events are more likely sites for generating
such a huge number of neutrons that will speed up the r-process (Fig. 19.4).
There is a great deal of attention on these processes now. The neutron
stars were predicted to exist very early on, soon after the discovery of the
neutron. Baade and Zwicky predicted that the neutron stars might be the
end product of solar evolution. Their existence was proven in the 1960s, with
the discovery of pulsars by Jocelyn Bell Burnell in 1967. Since then, many
such pulsars have been discovered, including some which appear as binary
pulsars with another neutron star as a companion. A famous example is the
binary pulsar discovered by Hulse and Taylor, for which they were awarded
the Nobel Prize. In the neutron star merger situation, the problem coming
from the neutrinos present in supernova mantle is not a major obstacle to
element formation. The evidence in favor of a binary neutron star merger
playing a role in heavy element formation came from observations in an
ultra faint dwarf galaxy called reticulum II. More precisely, it seems to have
provided evidence against supernova explosions being the site of the r-process
for the formation of heavier elements. Reticulum II is a small dwarf galaxy,
discovered in 2015 during the dark energy survey. It is part of the local group
of galaxies about 98,000 light years away from us (about 30 kps). It is loaded
with heavy elements of the kind which are hard to produce in the laboratory
and also which cannot be explained by the s-process nucleosynthesis. The way
it gave a clue to the heavy element nucleosynthesis is as follows: in this faint
galaxy, there are not that many stars but there have been observations of very
heavy element emitted light (such as from europium, gold, and barium) as
147
Fig. 19.4 Illustration of a binary neutron star merger. Source: Wikipedia.org
has been emerging in favor of another scenario where a rich neutron source is
a binary neutron star merger. Such events are more likely sites for generating
such a huge number of neutrons that will speed up the r-process (Fig. 19.4).
There is a great deal of attention on these processes now. The neutron
stars were predicted to exist very early on, soon after the discovery of the
neutron. Baade and Zwicky predicted that the neutron stars might be the
end product of solar evolution. Their existence was proven in the 1960s, with
the discovery of pulsars by Jocelyn Bell Burnell in 1967. Since then, many
such pulsars have been discovered, including some which appear as binary
pulsars with another neutron star as a companion. A famous example is the
binary pulsar discovered by Hulse and Taylor, for which they were awarded
the Nobel Prize. In the neutron star merger situation, the problem coming
from the neutrinos present in supernova mantle is not a major obstacle to
element formation. The evidence in favor of a binary neutron star merger
playing a role in heavy element formation came from observations in an
ultra faint dwarf galaxy called reticulum II. More precisely, it seems to have
provided evidence against supernova explosions being the site of the r-process
for the formation of heavier elements. Reticulum II is a small dwarf galaxy,
discovered in 2015 during the dark energy survey. It is part of the local group
of galaxies about 98,000 light years away from us (about 30 kps). It is loaded
with heavy elements of the kind which are hard to produce in the laboratory
and also which cannot be explained by the s-process nucleosynthesis. The way
it gave a clue to the heavy element nucleosynthesis is as follows: in this faint
galaxy, there are not that many stars but there have been observations of very
heavy element emitted light (such as from europium, gold, and barium) as