Have you thanked God for neutron and black hole merging events today? You should. A new study of an ancient dwarf galaxy shows that human life—and certainly a global high-technology civilization—might not have been possible if it weren’t for neutron and black hole merger events. Without such events, Earth and the rest of the universe would lack the abundance of elements heavier than zinc that are needed for the existence of billions of people on a single planet.
Astronomers have known for several decades that elements heavier than zinc are synthesized through rapid (r) and slow (s) neutron-capture processes. The r-process is known to occur in core-collapse supernovae (very massive stars whose cores collapse when nuclear fusion suddenly becomes unable to sustain the cores against the stars’ gravitational forces) and is responsible for the production of about half of all the elements in the periodic table that are heavier than iron (see figure). The s-processoccurs in asymptotic giant branch stars (medium mass stars that have evolved to become hyperinflated red supergiants) and is responsible for the production of the other half of periodic table elements heavier than iron. However, the s-process is not independent of the r-process. The s-process converts elements produced by the r-process into different heavy elements.
Figure 1: The periodic table. All elements heavier than zinc (30 Zn) are either r-process elements or s-process elements that are derived from the production of r-process elements. Arsenic (33 As), selenium (34 Se), molybdenum (42 Mo), tin (50 Sn), and iodine (53 I) are vital poisons.
Image credit: Wikimedia Commons/Sandbh
The new study calls into question the assumption that all the universe’s r-process elements are manufactured by core-collapse supernovae. Core-collapse supernovae are exploding all the time in galaxies throughout the universe. Thus, if core-collapse supernovae were the sole or primary source of r-process elements, these elements would be continually produced. However, the appearance of a plateau (a leveling out over a long period of time) in the abundance of europium in several dwarf spheroidal galaxies indicates that r-process element enrichment is not continual but rather the result of rare but highly efficient events.1
Motivated to test this hypothesis, four astronomers from MIT, the Carnegie Institution for Science, and the Joint Institute for Nuclear Astrophysics measured the abundance of several r-process elements in seven of the nine brightest stars in Reticulum II.2Reticulum II is an ultra-faint dwarf galaxy that has remained undisturbed by other galaxies or infalling intergalactic gas since it formed more than 10 billion years ago. The enrichment of the r-process elements that the four astronomers measured in the seven Reticulum II stars was “two or three orders of magnitude higher,” that is, approximately 100 to 1,000 times greater, than that which has been detected in any other ultra-faint dwarf galaxy.
This result shows the primary source of r-process elements is not core-collapse supernovae, but rare, highly productive events. Such events require the merging of two neutron stars, two black holes, a black hole and a neutron star, or either a black hole or a neutron star merging with a large star. Though indeed rare, when they do happen, the enormous densities and energies involved in such mergers generate and expel enormous quantities of r-process elements.
The amounts of r-process and s-process elements on Earth are both at the just-right levels for humans to exist and to make a global high-technology civilization possible. This fine-tuning is imperative because too much arsenic, selenium, molybdenum, tin, or iodine in our diets will kill us. Too little of any one of these elements in our diet will also kill us. Each one of these vital poisons must be consumed at a precise level.
Apparently, the universe is designed so that the just-right number and types of merging events occur to produce the necessary amount of r-process elements so that billions of human beings can enjoy a global high-technology civilization here on Earth and use that technology to take the Good News of salvation to all the people groups of the world.
Now, aren’t you motivated to thank God for creating and designing the universe so carefully?
- Takuji Tsujimoto et al., “Chemical Feature of Eu Abundance in the Draco Dwarf Spheroidal Galaxy,” Publications of the Astronomical Society of Japan 67 (June 2015): id. L3, doi:10.1093/pasj/psv035; Nial Tanvir et al., “A ‘Kilonova’ Associated with the Short-Duration Gamma-Ray Burst GRB 130603B,” Nature 500 (August 2013): 547–49, doi:10.1038/nature12505; A. Wallner et al., “Abundance of Live 244Pu in Deep-Sea Reservoirs on Earth Points to Rarity of Actinide Nucleosynthesis,” Nature Communications 6 (January 2015): id. 5956, doi:10.1038/ncomms6956.
- Alexander Ji et al., “R-process Enrichment from a Single Event in an Ancient Dwarf Galaxy,” Nature 531 (March 2016): 610–13, doi:10.1038/nature17425.