Using Osmium to Measure the Milky Way’s Age

Using Osmium to Measure the Milky Way’s Age

I received this email the other day.

I’m writing this with tears in my eyes, my family and i came down here to London, England for a short vacation to visit a resort and got mugged at gun point last night at the park of the hotel where we lodged. All cash, credit cards and cell were stolen off me. I’ve been to the embassy and the Police here but they’re not helping issues at all, our flight leaves today and I’m having problems settling the hotel bills.

The hotel manager won’t let us leave until i settle the hotel bills (1550GBP) now am freaked out. Please reply and let me if can you have the money wire to me through western union i promise to pay back as soon as i get back home.

[Name Deleted]

The fact that this email supposedly came from a good friend somewhat tempered my natural skepticism that developed over the last 15 years of Internet experience. How should such a claim be evaluated? I expected the email was a hoax, so I looked for multiple lines of evidence (suspicious email headers, multiple copies of email, obvious typos, inconsistencies with persons character, etc.) to confirm its fraudulent nature. Scientists use the same kind of process to validate or falsify the truth of scientific claims. Recently published research provides another confirming line of evidence for a universe that is billions of years old.

Scientists utilize a number of techniques to date the creation of the universe. Perhaps the most well-known technique relies on measurements of how quickly distant galaxies move away from us. The  straightforward interpretation of the measurements states that the universe is expanding from a small volume. Using the galaxy motions to map out the expansion history of the universe gives an age around 14 billion years.  Ever since Edwin Hubble first measured the galaxies motions and proposed this explanation, many Christians have expressed strong skepticism about such an ancient universe. But increasingly precise measurements continue to confirm an ancient cosmos and newer methods provide independent support as well.

One of the newer techniques looks to measure the age of the oldest objects in the universe. Most large galaxies (including our own Milky Way) formed within a billion years after the big bang creation event. Thus, dating the age of our galaxy provides a lower limit on the universe’s age. Remarkably, experiments in an European particle accelerator have helped determine the age of the Milky Way. Here’s how.

The first stars formed were very different from stars seen today. Specifically, their massive nature (up to 1,000 times more massive than the Sun) caused them to burn quickly and to explode catastrophically. These explosions produced chemical elements still detected today. One of those elements, rhenuim (Re), decays into osmium (Os) with a half-life of 41.2 billion years.  As with all radioactive dating techniques, an accurate date requires a good understanding of the initial amounts of the radioactive material and proper accounting of any contamination. The 187Re-187Os decay channel provides good tools for meeting these two criteria.

Only two processes synthesize 187Os: the decay of 187Re (made predominantly in supernova explosions) and low-mass stars going through the asymptotic giant branch (AGB) phase. While the Re production throughout the history of the Milky Way Galaxy remains an area of active research, understanding how much 187Os was made via AGB processes will lead to a better age estimation. A large team of international physicists used the neutron time-of-flight facility at CERN to study how astrophysical environments affect the formation and decay rates (referred to as cross sections) of different osmium isotopes.

Their results significantly reduced the uncertainties in the Os cross sections. The improved precision means that Re-Os dates now have error bars in the half-a-billion year range instead of 2–3 billion year range (excluding errors arising from the Re production history). Assuming the most realistic Re production history gives a Re-Os date for the formation of the Milky Way Galaxy around 14 billion years ago. Just as multiple lines of evidence showed the email from my friend was fraudulent, this research affirms the previous assessment  by a group of Christian astronomers that the universe is billions of years old.

  1. K. Fujii et al., “Neutron Physics of the Re/Os Clock. III. Resonance Analyses and stellar (<it>n,γ</it> Cross Sections of 186,187,188Os,” Physical Review C 82 (July 15, 2010): 015804.