Our Milky Way galaxy, like all large galaxies, grew by accreting many smaller galaxies billions of years ago. And, you or your spouse’s, wedding ring owe those galaxies a debt of gratitude.
When our universe first came into
existence nearly 14 billion years ago, it contained only hydrogen, helium, and
a trace amount of lithium. These are the three lightest and simplest elements. A
glance at a periodic table shows our universe contains 92 naturally occurring
elements with uranium being the heaviest. We have created another dozen or so
elements in laboratories around the world. Of those 92, all of them up to iron
are created inside normal stars, like our sun.
Stars form these heavier elements through
a process called nuclear fusion. The incredible heat in a star’s core slams
lighter elements together making heavier and heavier elements and releasing
more energy into the star’s core. But making iron requires more energy than it
creates. Fusion reactions almost instantly halt.
Stars like our sun die rather quietly
after that point. But, stars more than ten times larger than the sun die in a
spectacular supernova explosion. These events release so much energy that
elements heavier than iron can form. However, supernova explosions cannot
account for the amount of “jewelry store elements,” like gold and platinum, in
the universe.
Recent studies revealed that
collisions between two neutron stars release enough energy to create the amount
of gold in the universe. Astronomers have discovered hundreds of gold-rich
stars in the Milky Way. But they wanted to know when and where these stars formed.
Scientists from Notre Dame and Tohoku University in Japan used a powerful
supercomputer to run simulations. Their work showed these stars formed in dwarf
galaxies that merged with the Milky Way some ten billion years ago. In their
study, they said “The gold-rich stars (we see) today tell us the history of the
Milky Way. We found most gold-rich stars are formed in dwarf galaxies over 10
billion years ago. These ancient galaxies are the building blocks of the Milky
Way.”
Not only did these many dwarf galaxies grow our Milky Way, they also created most of the gold that exists on Earth. The universe does work in mysterious ways.
Each month, I write an astronomy-related column piece for the Oklahoman newspaper. After it is published there, I post that same column to my blog page.
This is reprinted with permission from the Oklahoman and www.Oklahoman.com.
