You came from somewhere else in the universe – Star Stuff


Understanding reality can lead to some rather astonishing insights, and so today I’d like to point out two of these mind blowing details.

  1. The death of a star led to your existence – All the atoms that you are made of were forged inside the heart of a star. The only reason you exist is because a star died and exploded emitting the matter you are made of.
  2. Many of those atoms did not come from our galaxy, but instead came from other galaxies.

How do we know that this is true?

Well the Bible says …. nah, just kidding. The first is an insight gained in the middle of the 20th century (1957 to be precise) and the second is a discovery that was published within a new paper last month.

Let’s take a look at each in turn.

We are Made of Star Stuff

Most of what is you is composed of oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. That accounts for about 99%. The rest consists of other elements such as magnesium, sulfur, and iron.

In 1957 a paper entitled “Synthesis of the Elements in Stars” that explained where these elements originated was published. Neil deGrasse Tyson is quite rightly quoted as calling this …

a seminal paper — one of the most important research papers ever published — that gave us the description of the origin of the elements … There was no lone scientist burning the midnight oil making the eureka discovery, It was a little messier than that. But the consequences of it are profound

Nicknamed the B2FH paper (the first letter of the surname of the four authors), it basically lays out the details for stellar nucleosynthesis, the process within stars that results in the formation of the heavy elements that we are made of.

You can find a PDF for that 1957 paper here. and the Journal link to it is here. [DOI:https://doi.org/10.1103/RevModPhys.29.547]

Many of your Atoms came from other galaxies

This image shows M81 (bottom right) and M82 (upper left), a pair of nearby galaxies where “intergalactic transfer” may be happening. Gas ejected by supernova explosions in M82 can travel through space and eventually contribute to the growth of M81. Photograph: Fred Herrmann, 2014

This second insight comes via a recently published paper. It has, quite rightly, attracted media attention, so you can read about it in many places, for example here in New Scientist, or here within the Guardian.

The paper itself, entitled “The cosmic baryon cycle and galaxy mass assembly in the FIRE simulations” is unfortunately behind a paywall (but I do have access to a copy). Ref: Monthly Notices of the Royal Astronomical Society, DOI: 10.1093/mnras/stx1517

Basically they ran 3D models of galaxy evolution within the universe and were surprised to discover that galactic winds (streams of charged particles powered by the exploding supernovae) resulted it as much as half the atoms in the larger galaxies (100 billion stars or more) being pushed out of the galaxy and then captured by neighbouring galaxies.

Here are a few nice quotes about it all …

We did not realise how much of the mass in today’s Milky Way-like galaxies was actually ‘stolen’ from the winds of other galaxies … We assumed that the winds were confined to the galaxies they came from – that they could recycle by falling back onto the galaxy that ejected them, but not transfer much mass from one galaxy to another” – corresponding author Claude-André Faucher-Giguère

Galactic winds as a mode of transfer has been underappreciated, Daniel Anglés-Alcázar uses one of the best simulations to do a detailed particle tracking analysis and really laid it all out for us.” – Jessica Werk at the University of Washington in Seattle.

Via the UK’s Guardian, here is an animation that illustrates this …

Bottom Line

A long time ago in a galaxy far, far away …. the basic elements that are now you were forged in the heart of a hot and burning fiery star. In a glorious moment that star very kindly died, exploded, and ejected these elements out across the universe. They rode the  galactic winds until eventually our own milky way galaxy captured them and so over time it took form, evolved, and became you.

It sounds like science fiction, but its not, it is science fact. Additionally, as some might argue, it is also very beautifully poetical.

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