1517 Does Astronomy & Astrophysics: The Physics of Supernovas
Advanced notes on a talk.
This post is a somewhat brief introduction to a session on supernovas being hosted by Dr Andy Howell. There are two parts,
Dr. Howell’s introduction to his talk.
A supernova is so catastrophic that the explosion of a single star can outshine the other hundred billion stars in a galaxy. The last time one was seen by humans in the Milky Way, it was obvious for weeks in the sky to most of the planet, and could even be seen in the daytime. It was one of the indications that the heavens were not perfect and unchanging, helping Galileo to chisel away at the Catholic Church's claim to be the single source of truth, and ushering in the modern scientific revolution.
In my lifetime we've gone from almost never seeing a supernova to discovering thousands per year in distant galaxies. Since supernovae achieve energies far beyond what humans could ever hope to produce, they are natural laboratories for probing the frontiers of physics. This has led to an explosion of knowledge spanning the origins of subatomic particles, the creation of black holes, the limits of relativity, the origins of the universe, and the discovery and study of Dark Energy. Even the origin of the elements depend on supernovae, as does our own existence — most of the raw material in your body was created in a supernova. They have impacted some of the biggest forces in human life too, including commerce and warfare.
At the forefront of this frenzy of new information sits Las Cumbres Observatory, a robotic network of telescopes placed around the globe so that they can observe as one instrument continuously, uninterrupted by daytime. It combines two of the most disruptive technologies in history - the telescope and the internet - to see the universe in a way never possible before. Our insights are also being used to shape the next generation of technology.
In 2024 astronomers will begin to use the Vera C. Rubin observatory -- a telescope that will image the entire visible sky every few nights, finding ten million things that change each night. This big data revolution is changing the way astronomers work, and like the invention of the digital camera, our technology will eventually impact the larger society. And in 2027 we plan to launch the Nancy Grace Roman telescope, a spy satellite repurposed to be our first wide-field infrared instrument in space. It will measure supernovae nearly back to the beginning of time, giving us the best possible insight into the nature of the elusive Dark Energy that dominates the universe.
Supernovas on human scales
The Soviet Astronomer Nikolai Kardashev proposed using energy as a marker for civilizational progression. Kardashev's model focuses on the harnessing of energy, but if we extend his model to include releases of energy, there are four moments that stand out in the history of humans (and our direct evolutionary ancestors);
The first is the taming of fire in the distant past. This event is old enough to have had a profound impact on our physiology. The proportion of your limbs; the shape of your teeth; and the development of your brain were all shaped by the hominid discovery of fire,
Indeed, recent studies demonstrate a preference by nonhuman primates for cooked food (Wobber et al. 2008). The higher food energy that cooking supplies, as well as the detoxifying effects of heating (which increased the diversity of available food), contributed to a fitness advantage in these early humans. Furthermore, cooking implied a delay in food consumption, which required the development of social abilities for the distribution of tasks within the group (e.g., collection, accumulation, cooking, defense, even stealing), as well as the socializing effect of gathering around nighttime campfires (Pyne 1995). These factors are thought to have prompted the evolution of large brains and bodies, small teeth, modern limb proportions, and other human traits, including many social aspects of human-associated behavior (Wrangham et al. 1999). Indeed, by softening food, fire could have had a large effect on extending the human life span beyond the age of good-quality teeth. This may have been very significant in social organization, including the “grandmother” hypothesis relating child care with social development and human evolution (Hawkes 2004).
The second is the discovery of gunpowder. This discovery shaped the history of civilization and the governance structures that undergird our world.
The third moment happened within a human lifespan, 77 years ago. Unlike the other two, we know exactly the moment when the threshold was crossed; 5:29 a.m. Mountain Time on July 16, 1945. A subgroup of humans achieved fission that day with a yield of at 24.8 ± 2 kilotons of TNT. Or, 103.8 ± 8.4 * 10^12 Joules. For the sake of simplifying calculations, we're going to round it out to 100 * 10^12 Joules. This event was Trinity.
From the cosmic perspective, humans released about the relativistic mass-energy equivalent of 0.042 ounces on that day. Or, 1.2g. Or, 3 and ⅔'s of a regular aspirin.
Humanity's fourth big step was taken on November 1st, 1952 at 07:15 local time (UTC+12). Humans released the energy of roughly 10,400 kilotons of TNT. Or, 43,510 * 10^12 Joules. (we'll be rounding this down to 43,500 for future calcs). This event was Ivy Mike.
Cosmically, our species released the relativistic mass-energy equivalent of 1.07lbs of matter. Or, 484g. Or, ⅖'s of a current gen Macbook Air. The highest we've ever achieved is the mass-energy equivalent of two Macbook Air's.
These are impressive numbers, but they don't hold a candle to nature. Dr. Howell was a part of the global group that discovered the first kilonova; an explosion caused by the merger of two neutron stars. This event released approximately ~1.5 * 10^47 Joules of energy. Or, about ~3.6 * 10^34 kilotons of TNT. These numbers are so big that they’re absurd, so let’s break them down.
From the human perspective, here's how the event chalks up against our breakthroughs,
— In terms of Trinity, the event the group found is approximately, 1,500,000,000,000,000,000,000,000,000,000,000 Trinities. That's still a very large number, it's 200 trillion times bigger than all the grains of sand on Earth (~7.5*10^18)
— Or, once again approximately, 3,450,000,000,000,000,000,000,000,000,000 Ivy Mikes. Which has fewer zeroes than Trinity (humanity is catching up!), but it's still 460 billion times all the sand on Earth times the pinnacle of current human energy release capability.
At these scales, these events aren't destructive. They're creative. All of the oxygen you breathe was created in a supernova. Almost all of the silver and gold that you've ever touched was created in this type of a neutron star merger. The event that Dr. Howell's team observed, GW170817, is thought to have produced somewhere around 3 to 13 Earth masses of gold. The fuel used by Zeno Power, Strontium1, was likely created in such a neutron star merger. More broadly, almost every single element on this planet above Oxygen was likely created in some form of supernova.
These aren't moments of destruction. They're forges of creation.
In this guest session, Dr. Howell will explore how such events act as natural laboratories for probing the frontiers of physics. And how they've led to an explosion of knowledge spanning the origins of subatomic particles, the creation of black holes, the limits of relativity, the origins of the universe, and the discovery and study of Dark Energy.
For further reading,
Illuminating Dark Energy with Supernovae by Dr Andy Howell
Strontium has been detected in the merger of neutron stars. Watson, D., Hansen, C.J., Selsing, J. et al. Identification of strontium in the merger of two neutron stars. Nature 574, 497–500 (2019). https://doi.org/10.1038/s41586-019-1676-3 accessible here