a supernova -- 7/10/24

Today's selection-- from Things That Go Bump in the Universe by C. Renée James. In 1987, Sanduleak -69 202 became the first supernova, the explosion of a star, visible to the naked eye in four centuries:

“Ten to the power of 57. That is, give or take, how many protons join with electrons to form neutrons during the collapse of a massive star's core, and with them come equal numbers of neutrinos to satisfy the universal accountant. It's the stellar core's last-ditch effort to relieve the incredible pressure, but the relief doesn't last. In a flash, a volume the size of the Moon shrinks to the size of a city, leaving the outer core at a loss. As the rest of the core tries to collapse inward, even more electrons are thrust into the protons, creating more neutrinos, and the collapse continues. Light, following Einstein's energy-mass equivalence, becomes particles and antiparticles, all of which are frantically interacting with each other to shed the intolerable energy. Soon the neutrino numbers have increased tenfold. Now there are ten to the power of 58. 

“One with 58 zeroes after it. 

“At this point, the center of the star has become an enormous, roiling, hot atomic nucleus. Neutrinos might see the rest of the material universe as an open window, but punching their way out of a city-sized neutron inferno is another matter entirely. Each of these newly generated neutrinos packs about the same energy as a trillionth of a crashing dinner plate, individually unimpressive but collectively beyond imagination. Together, they tear at the shrinking core with nearly 100 foes of energy, forcing great fluid blobs in the core to slosh back and forth and pushing at the collapsing walls like a terrified animal in a cage. That's a trillion years of solar energy yearning to break free from something that is quickly becoming smaller than a city and denser than a mountain per teaspoon. All of this frenzied activity occurs in the blink of an eye, the fluid blobs churning to and fro at nearly the speed of light. So much is going on that it takes months of supercomputing time to render just half a second of activity, but it's the most important half second in this star's life. 

SN 1987A was caused by the explosion of Sanduleak -69 202.

“The neutrinos do ultimately succeed in punching their way out. The push from the neutrinos is, it turns out, the tipping point for a supernova, as they carry with them 100 times the energy that the light does. It seems at first glance as though the tsunami of high-energy light and the shock wave from the core's sudden halt should do the trick, just as an enormous swell might look as though it will come crashing onto the beach and sweep away your sandcastle. But very often by the time that enormous swell makes its way to the sand, its energy has been sapped by the retreating wave that came before it. Instead of the anticipated frothing spray of saltwater, the wave becomes a whisper, a swish that barely creeps up the sand. 

“Without neutrinos, the outward surge of matter and energy accompanying core collapse meets the same fate. A rush of energy from the core promises to blast the envelope of the star into space, while the simultaneous infall always manages to quash the energy. But when conditions are this extreme, and neutrino numbers are this great, their infinitesimally small chance of interacting is all it takes to tip the energy scales. Without that extra neutrino push, gravity wins. 

“It doesn't take long for conditions in the star to once again become an open window for the neutrinos. Seconds, really. As they shove the wave outward, the material becomes less dense, more transparent to these ghost particles, which barely notice a trillion kilometers of lead. Within a few heartbeats, neutrinos are free to race out of the star ahead of the slower-moving, broiling-hot shock wave. Because they are nearly—but not completely—-massless, their speeds nearly match those of the photons, and they get a head start of hours to days. The difference between a photon's speed and a neutrino's speed is, at most, only about one part in a billion, so the journey of 168,000 light-years from the star formerly known as Sanduleak —69 202 was not nearly enough for the light to catch up. The neutrinos from that event arrived on Earth a few hours before the light did, spraying Earth with 10 trillion quadrillion neutrinos. 

What this means is that every single person alive at the time was dosed with about a quadrillion of these energetic subatomic particles, and nobody batted an eye."

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C. Renée James


Things That Go Bump in the Universe: How Astronomers Decode Cosmic Chaos


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