In the Lecture Hall: The Supernova’s Involvement in the Formation of the Solar System
“Excuse me. I’m sorry.”
I mumbled under my breath as I tried to shoulder my way through a group of students. They were engrossed in a poster put up on the right wall of the corridor.
I reached the end and took a sharp right turn. I walked briskly to Hall 407 and opened the door.
The professor and the scholar were sitting on two wooden chairs with their backs towards me. They were both analyzing something on the professor’s laptop that was kept on the center table.
“Hello!” I said as I closed the door behind me.
“Hello, my friend!” said the professor as he turned around and raised his hand. “Please come in, we have been waiting for you.”
“Traffic was horrible today.”
“That’s true,” said the scholar.
I made my way to a bench near them and sat down.
“We were just discussing your epiphany question that you asked yesterday,” continued the scholar. “We both went down a rabbit hole! It’s such an interesting topic.”
“I’m glad you found it fascinating! Please teach me,” I said as I leaned on the desk, eager to learn.
Question — How do we know a supernova was involved in the formation of our Solar System?
“What do you know about radioactivity?” asked the scholar.
“It’s a process where unstable atomic nuclei emit particles or energy to become stable,” I replied, with a hint of uncertainty in my tone.
“That’s right. A nucleus becomes unstable if there is an imbalance between the number of protons and neutrons. Through various complex processes, the nucleus would shoot out some heavy particles or photons to balance itself out.
In fact, bananas are radioactive by a tiny amount.”
Looking at my worried face, the professor chuckled. “Don’t worry. The radioactive element in a banana is K-40, an isotope of Potassium. Potassium is excreted by the body through urine.”
“That’s a relief,” I said. “What’s an isotope?”
“Ah! They are the unstable cousins of stable elements. A stable element has a equal number of protons and neutrons. An isotope has additional neutrons.”
“The additional neutrons make the nucleus unstable.”
“In most cases, yes,” said the scholar as he crossed his legs and shifted around in his chair. “Now, when an isotope’s nucleus is unstable and becomes radioactive, we can measure the radioactivity and derive important properties about the nucleus.
For example, we can know its average lifetime before it decays.”
“Along with that number, we can also calculate the time a given amount of radioactive substance needs to decay to half of its initial value,” said the professor as he turned off his laptop.
“Yes, now I remember,” I said as I leaned back and pinched the bridge of my nose. “That’s how we measure the ages of fossils. How is that related to the formation of our solar system?”
“Well, you answered your own question,” said the scholar with a smile. “Just like fossilized plants and animals help us understand the story of the ancient Earth, meteorites help us understand the ancient solar system.”
“Whoa!”
“Yep. Let me give you an example. Some meteors, called chondrites, are made of silicates and metals. A subclass -called Carbonaceous chondrites — condense out of the protosolar disk at relatively high temperatures.
This subclass of meteors contains compounds of Calcium and Aluminium. The oldest of these was dated back to approximately 4.5 billion years ago.
That was the early solar system.”
The scholar paused to let me sink in the new information. The professor stood from his chair and carried his laptop to a small bookshelf near the door. He plugged his computer to a power outlet and turned on the switch.
“That’s crazy,” I said, after a few seconds. “But what about the supernova?”
“That story is narrated by two isotopes — Al-26 and Fe-60,” said the professor as he walked back to his chair and sat down. “Let’s talk about Al-26 first. It has a mean lifetime of one million years, after which it decays to Mg-26.”
“And Mg-26 is stable,” I said.
“Exactly. Now usually, Mg-26 is formed when Al-27 decays.
But, when we compare the amount of Al-27 with Mg-26 in these chondrites, we notice that there is an additional amount of Mg-26.”
“That extra amount of Mg-26 is from Al-26.”
“Right on!”
“So the question becomes — where did the Al-26 come from?” said the scholar. “The situation is similar with Fe-60. It has a mean life of 3.8 million years and decays to Ni-60. When you compare that amount with Fe-56, you get an additional amount of Fe-60 embedded in these chondrites.”
“Interesting. So do we know where these isotopes are formed?” I asked.
“We have a decent idea. They are formed in the cores of stars and in the energetic environments of supernovae. The latter is especially true for Fe-60. The extreme pressure and heat during the explosion aids its formation.”
“Oh,” I said as the pieces finally fell in place. “Let me get this straight.” I closed my eyes to visualize the scenario.
“Meteorites fall on Earth. We break them down to study them. We measure the abundances of various stable and unstable isotopes. Since we know their lifetimes, we know when that meteorite formed.
By comparing their amount, we notice that some are highly abundant. That could only mean that external influence were somehow involved in the solar system’s formation.
And that external influence is most likely a supernova because isotopes like Fe-60 are formed there.”
I opened my eyes as I ended my monologue.
I feel enlightened.
“Exactly!”
I leaned back on my bench as stared up at the ceiling, deep in thought. “We know a supernova was involved. But how did the isotopes make it to our solar system?
You said some are produced in the cores as well. How did they reach here?”
“You are asking the right questions, my friend,” said the professor with a proud smile on his face. “Why don’t we answer that question tomorrow?”
“Definitely!”
Hardik Medhi
Stay Curious
