“…What happens to this collapsing core if the mass of the original star is great enough that even this limit will be exceeded? It would seem highly unlikely that they would invariably throw off so much mass that the resulting core necessarily lies below this neutron star limit. The expectation is that, instead, a black hole will result…”
Starlight yawned. Aware that she was now so tired that she was no longer taking in any of the text she was reading, she closed the book, levitated it to the shelf beside her bed, and snuggled down under her duvet. A few minutes later she was asleep.
Bright yellow flames lit up the star-filled palatinate purple sky, powered by an unknown magical luminescence process. This was accompanied by a cackle of evil laughter and a blast of heat emanating from a majestic alicorn figure floating in the air with huge white wings.
“I’m back. You will never be free from me Starlight Glimmer.”
“Daybreaker.”
Starlight Glimmer stared at the glowing eyes of the demonified princess of the sun, the evil twin of Celestia, created by her own fears. The memory of the dream-world battle between Daybreaker and Nightmare Moon flashed into her mind. The realisation that she was dreaming did little to abate her fear.
“Celestia defeated you. You were banished from my dream. Celestia swore you would never exist again.” Starlight fought her fear and stood firm. Or tried to imagine herself in a suitable power stance and not be distracted by the fact that she was actually standing on mist high above the towers of dream Canterlot. Her defiant retort was met by another burst of maniacal laughter.
“Celestia cannot destroy me. You know it Starlight. You don’t really expect her to stay docile forever after you introduced her to me. You showed her everything she could be. Everything she wants to be.”
“No,” cried Starlight. “Celestia would never become you. You’re just a dream. You don’t really exist.”
Daybreaker laughed again making Starlight flinch. Her heart beat fast as fear gripped her body. The fear that Daybreaker could somehow be real would not leave her. Could she really trust that Celestia would never turn this way? She shivered, despite the intense heat in front of her and wished she had Twilight’s unquestioning faith in the former ruler of Equestria.
“I will always be haunting your nightmares…”
Starlight swallowed hard. This is a dream, she told herself, I can deal with this. If I were Pinkie Pie I would just think of something funny and turn Daybreaker’s intimidating laughter into something to giggle at.
“…I am here for eternity.”
Nothing funny came to Starlight’s mind. She decided to try another approach. I need to follow the advice I give the students in counselling sessions, she reasoned. A bit of rational emotive therapy. Use rational judgement and show myself that Daybreaker is an absurdity and she will disappear. Find a flaw in her logic.
“No pony lives for eternity,” she said defiantly.
“I am no ordinary pony. I am the Sun. I shall burn forever!”
The evil alicorn laughed louder than ever. But Starlight’s mouth turned to a tiny smile. She had something to target. She could win this.
“The sun will not burn forever,” she said. “No star will. In a few billion years the hydrogen in your core will all be fused to helium. Your core will contract. As you burn your remaining shell of hydrogen, your outer layers will blow out and cool you down.”
As she said this, the star-pony-demon inflated until she was many times bigger than before. She turned redder and angrier. Starlight felt her confidence increase. This was a game she could win. Just go with the laws of physics. As easy as flying a kite. She stepped back from the expanding red giant, but kept her focus.
“Once hydrogen is gone, I will burn helium,” said Daybreaker.
But now Starlight had something to laugh at. She knew her stellar physics.
“Not for long. Your core will collapse and turn to degenerate matter before it is hot enough for that. Then it will ignite in a flash and fuse all helium to carbon and oxygen in minutes.” Starlight was now relaxed. “But you could still enjoy a quiet retirement—maybe you will then have another hundred million years before it’s all over—but then you will have nothing left to do but eject your outer layers as a planetary nebula and turn to a white dwarf and slowly fading away as you cool down.”
Daybreaker shrank to a tenth of her former size. Her mane and tail lost its fire and her halo of coloured gas dispersed into the night. She became dimmer and dimmer. Starlight smirked. This was completely ridiculous. She was arguing with a star about its mortality and end-of-life care. The absurdity made her laugh and the laughter took away her fear. Pinkie Pie would be proud. This was how to defeat a nightmare. This is your dream Starlight, she told herself, you take control of it.
However, dreams have a tendency to do their own thing. It was not over yet.
“You think you can defeat me that easily?” Daybreaker snarled. Her retort made Starlight stop smiling as the absurdity that had looked hilarious a moment ago now made her feel weak. “You think Celestia has just gone quietly into retirement and will life happily ever after at the Silver Shoals? How quaint. But no true ruler will go that easily. Power is addictive. She will soon crave to be back on the throne, in the centre of the action, and she will be tired of her dumb little sister.”
“That’s not true,” Starlight stammered back. “Celestia needs Luna. She has always said as much.” However inside, her fears and doubts had returned.
“Not yet maybe, but she will change. Do you really think the Red Giant Retirement Home can keep her entertained and amused for long? A princess used to ruling over all Equestria, shaping the lives of every unicorn, pegasus, and earth pony, will not just settle down so easily. She will get bored.” The plausibility of this scenario troubled Starlight. It could not be laughed at so easily. Her stomach fluttered again. “Do you really think Celestia will be content with sitting in a chair knitting? Going out to check the mail box? Chatting with the other old age ponies about the grand-fillies over tea and cake?”
“She likes cake,” said Starlight, feeling uneasy.
“Indeed she does. And a bored Celestia, sitting at home with nothing else to do, will eat plenty of cake. As well as doughnuts, cookies, and sugar-coated pastries. She will get through plate after plate of sweet treats. And before too long she will soon have a weight problem.”
An accretion disk of baked goods appeared around the white dwarf. Starlight watched as the pastries, doughnuts, cupcakes and slices of tart, orbiting in a halo of sprinkles, spiralled into the alicorn’s open mouth. Daybreaker grew fatter and taller.
“Celestia will not stay a white dwarf.” Daybreaker’s voice was now more menacing than ever. “She will want more. She will take it. She will grow fat as Equestria feeds her. And what happens when a white dwarf reaches 1.4 standard solar masses?
Starlight shuddered. “Th-the Chandrasekhar limit.” She had a sinking feeling. The consequences were clear. A white dwarf was held up only by the pressure of not being able to pack the electrons any closer together. If it reached this limit, the electrons would react with the protons to form neutrons, and the star would collapse to a tiny super-dense core of neutrons.
Daybreaker contracted to a tiny bright point surrounded by glowing dust, but her voice sounded in Starlight’s head even louder. There was a lot of energy in that point.
“Celestia would make a cute neutron star. But why would she stop there? She would keep growing more massive, eating more cake, with all Equestria to feed her, until she reaches the fate of a heavy neutron star—”
Starlight shuddered and felt fear grip her throat harder than ever.
“—a black hole! Collapsed under her own gravity into a pit of deformed spacetime. A dead star with a gravity so strong that not even light can escape. The princess that once shone across Equestria will become the ultimate realm of darkness. You will never see anything of her again, but she will continue to greedily absorb any matter getting too close. All Equestria will eventually be consumed behind her event horizon.”
Daybreaker was now a black pony shape surrounded by glowing dust. An even darker, more powerful, and more evil version of Celestia than her usual form. Her laughter echoed in Starlight’s head. Fresh terror took control of her. She lay down and put her hooves over her head. The reality of the laws of physics meant there was no denying what Daybreaker said. Once the escape velocity on the surface of a star exceeded the speed of light then nothing could escape. “What have I done?” she cried. “I thought I could defeat Daybreak with physics, and I’ve made her even more powerful.”
“You know it could happen Starlight,” sneered the black hole. “You know just what it’s like to have the power to bend time and space. You know just how tempting it is to use it to settle old scores and get revenge on everypony who has stood in your way. The attraction is very strong. Celestia will be drawn into that pit of darkness and become a black hole forever.”
“You’re not real,” whimpered Starlight. But she didn’t believe it. The threat of Daybreaker felt more real than ever.
“Your imagination, crossed with Celestia’s power, is a potent thing Starlight Glimmer. The dream realm is not as isolated from Equestria as you might like to think. I am stronger than Luna’s little Tantabus.”
As the nightmare voiced her fears, Starlight cowered and whimpered. “You’re not real. Why can’t I make you go away? You’re suppose to be ridiculous. Why can’t I giggle at you like Pinkie Pie? Why did I read a textbook on astrophysics before bed instead of a fun Daring Do fanfic?”
Images of the equation-filled pages she had studied came to her mind. A sudden unexpected spark lit up in Starlight’s head showing her a route out. Maybe she could still defeat Daybreaker using physics. She felt her bravery return and seized it and stood up to face the pony black hole.
“You’re wrong Daybreaker.” She stared at the evil villain. This gave her confidence. If you can stare at a black hole, she told herself, you can stare at anything. That thought might not have any basis in relativistic optics, but it made her feel stronger. “You’re wrong on two counts. Firstly, Celestia would never turn into you out of boredom. Why should she? If she tires of retirement, she can still do whatever she likes. Why should she stay in Silver Shoals? She can travel the world, try whatever she desires, and find new ways to help ponies, and shine across Equestria. Her reign was not an exercise of power but of responsibility. She stepped down as she was ready to move on and Twilight was ready to take over. But she now has many glorious years ahead of her with endless opportunities.”
Daybreaker was no longer black but had returned to white dwarf form.
“And secondly your stellar physics is completely wrong. A solar mass star would never end up as a black hole. That is only the fate of super-massive stars. Our sun will end its life with grace and style as a white dwarf.” Starlight felt stronger than ever now. “If it did somehow absorb material from somewhere and go above the Chandrasekhar limit, it would not end up as a black hole. The collapse would re-ignite runaway fusion. The atoms packed in the tiny core would fuse to heavier elements in seconds and it would explode as a supernova!”
At these words the star-pony in front of her exploded in a blinding flash of light. The sky turned bright white. Starlight relaxed with a smug face and let the shock wave blow through her mane. Her confidence was now back and she could trust her imagination to stick to happy dreams. She let herself float down and settled on a fluffy cloud. The sky had returned to its shade of purple. Daybreaker was gone, but there was a light on the horizon showing it would soon be dawn. It would soon be time to wake up and think about pancakes for breakfast, but right now she could sit and enjoy the dreamscape.
A portal appeared in the sky before her and Pinkie Pie jumped through.
“Hi Pinkie, you doing dream duty tonight?” said Starlight.
“Yes it’s my turn. And will I be glad to leave it to Rarity tomorrow. It’s been a tiring night. I don’t know how Luna coped on her own before she retired. Are you okay now? I saw you were having some problems, but I had to help a little filly deal with a gigantic scary chocolate fudge monster first.”
“It’s all sorted Pinkie. Do you want a doughnut?”
Pinkie sat down beside Starlight and accepted a dream cream doughnut, then looked up and saw the sky. Her mouth dropped open.
“What is that?”
The foreground to the star-studded sky was filled with a web of coloured glowing strands. Rings of yellow and red stood out against a more diffuse blue-green.
“Pretty isn’t it?” said Starlight. “It’s a supernova remnant. The debris from an exploded star. A hot gas full of many elements, heated by a shock wave and high energy particles.”
“What have you done?”
“Daybreaker threatened to corrupt Celestia and turn into a black hole and consume all Equestria and I turned her into a supernova and she blew up.”
“That makes no sense,” said Pinkie Pie, nodding with approval.
The two friends sat side by side and watched the cosmos.
“It is beautiful,” said Starlight. “And practical, in a way. It will spread through space. The pressure wave might trigger more clouds of hydrogen gas to collapse and form new stars. The heavy elements will form future planets. The gift to the universe of a dying star.”
A white rift opened in the sky before them and Luna and Celestia stepped through.
“Hello Starlight. Hello Pinkie,” said Luna. “We sensed that you had an astronomical problem, so I thought maybe we should check everything was okay, but…”
She stopped talking as both sisters looked around at the sky.
“It seemed you handled it fine on your own,” said Celestia.
“No problem,” said Starlight. “It was a piece of cake. How are you getting along at Silver Shoals?”
Luna and Celestia rolled their eyes.
“They called it retirement,” said Celestia. “We’ve never been busier in all our lives. We get invitations to everything. We were hoping for a little R&R.”