Useless Backstory

"Why are you waking me up Sergeant? And why did we enter near-light speed?"
"We received a distress call, and there wasn't enough time to notify you, sir."
"What kind of distress signal?"
"It came from System 235. It was jammed before we could get much out of it, sir."
"How long til we reach them?"
"1000000 years, universe time, sir."
"No man, local time."
"Given our Lorentz factor of about 9000000000, about an hour, sir."
"Is that enough time to prepare?"
"Given that we have no idea to the nature of the emergency, and that we lost communication, we are as ready as we will ever be."
1000000 years universe time. All sorts of things could have in that amount of time. If he remembered his Lorentz tables correctly, System 235's standard time runs on a Lorentz factor of 4500000000, so it will take about 2 hours of their time for them to get there. Nothing they could do about that though. They were already within 1% of the speed of light, and at that speed, it would take 2 hours of their time, regardless of their the ship's Lorentz factor.

Just then, they arrived. The ship pulled into the photon sphere of a docking black hole. "Scan the system, private."
"Yes, sir. Sir, the sun!"
"What man. Spit it out."
"The sun, is gone! It has collapsed into a black hole! All the planets are frozen, trillions dead!"
That star wasn't scheduled to collapse in such a short time. In fact, it wasn't supposed to collapse at all, it was supposed to become a white dwarf. "What happened!"
"I have no idea sir!"
"I may have an idea!"
"What, engineer?!"
"I think. THEY may have broke, the treaty, uh, sir."

End Useless Backstory

So, THEY have broke the treaty, as far as our intel can show. THEY have created a CrushSun, a starship capable of destroying moons, planets, and, mainly, suns. It works via the following principle:

  • The ship is spherical. It shoots a bunch of lasers toward the center, creating a black hole. See this (page 9). (How the micro black hole is created isn't important, just as long as it is created.)
  • When the black hole is at the right mass, the lasers are turned off, except one. It shoots the black hole out of a hole in the ship. The laser looks terrifying, but it is the black hole which destroys the system's sun, by crushing it.

My question is, how big and how much energy must such a device use? Use the link above as a starting point. (Considering the locomotion of the ship is optional.)

NOTE: Although a lot of hard science has been done on a similar device, which serves the same purpose, they are completely different designs. The death star needs to overcome the gravitational binding of energy of the target, whereas for this the target doesn't matter (cubic v.s. constant, with respect to scale). You can use that information roughly, but keep in mind that these devices are different.

BONUS: How much waste heat would it produce, and what kind of exhaust ports would be necessary?

  • $\begingroup$ A Hard Science question that puts out "this is not important" clauses rings some alarms off. If I was your reader and you used that paper (which hinges on the edge of physical possibilities and make so many assumptions it's hard to take seriously), I would just close the book and put in on the same shelf that J.J. Benitez works. If you want to continue hard-sciencey, I would recommend checking more of the relevant literature, including most recent advances regarding gravity. $\endgroup$
    – Mermaker
    Feb 19, 2016 at 15:11
  • 1
    $\begingroup$ @ThalesPereira Why not grace us with your vast understanding of the topic in an answer (for or against) rather than simply poo-pooing the idea in a comment that shows no real knowledge of the subject? $\endgroup$
    – Samuel
    Feb 19, 2016 at 17:08
  • $\begingroup$ @ThalesPereira It is all on the edge of possibility of our current engineering capability. It is all very standard physics though. $\endgroup$ Feb 19, 2016 at 17:52
  • $\begingroup$ How come your black hole doesn't destroy the SunChrusher? Still, cool idea. Also you could store the waste heat in molten irn and spray super heated iron at planets to kill them. $\endgroup$ Feb 19, 2016 at 21:00
  • $\begingroup$ @Sam It is a very small black hole at first. Its gravity is weak, and basically only absorbs matter through direct contact. (You have to take care that the black hole doesn't actually touch the ship though.) $\endgroup$ Feb 19, 2016 at 21:26

1 Answer 1


You need 9 × 1025 joules and a ship the size of a small moon

The research you linked (which I've read before) details the power output and lifetime of micro black holes.

The black hole will only grow if it's larger than an atomic nucleus (>1 attometers in diameter). This means it falls into the Bondi accretion regime. A black hole must have an effective radii larger than atomic size for it to be able to capture more mass. This paper also has a handy equation for estimating the accretion rate of your black hole depending on its mass (Eq. 20).

Your paper also says:

Since a nuclear laser can convert on the order of 10−3 of its rest mass to radiation, we would need a lasing mass of order 109 tonnes to produce the pulse. This should correspond to a mass of order 1010 tonnes for the whole structure (the size of a small asteroid).

Assuming you have a perfect conversion of that energy to mass, that's what you need to make a million tonne black hole, which is just over the 1 attometer size limit. But you're going to need some ship to house that, the crew, energy storage, tractor beams, exhaust ports, etc. So we'll say you need a small moon. That's also... not a moon.

  • $\begingroup$ For a reference, you would need to convert 1 billion kilograms of mass into power for the weapon for each shot, or 1/6 of a pyramid (one pyramid will let you destroy six things.) $\endgroup$ Feb 19, 2016 at 0:50
  • $\begingroup$ I'm not entirely clear. Is the sun supposed to be destroyed as the micro black hole evaporates and releases it's energy via Hawking radiation, or are you suggesting the black hole absorbs the Sun? Either way will take some time. $\endgroup$
    – Thucydides
    Feb 19, 2016 at 0:58
  • $\begingroup$ @Thucydides The black hole absorbs the sun is the idea I had. The micro black hole wouldn't have near enough energy to overcome the gravitational binding energy of even a planet probably. (Anyone know how long it takes for a micro black hole to eat a star/sun?) $\endgroup$ Feb 19, 2016 at 1:06
  • $\begingroup$ @Thucydides Absorbed. Yeah, it's going to take a while. A long while. I linked an equation to estimate the time. $\endgroup$
    – Samuel
    Feb 19, 2016 at 1:06
  • $\begingroup$ @Samuel Although, the star isn't being time dilated, only the people. The sun has 1000000 years to get absorbed, and it will seem like two hours to the inhabitants. (My idea is that we place the people around photon spheres of a bunch of smallish black holes, so they get lots of time dilation.) $\endgroup$ Feb 19, 2016 at 1:08

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