I was reading "Ringworld" by Larry Niven. I'll spare you most of the details of the story, and say that one of the parts of the plot is that the center of the Milky Galaxy blows up, because all of the stars in the galactic center are all so close that when one goes supernova, it causes the remaining stars to go supernova which results in an explosion that will annihilate Earth when the explosion reaches it in about 20,000 years. I'll let the book explain:

"The stars are too close together," said Louis. "An average of half a light year apart, all through the core of any galaxy. Near the center, they're packed even tighter. In a galactic core, stars are so close to each other that they can heat each other up...

"Then one star went nova. It let loose a lot of heat and a blast of gamma rays. The few stars around it got that much hotter... So a couple of neighboring stars blew.

"...The combined heat set off a few more. It was a chain reaction"

So, my questions are:

  1. Is it possible this could happen in our galaxy?
  2. Is it theoretically possible this could happen to some galaxy?
  3. If it is possible, how close would stars have to be, and how big would the resultant explosion be (for example would it be able to annihilate a planet 20,000 lightyears away)? *I understand that the jets emanating from supermassive black holes can travel over 100,000 lightyears, but I am specifically talking about the resultant supernova explosion. (If there is no difference between the two, educate me about that.)

My initial guess is that there is just too much space for something like this to happen, but I have zero qualifications to judge the plausibility of this.

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    $\begingroup$ Setting aside other issues, stars are so far apart (even in the crowded center) that they can't really affect each-other by exploding. If they weren't widely-spaced then they would collapse together under gravity very quickly. $\endgroup$ Commented Apr 14, 2022 at 6:50
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    $\begingroup$ Niven wrote Ringworld and other Known Space stories (particularly "At the Core" where this exploding core idea was first introduced) many years before the discovery that nearly all galaxies have a SMBH at the center, and that what was called "exploding galaxies" at the time really were caused by AGN (Active Galactic Nuclei) which in turn are caused by a SMBH. $\endgroup$ Commented Apr 14, 2022 at 15:31
  • $\begingroup$ i recall reading a similar story, although in that one there was some group of aliens who fulfilled all their contracts and mysteriously took off before it was discovered that the chain reaction in the center of the galaxy had already begun. $\endgroup$
    – Michael
    Commented Apr 14, 2022 at 20:37
  • $\begingroup$ @Michael Pretty sure that's the same book. $\endgroup$ Commented May 15, 2023 at 7:09

1 Answer 1


We don't see this happening in other galaxies (and there are plenty we've studied). Theory suggests no: generally, adding heat to a star stabilizes it. For type II, it's the collapse of the core due to a lack of heat generation that leads to the supernova. For a "single degenerate" type Ia, an external trigger is conceivable, but the star would have to be poised right at the threshold of instability, a rare circumstance.

You should not attempt to learn astrophysics from Larry Niven ツ

  • $\begingroup$ Learning astrophysics history from Niven's works is a different matter. Either in Ringworld or in one of the other stories in that universe he mentions that the chain reaction is turning the Milky Way into a Seyfert galaxy, and at the time he wrote that, one of the theories for the nature of a Seyfert galaxy was that it was experiencing a chain-reaction supernova outbreak in the core. $\endgroup$
    – Mark
    Commented Apr 15, 2022 at 0:27
  • $\begingroup$ @Mark Do you have a reference for that? I had a bit of involvement with Seyfert studies back then, and I never heard that idea outside of Niven's fiction. $\endgroup$
    – John Doty
    Commented Apr 15, 2022 at 0:38

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