# Threats within 100 light years

So I'm making this game where the player has to launch probes into interstellar space within a 100 * 100 light years map to detect threats that could wipe out humanity in a few decades. Everything is going well, except that I could not find enough scientific based threats.

I only came up with a few threats:

• Gamma-ray bursts
• Rogue Planets/Black holes/Stars (they do not really work because if the rogue object is going to enter the solar system within a few decades, it's probably a waste of making a 100*100 light years map)
• Alien life

So is there any other scientific based threats that could wipe out humanity within 100 light years range under a few decades? Or any way to make Rogue objects work?

• 100 x 100 is two-dimensional. You need the three dimensional 100 x 100 x 100. – RonJohn Sep 10 '18 at 1:28
• There aren't really any interstellar threats we could really hope to do anything about, so the detection seems kinda pointless. But anyways, another possible threat are supernovas. – Ryan_L Sep 10 '18 at 1:30
• Unless your aliens have FTL travel (and if they do have the technology for FTL engines, they're so powerful that you're hosed anyway), a 30 year threat window only requires a 30x30x30 box for GRBs, and substantially less for rogue bodies. – RonJohn Sep 10 '18 at 1:32
• @RonJohn it's actually three dimensional but the map is displayed as a plane. It's more like 100 x 100 x 35, also FTL engines do exist in the form of taychons – Epentibi Sep 10 '18 at 1:40
• If the threat is coming in few decades there is no way a probe at 100 lightyears would send the warning in time. "Hello Earth, you were wiped 80 years ago. Blame Einstein and his speed of light thing" – L.Dutch - Reinstate Monica Sep 10 '18 at 5:26

There are none, because of physics.

Let's say a probe at 100 light years out detects something. It sends a message back. It takes 100 years for the message to reach your planet.

By the laws of physics, it cannot possibly give you any warning of an event that will kill you in less than 10 decades = 100 years. It can't warn you of anything at all in a time less than 100 years.

Thus any 100 light year radius net of sensors must be interested in threats more than 100 years out, at an absolute minimum.

• I am aware of that, but that law of physics theoretically only limited to our universe. However it may not be the same in a parallel universe, there might be particles faster than light. In this condition, Taychon particles do exist and can travel a lot faster than light. They could also transmit data. – Epentibi Sep 10 '18 at 1:50
• @Epentibi If so, then none of the threats you will be interested are scientific threats. You will want to invent entirely new ones based around the entirely new physics of your parallel universe. – Cort Ammon - Reinstate Monica Sep 10 '18 at 1:51
• But I still want it to be based on some science. I'm trying to minimize the amount of fiction in this game. – Epentibi Sep 10 '18 at 1:59
• @Epentibi If you want to minimize fiction, then the rule is simple. 100% of things that can kill humanity within a decade are within 10 light years. Nearly all of them will kill via EM radiation. A hypervelocity star like PSR B2224+65 could kill a solar system with a dead hit, traveling at 0.0054c. It'd have to be no more than 20 light days out. Also, you'd be looking for things that you cannot observe from the home planet itself, which would have very nice and shiny telescopes in orbit that are much higher quality than drones spread across a massive grid. – Cort Ammon - Reinstate Monica Sep 10 '18 at 2:04
• Yeah I might just rework the map and system. Thanks for this suggestion. – Epentibi Sep 10 '18 at 3:10

Supernovae.

https://en.wikipedia.org/wiki/Supernova

a transient astronomical event that occurs during the last stellar evolutionary stages of a star's life, either a massive star or a white dwarf, whose destruction is marked by one final, titanic explosion. This causes the sudden appearance of a "new" bright star, before slowly fading from sight over several weeks or months or years.

Even then, however, the shock wave travels at a maximum of 10% of c, which limits you to a 3ly cube, and there are no stars within 3 light years.