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An anti-star is a star that produces energy via antimatter annihilation. As annihilation is 100% efficient at turning matter into energy, an anti-star the mass of the Sun produces 100 times as much energy. The energy produced by annihilation in its core helps prolong its lifespan. The sun has burned through half of its fuel reserve of 194 septillion tons of hydrogen as of the time I write this, and we will work with a anti-star with a mass equal to that of the Sun. The Eddington limit is 1.2610^31 W, and the wattage of the Sun is 3.82810^26 W, and if we times that by 100, we get 3.828*10^28 W. Thus, the anti-star would work in theory. Would such an space object be able to have a habitable zone that lasts long enough for complex life to arise?

And if so, how far out would the habitable zone be?

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    $\begingroup$ Uhm i think there is a pretty big flaw in your concept. Matter-Anti Matter annihilation needs 50% Mater to 50% Anti Matter to work. Thus your Star would have to be 50% Antimater. And since both types of Matter are so close to each other, the star would just explode and hjave a lifespan of 1sec... $\endgroup$
    – Erik Hall
    Dec 7, 2020 at 17:48
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    $\begingroup$ Probably needs to be all anti matter with a small but regular in fall of matter from a rotating disc of matter. $\endgroup$
    – Slarty
    Dec 7, 2020 at 17:51
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    $\begingroup$ If sufficient matter fell onto the anti matter say 4 million tonnes per second the energy generated would be equivalent to the output from the sun. If the ball of anti matter were the size of the sun the gravitational field would be sufficient to contain the outward pressure of the explosive forces. The only difficulty is spreading out the in fall of matter to provide a relatively uniform distribution. This might prove a sticking point. $\endgroup$
    – Slarty
    Dec 7, 2020 at 18:07
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    $\begingroup$ The other difficulty is that you're going to be getting mainly gamma rays from matter/antimatter annihilation, not visible light, which is going to make the "habitable" zone kind of rough. $\endgroup$
    – Cadence
    Dec 7, 2020 at 18:08
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    $\begingroup$ People are saying that a star made of 50/50 matter/antimatter would explode instantly, but I actually don't think it's obvious. I don't think much is really known about matter-antimatter interaction given that we haven't made more than a few atoms of antihydrogen. It could be that the much higher energy output of an "antistar" would lead to much higher temperatures, thus a much larger and less dense ball of gas with a much lower rate of collisions between atoms, which could end up as a sustainable reaction for all we know. (The gamma ray thing does seem like an issue though.) $\endgroup$
    – N. Virgo
    Dec 8, 2020 at 4:57

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How does this work? If the core of the star were made of 50/50 matter and antimatter, it would supernova immediately, so we know that's not what's happening. You must have a star that is mostly one type of matter, and is steadily supplied with the other. Lets talk about that.

When anti-protons encounter protons they self annihilate and produce gamma rays. If the stream of antimatter fell on the outside of the star then all those gamma rays would be produced at the surface. Gama rays are very bad for energy. They go through almost everything, so it's hard to absorb them the way plants absorb light. They also carry so much energy that when they finally are absorbed they tend to destroy molecules. It is very difficult to imagine a type of life that could consume gamma rays. Nuclear fusion in our sun produces gamma rays, but they are absorbed by thousands of miles of sun and re-emitted as lower frequencies of light including visible.

You also can't have an anti-matter star fed with a stream of matter. Not if it's surrounded by a universe made of regular matter (which it is, whichever type of matter the universe is made of is the regular one), then stray particles falling into the sun would turn the solar system into the gamma ray disaster I mentioned earlier.

If your anti-mater star is going work it has to be made of regular matter, but a steady stream of anti matter has to be created in the core. This is impossible. There's no known mechanism for it. Creating anti matter takes exactly as much energy as it releases when it annihilates. But, lets go ahead and assume that it's happening. Maybe you've got magical clark-tech in your world.

If it existed, you can actually treat it just like a regular sun. You have a sun massed object with nuclear energy in the center that heats the whole object till it glows. The color would be in the range of colors for stars. The habitable area would be in a normal place for a star with a similar energy output.

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    $\begingroup$ Although if you have a sun-massed object, it doesn't need a flow of antimatter at its core to glow like a star. $\endgroup$
    – jdunlop
    Dec 7, 2020 at 20:37
  • $\begingroup$ Hard to imagine life that can consume gamma rays? $\endgroup$
    – Mark
    Dec 8, 2020 at 8:14
  • $\begingroup$ @Mark: That says "radiation", but doesn't specify which kind. To a gamma ray, I doubt melanin would be much different from any other organic compound. $\endgroup$
    – Lars H
    Dec 8, 2020 at 8:26
  • $\begingroup$ Maybe a star made of either anti-matter or regular matter that has a magnetic field that suspends and regulates the rate that the other matter falls into it at? Or pick a binary star system. $\endgroup$
    – DKNguyen
    Dec 9, 2020 at 0:39
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Matter-Antimatter annihilation produces gamma rays if it happens at low energies or exotic particles if it happens at high energies.

For the electron-positron annihilation:

When a low-energy electron annihilates a low-energy positron (antielectron), the most probable is the creation of two or more photons, since the only other final state Standard Model particles that electrons and positrons carry enough mass-energy to produce are neutrinos which are approximately 10,000 times less likely to produce, and the creation of only one photon is forbidden by momentum conservation—a single photon would carry nonzero momentum in any frame, including the center-of-momentum frame where the total momentum vanishes. Both the annihilating electron and positron particles have a rest energy of about 0.511 million electron volts (MeV). If their kinetic energies are relatively negligible, this total rest energy appears as the photon energy of the photons produced. Each of the photons then has an energy of about 0.511 MeV.

Gamma rays are used to sterilize surfaces, so there is nothing like a habitable zone for a star emitting gamma rays.

For reference, gamma rays emitted by nearby supernovas are thought to have caused mass extinctions on Earth in the past. And we are talking more than tens of light years away.

While in a normal star one needs high pressure and time to achieve nuclear fusion. This makes fusion happening in the core of the star, below kilometers of ionized gases which absorb the gamma photons. On the other hand in this star annihilation will happen anywhere two suitable atoms meet each other.

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  • $\begingroup$ I knew it wouldn't work out... $\endgroup$ Dec 7, 2020 at 20:31
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    $\begingroup$ The nuclear fusion happening in the Sun also produces gamma rays, but they don't reach the Earth because the mean free path for photons in the core of the Sun is small, so they heat the Sun instead of escaping. $\endgroup$ Dec 8, 2020 at 2:36
  • $\begingroup$ @2012rcampion, in a normal star one needs high pressure and chances to achieve nuclear fusion. In this star annihilation will happen anywhere the two reagents meet each other. $\endgroup$
    – L.Dutch
    Dec 8, 2020 at 4:17
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I googled up to see if I could find anything on "antistars". The only use I found related to antimatter was about stars made entirely of antimatter, not of a mix of both matter and antimatter.

If you do have a start that is made of both, you have a big problem. In a regular star you have an equilibrium between gravity and pressure from fusion, which means that there is a steady flow of star fuel to the core. In a mix of matter and antimatter, you don't need pressure to have a reaction. You just need both to get in contact. If they mix at any pressure at all, they will blow up in an instant. Your star's lifetime will be very short, measured in very small fractions of a second. That does not bode well for life (or even for planets to form where such life could exist).

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Physicist here. I agree with the answers so far, there'd be a bunch of problems for a reaction of a 50/50 mix on the inside of your star - but mate, don't let that stop you :)
There's a ton of ways you can turn that "bug" into a feature:

  • Even if there was a matter/antimatter core, the pressure from the sudden annihilation would tear the star apart from the inside, like a supernova. Hence, yeah, why not find out (somehow) that there is antimatter in your star (which would act just like a normal star), but none of your scientists knows how it got there. This is not as obvious as aliens landing, and the world could go mad slowly. Religious cults develop, change, the military experiences various schisms between paranoia and an interest in the technology, and just as the headlines have forgotten about it, another anti-star is discovered.
    This is not new, in Star Trek, it's the Dilithium chamber that controls the reaction in the warp core. Who knows what it is here.
  • It's a normal star, just made of anti-matter. That's fine, photons are their own anti-particles, so life could develop just the same. But instead of the old "asteroid-smashes-into-earth", there could be a scenario where "asteroid-smashes-into-star" becomes a massive threat because the resulting explosion would overwhelm the world's magnetic field and toast the side facing the sun. Of course, there are plenty of conspiracy theories going bonkers, people claiming the asteroid is a weapon of invading aliens while others say it's going to hit the other side of the sun anyway and it's just another power grab by conservatives/communists/big business/anarchists, what have you. The team of scientists and engineers trying to figure out what's really going on and how to deal with it has their work cut out for them, though. Especially since their families are all different kinds of people, some live on the other side of the planet, some are fanatically religious, some are apathetic, and all have different opinions and demands on the characters. There is great stuff here.
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