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What would a teaspoonful of neutron star do to you? (io9.com)
161 points by rizumu on May 28, 2011 | hide | past | web | favorite | 38 comments

I find it fascinating that people often talk about science removing the magic of the Universe. And yet, science has revealed amazing, mind-boggling, alien wonders of the Universe that are far more fascinating than any anthropomorphic pantheons.

Is there anything in the bible, or in any religious text, that comes close to the story of a supernovae? A supermassive star putting forth unimaginable amounts of light and heat over its few million year lifespan, transmuting its component elements from Hydrogen and Helium all the way to Iron. And then creating this extremely bizarre stuff of neutron star matter during its death throes when it flashes so incredibly brightly that it can briefly outshine the entire galaxy it resides within and can be seen by the naked eye from so far away that it takes longer than the span of time that human beings have used tools for the light to travel that distance.

And think, every single human being alive contains within them atoms that were forged in just such an event.

To me that's far more awe inspiring than any origin fable.

..the Universe is not only stranger than we imagine; it is stranger than we Can imagine.

Looks like someone has been reading Niven. That picture shows a ship built off a General Products #2 hull, and is come straight off the book "Neutron Star": http://ca.pbsstatic.com/l/41/6941/9780345336941.jpg

With that hull you could fly past a neutron star and live, if you could survive the tidal forces.

The point of Neutron Star is that the tidal forces kill you - although the #2 hull will be fine.

Actually, we should be precise - particularly as I first learned about how tides worked from that particularly novel - the tidal forces will only kill you if you are at either extremity of the ship. If you manage to stay balanced right at the very center-of-gravity, you'll be fine.

(We'll leave aside, for now, the highly unlikely scenario of a space travelling civilization visiting a neutron star in close orbit and not taking extreme caution regarding it's tidal forces)

But that's impossible to do. Just the length of the human body already counts as not in the very center of gravity.

But the guy in Niven's storey survived! By balancing in the center of his ship.

Great sense of humor:

  > Do not stand in your cargo bay when you beam up your
  > neutron star material. I cannot stress this enough.

Based on the rest of the post, I wouldn't want to be anywhere on the ship - in fact I'd like to be quite some distance away. Trillion megaton nuclear device equivalent? Riiight (requisitions shuttle)

Without running the numbers, I'd prefer the distance to be meaningfully measurable in light years.

That's excessive. As the article mentions, a neutron star can't exceed a few solar masses. You're much less than a light year from the sun without any ill effects from its gravity.

In case you're looking for a talking point for your next cocktail party, you might also be interested in knowing that degeneracy pressure (of electrons, rather than neutrons) are also what hold up white dwarves.

I can quite definitely state that I've never been to a party where that kind of observation would gain anyone's attention. In fact I'm picturing the audience backing away slowly, looking around for someone---anyone---else to talk to. Not sure if that's good or bad.

I think that's the joke.

Last party I went to there were literally no non-techies present. That kind of fact would definitely have gotten you some points.

Good or bad? I'm not sure. At least you know some non-techies. In my social circle, being a windows user marks you as a target for victimisation. Using IE makes you an enemy. Not even knowing about OSs and their politics - let alone physics - makes you a second class subhuman non-participant.

Again, good or bad? I'm not sure. Time will tell I guess

I have actually heard people cursing at others with "you are not even a proper nerd!".

Strange times and strange places.

If the half-life of a neutron (outside atomic nuclei) is 10 minutes, why is it stable inside a Neutron star and what is it that makes it stable?

It's a reversible equilibrium reaction. Neutron <-> proton + electron + antinutrino + energy. The forward reaction is beta decay, and is favored by lone neutrons and by the neutrons in some atomic nuclei (i.e. radioactive isotopes that undergo beta decay). Presumably the half-life of a nucleous is determined by the degree of favorability of the beta decay reaction within that nucleus. The article already mentions that the reverse reaction (neutron formation) is favored under the conditions of a neutron star, since the pressure favors the side of the reaction with fewer particles. The gravitational potential energy released as the neutron star collapses supplies the energy required for the reverse reaction.

Disclaimer: I am not a physicist.

In simple terms, it does decay, then immediately recombines.

When a neutron decays it makes two charged particles. But inside a neutron star those two charged particles (proton and electron) have no room to separate, instead, because they attract each other they immediately recombine.

Normally they can not recombine because of the energy gap - they need some extra energy to become a neutron (which is why hydrogen, which is also a proton and an electron doesn't just turn into a neutron).

But inside a neutron star that energy is not lost, instead it's transfered to some other set of protons and electrons, giving them the energy they need to become neutrons.

According to the article, degeneracy pressure.

I think there are actually two forces at play, according to the article: gravity and degeneracy pressure.

One the one hand, the neutrons are stable and not decomposing into protons, electrons, etc. by the extreme gravity. At a previous point in the star's lifecycle, it was comprised of normal atoms which contain electrons, protons, and neutrons. In atoms under typical conditions, there is a force which keeps the electrons from falling into the nucleus. Later in the star's life, as the star ran out of fuel, gravity overcame the force that normally keeps electrons from falling into the nucleus and so the protons and electrons fused to become neutrons. Hence, a neutron star.

If one were to release the gravitational pressure, the neutrons would become unstable and you'd get the decay back to protons, electrons, and the radiation that's mentioned. It would be a huge release of energy, as the article states.

The degeneracy pressure is the other force at play. It's what keeps the neutrons from collapsing onto one another and becoming a black hole. I think it's essentially the Pauli exclusion principle, but I could be wrong there.

So, the degeneracy pressure keeps them separated as individual neutrons, but gravity is what is stabilizing the neutrons themselves as neutrons.

If the star were large enough, gravity would overcome even the degeneracy pressure, resulting in a black hole.

At least, I think that's how it works.

Degeneracy pressure is why the whole thing is stable against gravitational collapse, but I don't think it's why individual neutrons don't decay. (I'd say what is if it weren't for the trivial obstacle that I don't know. Handwavily, I think it's often the case that large ensembles of particles can get into nice stable low-energy states for subtle quantum-mechanical reasons.)

Perhaps the same reason neutrons bound in atoms don't decay.

I wish he hadn't glossed over this. What is it that keeps them stable in atoms?

Edit: Wikipedia isn't very helpful, I may just be too dumb to understand this paragraph:

"When bound inside of a nucleus, the instability of a single neutron to beta decay is balanced against the instability that would be acquired by the nucleus as a whole if an additional proton were to participate in repulsive interactions with the other protons that are already present in the nucleus. As such, although free neutrons are unstable, bound neutrons are not necessarily so. The same reasoning explains why protons, which are stable in empty space, may transform into neutrons when bound inside of a nucleus."

In some senses, protons exert an "electrostatic pressure" on each other. The bound neutron cannot become a proton, because of this electrostatic pressure applied by its companion protons - if it were to become a proton, it would need to get over the hurdle of that "pressure". In empty space, this "pressure" doesn't exist, so the neutron can easily slide into a proton-electron-antineutrino state.

As an analogy, when you're hot (say temperature t1) you take your jacket off. However, if you are in a really cramped room with a lot of other people, you'll need to become a lot warmer (say temperature t2) to go through the hassle of removing your jacket and elbowing your neighbour in the eye. If the room is air-conditioned so that you only ever get to temperature t1.5 (where t1 < t1.5 < t2), you'll not take your jacket off, even though you would if you were in a free state.

The basic idea is that a neutron all by itself has a lower energy state available to it, which is to decay into a proton, an electron, and an antineutrino. On the other hand, in the nucleus of a stable atom, a neutron decaying would result in a higher energy state for the whole nucleus.

Does that help?

The difference can be explained by potential energy. A neutron decaying in empty space causes a proton and an electron to wink into existence on level ground. A neutron decaying near a proton causes a proton to wink into existence on top of a cliff (the proton's electromagnetic field) and an electron to wink into existence at the bottom of a trench (ditto).

As far as what critical line is crossed, I can't really say. In fact, I'm not even sure if QCD / Electroweak Theory are yet able to calculate that.

Seems like a viable plot device for a campy space opera.

Indeed, "the energy put out by the sun in 2 or 3 seconds" - sounds like a Culture handgun ;-)

In 'consider phlebas' it mentions the Culture use "CAM" or collapsed antimatter, as a weapon. It's a ship-to-ship rather than handgun-sized deal though- probably a good thing, since 200% of the mass gets converted to energy when it hits regular matter, not a measly 0.08%...

> sounds like a Culture handgun

Which springs from memory matter disguised as a false tooth!

I love the analogies, but I got a little lost on the energy output. What kind of effect would "the energy put out by the sun in 2 or 3 seconds" have if released relatively slowly? (The half-life of neutrons is ~ 10 minutes according to the article.)

the analogies break down at some point. Turns out we haven't tried this particular experiment. And probably won't. Divide a trillion megaton bombs by ((10 min * 60 s/min)/3 s), and you still end up with 5 billion megaton blasts, sustained for 10 minutes. Would the teaspoon of mass survive that long? No. I'm pretty sure that the first quarter nanosecond of release would be sufficient to ruin anything on a human scale.

What would happen if an asteroid (say 30km) impacted a neutron star? Mind you, that rock would be larger, although much less massive. Is it possible for something like that to blast off material from the star?

I imagine something like a black hole feeding, the asteroid flattened into a disk and heated up, jets of x-rays from the magnetic poles of the star.

It would undergo something like the crab nebula. The mass would vaporize, but continue in toward the star, accelerating into the gravity well. The electrons would be stripped away as the nuclei accelerated, and eventually (eg, nanoseconds) the nuclei would either bounce off or be absorbed into the outer layer. Probably some of both. From space, it would just look like a bright puff.

Mind you, that rock would be larger, although much less massive. Is it possible for something like that to blast off material from the star?

I doubt it. Second neutron star on the other hand...


Thanks. That link also works with JavaScript disabled, something the original link doesn't. Makes me shiver when a simple blog requires JavaScript in order to access the content.

the gawker network (which the io blog is part of) replaced their CMS with some hell-brewn javascript CMS some months ago. their blogs are rendered with JS now - which means without JS you will only see an empty page.

oh, and the performance is horrible.

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