To bring understanding neutron stars’ bizzaro physical nature within the grasp of the laymen, it seems every pop star astrophysicist since Carl Sagan spin the yarn that a teaspoon of neutron star is sooooo heavy it’ll punch a hole clean through the Earth if dropped, where, after a bazillion cyclic plunges, friction eventually brings the stuff to rest in the planet’s center. Thusly, these astrophysicists suggest the incredible mass contained within a teaspoon of neutron star. Gotcha.
But I always wonder… wouldn’t such incredible mass also possess incredible gravity? In other words, wouldn’t the Earth (and Moon) attract inescapably towards, then slam into, that teaspoon of neutron star as it casually passed through space? I mean, this is just Newtonian physics, right? Presuming my conjecture is correct, seems to me this makes for an even more interesting fact to impress the laymen with.
No. It’s only as heavy as a mountain and thus only contains the gravity of a mountain. Things close to it (like within a meter) might be attracted to it, though. But in reality it wouldn’t fall through anything, but rather instantaneously explode due to the enormous pressure, which would probably be a bigger explosion than all human-created explosions ever. ETA: combined.
If you are a mountains distance from the mass of a mountain the gravity is going to be pretty darn weak. Pretty close to a mountains mass thats the size of spoon and the gravity is going to be a good bit stronger. How much I don’t know off the top of my head. Somebody break out the calculators!
Using the Wikipedia density of 5.9e17 kg/m^3 and positing about a cubic centimetre of material gives a mass of 5.9e11 kg. The gravitational constant in MKS units is G = 6.67e-11 making the product around 30. A metre away from it and you’d be looking at 3Gs-sh of acceleration towards it.
Sounds good to me (though I didn’t check the numbers). A foot away and its more like 10 Gs! Once you started getting into cubic feet levels that stuff starts to get a bit scary G wise (even IF it didn’t blow the frack up).
I brought up a similar question not to long ago precisely about this popular mental exercise. I wondered if the neutron soup wouldnt blow the f up. Indeed it would.
The series of events had my arm being shredded do to tidal forces and being pulled towards the spoon while an instant later I and everything in a huge area around me is vaporized by the tremdendous release of energy as, without the gravitational force of a neutron star, all those neutrons will want to get the heck out of Dodge.
There is a Larry Niven Known Space series story about this. Someone puts a stasis field around a chunk of neutronium (so it doesn’t explode) and puts it into space as a trap for people who are looking for random unclaimed stasis boxes to salvage. That big of a chunk of neutronium would tend to cause a ship pulling up to grab it to instead get pasted all over the outside.
Although you’d think a spaceship would have some sort of detectors for unexpected gravity sources, tides, and similar effects.
Yeah, but a ball of neutronium say around 6 feet across would be too small to produce noticeable gravity a long ways away, especially if in orbit around a big planet, but when you get really close the gravity gradient would trap you/plaster you on the surface like paint. Their gravity detectors for hyperspace were meant for detecting stellar masses.
A six foot wide block of neutronium would have stellar mass. It would not have what we think of as stellar volume, but it would have the mass. (Which was pretty much the point of the OP, even if garbled a bit.)
Density of neutronium is ~4x10^20 g/m^3. Mass of the Sun is ~2x10^33g. So to reach solar mass you need around 5*10^12 cubic meters of neutronium. That’s a bit more than a few cubic feet. Asteroid Eros’s volume is in the same order of magnitude.
Or more basically a neutron star is roughly 1.4 solar masses in a 12km radius. It stands to reason a 1 solar mass of neutron material would be only slightly less (~10 km).
Which is, ballpark, 880 billion pounds. Or 440 million tons, if you prefer.
Let’s compare that to Mauna Kea, which from this link, is 75 miles long, 64 miles wide, and 13,677 feet above sea level. Treating Mauna Kea as a cone, and averaging the length and width, I get a diameter of 70 miles, and a resulting volume of 4.89 x 10^14 cubic feet. At ~180 pounds per cubic foot for basalt, that’s a total weight of 8.84 x 10^16 pounds. So, it’s ~1/100,000 th the weight of Mauna Kea. Wow, way too big.
Would the weight of something like Half Dome be close?
Was it related to the chunk of neutronium left over from Brennan’s habitat towards the middle of Protector? Or did that end up in Julian Forward’s black hole catcher?
Indeed it is. However, in Tide, no-one’s playing games with any stasis boxes. Louis’s stasis-box detector is also pinged by anything else that blocks neutrinos, which a ten-metre neutronium sphere will do quite handily. The detector isn’t that accurate so Louis then has to spend time searching for the “stasis box”, and he realizes what’s going on only as the alien Trinoc ship, which arrived in-system about the same time, heads for the mysterious object in low orbit.
Using a stasis box as a trap was done by the Kzinti in The Soft Weapon, and no neutronium was involved. The stasis box was used to draw in curious strangers so they could be robbed, and they thought they’d hit big paydirt when they snared Jason Papandreou, Nessus, and what turned out to be a tnuctip stasis box which promised ancient technology orders of magnitude better than had been found to date. It did, in a way…
