# Thorne Zytkow Planets $-$ Can a Gas Giant have a Neutron Star core?

Said gas giant is about 5 times the mass of Jupiter, hence a Super-Jupiter. This gas giant is rogue and has no parent star. Its composition is the same as regular gas giant, i.e. it is composed of hydrogen, helium etc. but here's a catch.

The gas giant, when it formed, accidentally swallowed up a neutron star, which is now located at the center of the planet. The neutron star in question is a pulsar with 1.8 solar masses with a rotational speed of over 60x a second. The star is embedded in the planet's rocky core. Surface temperature of neutron star is about 1,000,000 K. Sort of like a Thorne–Żytkow object

What would happen if a Gas Giant had a neutron star at its core?

Guesses

I guess that the neutron star's gravity and extreme temperature would cause interesting phenomena such as wind patterns, and mascons happening at various places.

Diagram for reference:

EDIT: This question does not ask what would have happened during the collision. Rather, this question asks what would happen to a gas giant with a neutron star at its core.

• The distinction between the collision and an already-established combination is irrelevant, because the answer is the same either way. Commented Oct 7, 2022 at 19:05
• If these things already have a name then what is the point of the question? You can just look them up for yourself. Commented Oct 11, 2022 at 20:53

With our current understanding of what a neutron star is, it would be impossible to have it 'embedded' in a planet. Nothing we know of is strong enough to support the mass of a planet and keep it from collapsing onto the surface of the neutron star itself. The "atmosphere" of a neutron star is hypothesized to be at most a few micrometers thick. Below that is a solid lattice of atomic nuclei.

The "surface gravity" is estimated to be about 10^11 times the gravity at the surface of the Earth. If you could use some kind of magic to stand on the surface of a neutron star and hold a tennis ball at arm's length and let go, it would hit the surface and it's nuclei would smear onto the surface after just 1.87 microseconds travelling at a speed of about 1870km/s.

Mass-wise it would be like a pickup truck 'embedding' itself in a crow.

If you could magically teleport a neutron star to the core of the largest gas giant observed with a radius of 130,000 km, I think you would get a miniature nova. At that radius the gravity would be much less, only about 7000 m/s2 (about 700 times earth gravity). After about 13 seconds an object dropped from that height would be travelling at roughly 60,000 km/s, a significant fraction of the speed of light, and would hit the surface before 14 seconds elapsed.

For a gas giant the story is more complicated because the falling material would produce enormous friction and pressure and release a lot of energy before smearing on the surface, and the nuclei could undergo nuclear fusion before reaching stability in the surface lattice.

Star Eats Planet

Painting by Dana Berry for NASA

The star is 400 times as massive as the gas giant with 400 times the gravity.

The gas giant does not swallow up the star. Instead the star swallows up the planet. It barely notices.

The result is a slightly larger neutron star and no gas giant.

• This actually understates things quite a bit. 400 times the gravity at a given distance from its center. A neutron star is about 10 km in radius (compared to about 70000 km for a large gas giant), so its surface gravity is about 20 billion times that of the gas giant. But in the end your description is accurate: there is no more rocky core, no more gas giant, just a neutron star with a thin layer of freshly accreted material and perhaps a disk of material still falling in. Commented Oct 7, 2022 at 20:33

A gas giant with a neutron star at its core is impossible.

The gravity of a neutron star is pretty strong. It would end up swallowing all the matter of the gas giant, turning it into nuclear pasta.

While it might be possible for something to orbit a neutron star, it can be nothing as dense as a gas planet: friction in the gas would end up removing momentum and causing orbital collapse. This would happen at the moment of merging.

• "pretty strong" -- are you trying for the understatement of the year award? Commented Oct 7, 2022 at 12:01
• @L.Dutch - I'm a little surprised to hear that "friction in the gas" of a planet would cause orbital collapse. Are you talking about tidal effects? I thought those would circularize an orbit, but not shrink it indefinitely? Or is that just an approximation that holds for orbiting a normal star, but not a neutron star...?
– Qami
Commented Oct 7, 2022 at 14:56
• nuclear pasta great, now I'm hungry! Commented Oct 7, 2022 at 19:37
• @Qami: No, not tidal effects. Plain old ordinary turbulence. You cannot have each and every molecule of gas moving obediently in a perfect circle with the perfect speed. They will collide. Commented Oct 8, 2022 at 13:26
• @AlexP Oh, I see. I misunderstood. When you said "While it might be possible for something to orbit a neutron star, it can be nothing as dense as a gas planet", I thought you were talking about a body orbiting externally, at a distance. But I see you were still talking about the OP's original configuration, in which case what you said makes perfect sense. xD
– Qami
Commented Oct 10, 2022 at 4:49

Type Ia supernova

A Type Ia supernova is usually created in Binary star systems when the white dwarf pulls enough matter from its sister star onto its surface to achieve Chandrasekhar mass (critical mass) they reignite and in some cases trigger a supernova explosion.

As above this usually happens with a white dwarf. I am not certain if this can happen with a neutron star, and likely not with only a gas giant planet to work with.

But knowing SEWB assume little as possible. You do not say exactly how it swallowed up the neutron star. If they approached each other in space the neutron star would be the one swallowing up the gas giant. If however the neutron star was just teleported or just somehow appeared at the core of the gas giant, then I would wager yes "Big Boom today".

• +1 for “Big Boom today” :) Commented Oct 7, 2022 at 12:28
• @BlueSkinandGlowingRedEyes There's always a boom tomorrow. Commented Oct 9, 2022 at 12:10

The Roche limit around the neutron star that size is going to entirely contain the volume of the gas giant. So the mass of the gas giant will be shredded into rings and eventually be consumed by the neutron star.

Reducing the mass of a neutron star enough to reduce the Roche limit would likely also reduce its gravitational force enough to no longer be a neutron star.

Perhaps play with placing a (very) small black hole at the center of the planet? A black hole wouldn't have the minimum mass requirement that a neutron star would, but you would still need to make it a very small black hole to prevent it from shredding the planet.

• There are answers elsewhere on here that give some pretty amazing numbers for planetary survival after eating a black hole. I don't think they are on target (I believe degeneracy would cause the planet to be eaten a bit faster) but the truly tiny eating area means it doesn't just go slurp. Commented Oct 8, 2022 at 1:12

At the moment of collision part of gas giant will drop on neutron star due to gravity and rest will form plasma ring around equator. Then part of ring will drop on neutron star and merge with it and rest will be spreaded around by jets from poles. Small amount of mass will be spreaded in equator.

With small collision speed almost all mass of gas giant will be eaten by neutron star, with big speed You can get something like apple shoted by bullet effect and most of mass will be spreaded around.