neutron star

If a small neutron star were to sneak within a light-day past our solar system, what do you think would happen?
My hunch tells me we'd all be extinct within a year, either from freezing or boiling, as all our orbiting planets go off the rails.

@bunnyknight said
If a small neutron star were to sneak within a light-day past our solar system, what do you think would happen?
My hunch tells me we'd all be extinct within a year, either from freezing or boiling, as all our orbiting planets go off the rails.

The orbit of Eris extends to something a little shy of 100 AU [1]. This is a little under 14 light hours. So your neutron star (incidentally they're in a fairly tight mass range so small is slightly more than the mass of the sun [2]). If its closest approach is of the order of 200 AU then it's going to create havoc in the Kuiper Belt, causing large objects to be scattered in all sorts of directions. There is a microscopic risk that something the size of Pluto could be sent inwards. Nevertheless the chances of a collision with Earth are remote. So I don't think it's the "Extinction of Everything" event that you're imagining. For one thing these objects are pretty common. The Earth's been around for something of the order of 4 billion years. There's some large scale extinction events at least one of which was caused by a huge meteorite, but even so, we're all still here.

[1] https://en.wikipedia.org/wiki/Solar_System
[2] https://en.wikipedia.org/wiki/Neutron_star

@DeepThought
I think that even in the best case scenario, where nothing crashes into us, the slightest gravitational pull upon Earth in any direction would significantly change its orbit ... and then it's game over.

What about the stupendously powerful magnetic field of many neutron stars?
Could that also give us some serious problems?

@humy
I'm assuming the neutron star is non-rotating, thus no significant magnetic field. I'm also assuming that it doesn't swallow Pluto or Neptune, which might cause a catastrophic burst of energy.

@bunnyknight
is that where Gamma Ray Bursts come from?

@ogb said
@bunnyknight
is that where Gamma Ray Bursts come from?

A merger of 2 neutron stars is one way to get a Gamma Ray Burst, but a merger with Pluto might produce a much smaller burst, yet still big enough to possibly vaporize Earth's surface.

@bunnyknight said
A merger of 2 neutron stars is one way to get a Gamma Ray Burst, but a merger with Pluto might produce a much smaller burst, yet still big enough to possibly vaporize Earth's surface.

Might it also possibly produce nothing relevant to Earth?

@wildgrass said
Might it also possibly produce nothing relevant to Earth?

It's possible. Our sun could shield us from the quick and violent destruction of Pluto.

@bunnyknight
The effects seems to me would be the same if a real star the same mass came within 200 AU of Earth, basically not much. It has been shown dynamically the two closest stars of the Alpha Cenauri trinary that planets could be in stable orbits even though the stars themselves are about as close as Uranus, a LOT closer than 200 AU.
I think maybe you picked a number you thought really close, one light day.
So 24 hours and light flys at around 670 million miles an hour so about 175 AU which is about 4 times further than Pluto.
As for changing Earth's orbit, at that distance it would represent a gravitational field on Earth about 1/30,000ths of the sun. So the sun having 30,000 times more attraction than our reputed star would mean very little change in our orbit, certainly not enough to have Earth fly off the handle so to speak and get shot out of the solar system or some such. I would think mainly there would be small changes in tides once a year when Earth was on closest to the star, similar to the tides that happen from the sun but a LOT smaller. Don't see much happening to Earth orbit.
Just intuitively, it looks to me like a sun size star at 175 AU would have about the same gravitation effects as Jupiter which is roughly a half billion miles or roughly 33 times closer than that star and I would think, as it clocks in about 1/1000th the mass of the star the gravity would be pretty much the same.
The gist of that is we have been living with Jupiter for billions of years now, Earth has that is, and has been hit by fairly large asteroids maybe once every 100 miillion years or so, last big one 66 million years ago.
Don't see that changing much since any perturbation of objects in the Kuiper belt could sling stuff our way but like Humy said, the solar system is pretty vast and it would be a statistical game of very low proportions that one of those objects would crash into Earth. Don't forget, if stuff was perturbed inwards it would have to go by the gravity of Jupiter and that would make Jupiter more of a target than Earth. And there are other large planets out there, Saturn, Uranus, Neptune, so such incoming stuff would have to get by all their gravity fields to get inside to the inner system.

@sonhouse
Sounds reasonable. A distance of 8 light-hours would probably pose a far greater danger.

@humy said
What about the stupendously powerful magnetic field of many neutron stars?
Could that also give us some serious problems?

The magnetic field itself no. The Wikipedia page talks about this, what it says is that the strength of the field is not entirely explained by the reduction in surface area of the parent star, but mostly. The total magnetic flux increases, but not that much, so as far as the field is concerned it would have about the same strength as it had at the surface of the original star. So the magnetic field of the Sun at 1AU would dwarf the field from the neutron star as seen from Earth.

If it's a Magnetar the field might be a problem - I'd need to do a proper calculation rather than just guessing, or if it undergoes a starquake then we can be wiped out by a soft gamma repeater burst. This is a copy and paste from the relevant Wikipedia page:

The largest recorded starquake was detected on December 27, 2004 from the ultracompact stellar corpse SGR 1806-20. It has been calculated that the energy release would be equivalent to a magnitude 32 quake. The quake, which occurred 50,000 light years from Earth, released gamma rays equivalent to 10^37 kW. Had it occurred within a distance of 10 light years from Earth, the quake could have triggered a mass extinction.

https://en.wikipedia.org/wiki/Quake_(natural_phenomenon)#Starquake

The page on Soft Gamma Repeaters mentions SGR 1900+14 - an event in 1998 where a burst of gamma radiation from 20,000 light years away ionized the top of the night side atmosphere as much as the Sun ionizes the day side atmosphere. I think that at 200 A.U.s then unless the Earth is directly behind the Sun at the time we would have had it if a passing Neutron Star emitted a SGR burst at a range of 200 AUs.

Edit: 1037 ---> 10^37

@DeepThought
There might be another possible outcome: As in the original scenario, the neutron star, cold and non-spinning, quietly approaches, then falls into orbit around our sun forming a binary. By the time all our planets realign to a state of equilibrium, Earth might be completely uninhabitable even if no collisions occur.

@bunnyknight said
@DeepThought
There might be another possible outcome: As in the original scenario, the neutron star, cold and non-spinning, quietly approaches, then falls into orbit around our sun forming a binary. By the time all our planets realign to a state of equilibrium, Earth might be completely uninhabitable even if no collisions occur.

Bear in mind that this is not an object gravitationally bound to the system. In fact, since it's a neutron star its mass must be higher than the Sun's, so it's more of a case of the neutron star capturing the sun rather than the other way round. For capture to happen the combined system needs to shed energy, so bodies need to be ejected. The planets can't realign because they won't all be there.

@DeepThought
So you are saying in the case of already existing binary systems, they got that way by ejecting planets and other mass from the system or they could not have assumed a binary stable orbit?

Wouldn't it be valid to say some binaries are made because the cloud that condensed to be stars and planets happen to have been large enough for two stars to independently be born but the mass that made the two were already in an orbit around each other so they were BORN in stable orbits?