I started a thread the other day concerning a show on NatGeo about the imminent arrival of a neutron star that is headed straight for the solar system. My question here though is, lets say we detected this neutron star headed for us a century or so in the future. It’s unavoidable, and it’s definitely headed in such a way that it will go right though the solar system. Question one would be…when would the effects of this start start to be felt in the solar system? What are the possible/likely effects? Question two…what are the likely or probable effects it would have on earth, and when would we start to experience them? And, as a follow up, what would be the most likely thing to kill us all from this, and when would it happen? Would the neutron star be bombarding the solar system with radiation, or would it disrupt the orbits of the planets? Or would we be bombarded by debris from the outer solar system flung in-system?
As a bonus question, what would likely happen to the sun? Would it be destroyed if a neutron star went through the solar system, or could they go into orbit around each other?
I think orbital disruption would be a more likely killer than radiation if it went through the inner solar system. It’s unlikely to hit, or even get all that close to anything, and I don’t think neutron stars are particularly radiation-emitting.
If it passed through the Oort cloud, it might make for some heavy bombardment years to decades later but I’d think would be too far away to do much orbital disruption in the inner solar system.
Neutron stars emit huge amounts of radiation; not only are they extremely hot, but they rotate extremely fast, which causes their magnetic fields to radiate enormous amounts of energy. There are also pulses of radiation from the poles (sometimes?).
How fast is it moving? The answer will depend tremendously on this. If it’s moving rather fast, say, 2000 km/s, it will only be a dominant gravitating body for the Earth for a day or so, assuming it’s passing through some random corner of the solar system. If it’s moving much slower, then it will wreak havoc on the orbits of everything.
The gravitational environment of the solar system has been measured in a variety of ways, but taking the Pioneer spacecraft as a starting limit, we know the neutron star has to be at least 1000 AU away at T=-100 yr or else it would be a larger effect than the Pioneer anomaly. (There may very well be other measurements that push this distance further, though.) Thus, the lowest speed the neutron star could have is about 1000 AU/century, or 50 km/s. That speed is definitely in the havoc-wreaking range.
A neutron star is only as (or nearly as) massive as a normal star, correct? Maybe even a bit less. As such, if it were moving fast enough (as stated above) or far enough out in the system, I don’t know that it would perturb orbits too much? Would also depend on how far it was for another planet during flyby (if it passed the orbit of Saturn, while Saturn was on the other side of the Sun, it wouldn’t have much effect?)
As to radiation, do neutron stars emit equally in all directions, or is it more heavily oriented to the equatorial spin of the star? If so, the axial tilt would be important, I’d think.
I’ll echo the earlier comment that cometary bombardment from the Oort could would be a bigger problem unless the star was aimed exactly right to cause huge problems in-system. Space, remember, is big.
On radiation: a rapidly spinning neutron star might radiate energy at 10[sup]30[/sup] W. If it were 5 AU from Earth and beaming in our general direction, it could be as much as 1 MW/m[sup]2[/sup] of energy flux at Earth, or about 1000 times larger than that of the Sun.
A couple of solar masses, give or take. How long it sticks around is the most important thing orbitally, as it’s gravitational effects will be comparable to the sun’s at comparable distances, so it had better stick around for a small fraction of an orbital period if it is not to have a big effect on the orbits.
It’s fairly directional. Note, though, that in the limit of perfect directionality, the Whirling Beams of Death define a plane that will, at some point, intersect the Earth.
As long as there’s no axial wobble to the neutron star, there would be a huge number of ways it would pass through the ecliptic without either a polar jet or equitoral band hitting Earth directly? Unless it descends though the solar system with it’s poles nearly aligned with the Sun, of course. If it passed through on, say, a 90’ tilt, then unless the polar jets hit Earth I’d think it would be an astronomical () chance of a hit.
Note; not an astronomer, just always wanted to be one until “math” reared it’s ugly head. Follows as much “pop-sci” astronomy as I can devour. Mileage may vary.
For a pulsar with magnetic poles near its rotational equator, you’d have a picture like this:
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death ray
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rotating
death ray
It doesn’t matter which way you choose to move the star in that diagram. The Earth will get sprayed at some point. In reality, the radiation is not perfectly directional, so in the extreme geometric when the star it somewhat distant when the Plane of Death hits Earth, the flux would be reduced. But that’s the rarer geometry rather than the typical one.
(In general the magnetic poles will be at some random angle with respect to the rotation axis making a Cone of Death rather than a Plane of Death, but even a cone will eventually intersect the Earth. For instance, if the magnetic poles are 15 degrees from the rotation axis instead of a more impressive 80 degrees, say, then the best you could do is have a carefully aimed trajectory where the star is four times farther than its closest approach when the radiation is directed at Earth.)
But neutron stars lose energy and slow down their spin the longer they radiate. So couldn’t a very old virtually non-radiating neutron star pass through the solar system and only have gravitational effects? I don’t know how long this takes, but there presumably must be some in the Milky Way that are nearly as old as it is.
What about the fact that interplanetary space is more densely populated with gas and dust than interstellar space? Would accretion onto the neutron star be a significant factor in its radiation output? Even a small meteoroid impacting at a substantial fraction of the speed of light would be pretty violent.
Thats a good point. ISTM even a nearly “dormant” neutron star would start emitting a fair bit of radiation once it starts sucking up the dust in our solar system.
And in regard to the gravitational effects. Unless it was a particularly bad approach geometry wise I doubt changed orbits would be an immeditate problem. However, I suspect that long term (on the order of thousands of planetary orbital periods time wise) bad things could happen as a result of the passing. The solar system is in a sort of long term equilibrium. The passing neutron star would probably mess that up.
Although I can see a lot of dishes breaking in any event, here you’re talking about its translational movement, right?
I didn’t get the 2000km/s and 50km/s mentioned by Pasta above. Translational? Rotational?
When do rotational gravitational effects on Earth overtake those of translational? Ie, when would I rather have the star perched somewhere spinning away than have it come barreling by slowly rotating? Assuming I didn’t want my planet to be shredded, that is.
The Sun causes roughly half the tide that the Moon does, and the Neutron Star is roughly twice the mass of the Sun, so if the neutron star passes at 1 AU from Earth, the tides should be about the same strength as the Moon’s.
Tides go like distance cubed, so if it’s half an AU away, the tides should be larger than the Moon’s by a factor of 8.
Not sure if this helps answer your question at all, though.
You can’t say anything about the influence on the orbits without knowing how fast the neutron star is moving relative to the solar system. If if zips through the solar system in a matter of hours, the orbital effects will be small barring an unfortunate close-pass of some object. However, if the neutron star ambles through, taking months or years to cross the solar system, then it will be the dominant gravitating object in the solar system for a time that is manifestly orbitally significant, since months and years are the time scales relevant for solar orbits.
This is why I made the above crude estimates of the speeds we might be talking about. On the low side: if the neutron star is moving slower than 50 km/s relative to the sun, then it must already be closer than 1000 AU if it is going to get here in 100 years (per the OP). However, if it were already within 1000 AU we would have noticed it in the Pioneer acceleration data. Therefore: our hypothetical neutron star must be moving faster than 50 km/s. At that speed, it will travel 10 AU in 350 days, which means it will be hanging around for plenty long enough to do serious orbital damage.
On the high side: our hypothetical neutron star could be moving as fast as we please, but to keep some realism in the story, I considered 2000 km/s, which is a bit higher than the highest speeds of stars relative to the Sun. At this speed, the neutron star would be in and out of the solar system in a matter of days, so orbital effects would be considerably smaller.
At that distance, it would have been detected directly. 1000 AU is only about a fifth of a light year. A neutron star at that distance should be one of the brightest things in the sky in UV and X-ray wavebands and perhaps others.
But exactly how bright it is depends on its temperature. There’s probably a minimum temp for neutron stars, but I don’t know what it is. For White Dwarfs, it’s about 5000 K. It’s not that they aren’t capable of getting cooler, it’s that the universe has not existed long enough for WDs to have cooled more than that. Neutron stars are considerably smaller than WDs, so you’d expect their minimum temp to be higher, but as mentioned above, neutron stars have cooling modes that WDs lack.
) chance of a hit.