If Sun would be hit by a comet with 100 km diameter [...] the energy of the impact would be 1000 times more than Sun’s output in a second, which means that for a few seconds the Sun will became hundreds times brighter and this could cause fires everywhere. And also it could provoke strong magnetic event and some nuclear reactions in the moment of the impact, the main risk from which is not energy boost but radioactive contamination of space and Earth.
That all sounds very very wrong. The impact introduces kinetic energy, which presumably manifests as some sort of temporary turbulence at the impact site in the outer layer of the sun. It’s not going to turn into radiative energy. Similarly, there is no reason for the impact to produce nuclear reactions—the spread-out substance of the vaporized comet would just become a minor contaminant of the mostly-hydrogen sun, spectroscopically detectable for some years. Maybe the impact would make a small coronal hole, but giant ones happen naturally anyway.
Impact speed would be 600 km/sek which is equal to temprary rise of temperature to around 500 million C in the place of impact. On this temperature some nulear reactions are possible but their enegry will not dominate impact energy. Also a lot of light will be emited by impact place on this temperature.
I thought about it more… We have a giant rock—a small world in itself, but still just a pebble to the sun—dropping like an anvil into a ball of superheated gas. It has been falling through space for years and by the time it arrives it’s moving like a super-bullet.
From the comet’s perspective, each particle in its path arrives at its surface like a cosmic ray. So as it gets closer to the sun, it experiences a rain of particles, and the rain gets heavier and heavier. This “rain” will kick up a plasma on the surface of the comet, as the particles smash into the atoms of the comet’s surface and splash them apart. As this surface plasma builds, increasingly the solar particles are colliding with the plasma and not directly with the comet surface. The cometary plasma is a shock wave travelling just in front of the comet as it approaches the surface of the sun. Some of the plasma will stream across the comet’s face and out of its path, but the shock wave will grow as the density of arriving particles increases.
Eventually the comet and its shock wave will fall as far as the sun itself. If the comet is big and hard enough, I see no reason why it couldn’t sink all the way to the core, where it might just drift around, melting and shrinking until it had boiled away completely, like an aspirin pill in a bathtub of boiling water. So I think the question is, what is the history of the shock wave of plasma that accompanies the comet as it falls into the sun? Does some zone form inside it, where the collisions are intense enough that fusion occurs, and if so, how large is it and how long does it last? Is it just a burst or is it a sustained burning that consumes a significant part of the comet’s leading face? Or alternatively, does turbulence in the shock wave damp the force of its collision with the solar atmosphere, enough to mostly avoid fusion?
So now I believe it could happen. Though I would want to understand that shock wave, to really decide… Where did you get the estimate of “1000 times more than Sun’s energy output in a second”?
It is important in my idea that it is a comet—that is large chunk of not connected ice, not a hard rock. As we know from examples of Tunguska event 1908 and Chelabinsk event this year, such bodieas tend to desintegrate on high altitude in large explosion because they quickly fall apart.
Chelabinsk flash video.
https://www.youtube.com/watch?v=OPSzpnHHwos
Estmation of the energy is based on the speed of imact, that is 600 000 meters per second (second cosmic speed on the Sun surface), mass of the object—that is 10++18 kg (based on water density and size of a cube with 100 km rib) and formula for kinetic energy, that gives us enegry of impact 3.6x10xx29 J.
Energy output the Sun is 10x26 J per second. So, total energy of impact would be 3600 times more than Sun’s output. Not all energy will go in radiation so 1000 times seems to be good estimate.
In fact I started from the question «What is the size of the body, which could cause harm to the Earth if it fall on Sun?” And find that 1 km will not be even visable, but 100 km is dangerous.
Now I need estimation of the frequency of such impacts.
First correction, the Sun’s luminosity is ~3.827E+26 W, so the falling ice-cube would have a kinetic energy of ~1,000 seconds of solar output. However an object falling into the Sun—such as a 100 km ice-cube—would only release its kinetic energy in such a burst if it was brought to a sudden halt. At 600 km/s the object is a solid surface moving through a fairly diffuse gas—the outer layers of the Sun are thin, hot plasma. A good estimate of the braking effect would be Newtonian Flat Plate drag—i.e. the stuff of the Sun immediately in front of the object is ramming into it, causing drag, with essentially no flow around the object. At 600 km/s the dynamic pressure on the front face is 360 GPa times the plasma density—enough to decelerate the ice-cube (with 100,000 tonnes per square metre areal density) at 3600 m/s^2 if the plasma density was just ~1 kg/m^3. Of course the object won’t decelerate until the gas drag is greater than the Sun’s gravity—equivalent to ~28 GPa pressure on the front face, which is achieved about 4,000 km below the Photosphere. The dynamic pressures would obliterate the mass eventually, but sound in ice only travels at ~3 km/s, so the main mass should travel for about ~30 seconds before starting to fragment as pressure waves travel from the front to the back of the 100 km block. But if it ablates, then it may travel some distance after that. Seems likely to be a rather protracted process, which might produce a flash, but the only hazard to Earth would be if it was in the line of sight of the impact, I suspect.
I think that the comet would desintegrate quicker than with speed of sound, and more like with the speed of incoming gases that is 600 km/sec, so it would be destroed in less than 1 second. Comet is not asteroid - it is very fragile and it will start to desinegrate even before the impact bacuse of gravitational forces—it will be inside Roshe limit of Sun and tidal forses will start to elongate it.
The mass of whatever the impactor is has to be brought to a halt and for a 100 km chunk massing as much as you’ve computed, that’s not happening in an instant in the photosphere of the Sun. Computing exactly how long is a non trivial task and at that speed is more like the injection of a supersonic fluid through a much lower density medium since the internal strength, heat capacity and even the ionization energy of the object is trivial against the kinetic energy it is dissipating.
That all sounds very very wrong. The impact introduces kinetic energy, which presumably manifests as some sort of temporary turbulence at the impact site in the outer layer of the sun. It’s not going to turn into radiative energy. Similarly, there is no reason for the impact to produce nuclear reactions—the spread-out substance of the vaporized comet would just become a minor contaminant of the mostly-hydrogen sun, spectroscopically detectable for some years. Maybe the impact would make a small coronal hole, but giant ones happen naturally anyway.
Impact speed would be 600 km/sek which is equal to temprary rise of temperature to around 500 million C in the place of impact. On this temperature some nulear reactions are possible but their enegry will not dominate impact energy. Also a lot of light will be emited by impact place on this temperature.
I thought about it more… We have a giant rock—a small world in itself, but still just a pebble to the sun—dropping like an anvil into a ball of superheated gas. It has been falling through space for years and by the time it arrives it’s moving like a super-bullet.
From the comet’s perspective, each particle in its path arrives at its surface like a cosmic ray. So as it gets closer to the sun, it experiences a rain of particles, and the rain gets heavier and heavier. This “rain” will kick up a plasma on the surface of the comet, as the particles smash into the atoms of the comet’s surface and splash them apart. As this surface plasma builds, increasingly the solar particles are colliding with the plasma and not directly with the comet surface. The cometary plasma is a shock wave travelling just in front of the comet as it approaches the surface of the sun. Some of the plasma will stream across the comet’s face and out of its path, but the shock wave will grow as the density of arriving particles increases.
Eventually the comet and its shock wave will fall as far as the sun itself. If the comet is big and hard enough, I see no reason why it couldn’t sink all the way to the core, where it might just drift around, melting and shrinking until it had boiled away completely, like an aspirin pill in a bathtub of boiling water. So I think the question is, what is the history of the shock wave of plasma that accompanies the comet as it falls into the sun? Does some zone form inside it, where the collisions are intense enough that fusion occurs, and if so, how large is it and how long does it last? Is it just a burst or is it a sustained burning that consumes a significant part of the comet’s leading face? Or alternatively, does turbulence in the shock wave damp the force of its collision with the solar atmosphere, enough to mostly avoid fusion?
So now I believe it could happen. Though I would want to understand that shock wave, to really decide… Where did you get the estimate of “1000 times more than Sun’s energy output in a second”?
It is important in my idea that it is a comet—that is large chunk of not connected ice, not a hard rock. As we know from examples of Tunguska event 1908 and Chelabinsk event this year, such bodieas tend to desintegrate on high altitude in large explosion because they quickly fall apart. Chelabinsk flash video. https://www.youtube.com/watch?v=OPSzpnHHwos
Estmation of the energy is based on the speed of imact, that is 600 000 meters per second (second cosmic speed on the Sun surface), mass of the object—that is 10++18 kg (based on water density and size of a cube with 100 km rib) and formula for kinetic energy, that gives us enegry of impact 3.6x10xx29 J.
Energy output the Sun is 10x26 J per second. So, total energy of impact would be 3600 times more than Sun’s output. Not all energy will go in radiation so 1000 times seems to be good estimate.
In fact I started from the question «What is the size of the body, which could cause harm to the Earth if it fall on Sun?” And find that 1 km will not be even visable, but 100 km is dangerous.
Now I need estimation of the frequency of such impacts.
First correction, the Sun’s luminosity is ~3.827E+26 W, so the falling ice-cube would have a kinetic energy of ~1,000 seconds of solar output. However an object falling into the Sun—such as a 100 km ice-cube—would only release its kinetic energy in such a burst if it was brought to a sudden halt. At 600 km/s the object is a solid surface moving through a fairly diffuse gas—the outer layers of the Sun are thin, hot plasma. A good estimate of the braking effect would be Newtonian Flat Plate drag—i.e. the stuff of the Sun immediately in front of the object is ramming into it, causing drag, with essentially no flow around the object. At 600 km/s the dynamic pressure on the front face is 360 GPa times the plasma density—enough to decelerate the ice-cube (with 100,000 tonnes per square metre areal density) at 3600 m/s^2 if the plasma density was just ~1 kg/m^3. Of course the object won’t decelerate until the gas drag is greater than the Sun’s gravity—equivalent to ~28 GPa pressure on the front face, which is achieved about 4,000 km below the Photosphere. The dynamic pressures would obliterate the mass eventually, but sound in ice only travels at ~3 km/s, so the main mass should travel for about ~30 seconds before starting to fragment as pressure waves travel from the front to the back of the 100 km block. But if it ablates, then it may travel some distance after that. Seems likely to be a rather protracted process, which might produce a flash, but the only hazard to Earth would be if it was in the line of sight of the impact, I suspect.
I think that the comet would desintegrate quicker than with speed of sound, and more like with the speed of incoming gases that is 600 km/sec, so it would be destroed in less than 1 second. Comet is not asteroid - it is very fragile and it will start to desinegrate even before the impact bacuse of gravitational forces—it will be inside Roshe limit of Sun and tidal forses will start to elongate it.
The mass of whatever the impactor is has to be brought to a halt and for a 100 km chunk massing as much as you’ve computed, that’s not happening in an instant in the photosphere of the Sun. Computing exactly how long is a non trivial task and at that speed is more like the injection of a supersonic fluid through a much lower density medium since the internal strength, heat capacity and even the ionization energy of the object is trivial against the kinetic energy it is dissipating.