by JohnD » Fri Jan 10, 2014 5:20 pm
Chris Peterson wrote:greenewr wrote:Some questions occurs to me. If one lived on a planet of a star that had the expanding nebula 'engulf' it (we are only 4.4 ly from Alpha Centauri), what effects would one experience? Would the background radiation become fatal? Would there be an effective temperature rise? How much would the presence of the nebula affect local viewing of space?
Would one perceive the advancing shock wave as it entered and passed through their system?
The radiation levels are quite low. The peak is in the ultraviolet, and would be largely blocked by the atmosphere. Even though the gases are hot, they are also very thin, similar to the best vacuum you could create in a lab. So there would be no temperature rise. (The region of space that the ISS orbits in has a gas temperature of thousands of degrees, and those gases are denser than what we have in a nebula.) Without some good technology, people living on a planet that was engulfed by this nebula might not even be aware it existed. It might slightly attenuate the night sky, but that would seem normal. And within the stellar system itself, there probably wouldn't be enough nebular material to collect and study with a Stardust like probe, because the local solar wind and radiation pressure would clear a bubble in that region of the nebula.
Up to a point, Lord Copper! But you were answering the question directly.
Don't planetary nebulae occur when the star is running out of hydrogen, cools and expands towards red giant status? They'd notice that, even if the star didn't engulf them, as we are told the Sun will do one day! Then, as the outer layers are ejected to form the nebula, the hotter inner layers of the star are exposed, before fusion slows and it cools towards being a white dwarf. That would take ?10,000 years, but surely even protoplasmic blobs would notice?
John
[quote="Chris Peterson"][quote="greenewr"]Some questions occurs to me. If one lived on a planet of a star that had the expanding nebula 'engulf' it (we are only 4.4 ly from Alpha Centauri), what effects would one experience? Would the background radiation become fatal? Would there be an effective temperature rise? How much would the presence of the nebula affect local viewing of space?
Would one perceive the advancing shock wave as it entered and passed through their system?[/quote]
The radiation levels are quite low. The peak is in the ultraviolet, and would be largely blocked by the atmosphere. Even though the gases are hot, they are also very thin, similar to the best vacuum you could create in a lab. So there would be no temperature rise. (The region of space that the ISS orbits in has a gas temperature of thousands of degrees, and those gases are denser than what we have in a nebula.) Without some good technology, people living on a planet that was engulfed by this nebula might not even be aware it existed. It might slightly attenuate the night sky, but that would seem normal. And within the stellar system itself, there probably wouldn't be enough nebular material to collect and study with a Stardust like probe, because the local solar wind and radiation pressure would clear a bubble in that region of the nebula.[/quote]
Up to a point, Lord Copper! But you were answering the question directly.
Don't planetary nebulae occur when the star is running out of hydrogen, cools and expands towards red giant status? They'd notice that, even if the star didn't engulf them, as we are told the Sun will do one day! Then, as the outer layers are ejected to form the nebula, the hotter inner layers of the star are exposed, before fusion slows and it cools towards being a white dwarf. That would take ?10,000 years, but surely even protoplasmic blobs would notice?
John