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 Changing mass (Read 22017 times)
 Tony YaBB Administrator Posts: 1058 Gender: Re: Changing mass Reply #16 - 06/28/07 at 09:57:10   Quote from Mal on 06/28/07 at 00:25:39: I'm not sure what the effect of changing the timescale of the mass change is. Obviously (as I discovered earlier) if you do it instantly then you just end up losing all the asteroids. But as long as it's not instantaneous, does it make any difference if you change the mass over a year, or 100 years, or 1000 years, or longer? Does the effect on the orbit depend on the initial orbit period at all? (i.e. if the change takes place faster than a single orbit is completed, does that make a difference?)   The instant mass loss is easy to descirbe with the circular and escape velocity formulas.  I would imagine it has a lot to do with the time span during which the mass is lost, compared to the period of an orbit.  Looking at your diagram, I would have guessed that there would be a nice smooth spiral out, but it doesn't look like that's the case.   I'm not sure how long it takes a star that is blowing off layers to lose its mass.  When a star goes supernova, does it take minuts, hours, days, or weeks to lose its mass?  How about stars like the sun that form planetary nebula.  I think they lose their mass gradually.  Before I improve the dynamic mass feature, it would be nice to know what models are realistic.  Hmmm.... the more we learn, the less we realize we know Back to top IP Logged
 EDG Ultimate Member oh, crumbs!!! Posts: 611 Gender: Re: Changing mass Reply #17 - 06/28/07 at 13:17:29   Quote from Tony on 06/28/07 at 09:57:10:The instant mass loss is easy to descirbe with the circular and escape velocity formulas. I would imagine it has a lot to do with the time span during which the mass is lost, compared to the period of an orbit. Looking at your diagram, I would have guessed that there would be a nice smooth spiral out, but it doesn't look like that's the case.   I should really try this with just one object instead of 100 .   I think it's because the eccentricities are changing (being amplified?). Not only are the semimajor axes increasing, but the eccentricies (alraedy between 0 and 0.4) are also going up and on bigger orbits the difference is much more noticeable, maybe?       Quote:I'm not sure how long it takes a star that is blowing off layers to lose its mass. When a star goes supernova, does it take minuts, hours, days, or weeks to lose its mass? How about stars like the sun that form planetary nebula. I think they lose their mass gradually. Before I improve the dynamic mass feature, it would be nice to know what models are realistic. Hmmm.... the more we learn, the less we realize we know   I've got a paper at home about how planetary nebulae form, that might have a timescale.   With supernovae the mass loss is pretty much instant - the star goes kaboom, but the mass is thrown off at a certain speed so it takes a bit of time for the shell of matter to pass through the system. Of course, planets and asteroids have other things to worry about in a supernova than their orbits shifting . Back to top (formerly known as Mal)   IP Logged
 Tony YaBB Administrator Posts: 1058 Gender: Re: Changing mass Reply #18 - 06/28/07 at 13:31:34   If it blows off its mass instantly, then the planet should get pushed by the expanding sphere of matter.  The amount of mass lost divided by the area of a sphere, 4 pi r2, should give you the flux of matter at a planet's distance, r.  Multiply this by the planet's cross section, pi r2 to get the total mass slamming into a planet, then using the velocity of the expelled matter to compute the momentum delivered to the planet.  I'll bet that alone is enough to knock a planet out of orbit. Back to top IP Logged
 EDG Ultimate Member oh, crumbs!!! Posts: 611 Gender: Re: Changing mass Reply #19 - 06/28/07 at 19:01:55   Well I did one project where I calculated the effect on a planet orbiting a Brown Dwarf that was 1000 AU from Antares when it blows. I figured that the material would hit the planet at 10,000 km/s but had a density of 2.9e-11 kg/m3 and hit with a dynamic pressure of 1460 Pa. Somehow I figured it would impact the surface at an equivalent of 0.27 megatons of TNT per square metre, applied for the 75,000 seconds.     This is after the initial luminosity spike (up to 10 billion Sols!) melts the surface of the planet... in fact it's just starting to cool down when the blastwave hits... Back to top (formerly known as Mal)   IP Logged
 Tony YaBB Administrator Posts: 1058 Gender: Re: Changing mass Reply #20 - 06/28/07 at 19:27:28   Quote from Mal on 06/28/07 at 19:01:55:... in fact it's just starting to cool down when the blastwave hits... not a good day in the neighborhood Back to top IP Logged