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[Sirus]

Yeah, if I remember correctly you need the ridiculous temperatures produced by a supernova to fuse elements like uranium or gold.

[wierd]

Ninja'd--- This is in answer to "Shooting planets at stars" question.

Probably not.

Some supernova remnants actually have burned cinders of planetary cores remaining, (Meaning that in the red supergiant stage, these cores were actively orbiting in the fusion region of the star's photosphere!!)

http://io9.com/5870506/tiny-charred-planets-dove-inside-their-dying-starand-survived

Other types of "Exotic star" have more unusual circumstances, far more exotic that just shooting a giant iron ball at a star.  Take for instance, the situation where a normal star collides with a neutron star core remnant. Such strange things are called Thorne–Żytkow objects, and one such object was recently discovered by astronomers, making them a REAL thing.

http://www.caltech.edu/news/kip-thorne-discusses-first-discovery-thorne-ytkow-object-43149

A small yellow dwarf star like ours is pretty stable; it has enough mass to have good, energetic fusion-- but not so much that it wastes energy just staying "lit", like heavier stars do.  It isnt so light as to have low radiance, like a red dwarf star (far more common in our part of the galaxy), so it's pretty fortuitous for us that ours is so well behaved.



Now, in answer to "Where do the really heavy elements come from?"

Some astrophysicists have suggested collisions of supernova remnants (Large chunks of neutron degenerate matter) as being good sources of large quantities of heavy elements.

http://www.dailygalaxy.com/my_weblog/2013/07/the-earths-gold-astronomers-say-a-neutron-star-collision-was-the-original-source.html

[Il Palazzo]

Yup.  Thankfully our star is pretty small, so it cant fuse heavier than iron at a huge loss, like larger stars do. It hits iron nuclei, and then stops as a dense plasma of the stuff.

Oy, where did you get that from? Sun isn't and won't ever fuse no iron.

A small yellow dwarf star like ours is pretty stable; it has enough mass to have good, energetic fusion-- but not so much that it wastes energy just staying "lit", like heavier stars do.  It isnt so light as to have low radiance, like a red dwarf star (far more common in our part of the galaxy), so it's pretty fortuitous for us that ours is so well behaved.

How is low luminosity a problem? That only changes the placement of the habitable zone.

[Arx]

Yup.  Thankfully our star is pretty small, so it cant fuse heavier than iron at a huge loss, like larger stars do. It hits iron nuclei, and then stops as a dense plasma of the stuff.

Oy, where did you get that from? Sun isn't and won't ever fuse no iron.

That's what wierd is saying.

[Sergarr]

Yup.  Thankfully our star is pretty small, so it cant fuse heavier than iron at a huge loss, like larger stars do. It hits iron nuclei, and then stops as a dense plasma of the stuff.

Oy, where did you get that from? Sun isn't and won't ever fuse no iron.

That's what wierd is saying.

Yup.  Thankfully our star is pretty small, so it cant fuse heavier than iron at a huge loss, like larger stars do. It hits iron nuclei, and then stops as a dense plasma of the stuff.

Il Pal says that's not gonna happen.

[miauw62]

Hm, I wonder how plausible life on a planet orbiting a binary star would be. (If the planet is close enough to the stars that it is obvious that it is a binary system)

[Il Palazzo]

Not particularly. Sun already makes up >99.8% of the solar system's mass. It probably has a Saturn or two's worth of iron in it already.

Edit: Yep. Saturn is about 5.683x10^26 kg, while the iron content of the Sun, 0.14% of 1.989x10^30 kg is about 2.7846x10^29 kg

So there's about 480 times as much iron already in the Sun as there would be in a Saturn-sized mass of iron.

You borked the calculations there by two orders of magnitude (^27 not 29).

And if you want it to be a Saturn-sized ball of iron, then let it be Saturn-sized. That is the same radius but ~10 times denser.

So in the end it's tripling the total iron content.

[Arx]

Yup.  Thankfully our star is pretty small, so it cant fuse heavier than iron at a huge loss, like larger stars do. It hits iron nuclei, and then stops as a dense plasma of the stuff.

Oy, where did you get that from? Sun isn't and won't ever fuse no iron.

That's what wierd is saying.

Yup.  Thankfully our star is pretty small, so it cant fuse heavier than iron at a huge loss, like larger stars do. It hits iron nuclei, and then stops as a dense plasma of the stuff.

Il Pal says that's not gonna happen.

Ah. Some kind of weird meta rading comprehension fail then, whoops.

[wierd]

In my defense, I was quite sleepy when I posted that. 


The issue with red dwarf stars is that any planet in its habitable zone after it enters the stable phase of life, will first have been stripped of its atmosphere during the star's early life.  Unless the planet is a captured celestial body, or started life as a hot neptune, or migrated in from the outer system later, it is going to be an airless rock.

this is because the habitable zone is physically too close to the star for the planet to keep its atmosphere when the star ignites. The initial craziness of the star will produce excessive solar wind particles that will sandblast the planet's atmosphere right off.


Our G type star has its habitable zone further out, which means that our magnetosphere was able to deflect the less dense solar plasma, and we kept our atmosphere. That's why the greater luminosity is important.

[Lagslayer]

Hm, I wonder how plausible life on a planet orbiting a binary star would be. (If the planet is close enough to the stars that it is obvious that it is a binary system)

http://en.wikipedia.org/wiki/Binary_star#Planets

[Il Palazzo]

this is because the habitable zone is physically too close to the star for the planet to keep its atmosphere when the star ignites. The initial craziness of the star will produce excessive solar wind particles that will sandblast the planet's atmosphere right off.

Can you back this up? I'd think the dimmer star produces proportionally less intense solar wind giving the same flux at the HZ distance.

[wierd]

https://www.cfa.harvard.edu/news/2014-11

Sure can.

The closeness also increases the odds of being tide locked as an added bit of fun.

[Il Palazzo]

Thanks.
Don't you hate it when they don't provide a link to the relevant paper? I know the article is from before publication, but they could've just added a comment or something.

Anyway, judging by the author and the date, I think this one's the one:
http://arxiv.org/abs/1405.7707

If so, then it provides both stronger and weaker statements than yours, weird.
According to the above, planets in HZs around such stars may be subject to up to three orders of magnitude more extreme solar wind conditions than the Earth is - at all times. It says nothing about only being so during stellar ignition phase, so if it's bad news for the HZ it's bad news for the conceivable future.
On the other hand, while the article doesn't aim to model atmospheric loss, the authors suggests that denser atmospheres or at least Earth-like magnetic fields might be sufficient to allow atmospheric retention.

We should also keep in mind the assumptions used and how they can change the outcome.



If that's not the article you meant then do help us find the right one.

And have you got something on the stellar wind peaking during the ignition phase?

[wierd]

I can find you some good papers, but it will be awhile. I have to go to work right now.

That article was just one of many I have read on this subject; Basically, when the star leaves the protostar stage, and initates fusion, there is a blast wave that leaves the star. This is true of all stars that achieve fusion. (Brown dwarfs dont count, because they dont really achieve fusion like a higher magnitude star does.) The proximity of the potential habitable planet to the star, increases the apparent intensity of this blastwave. 

Immediately following the ignition of fusion, the star has to "coalesce" into convective strata. Before the star has this happen, it is all mixed up gasses, more or less.  This has the effect of increased flare activity, and increased CME phenomena.

Coupled with the increased stellar radiation of HZ near red dwarf stars in general, the picture isn't very happy for HZ planets of red dwarf systems.

That said, there ARE circumstances where a habitable planet can be found there--  Hot neptune in HZ gets blasted down to planetary core with "trace" (ahem, compared to what it had originally) atmosphere, captured celestial object, and migrating outer system object.

Getting sources for all those will take more time than I have. Gotta eat and run, and head to work now.

[Il Palazzo]

If you can be bothered get me just the one on the ignition phase. I'm interested to see the relative difference in intensity from late-stage quiescent levels and timescales involved.