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View Full Version : [SF] Habitability/planets near an O V star?



EDG
2009-Dec-11, 05:03 PM
In the SF setting I'm working on, I have a young O8 V star surrounded by other (AFGKM) main sequence stars that have planets (some of which may be habitable).

The O8 V star is about a million years old, so it's still blue and on the main sequence - it's 21.5 solar masses (though it's lost 0.05 solar masses through its solar wind so far), current luminosity is 53,000 Sols (mostly in the UV, I guess).

The O8 V does not have any planets orbiting it, but I'm wondering how it's going to affect the planets orbiting nearby stars (the closest star is 3.3 ly from the O V). Is the UV output going to be significant for planets around nearby stars? Could it even prevent planets forming around other nearby stars (I think I remember reading something to that effect at some point?). Or is it just going to be a very bright star in their sky (possibly with some nebulosity around it?).

And is it possible to even form a solo O V star, or would they always form in OB associations?

EDG
2009-Dec-11, 05:17 PM
I did find this (which may have been what I remembered reading)

http://www.physorg.com/news148752771.html

Though this describes the disks of some sun-like stars that are about a lightyear from a clump of four 20 solar mass stars being evaporated away by them - which is more extreme than the situation I'm describing here.

I'd think that one 20 mass star wouldn't cause significant issues for planet formation around stars over three lightyears away, but if anyone's got any more info that can shed light on the subject (no pun intended!) then that would be appreciated.

cjameshuff
2009-Dec-11, 08:02 PM
It'll be 53000 times as bright as Sol at any given distance. At a distance of 230 AU, it will be as bright as Sol is on Earth. It's total output will be about a millionth of that at 3.3 light years...so, not an issue.

The linked article...dust and gas from a planet-forming disk are being blown off from the fringes of the forming systems by radiation pressure and solar wind. I'd guess the sun-like stars don't have much of a heliosphere yet, much of their radiation and solar wind being blocked by the material in the disks...I wouldn't be surprised if the fringes of the disk are directly exposed to the solar winds of those giants.

The atmosphere of a planet would take far more energy to strip away, it's much deeper in a gravity well, and a life-bearing world will be far deeper in in a much more mature system (and will have formed there before those giants existed), likely protected by the heliosphere of its primary.

EDG
2009-Dec-11, 11:15 PM
So maybe if a system was forming nearby at the same time as the O V star, it could be in trouble due to photoevaporation - but a mature system should be OK?

I was more concerned about the UV radiation that the O V star is putting out - would that do nasty things to atmospheres (more ozone?) and organics at a range of a few lightyears, or would they be unaffected at that distance?

(course, when the star blows up as a supernova, I wouldn't want to be anywhere near it but that's several million years further down the road :) )

cjameshuff
2009-Dec-12, 12:11 AM
So maybe if a system was forming nearby at the same time as the O V star, it could be in trouble due to photoevaporation - but a mature system should be OK?

From the description in that article, it might be short a Kuiper belt or have less massive outer gas giants. It doesn't sound like it'd make terrestrial worlds less likely. It might thin out cometary bombardment, though. And it'll get a little toasted later, but there probably won't be life around yet when the giant goes supernova.



I was more concerned about the UV radiation that the O V star is putting out - would that do nasty things to atmospheres (more ozone?) and organics at a range of a few lightyears, or would they be unaffected at that distance?

Well, like I said, light from that star will be about 1 millionth as bright as the star the planet's circling. Even if it's all far-UV, it'll be lost in the fluctuations of the parent star.

Murphy
2009-Dec-12, 02:08 AM
I don't know anything about the possible effects of UV and all that, but if you do the calculation with this program... http://web.archive.org/web/20011118213628/www.geocities.com/albmont/mseqstar.htm, you get...

Luminosity = 53,000 sol's
Distance = 3.3 LYs (208,696 AUs)
Luminosity at Planet = 0.0000012 Earth's insolation, or ~0.00166 watts per square metre

A very tiny amount, that I can't see having any real effect. Should be just a bright star from the perspective of the planet.

EDG
2009-Dec-12, 04:13 AM
Ok, sounds good enough to me :)

Still curious about one thing though - do such massive stars HAVE to form in OB associations, or can they form on their own?

Romanus
2009-Dec-12, 05:28 PM
^
Though astrophysics isn't my forte, I've never heard of really massive stars forming alone. Part of this is kind of a selection effect; because they're very short-lived, they never have time to drift far from their "spawning ground". It also seems to be difficult to form massive stars; any cloud substantial enough to form them is also capable of forming many more of intermediate and low-mass.

I note that your O-star is quite young, much younger than any stars with habitable planets could be; is your main system moving through a nebulous OB association? If so, you could throw in some more spectacular descriptions of the star in a nebula-hazed night sky. :)

EDG
2009-Dec-13, 07:57 AM
No... it's a function of the star system generating program I'm using - it doesn't generate clusters of stars with similar ages that are physically packed into a relatively small volume (a few ly across), it just generates star systems on their own with random ages. I know that isn't realistic, but it'd be difficult to figure out the code to make clusters around or containing the O and B stars.

Maybe that's for the next version ;).

Murphy
2009-Dec-14, 12:42 AM
Can I ask what this program is? And where can I get it? Sounds interesting.

EDG
2009-Dec-14, 02:04 AM
Can I ask what this program is? And where can I get it? Sounds interesting.

It's just something I wrote myself for making my SF setting. I don't have any plans to make it available though.

Murphy
2009-Dec-14, 04:08 AM
Ok, just wondering. If you do ever make it into a finished form it might be something interesting to see though.