So before we get too complacent and think we actually understand what's going on here
lets show a couple of recent oddball results that seem to cast some doubt on this theory.
These may go away or they might fatally flaw everything I've just told you. Here is a very
weird case of a very recent paper, this is a star, here's it's optical light, this is
what you'd expect it's spectrum to look like if there was no dust around it.
Bu, when it was observed between 2006-2008 the spectrum climbed up so that it looked
like it had a debris disc around it so you'll see the infra-red wave lengths energy is much
higher than you'd predict. However, they went back and re-observed it
a couple of years later, 2011, and the points had jumped from here all the way down to there.
- Right, so, you're telling me in the case of two or three years that somehow this star
completely cleared it's debris disc? I thought the processes we were talking about were going
to take tens of thousands of years at least. -It's pretty weird, it seems to have had a
debris disc that went away as you said you can't clear the dust out by any of the methods
we've talked about that fast - alright so, what do you thinks going on
here? - well I'm damned if I know... people think
that maybe the infra-red excess is due to something other than a debris disc to begin
with maybe a solar flare, solar flares don't usually produce a spectrum like that...
-wow OK, so the solar flare would be up there or the solar flare would have destroyed the
debris disc or something? who know? So you used the plural when you said "Oddballs"
so this is one oddball... -OK, well this is another family of oddballs
I guess, this is the European Space Agency's Herschel space mission which is a bit like
IRAS we talked about in the beginning an infra-red telescope sitting inside a dewar flask to
keep it very very cool but this one worked at much lower temperatures and much longer
wavelengths where it was incredibly sensitive. And what they discovered was that normal debris
discs, the spectrum's climbing up over here out at around maybe 10 microns. This one's
only gently climbing at several hundred microns so what that's telling you is that you've
got a very cold debris disc. because remember that the wave length at which
something peaks depends on it's temperature, a hot thing peaks over here cool things peak
further into the infra-red this'd be a temperature of only 38 kelvin, so an incredibly cold debris
disc. -Paul, that's all well and good but this is
a debris disc we think, of dust and I note that we're making measurements here at a thousand
microns, that's a millimetere, and you can't emit light that is longer in wavelength than
your length and so that would seem to indicate to me at least that we're not...dust isn't
a millimetre that's like sand so somethings not right here.
- Yes so the dust we've been talking about is a micrometer in size a thousand times as
small so a micrometer can produce things out here, maybe ten microns but a thousand microns
you need to have sand the trouble is if you have something the size of sand first of all
you need alot more mass because you have much less surface area per unit weight so the disc
has to be much heavier and it's colder and further out but also if you have an orbiting
disc of dust and we produce it the same way where we smash big things together what would
normally happen, you smash big things and they make slightly smaller things they get
smashed to make smaller things still until you end up with things so small they get blown
away so most of the area should end up in the smallest things that can survive without
being blown away. And we're talking about very cold a long way
out so even very very small grains should be able to survive out there so most of the
radiation should always be from the smallest grains that can survive being blown out which
would be a micron or even less than a micron in this case.
- Alright so it does seem not to add up for some reason there is literally a sand box
around the outside of this star, or, something else other than what we think is causing this
emmision.