Re: ASTRONOMY: Dark Matter & White Dwarfs

From: Robert J. Bradbury (
Date: Sat Mar 24 2001 - 12:51:05 MST

On Sat, 24 Mar 2001 wrote:

> "Robert J. Bradbury" wrote:
> > Now personally, I cannot imagine any artificial structures that
> > would match the spectra of these two objects. But its
> Can you describe the most prominent features of these weird
> spectra in words? (I've let the Science subscription lapse).

Sure, Fig 4B has a 4000 K Blackbody curve running across the top
(very smooth). The x-axis goes from 0.5 to 1 microns and the Y-axis
is normalized log Flux_lambda WD2356-209 lies just underneath that
BB curve with a flux variation of log -15 to -16. The wierd part
is that it dips from 0.5-0.6 microns, rises back up to peak at 0.7
microns then starts trailing off again (kind of mimicing the BB
curve) out to 1 micron. The "noise" on the curve looks similar
to their other real white dwarf stars. (They do in the article
mention though something that makes me think you should treat
the noise as 'significant' (though 0.1-0.5 noise 'spikes' I
would consider significant).

LHS 1402 on the other hand trails off from -16 to -17.2 from 0.5 to
1 microns, but much faster than the BB curve. Its very very smooth
with only a little noise from 0.9-1 microns. It looks much smoother
than the other white dwarf curves.

Commenting on your other note -- it isn't clear what you are going
to see is a 'dusty' star (there are differences in the curves of
'dusty' stars v.s satellite enshrouded stars because there is some
variation in the BB curve in depending on whether the particles
radiating are larger or smaller than the wavelengths being radiated.
I don't fully understand this, but it is Kardashev who has said
it so I believe it.)

How long you see MBrains under construction depends in large part
on the value of 'present' thought vs. 'future' thought and the
quantity of material you have available to work with. If you want
to 'fully' develop a system, it may take hundreds or even thousands
of years. So as we begin to watch billions of stars the likelyhood
that among them will be an MBrain under construction goes up.

The concept that the expansion envelope is past us assumes a host
of things, not the least of which are:
a) That remote colonization is in some way valuable.
b) That the expansion would occur at some reasonable fraction of the
   speed of light.
c) That one wants to develop 'stars'.

As I've stated before, I think these assumptions have problems.
I'll be writing up a more complete paper on this soon for people
to throw stones at, so lets not get into another debate over it
at this point.

The expansion envelope could well be past us and we could still
see stars if it is much better to develop brown dwarfs. From
the looks of things there are a lot more of those out there
than there are stars.


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