Re: ASTRO: Finding large cold clouds of atomic hydrogen

From: Miriam English (
Date: Wed Jul 25 2001 - 03:26:05 MDT

Here is a thought: the steady-state theory was never really satisfactorily
disposed of. Hoyle and Gold made some small adjustments a while back and it
actually fits pretty-much as well as the big-bang theory now.

One of the things that caused a lot of people to discard the steady-state
theory is the idea of atomic hydrogen spontaneously dropping into existence
in the large voids between galaxies. Now that they are finding large cold
clouds of atomic hydrogen in the voids... well... :-)

I actually think the steady-state theory makes a LOT more sense than the
entire universe popping into existence in one instant, but I am not wanting
to argue that here.

Best wishes,

         - Miriam

At 08:26 AM 22/07/2001 -0700, Robert J. Bradbury wrote:

>Nature is reporting on discoveries by the Canadian Galactic
>Plane Survey and other observations by the Green Bank Radio
>Telescope of finding several large-cold clouds of atomic hydrogen.
>These "violate" the standard theories of how hydrogen is recycled
>from hot atomic hydrogen generated by supernovas eventually
>becoming cold *molecular* hydrogen that should eventually
>collapse under gravity to form starburst clouds, like the Orion
> From the Dickey's summary:
> > Knee and Brunt have discovered a new kind of cloud in data from
> > the Canadian Galactic Plane Survey. The structure they found is
> > made of atomic hydrogen so cold (about 10 K) that it is visible
> > only because it absorbs background radiation essentially throwing
> > a dark shadow across the sky.
> > The newly discovered dark arc seems to be similar to these cold clouds,
> > but much larger and more massive. Knee and Brunt1 estimate that it is
> > 6,000 light years across, with a mass at least 20 million times that
> > of the Sun.
> > We do not yet know the origin of the dark arc. But in the meantime,
> > others are finding similar clouds that are almost as cold. An immense
> > atomic cloud discovered by astronomers using the Green Bank Telescope
> > in the United States is somewhat smaller and warmer than the dark
> > arc, but is similar in having very little star formation.
> From the paper:
> > The conventional wisdom that cold, massive clouds in the
> > interstellar medium are always predominantly molecular has
> > achieved near-axiomatic status. The discovery that H I
> > supershells can contain some of the coldest gas in the Galaxy
> > will require a re-evaluation of this view.
>Cold. Dark.. Large... No stars visible.... Hmmmm...
>(Don't ask me any questions, I'm simply reporting the data...
>Note that if it turns out that these are abundant, they may
>account for some of the missing baryonic dark matter. But
>they are going to have to be *really* abundant.)
> Astronomy: Dark arc casts a long shadow, John M. Dickey
> Nature 412:292-293 (2001)
> A massive cloud of cold atomic hydrogen in the outer Galaxy
> Knee, L. B. G. & Brunt, C. M.
> Nature 412, 308-310 (2001).

Q. What is the similarity between an elephant and a grape?
A. They are both purple... except for the elephant.
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