Another candidate for Dark Matter in spiral galaxies, weighs in...

http://groups.google.com/group/sci.s...9b729a0725bb1d
.... if the Milky Way is not too special...

David A. Smith

On 26/02/2012 10:30 AM, dlzc wrote:
http://groups.google.com/group/sci.s...9b729a0725bb1d
... if the Milky Way is not too special...

David A. Smith

Well, invisible planets are part of the MACHO form of dark matter, so
it's not really a new candidate. But we mustn't talk about MACHO's, they
don't fit in with the prevailing sci-fi aspect of modern cosmology.

Besides, even if there are billions of planets floating around out
there, they are tiny compared to stars. Each star outweighs a Jupiter
mass planet by around a 1000 times. You'd need a trillion Jupiter mass
planets just to weigh about the same as the population of stars in the
Milky Way, and dark matter is supposed to not just weigh as much as
normal matter, but to outweigh it by 10 times at least. So you'd need 10
trillion Jupiters floating out there. If there were 10 trillion
Jupiters, then no matter how big the Milky Way was, you should be able
to see several of them in the immediate neighbourhood.

Yousuf Khan

Dear Yousuf Khan:

On Thursday, March 1, 2012 10:57:19 PM UTC-7, Yousuf Khan wrote:
On 26/02/2012 10:30 AM, dlzc wrote:
http://groups.google.com/group/sci.s...9b729a0725bb1d
... if the Milky Way is not too special...

Well, invisible planets are part of the MACHO
form of dark matter, so it's not really a new
candidate. But we mustn't talk about MACHO's,
they don't fit in with the prevailing sci-fi
aspect of modern cosmology.

Well, as long as they continue to try and disprove such such hypotheses, I can't bitch too much.

Besides, even if there are billions of planets
floating around out there, they are tiny
compared to stars. Each star outweighs a Jupiter
mass planet by around a 1000 times. You'd need a
trillion Jupiter mass planets just to weigh
about the same as the population of stars in the
Milky Way, and dark matter is supposed to not
just weigh as much as normal matter, but to
outweigh it by 10 times at least. So you'd need 10
trillion Jupiters floating out there.

And if our estimates of interstellar "gas" density is based on it not being a plasma, we'll have most of what is required.

If there were 10 trillion Jupiters, then no
matter how big the Milky Way was, you should be
able to see several of them in the immediate
neighbourhood.

We've found brown stars, which brings down the count, and there is still the evidence for a 4x Jupiter planet around the Sun (Tyche). We haven't *seen* it yet. Between neglecting the center of spiral galaxies as swept clean, where luminosity vs. total normal mass is calibrated, and the "surprising" collections of normal mass, I think we are getting much closer to killing Dark Matter as some new exotic particle to be looked for in/around spiral galaxies.

More to be seen...

David A. Smith

On 26/02/2012 10:30 AM, dlzc wrote:
http://groups.google.com/group/sci.s...9b729a0725bb1d
(is actually a press release about possible life on nomad planets)

In article ,
Yousuf Khan writes:
Well, invisible planets are part of the MACHO form of dark matter, so
it's not really a new candidate.

Right, not a new candidate at all. Existing upper limits say that
nomad planets are at most 10% or so of the Milky Way dark matter
halo.

But we mustn't talk about MACHO's, they
don't fit in with the prevailing sci-fi aspect of modern cosmology.

There have been several past searches for MACHOs, and at least one is
ongoing. That's where the upper limits (and recent detections) come
from.

Besides, even if there are billions of planets floating around out
there, they are tiny compared to stars. Each star outweighs a Jupiter
mass planet by around a 1000 times.

Yes, that's the point.

Some years ago, my favorite candidate for baryonic dark matter was
very old (hence very cold) white dwarfs. At something close to a
solar mass each, you wouldn't need a gigantic number of them. By
now, though, the MACHO searches seem to have ruled these out, at
least in sufficient numbers to explain the dark matter halo.

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