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PetTastic
2015-May-30, 08:25 AM
I was looking at the "Fun papers in Arxiv" thread and noticed one on high speed sensors.

I think there is the real possibility of a new generation of faster sensors exposing all kinds of selection effects, maybe even dark matter.

It is currently possible even using state of the art sensors that we are missing small building sized (of the order of 10m) interstellar objects made from volatile ices.
Equally there is no evidence these objects do exist, but it would take a very thin population to explain DM.

A 10m object could be travelling at a thousand times its own length per seconds, so only a faint blur in a one second exposure.
They could transit between us and a star at a detectable distance in a microsecond against a background of billions of them too far away to see.

If we detected more than one millisecond transit event per star every 80 years it would explain dark matter.
The problem is how do you look at thousands of stars at a time looking for millisecond events.

--- based on ----
DM density 1/3 proton per cm3 1.67e-27/3 *1000 = 5.56e-25 g/cm3
Ice 1 g/cm3

1 volume of ice to 1.8e24 empty space

One 10m object (vol 1000 m3) per 1.8e27 m3 space

Average spacing 1.8e27 ^(1/3)=1.2164E9 metres or a million km

Number per m3 volume 1/1.8e27= 5.56e-28

Mean free path = (1.41 * 100 * 5.56e-28)^-1=1.27E25m 1,342,419,000 light years

Detectable volume between us and star out to 10AU could be 7e14 m3
Probability of one in volume = 7E14/ 1.8e27=3.93e-13

Slow moving a 1 second event every 1/(3.93e-13)=2.5445E12 seconds 80632 years
Fast moving a 1 millisecond event every 80 years

Shaula
2015-May-30, 09:46 AM
If we detected more than one millisecond transit event per star every 80 years it would explain dark matter.
As has been said to you in other threads it would essentially require a rewrite of most of what we think we know about gravity, plasma behaviour and, for that matter, nuclear fusion. It also wouldn't explain dark matter as there is no known way for that material to be where it would have to be on anything like the timescales required.

PetTastic
2015-May-30, 03:36 PM
As has been said to you in other threads it would essentially require a rewrite of most of what we think we know about gravity, plasma behaviour and, for that matter, nuclear fusion. It also wouldn't explain dark matter as there is no known way for that material to be where it would have to be on anything like the timescales required.

If my numbers are correct then with current tech it would be harder to detect the ice if it was there than WIMPS.

I agree it should not exist in theory but that has been said about almost every other selection effect before observation proved it wrong.
(Stars smaller than the sun, stars between galaxies etc.)

I think I prefer Ice to MOND, both cause havoc with any theories for the early universe.
Ice in blocks bigger than 10cm does fit some recent observations on colliding galaxies and clusters with a mean free path greater than 10 million light years.
It is not a bad fit for gravity models now, but like MOND it does not fit the theoretical formation of large scale structure etc.

Your plasma comment I do not understand. I work in semiconductor industry (designing SuperFX chip for Nintendo and Arc processors)
Vapour deposition and partial pressures etc is key to making chips. If micron dust can exist for millions of years without evaporating then larger objects should be growing.
With many billions of years between collisions a population could exist by growing at less than a nanometre per year.

If we did start seeing small collisions on KBOs or the moons of the outer planets. Or maybe detecting thousands of micro comets vaporising in the outer solar system then I agree it would be very tricky to explain how the material was created.

Shaula
2015-May-30, 04:12 PM
The plasma comment related to galactic cluster dynamics. And, as has been said, it is not a good fit to gravity models. Because there isn't a stable halo distribution. It may fit a given snapshot of a galaxy but it doesn't fit an evolving galaxy. But we did this to death before, I see no point re-hashing the arguments.

Cougar
2015-May-31, 10:43 PM
It is currently possible even using state of the art sensors that we are missing small building sized (of the order of 10m) interstellar objects made from volatile ices.

That's a lot of chunks of ice to distribute throughout the galactic disk and then extend well beyond it. How did they form?

And to mimic dark matter, they'd have to permeate the disk and provide ~7 times the gravity than provided by all the visible stars, gas, dust, molecular clouds, central black hole, etc., in the disk.

And why do you have them moving so fast? If they're throughout the disk, wouldn't they generally be going with the flow?

antoniseb
2015-Jun-01, 01:39 PM
[QUOTE=Cougar;2292136... And why do you have them moving so fast? If they're throughout the disk, wouldn't they generally be going with the flow?[/QUOTE]
If they are in a ellipsoidal configuration, as needed to explain the phenomena, they would not be coorbiting with the Sun, many would be in circumpolar galactic orbits, and everything in between.

PetTastic
2015-Jun-01, 02:25 PM
The plasma comment related to galactic cluster dynamics. And, as has been said, it is not a good fit to gravity models. Because there isn't a stable halo distribution. It may fit a given snapshot of a galaxy but it doesn't fit an evolving galaxy. But we did this to death before, I see no point re-hashing the arguments.

I totally agree ice as dark matter does not work for current models of how galaxies formed in the early universe but it does look a good match for observed cluster dynamics.
The study of 72 galaxy cluster collisions did indicate very little self interaction and therefore a very long mean free path like I am predicting for ice.
One the other hand a recent paper shows some indication of interaction. (the ice got vaporised by heat in the gas collision? :) )

I am just saying that if it is there we could not detect it with current technology.
There is strong evidence something is there.
Selection effects are all the fashion these days. There must be ice between the stars there is just no observational evidence to say if it is a tiny amount or a massive amount.
I've read old collections of papers that explain why stars smaller than the Sun can't form and then that Proxima is an exception to the rule.

PetTastic
2015-Jun-01, 02:40 PM
That's a lot of chunks of ice to distribute throughout the galactic disk and then extend well beyond it. How did they form?

And to mimic dark matter, they'd have to permeate the disk and provide ~7 times the gravity than provided by all the visible stars, gas, dust, molecular clouds, central black hole, etc., in the disk.

And why do you have them moving so fast? If they're throughout the disk, wouldn't they generally be going with the flow?

There is no evidence these objects exist.

However, the very earliest galaxies do have a high (described a near modern) metal and dust content.
If the metal content gets too low micron dust will evaporate when the level gets higher larger objects must start to grow.
These objects could have been growing by accumulating dust and ice at rates as slow as a nanometre per year the be many metres across but now.

They can't grow by collision as they almost never collide within the age of the universe.

For doing the numbers, I assume they travelling with a similar velocity distribution to the stars oscillating up and down through the disk.
Any slower and the chances of them being in detectable range is reduced.

If they are volatile ices (carbon monoxide, methane and ammonia) the faster they are travelling the closer they could get to us and the Sun before evaporating as micro comets.