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Starlight Glimmer
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23 Jan 2019 10:00

midtskogen wrote:
Sounds more like eddies of interplanetary dust and the name "moon" or "satellite" is misleading.  They're for practical purposes made up of vacuum, probably a far better vacuum than we can produce on Earth.  The interesting part is that it is possible to observe them.

I wonder if there is a way to observe them, like to see them through normal telescope if that is possible, given their size and the fact there is 2 of them that is likely, though they are rather difficult to observe.
 
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23 Jan 2019 18:52

Starlight Glimmer wrote:
Source of the post I wonder if there is a way to observe them, like to see them through normal telescope if that is possible,

No. The article clearly states that even for professional astronomers it was difficult to image these Kordylewski clouds. From what I've read on them, they are likely absolute magnitude -15 or even worse and thus almost invisible against the ambient light pollution of space from the sun, other stars and the galaxy itself.  Some observers have claimed to have seen these clouds atop mountains and in dry deserts with the naked eye, but those were exceptional viewing conditions. To view them properly through any device would require expensive polarized lenses, as the authors pointed out.

I'm more interested in the potential dangers they pose to spacecraft venturing into those Lagrange points.
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24 Jan 2019 02:55

If there is a danger posed by them, we might have to "vacuum" them up at some point ;-)
 
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24 Jan 2019 12:41

Stellarator wrote:
Source of the post I'm more interested in the potential dangers they pose to spacecraft venturing into those Lagrange points.

Pretty much none.  The number of grains encountered by something passing through that region is less than the number of grains encountered going between Earth and Mars or Venus.  Impacts with grains of those size also does not result in catastrophic failure, but rather just small pitting of the surface, which over very many collisions can erode it.  But again there's far too few collisions for that to be a serious issue.

Cumulative impacts with dust grains is a bigger problem for much higher velocity craft leaving the solar system, such as in Project Starshot.
 
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25 Jan 2019 00:09

Watsisname wrote:
Source of the post Cumulative impacts with dust grains is a bigger problem for much higher velocity craft leaving the solar system, such as in Project Starshot.

That's what I was considering. Perhaps also for other high-velocity craft like the Parker probe or whatever we send to study 'Oumuamua up-close 8-).
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25 Jan 2019 08:11

Can we alleviate those concerns for Project Starshot by using some sort of magnetic field on the craft or some kind of repellent shielding?
 
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25 Jan 2019 09:21

A-L-E-X wrote:
Source of the post Can we alleviate those concerns for Project Starshot by using some sort of magnetic field on the craft or some kind of repellent shielding?

Dust isn't magnetic, and making a strong magnetic field would take too much mass anyway.  The best way to minimize this problem is instead to minimize the cross sectional area of the probe in the direction of its motion, perhaps by folding it up into an arrow shape.  An additional 'sacrificial shield' in front of the probe can also help, provided it doesn't require too much mass (light weight is everything for such a probe to be accelerated to high velocities).
 
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26 Jan 2019 03:58

Wat the weird thing about dust not being magnetic is that I do see dust be attracted to certain things (like electronics screens!).  I wonder what causes dust to be attracted to certain things and not others- assuming of course that terrestrial dust has a similar composition to space dust!

I like the streamlined shape solution you proposed, as well as a frontal shield, but could this shield be made of energy rather than something that has mass?
 
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26 Jan 2019 05:26

A-L-E-X wrote:
Source of the post Wat the weird thing about dust not being magnetic is that I do see dust be attracted to certain things (like electronics screens!).

That is "static cling", which is an electrical phenomenon.  When the dust comes near an electrically charged surface (let's say negatively charged), the negative charges in the dust get pushed slightly to the far side, leaving more positive charge on the near side, and we say it is then electrically polarized (but could still be electrically neutral overall).  Then because the positive charge on the dust is closer to the negatively charged surface, the dust feels a net attractive force to it, and can get stuck to it.  

This explanation doesn't quite work for insulators (which includes dust), where the charges are not free to move.  What's really happening is that rather than the charges being free to move as in a conductor, the charges in an insulator are locked up in little pairs called dipoles, and in response to the surrounding electric field those dipoles orient themselves with that field.  But the end result is the same: the object becomes electrically polarized, and you get an attraction.  This is why things like dust, hair, paper, balloons, etc., can be made to stick to an electrically charged surface.
 
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27 Jan 2019 04:53

ah so this cant be used to repel dust by reversing the charge?  So a shield made of energy (even onboard lasers) would not work in this case because some dust will stick to it regardless.
 
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27 Jan 2019 08:23

A-L-E-X wrote:
Source of the post ah so this cant be used to repel dust by reversing the charge?

Correct.  If you reverse the charge, then the dust will become polarized the other way, and still stick.  But electrostatic forces on dust are irrelevant when traveling at 0.2c, anyway.  The better way to minimize impacts with dust at those speeds is to minimize the area of the surfaces being exposed to it.
 
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28 Jan 2019 17:35

New Insights into the Early Formation of Massive Black Holes.

The insight comes from new simulations of the formation of structure, involving the processes that lead to the first galaxies and the cosmic web, seeded by the fluctuations in the density of dark matter.  In regions where these dark matter halos grow quickly, star formation is stifled, and the conditions instead become conducive for massive black hole growth.  This is in the same vein as the "direct collapse" explanation for how these black holes formed, except that the dark matter turns out to play an important role in the physics. :)

phys.org article
Wise et al. (2019)
 
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28 Jan 2019 23:19

Best image of Ultima Thule so far.
Image
NIL DIFFICILE VOLENTI
 
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29 Jan 2019 01:02

Watsisname wrote:
Source of the post New Insights into the Early Formation of Massive Black Holes.

This image of the galaxy cluster is beautiful:
Image
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29 Jan 2019 04:40

Watsisname wrote:
New Insights into the Early Formation of Massive Black Holes.

The insight comes from new simulations of the formation of structure, involving the processes that lead to the first galaxies and the cosmic web, seeded by the fluctuations in the density of dark matter.  In regions where these dark matter halos grow quickly, star formation is stifled, and the conditions instead become conducive for massive black hole growth.  This is in the same vein as the "direct collapse" explanation for how these black holes formed, except that the dark matter turns out to play an important role in the physics. :)

phys.org article
Wise et al. (2019)

That's fascinating, Wat!  Do you think we'll ever be able to create dark matter in the lab and make any practical use of it?

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