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https://www.astro.princeton.edu/~eco/research/spurs/project.html
Quote from: Bored chemist on 08/12/2021 18:11:59https://www.astro.princeton.edu/~eco/research/spurs/project.htmlThanksIn the article it is stated:https://www.astro.princeton.edu/~eco/research/spurs/project.html"At the high densities present within arms, gravity is stronger, and this gravity begins to cause the gas to concentrate locally."Some molecular gas condensations, containing up to ten million times the mass of the Sun, collapse all the way to make gravitationally bound clouds in the arm.So, is it all about gravity?Therefore, do you confirm that this splinter which is full of stars (at a size of 3000Ly) holds locally all its stars by gravity?
What other plausible answer is there?
local gravity and not by central gravity?
One plausible answer is that said 'splinter' doesn't hold itself together at all.
The article about the 'splinter' in question showed only 23 distinct stars in it, a good percentage of which were depicted still in the Sagittarius arm.
https://en.wikipedia.org/wiki/Stellar_density"The true stellar density near the Sun is estimated as 0.004 stars per cubic light year, or 0.14 stars pc−3"Given a volume of radius 50 LY, (~14175 pc³) this works out to very close to 2000 stars within that radius of us, hardly 64. I've brought up this point before, but Dave is still asserting things from prior threads.
The simulation has splinter-looking structures all over the place, and they don't seem very stable. They don't seem to hold themselves together at all over time. They're more like temporary densities in the turbulence of the shear forces going on, and the result of gasses being pushed away by the solar wind pressure of new stars forming.
https://www.astro.princeton.edu/~eco/research/spurs/project.html"At the high densities present within arms, gravity is stronger, and this gravity begins to cause the gas to concentrate locally."Some molecular gas condensations, containing up to ten million times the mass of the Sun, collapse all the way to make gravitationally bound clouds in the arm.
There is only one gravity.If you let go of a test mass, it accelerates off in one, and only one direction.So this "local gravity and not by central gravity" idea is meaningless.
So, don't you agree that the use the "wood" in order to show that this splinter is a solid/rigid object?
like a splinter
The moon orbits around our planet while they both orbit around the Sun.
no, of course not, Like all features of a galaxy, they are mainly empty space. You could hardly imagine anything less solid than blobs of gas floating in space.
Hence based on this stellar density in the Orion spiral arm, there are at least 8000 * 500 = 4,000,000 stars in a sphere of 1000LY.
https://www.astro.princeton.edu/~eco/research/spurs/project.html"The first step in the process is the flow of diffuse gas from interarm regions into spiral arms."Then they claim that:"At the high densities present within arms, gravity is stronger, and this gravity begins to cause the gas to concentrate locally"
The path of the Moon is roughly a circle with 13 sided lumps on it, round the Sun.
What do you mean by empty space?
Do you claim that the following stellar density in the Orion spiral arm is incorrect?
QuoteQuote from: Dave Lev on Today at 05:24:14What do you mean by empty space?Stuff you could drive a space ship through.
Quote from: Dave Lev on Today at 05:24:14What do you mean by empty space?
QuoteQuote from: Dave Lev on Today at 05:24:14Do you claim that the following stellar density in the Orion spiral arm is incorrect?No,
Quote from: Dave Lev on Today at 05:24:14Do you claim that the following stellar density in the Orion spiral arm is incorrect?
I am simply pointing out that comparing it to a piece of wood is idiotic.
You could hardly imagine anything less solid than blobs of gas floating in space.
Do you mean that we can claim that the observable universe is empty?
However, as we go out from the arm it seems that the density of stars falls down dramatically.If we look directly in the direction of that Sagittarius arm do we agree that there are almost zero stars between the arms?
"it is that one of our galaxy’s spiral arms – located some 4,000 light-years from Earth – is jutting out at a weird angle. They’re calling it a break in one of the Milky Way’s spiral arms.""Stars and nebulae jut out like a splinter from a piece of wood on the Sagittarius Arm of the Milky Way. The inset gives you a better idea of the spiral arm break and where it’s located in relationship to our sun."We clearly observe that splinter from a piece of wood at the spiral arm.Don't you agree that this indicates that the arm has some rigid/wooden structure?
do you confirm that the entire science community clearly observes that "splinter from a piece of wood on the Sagittarius Arm of the Milky Way"
don't you agre that the use the "wood" in order to show that this splinter is a solid/rigid object?
If they were not together as you claim, why they call it "splinter from a piece of wood"?So, don't you agree that the use the "wood" in order to show that this splinter is a solid/rigid object?
How can we accept the density wave while it can't explain the full structure of the spiral galaxy including the Bulge, Bar, Ring density of stars in and out the arms and even that broken arm that looks as a splinter from a piece of wood?
So you confirm that there is no real theory for spiral galaxy and the density wave theory is useless.
72% of the galaxies are spiral galaxies and we observe them when the Universe was very young.
Therefore, we could assume that an average spiral galaxy should keep its spiral structure for more than 12 B years.
and they all don't have a basic clue how it really works?
No more "our scientists" or "the entire science community".Promise!
What kind of force could hold so many stars together in that shape of a wooden splinter?
Hence, if local gravity hold stars together in the splinter why can't we assume that the same local gravity holds the stars in any spiral arm?
Hence, can we agree that stars in the splinter & in any spiral arm are bonded in their location by local gravity and not by central gravity?
Hence, in order to hold the Sun in the Orion arm a requested density of 64 stars per 50 LY sphere is needed.
Do you agree that only local gravity force can fully explain all the features of the spiral arm?
I compare a stars cluster to the Earth/moon orbital system while the sun represents the center of the galaxy.
In the same token any star in the stars-cluster orbits locally around the center of mass in the cluster,
However, if we set this stars cluster in the galactic disc next to any spiral arm, it would have the wood splinter shape.
I have no intention to offer any solution for our Universe.
The bobbling motion of the sun proves that it orbits locally around a center of mass while that center of mass orbits around the galaxy.
Don't fall into name calling...
QuoteQuoteIn the same token any star in the stars-cluster orbits locally around the center of mass in the cluster,This totally violates Newtonian physics, and is nonsense.
QuoteIn the same token any star in the stars-cluster orbits locally around the center of mass in the cluster,
There is no orbital motion within a globular cluster. It is an N-body system with chaotic motion. A given mass might accelerate away from the center of mass of the cluster. Nice neat orbits only work for 2 body systems.
Yes, gravity is one of the primary forces pushing and pulling on all the matter in the galaxy, but it doesn’t tend to hold anything together except gravitationally bound things (like Alpha Centauri, globular clusters and such).
QuoteQuoteHow can we accept the density wave while it can't explain the full structure of the spiral galaxy including the Bulge, Bar, Ring density of stars in and out the arms and even that broken arm that looks as a splinter from a piece of wood?The university simulation that BC found showed all that, and showed density waves since most newer models build on older ones, not replace them, just like Einstein’s theories build on Newtons work, not invalidating it.Not saying the problem has been completely solved, but it’s an actual working model instead of just you making unbacked assertions.
QuoteHow can we accept the density wave while it can't explain the full structure of the spiral galaxy including the Bulge, Bar, Ring density of stars in and out the arms and even that broken arm that looks as a splinter from a piece of wood?
QuoteQuote from: Dave Lev on 08/12/2021 19:22:30Hence, if local gravity hold stars together in the splinter why can't we assume that the same local gravity holds the stars in any spiral arm?This question is reasonable.
Quote from: Dave Lev on 08/12/2021 19:22:30Hence, if local gravity hold stars together in the splinter why can't we assume that the same local gravity holds the stars in any spiral arm?
But gravity doesn’t hold the stars in them. The stars are fairly evenly distributed, not concentrated in the arms. Only the really bright ones are there because the arms are a birthing place and the big ones don’t live long enough to travel between the arms. Our star is small enough to make the trip, and is indeed located significantly outside the thick of the Orion arm nearby. The diagram on your ‘splinter’ site shows the sun well outside the gray stripe designating the Orion arm.
QuoteConcerning the Sagittarius ‘break’ article:Quote"it is that one of our galaxy’s spiral arms – located some 4,000 light-years from Earth – is jutting out at a weird angle. They’re calling it a break in one of the Milky Way’s spiral arms."
Concerning the Sagittarius ‘break’ article:
QuoteQuote from: Dave Lev link=topic=83638.msg662613#msg662613What kind of force could hold so many stars together in that shape of a wooden splinter?Nothing said it was ‘held together’. If it was, no force is required. Force is needed to accelerate it is all. A real piece of wood, even one that size, could float out there without any force keeping it together at all. But again, no article claimed that the structure was static, rigid, or otherwise ‘held together’.
Quote from: Dave Lev link=topic=83638.msg662613#msg662613What kind of force could hold so many stars together in that shape of a wooden splinter?