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Watsisname
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04 Jun 2019 02:43

No worries!  I just didn't want anyone thinking that I'd just deliberately ignore a question directed to me.  I love questions! :)  

PlutonianEmpire wrote:
Source of the post Also, in FFT's first vid, could that also be how IC 1101's current appearance may have formed?

Yes, this is a very good visualization for how galaxies like IC 1101 are formed.  The gravitational center of a rich galaxy cluster is a chaotic place, with smaller galaxies regularly falling into it and colliding to build up a giant elliptical galaxy.  Very often we find giant ellipticals are present at or close to the centers of these galaxy clusters.

Here's another n-body simulation of an evolving galaxy cluster.  It's older, and its physics is not as sophisticated (just modelling the gravitational forces between particles; no dust or gas or star formation/death processes, and it starts with some initial configuration of galaxies rather than the cosmic evolution after the Big Bang), but I think it still does a great job illustrating the dynamics of how these giant ellipticals form.



And for comparison, a deep exposure of NGC1316, showing the surrounding shells and streamers of stars -- evidence of the chaos that built it.
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A-L-E-X
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04 Jun 2019 15:47

Wat is that galaxy really the largest in the known universe?!  I found a video about it

https://www.youtube.com/watch?v=fwpPy2IDNwE
 
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Watsisname
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04 Jun 2019 16:53

A-L-E-X wrote:
Source of the post Wat is that galaxy really the largest in the known universe?!

Maybe, but I would prefer to say it is just the largest of galaxies whose sizes have been reasonably well measured, which applies only to galaxies that are sufficiently bright and nearby so that we have images that capture all of their details (not just their brightest central regions).  IC 1101 is millions of light years across, but most of that is a very diffuse halo of stars, which would not be easily imaged if it were much farther away.

Actually, I don't think the physical size of a galaxy is a very useful measurement.  In many cases it's a bit ambiguous, especially for ellipticals which do not have well defined edges.  The above image of NGC1316 is a good example of that.  Most images of it only show the brightest central region.  The longer exposure reveals more of the faint and diffuse streams of stars farther out.

I think something more interesting and useful to know about galaxies, and their host clusters as a whole, are their masses, and especially the fraction of the mass that is in the form of stars, gas, and dark matter.  This tells us a lot more about the dynamics behind galaxy formation, and how these enormous structures evolve over time. :)
 
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04 Jun 2019 16:57

I totally agree!  I was actually looking for the galaxy with the most number of stars!  I wonder what that might be?!
 
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Watsisname
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05 Jun 2019 01:52

A good question.  IC 1101 would not be a bad bet.  Otherwise, look for galaxies with both a high luminosity and red color temperature (after adjusting for cosmological redshift).  On a color-magnitude diagram, that would be far up and to the right, in the so-called "red sequence" of galaxies:

Image


The red color is important because red main sequence stars have much less luminosity per unit mass than blue stars, so there must be more stars for the galaxy to have the same total luminosity.
 
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05 Jun 2019 12:23

Do you think that galaxies further away from us would be more massive?  Would the earliest galaxies formed probably contain the most mass?  Also is the total mass of a galaxy and the number of stars it has closely connected to the mass of the supermassive black hole at its heart?
 
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05 Jun 2019 21:42

Watsisname wrote:
No worries!  I just didn't want anyone thinking that I'd just deliberately ignore a question directed to me.  I love questions! :)  

PlutonianEmpire wrote:
Source of the post Also, in FFT's first vid, could that also be how IC 1101's current appearance may have formed?

Yes, this is a very good visualization for how galaxies like IC 1101 are formed.  The gravitational center of a rich galaxy cluster is a chaotic place, with smaller galaxies regularly falling into it and colliding to build up a giant elliptical galaxy.  Very often we find giant ellipticals are present at or close to the centers of these galaxy clusters.

Here's another n-body simulation of an evolving galaxy cluster.  It's older, and its physics is not as sophisticated (just modelling the gravitational forces between particles; no dust or gas or star formation/death processes, and it starts with some initial configuration of galaxies rather than the cosmic evolution after the Big Bang), but I think it still does a great job illustrating the dynamics of how these giant ellipticals form.



And for comparison, a deep exposure of NGC1316, showing the surrounding shells and streamers of stars -- evidence of the chaos that built it.
Image

Ja thank you! Very informative!
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06 Jun 2019 00:02

A-L-E-X wrote:
Source of the post Do you think that galaxies further away from us would be more massive?  Would the earliest galaxies formed probably contain the most mass?

While there are some very massive galaxies far out in the depths of the universe who dwarf our own Milky Way, it would be wrong to say that there is a direct connection between galaxy distance and mass. There are dwarf galaxies at the same distance as the supermassive ones. The only time frames one could assign relevance to with this notion of mass/distance scaling is with some of the earliest galaxies in the universe, some ten billion years ago.

A-L-E-X wrote:
Source of the post Also is the total mass of a galaxy and the number of stars it has closely connected to the mass of the supermassive black hole at its heart?

Not really. There are fairly tiny galaxies with very massive blackholes in their guts. So-called ultra-compact dwarf galaxies (UCDs) are recent discoveries in this regard, having been found to harbor supermassive blackholes.
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Watsisname
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06 Jun 2019 02:17

A-L-E-X wrote:
Source of the post Also is the total mass of a galaxy and the number of stars it has closely connected to the mass of the supermassive black hole at its heart?


Actually, there is a connection, although it is a little more subtle.  It is the M-sigma relation, which is a relation between the mass (M) of a galaxy's central supermassive black hole (SMBH) and the velocity dispersion (sigma) of the stars in its bulge.  Velocity dispersion means how much variation or spread there is in the orbital velocities of the stars, about the mean value.  (Think "standard deviation" in statistics).  For a system of orbiting particles, the velocity dispersion acts as a measure of the total mass of the system.

What the M-sigma relation shows us is that the mass of the SMBH is closely related to the velocity dispersion of stars in the galaxy's bulge.  It goes approximately as the velocity dispersion to the 4th to 5th power (depending on the type of galaxy and whether it is active or quiescent).

Image


The relation also holds between the mass of the SMBH and the galaxy's luminosity.

As most relations go, there can be exceptions, like the Ultra Compact Dwarf galaxies Stellarator mentioned.  This is because those galaxies have apparently been stripped of most of their stars so that only the core region remains.  Aside from those exceptions though, the relation is very robust and is commonly used.  Because the relation is so tight, by measuring the velocity dispersion of a galaxy's bulge we can get an accurate measure of the mass of its central black hole.  This method even helped resolve discrepancies between other earlier methods of estimating SMBH masses.

The M-sigma relation is also surprising when you think about it.  It implies a close connection between black hole growth and the evolution of the host galaxy.  But why, when the SMBH is so much smaller by both size and mass than the rest of the galaxy it resides in?  

The understanding, which only came about in the last couple decades (and which I am also grossly oversimplifying here), is that the black hole extends its influence not just by gravity, but also by its jets.  When the black hole is active and accreting at a higher rate, its jets and outbursts are more effective at blowing away the surrounding intergalactic medium, preventing material from falling in to feed the galaxy.  This is called AGN feedback, and represents a way in which the tiny powerhouse at the galactic center is capable of driving large scale dynamics in the galaxy's environment.  Black holes are even more remarkably powerful than just their gravitational fields would suggest. :)

A-L-E-X wrote:
Source of the post Do you think that galaxies further away from us would be more massive?  Would the earliest galaxies formed probably contain the most mass? 

In this case there isn't so strong of a relation, but overall galaxy clusters and especially the giant elliptical galaxies within them do grow more massive with time.  This is simply because more material is constantly falling into them: gas and dark matter from the surrounding intergalactic medium, and also other galaxies in the cluster randomly colliding and merging together.  As we saw with the earlier image of Laniakea, very large regions of the universe "break off" from the expansion and the material collapses together, especially along those sheets and filaments connecting nearby regions of the cosmic web.
 
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07 Jun 2019 22:35

JackDole wrote:
I believe that a Type IV or Type V civilization can create an artificial universe, and thus survive a Big Rip.

In other words, something that can arise naturally can also be produced artificially.  8-)

Interesting. If a civilization is powerful enough to create a universe, could they do entropy reduction to survive the Heat Death?
 
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08 Jun 2019 01:56

default0.0player wrote:
Source of the post could they do entropy reduction to survive the Heat Death?

Entropy in a system will always increase, as per the Second Law of Thermodynamics. Increasing entropy overtime in a system is the natural result of that system existing. It's deterioration into a high entropy state cannot be "reversed" or "reduced" - not without increasing entropy elsewhere and thus maintaining the general amount overall.
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08 Jun 2019 02:59

default0.0player wrote:
Source of the post could they do entropy reduction

I think that perhaps one can reverse the entropy in a limited space. However, this would increase the entropy outside of this range.
(That's just my amateur opinion, I'm not a physicist.)
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08 Jun 2019 12:40

default0.0player wrote:
Source of the post If a civilization is powerful enough to create a universe, could they do entropy reduction to survive the Heat Death?

Let's first take a look at what entropy is. let's start with an example, say it's winter and it's freezing outside, so, you turn your heater on (or up). the tempertures are now different inside and outside and therefore the entropy is low outside, and high inside. the hot air molecules in your house give off their heat energy to the cold air molecules outside, and over time the heat energy is evenly distributed amongst the two systems, and they have reached thermodynamic equilibrium, this is the increase in entropy. Therefore entropy is the movement towards thermodynamic equilibrium, and since energy is always conserved, hence the first law of thermodynamics, entropy must increase, hence the second law. Now back to your statement, as Stellarator said, "Increasing entropy overtime in a system is the natural result of that system existing." because of the particles' energies within a closed system, in this case that closed system is the entire universe, but the universe isn't very closed, in fact, it's infinite, therefore all the energy in the universe will eventually be evenly spread out amongst an infinitely huge universe, even to this day on it's way to higher infinities, and since any elementary particle, massive or massless is an energy wave, hence QFT and the mass-energy equivalence E = mc2, they will too be smeared across our universal plane, that is the heat death of the universe, or rather cool death because the energy will be smeared out amongst an infinite universe and therefore be infinitely low, or as low as it can be, but i'm getting off track. Now you should see, that there is no way to reverse entropy like that, all we could do is ether make a giant cold substance for the energy to go into, still increasing entropy, or make a giant hot substance that would lose it's energy to the cold and once again increase entropy, but nothing that would stop our demise, no matter how advanced we, or other civilizations might be.

PS sorry for all the "amongst"'s "hence"'s and "infinite"'s, this post was way to redundant.  
 
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08 Jun 2019 15:59

Stellarator wrote:
Source of the post Entropy in a system will always increase, as per the Second Law of Thermodynamics. Increasing entropy overtime in a system is the natural result of that system existing.

Entropy of a closed system can also be constant.  Example:  An expanding universe filled with photons is isentropic, or has a constant entropy.  Why?  Because expanding a sea of photons is a reversible process -- no useful energy is lost and the system could evolve the other way just as easily.  To be precise, the entropy of a sea of photons is proportional to its volume times its temperature cubed.  But its temperature is inversely proportional to the size (scale factor "a" of the universe), while volume is proportional to scale factor cubed.   So the entropy is proportional to VT3 ∝ a3/a3 = constant.

The layman's interpretation of the 2nd law really should not be that "entropy of a closed system always increases", but rather that "entropy of a closed system cannot decrease."  Actually, even that is wrong.  It can decrease, too!  It's just vastly less probable for it to decrease, especially if the size of the system (and number of particles it contains) is very large.

To make sense of this, and what entropy means in a rigorous statistical mechanics sense, I like to use an analogy with coins, such as here where I also use it as a way to understand the concept of negative temperature.  For a bunch of coins, the entropy is the logarithm of the number of ways the individual heads and tails could be arranged (the microstates of the system) to yield the same total number of heads and tails (the particular macrostate of the system).  Then the 2nd law here states that if you have a large number of coins, and start flipping them randomly, then you are statistically more likely to trend toward the macrostate that has the largest number of microstates.  That would be half of them being heads and half of them being tails.  

Image


There's nothing mysterious about why the system evolves in that direction.  There are simply many more ways for it to evolve in that direction!  If all ways have equal probability (this is the "fundamental assumption of statistical mechanics"), then you expect the system to evolve in the direction that has the most ways of getting there, and thus increases the entropy.  Getting all heads or all tails out of coin flips isn't impossible, it's just very unlikely if you have a lot of coins.
 
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08 Jun 2019 17:58

Propulsion Disk wrote:
default0.0player wrote:
Source of the post If a civilization is powerful enough to create a universe, could they do entropy reduction to survive the Heat Death?

Let's first take a look at what entropy is. let's start with an example, say it's winter and it's freezing outside, so, you turn your heater on (or up). the tempertures are now different inside and outside and therefore the entropy is low outside, and high inside. the hot air molecules in your house give off their heat energy to the cold air molecules outside, and over time the heat energy is evenly distributed amongst the two systems, and they have reached thermodynamic equilibrium, this is the increase in entropy. Therefore entropy is the movement towards thermodynamic equilibrium, and since energy is always conserved, hence the first law of thermodynamics, entropy must increase, hence the second law. Now back to your statement, as Stellarator said, "Increasing entropy overtime in a system is the natural result of that system existing." because of the particles' energies within a closed system, in this case that closed system is the entire universe, but the universe isn't very closed, in fact, it's infinite, therefore all the energy in the universe will eventually be evenly spread out amongst an infinitely huge universe, even to this day on it's way to higher infinities, and since any elementary particle, massive or massless is an energy wave, hence QFT and the mass-energy equivalence E = mc2, they will too be smeared across our universal plane, that is the heat death of the universe, or rather cool death because the energy will be smeared out amongst an infinite universe and therefore be infinitely low, or as low as it can be, but i'm getting off track. Now you should see, that there is no way to reverse entropy like that, all we could do is ether make a giant cold substance for the energy to go into, still increasing entropy, or make a giant hot substance that would lose it's energy to the cold and once again increase entropy, but nothing that would stop our demise, no matter how advanced we, or other civilizations might be.

PS sorry for all the "amongst"'s "hence"'s and "infinite"'s, this post was way to redundant.  

1. Why entropy "must" increase?
2.If a civilization is able to create another universe, this is already violate the First Law of Thermodynamics. "JackDole wrote:I believe that a Type IV or Type V civilization can create an artificial universe, and thus survive a Big Rip."

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