Astrophysicists report first simulation to create a Milky Way-like galaxy

Aug 29, 2011 By Tim Stephens
This image of the Eris simulation shows the stars in the galaxy as observers would see it. Blue colors are regions of recent star formation, while redder regions are associated with older stars. The spiral arms are typically star-forming, and the central bulge is basically "red and dead." Credit: J. Guedes and P. Madau.

(PhysOrg.com) -- After nine months of number-crunching on a powerful supercomputer, a beautiful spiral galaxy matching our own Milky Way emerged from a computer simulation of the physics involved in galaxy formation and evolution. The simulation by researchers at the University of California, Santa Cruz, and the Institute for Theoretical Physics in Zurich solves a longstanding problem that had led some to question the prevailing cosmological model of the universe.

"Previous efforts to form a massive disk galaxy like the Milky Way had failed, because the simulated galaxies ended up with huge central bulges compared to the size of the disk," said Javiera Guedes, a graduate student in at UC Santa Cruz and first author of a paper on the new simulation, called "Eris." The paper has been accepted for publication in the .

The Eris galaxy is a massive with a central "bar" of bright stars and other structural properties consistent with galaxies like the Milky Way. Its brightness profile, bulge-to-disk ratio, stellar content, and other key features are all within the range of observations of the Milky Way and other galaxies of the same type. "We dissected the galaxy in many different ways to confirm that it fits with observations," Guedes said.

According to coauthor Piero Madau, professor of astronomy and astrophysics at UC Santa Cruz, the project required a large investment of supercomputer time, including 1.4 million processor-hours on NASA's state-of-the-art Pleiades supercomputer, plus additional supporting simulations on supercomputers at UCSC and the Swiss National Supercomputing Center. "We took some risk spending a huge amount of supercomputer time to simulate a single galaxy with extra-high resolution," Madau said.

The results support the prevailing "cold dark matter" theory, in which the evolution of structure in the universe is driven by the of dark matter ("dark" because it can't be seen, and "cold" because the particles are moving slowly). Gravity acted initially on slight density fluctuations present shortly after the Big Bang, pulling together the first clumps of dark matter, which grew into larger and larger clumps through the hierarchical merging of smaller progenitors. The ordinary matter that forms stars and planets (less than 20 percent of the matter in the universe) has fallen into the "gravitational wells" created by large clumps of dark matter, giving rise to galaxies in the centers of dark matter halos.

This comparison shows the Eris simulation (top) and the Milky Way (bottom). Credit: S. Callegari, J. Guedes, and the 2MASS collaboration.

For the past 20 years, however, efforts to reproduce this process in have failed to generate massive disk galaxies that look anything like the Milky Way, with its spiral arms in a large flat disk around a small central bulge made up of old stars. A realistic simulation of star formation was the key to Eris's success, Madau said.

"Star formation in real galaxies occurs in a clustered fashion, and to reproduce that out of a cosmological simulation is hard," Madau said. "This is the first simulation that is able to resolve the high-density clouds of gas where star formation occurs, and the result is a Milky Way type of galaxy with a small bulge and a big disk. It shows that the cold dark matter scenario, where dark matter provides the scaffolding for , is able to generate realistic disk-dominated galaxies."

To perform the Eris simulation, the researchers began with a low-resolution simulation of dark matter evolving to form the haloes that host present-day . Then they chose a halo with an appropriate mass and merger history to host a galaxy like the Milky Way and "rewound the tape" back to the initial conditions. Zooming in on the small region that evolved into the chosen halo, they added gas particles and greatly increased the resolution of the simulation. High resolution means tracking the interactions of a huge number of particles.

"The simulation follows the interactions of more than 60 million particles of and gas. A lot of physics goes into the code--gravity and hydrodynamics, star formation and supernova explosions--and this is the highest resolution cosmological simulation ever done this way," said Guedes, who is currently a postdoctoral researcher at the Swiss Federal Institute of Technology in Zurich (ETH Zurich).

The high resolution allowed for a more precise recipe for star formation. In a low-resolution simulation, with gas densities averaged out over relatively large areas, the threshold density for star formation has to be set so low that stars tend to form in diffuse gas throughout the galaxy. In the Eris simulation, the star-formation threshold allowed stars to form only in high-density regions, resulting in a more realistic distribution of stars.

An important consequence is that when stars explode as supernovae within these localized, high-density regions, the energy injected into the interstellar medium blows a lot of gas out of the galaxy. "Supernovae produce outflows of gas from the inner part of the galaxy where it would otherwise form more stars and make a large bulge," Madau said. "Clustered and energy injection from supernovae are making the difference in this ."

Explore further: Fermi satellite detects gamma-rays from exploding novae

More information: arxiv.org/abs/1103.6030

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LKD
3.7 / 5 (3) Aug 29, 2011
I'd love to see the images as it develops from a large diffuse gas cloud into a galaxy and how long it was proposed to take to see how that matches up to the galaxies seen 13 billion light years out.
LariAnn
2.7 / 5 (7) Aug 29, 2011
This simulation would carry more weight, IMHO, were all galaxies similar to ours. However, there are a number of other types, including some with large bulges and virtually no disk. I'd like to know if some older galaxies have been observed with a lot of young stars in the center bulge. If so, that would also argue against the idea that all galaxies form as in this simulation.
SemiNerd
3.7 / 5 (3) Aug 29, 2011
This simulation would carry more weight, IMHO, were all galaxies similar to ours. However, there are a number of other types, including some with large bulges and virtually no disk. I'd like to know if some older galaxies have been observed with a lot of young stars in the center bulge. If so, that would also argue against the idea that all galaxies form as in this simulation.

Read the article more closely. They specifically said they developed a number of simulations to the point where they got something at low res that matched a spiral galaxy (lots of people have done that), then went back and used those same starting conditions at high res.
ubavontuba
2.5 / 5 (21) Aug 29, 2011
I love that photo comparison of Eris and the Milky Way galaxy. So, how did they get the distant picture of the Milky Way? Did Captain Kirk send it through a worm hole with kind regards?

Anyway, that you can simulate a galaxy does not necessarily mean much. There's still no direct (laboratory) experiment which proves the existence of dark matter. Without that, this simulation is really little more than conjecture based upon suppositions (a house of cards).

And, 60 million particles is nothing (well, almost nothing). There's zillions of times more particles than that in just one of the grains of Splenda I'm stirring into my coffee... Oh! Looky there... I just modeled a spiral galaxy! LOL!

Deesky
4 / 5 (19) Aug 29, 2011
So, how did they get the distant picture of the Milky Way? Did Captain Kirk send it through a worm hole

There are many observations, in numerous spectral ranges, which combine to provide an accurate representation of our galaxy.

Anyway, that you can simulate a galaxy does not necessarily mean much.

It means quite a lot.

There's still no direct (laboratory) experiment which proves the existence of dark matter.

Nice use of qualifiers there. You've been burned on this issue before, so I guess you require them.
Deesky
4.4 / 5 (18) Aug 29, 2011
Without that, this simulation is really little more than conjecture based upon suppositions

It's based on the best evidence of how DM behaves from various lines of observation and measurement. Indeed, had they completely ignored DM, they would never get anything even approaching our galaxy (and others). But not only that, if DM is not used in simulations of the evolution of the universe from the BB, then the results look nothing at all like our universe.

And, 60 million particles is nothing (well, almost nothing). There's zillions of times more particles than that in just one of the grains of Splenda I'm stirring into my coffee

Argument from incredulity/ignorance doesn't bolster your case.
ubavontuba
1.9 / 5 (9) Aug 30, 2011
There are many observations, in numerous spectral ranges, which combine to provide an accurate representation of our galaxy.
Hardly. This is the best guess we have, and lots of it is extrapolated:

http://cdn.physor...anta.jpg

And this is the recent science it's based upon:

http://arxiv.org/...23v1.pdf

It means quite a lot.
It means we modeled something that looks kind of like a galaxy.

Nice use of qualifiers there. You've been burned on this issue before, so I guess you require them.
What are you talking about?

It's based on the best evidence of how DM behaves from various lines of observation and measurement.
Sure. It's looking more and more like the WIMP model wins out. But we already knew that.

Argument from incredulity/ignorance doesn't bolster your case.
You have no sense of humor at all, do you?

ubavontuba
2.5 / 5 (11) Aug 30, 2011
There are many observations, in numerous spectral ranges, which combine to provide an accurate representation of our galaxy.
Hardly. This is the best guess we have, and lots of it is extrapolated:

http://cdn.physor...anta.jpg

And this is the recent science it's based upon:

http://arxiv.org/...23v1.pdf

It means quite a lot.
It means we modeled something that looks kind of like a galaxy.

Nice use of qualifiers there. You've been burned on this issue before, so I guess you require them.
What are you talking about?

It's based on the best evidence of how DM behaves from various lines of observation and measurement.
Sure. It's looking more and more like the WIMP model wins out. But we already knew that.

Argument from incredulity/ignorance doesn't bolster your case.
You have no sense of humor at all, do you?

ubavontuba
1 / 5 (2) Aug 30, 2011
My apologies for the double post (above). the site went down between posting and editing.

Teddyrodo
not rated yet Aug 30, 2011
Isn't there a difference between 13 Byn yrs and 13 Byn light yrs?
bluehigh
1.7 / 5 (11) Aug 30, 2011
@Deesky

Anyway, that you can simulate a galaxy does not necessarily mean much.

It means quite a lot.


Such as? Or are you just being contrary again?

Argument from incredulity/ignorance doesn't bolster your case.


... better than no argument at all!
Thecis
5 / 5 (3) Aug 30, 2011
With former simulations, it has been concluded that NOT using dark matter into the equations ment that could not simulate a galaxy at all. This means that what they have done will actually have some meaning. It means that we cannot see all the mass that is present. This has been confirmed by multiple observers (most easy is of course the brown dwarfs which should be quite numerous)...

Of course simulations are based on emperical data. The equations are to difficult to solve completely without emperical data.
For those who doubt, solve the hamilton for 1 particle in a two dimensional box. When you succeed either do 2 particles or 1 particle in 3D...

If people who follow the Electrical/plasma Universe theories (etc) can provide the same data, the same simulations, why should the community doubt their claims?? (I know the world doesn't completely work like that but you have to start somewhere).
Thecis
5 / 5 (2) Aug 30, 2011
All in all, this simulation holds very much information. It is
a possibility the universe actually works like that.

As a famous investigator once said: "when you look at all the possiblities and eliminate those which are impossible, the true solution will present itself how improbable it may seem".

This means that also dark matter, as well as other options, should be looked at until we can cross out the ones that are impossible.

Good luck everyone!
Occupodies
1.7 / 5 (6) Aug 30, 2011
I like how they repeatedly said the Milky Way is a spiral galaxy, when in reality we don't know and only suppose that it is.
Deesky
4.7 / 5 (12) Aug 30, 2011
Isn't there a difference between 13 Byn yrs and 13 Byn light yrs?

The former is a measure of time and the latter is a measure of distance.
Deesky
4.7 / 5 (13) Aug 30, 2011
I like how they repeatedly said the Milky Way is a spiral galaxy, when in reality we don't know and only suppose that it is.

No, the reality is that we DO know that the Milky Way is a (barred) spiral galaxy. That is not conjecture, but observation, made by the Spitzer space telescope, et al.

Ricochet
not rated yet Aug 30, 2011
If you zoom in to one of the planets in this solarsystem, you can see:
http://www.google...p;zoom=1
bluehigh
1.6 / 5 (13) Aug 30, 2011
No, the reality is that we DO know that the Milky Way is a (barred) spiral galaxy. That is not conjecture, but observation, made by the Spitzer space telescope, et al.


Well go ahead and cite a reference and at least we might have some information other than just your opinion. Put up or Shut up.

FrankHerbert
2.7 / 5 (20) Aug 30, 2011
No, the reality is that we DO know that the Milky Way is a (barred) spiral galaxy. That is not conjecture, but observation, made by the Spitzer space telescope, et al.


Well go ahead and cite a reference and at least we might have some information other than just your opinion. Put up or Shut up.



"It is agreed that the Milky Way is a barred spiral galaxy..." (Wikipedia)

For being so wrong you are really quite rude about it.
mmead
3.2 / 5 (5) Aug 30, 2011
I agree with ubavontuba....its a nice simulation....but in the end it is just a simulation based on years and years of theory and indirect observations.
bluehigh
1.7 / 5 (10) Aug 30, 2011
When did Wikipedia become a reputable source of information Frank? Even in elementary school the kids are not permitted to cite Wikipedia.

I did not suggest that the Milky Way is or is not a Spiral Galaxy, I simply noted that just being negative or saying someone is wrong counts for nothing unless explained.

No and Wrong as comments dont contribute anything to the discussion and are far more rude. I would have expected you to know that especially since you took the trouble to look for a source of verification. However your reference as it stands is hearsay.

Hengine
5 / 5 (11) Aug 30, 2011
bluehigh, is NASA a good enough citation?
http://imagine.gs...14a.html
Yellowdart
2.3 / 5 (6) Aug 30, 2011
With former simulations, it has been concluded that NOT using dark matter into the equations ment that could not simulate a galaxy at all. This means that what they have done will actually have some meaning.


Because former simulations all run under the assumption of billions of years, so a filler, aka dark matter is needed. Further, this article clearly expresses past failures even with DM included.

There's two issues though I find with this. What is the implications of high density vs. low density in their simulation and is high density reflective of actual conditions? Does that equate to high concentration of material available?

Secondly, this article doesn't say if they accounted for frame dragging or gravity of the Milky Way itself, which was discussed in another recent article on physorg.

jsa09
5 / 5 (2) Aug 30, 2011
The immense difficulty in doing simulations of this type relates back to simultaneity of movement. Multi-body gravity simulations are most difficult and I am not convinced that this simulation (or any other) has actually solved this problem. Running through iterative calculations is about as close as we have, and the more bodies the more interference that needs to be accounted for. 60,000 trackable units does little to account for gas clouds and accumulation of bodies to form a star.

It is a good effort just the same, but any resemblance to reality is merely superficial.
ubavontuba
2.5 / 5 (8) Aug 30, 2011
It is a good effort just the same, but any resemblance to reality is merely superficial.
Excellent cutting to the chase there, jsa09.

What we learn from simulations like this is where to look for dark matter, if it works as we suppose it works. But, until it's isolated and quantifiably described, it's nothing more than a ghostly supposition.

lengould100
5 / 5 (1) Aug 31, 2011
There's still no reason to suppose that the explanation for galaxy formation is some undetectable "dark matter". Its far more likely that our equations of gravity are missing a factor which diminishes the graviational effect with distance. MOG.
GSwift7
3 / 5 (6) Aug 31, 2011
There's two issues though I find with this. What is the implications of high density vs. low density in their simulation and is high density reflective of actual conditions? Does that equate to high concentration of material available?


Observations of star formation regions show that stars only form in relatively high density gas clouds, or more specifically, higher density regions of gas clouds (nubulae).

The term "high density" is relative though. If you were floating in the middle of one of those "high density" areas, you would still not be able to see any visible sign of the gas around you. You're still talking about only a few molecules or ions per cubic volume of space. The air here on Earth is many times more dense, and you can't see it, for example. Those would later combine to form dust grains (aerosols). That's what we observe when we look at places like the Orion Nebula, so that's what the theory assums.
Pyle
2.6 / 5 (5) Aug 31, 2011
There's still no reason to suppose that the explanation for galaxy formation is some undetectable "dark matter". Its far more likely that our equations of gravity are missing a factor which diminishes the graviational effect with distance. MOG.
Too much Kool-Aid. I like MOG, but there is plenty of reason to suppose for dark matter, in addition to additional baryonic matter we can't "see".

I look on the simulations kind of like Eddington with his eclipse measurement. If the DM hypothesis proves out, we still might hold this simulation up as a confirmation of the theory even though it is ultimately determined the simulation was flawed. And with only 60,000,000 particles it can't help but be flawed.
FrankHerbert
2.2 / 5 (16) Aug 31, 2011
When did Wikipedia become a reputable source of information Frank? Even in elementary school the kids are not permitted to cite Wikipedia.


My using wikipedia was meant to be taken as an insult, but I guess that was lost on you. You could have performed any number of searches in google to find out you were wrong before being so righteously rude in your ignorance. You could have actually checked wikipedia's source (like I did ;-) ).

I also wanted to see if you would attack the source, which is specifically why I used wikipedia. Generally, the only time I see someone rail against wikipedia is when they are really wrong and refuse to accept they may be so. Upon seeing the information in wikipedia, you automatically disregarded it instead of trying to vet wikipedia's source or finding an alternative one that may or may not support it.

In an academic setting I would not use wikipedia, but when dealing with someone that isn't interested in evaluating his own ideas, its appropriate.
GSwift7
2.6 / 5 (5) Sep 01, 2011
Frank, I've had the same issue with Bluehigh in other threads. He gave me 1/5 for using wiki. I suspect he is actually the same person as a couple other profiles and/or is very young and not a very good critical thinker. He's certainly not very good at debate or fact checking before he posts. Just ignore him unless he posts something that is totally wrong. In that case, just post a correction with links for the benefit of everyone else. Don't get into an argument with him. It's a waste of time. He might even be an alternate account for howhot/calliban. They certainly have the same posting habits.

I gave more solid references, including the USGS, and he still didn't like my references because they don't agree with his wild speculation and agenda. Don't bother.
GSwift7
2 / 5 (4) Sep 01, 2011
Frank is right as far as I can see. This is basic stuff.

Bluehigh doesn't ever give references at all, but derides other people who do. Wiki can be either a good reference or a bad one. The key to using wiki is looking up the source of the info in the wiki before you use it as a reference. As long as you make sure that the wiki has good info, it's as good a source as some and a better source than others. The assumption that wiki is wrong is falacy. Bluehigh is using tacticts of personal attack, illogical arguments, and unsupported arguments, as well as emotional appeal and comedy to support his view. There's nothing corect or supportable about his point of view. I will stick with the evidence, regardless of my own political preference. When I can't support my political views with facts I'll just keep quiet. Personal and irrational attacks aren't helpful to support my side. It just makes a person look like a fool and detracts from the persuasiveness of thier side. Let him be a fool
bluehigh
1 / 5 (2) Sep 01, 2011
I guess it must be that neither of you can read. I did NOT offer an opinion in these comments regarding the topic. I simply pointed out that you both quickly descend into insults when you are unable to support you views. As in another thread GSwift7 it is your credibility that is in question and I gave you 1/5 for using derogatory terms and not about using Wikipedia. Same with you Frank, you are too quick to say "Wrong" and "No" to others without backing up your argument.

GSwift7
2.6 / 5 (5) Sep 01, 2011
When someone says something that's clearly wrong, I say so. I have been able to back that up with references. I used wiki first. When you complained about wiki, I provided other sources. I usually don't use wiki, unless it's basic stuff like this.

Over the past couple of years I've learned a LOT about how to spot BS around here. There's even a couple people I used to fight with regularly whom I now converse with by PM as friends. It's not about making anybody look bad for me any more. I just enjoy the challenge of trying to figure out when these articles are saying something fishy and correcting people who post nonsense or political propaganda.
bluehigh
2.1 / 5 (7) Sep 01, 2011
Deesky has in the past been inclined to descend into "No" and "Wrong" rather than engage in productive discussion. However I notice in another thread today that Deesky made a reasoned comment without the rudeness - I gave him 5/5. Well done Deesky.
bluehigh
1.8 / 5 (5) Sep 01, 2011
GSwift7: Initially I complained that you became rude to others. Review the (other) thread and you will see that I did not take a position in the discussion and in fact I tend to agree with you. Instead of comprehending you jumped to conclusions. If you believe you have a monopoly on whats right and wrong then you need to seek professional help.
GSwift7
1 / 5 (1) Sep 01, 2011
Yeah, I've given you some 5's too I think. I don't hold a grudge as soem people do. Deesky has been around here a while. He knows how to make a good point when he wants to, as well as be a butt-head. lol
GSwift7
1 / 5 (1) Sep 01, 2011
GSwift7: Initially I complained that you became rude to others.


Yeah, I got fed up with howhot. guilty as charged. He earned it thoug, and he was wrong as usual. I was responding to his personal attack against me. I'm human I guess. lol. Evidence seems to suggest that I am. :)
GSwift7
1 / 5 (1) Sep 01, 2011
kinda an interesting thread here, though way off topic. Posting habits are studied by social science quite a bit. It's really a unique form of communication and raises a lot of cool questions about personality traits and such. Not to mention how easy it is for someone to misunderstand something typed by someone else.

I try to keep the serious posters seperate from the casual ones. Howhot is a habitual poster who repeatedly posts stuff that he just makes up in his head. I don't give him much slack. Someone who is new or just makes an occasional mistake (like me) deserves a lot of courtesy, but howhot is a repeat offender and I think he does it on purpose semetimes. I just get tired of him, so I'm harsh with him. It's not like I treat other people that way, really. I promise.
bluehigh
2 / 5 (8) Sep 01, 2011
Its good to disagree sometimes. I enjoy a lively discussion. Just to clarify; yes I can be a fool, I am human too. I am far from young. I do not have any other profiles. I enjoy a a bit of comedy to let the steam out of some of the discussions. I hope that clears the air a bit and we can continue to exchange views.

GSwift7
1 / 5 (1) Sep 01, 2011
Okay, that's fair. Feel free to ask me for references any time you think I'm making stuff up. I like doing that. I'm even wrong sometimes.

On a totally differeent note, the biggest problem I have is when people say stuff and try to make it sound more concrete than it really is. Lots of studies and press releases do that. That's my biggest pet peeve. I LOVE pointing out the uncertainties and unspoken problems when they deliberately leave them out. That's fun for me. lol. I'm a geek.

howhot hates it when I point out those things in pro-invironmental subjects. That's his thing against me. I do it with non-environmental stuff too though. He's just a big tree hugger kinda guy. I like women better, lol.
MorituriMax
5 / 5 (2) Sep 02, 2011
Isn't there a difference between 13 Byn yrs and 13 Byn light yrs?

The former is a measure of time and the latter is a measure of distance.


Baloney, "You've never heard of the Millennium Falcon?It's the ship that made the Kessel Run in less than twelve parsecs." - Han Solo

Hah!
Temple
5 / 5 (4) Sep 03, 2011
Baloney, "You've never heard of the Millennium Falcon?It's the ship that made the Kessel Run in less than twelve parsecs." - Han Solo


Complete aside here.

There are a number of possible constructions of a "run" in which the total distance a ship travels is directly proportional to its speed during the "run".

In the easiest to comprehend case, imagine a Kessel Run where the objective is to chase down two ships both leaving the same location going in opposite directions. The faster your vessel, the less distance you'd have to travel.

Actually, the simplest case would be a Kessel Run where You travel a straight line between two fixed points. Relativistically speaking, the faster you travel, the less distance you actually travel when compared to the distance measured by a 'stationary' observer. For example, if Kessel is 15 parsecs from Coruscant (as measured by those motionless with respect to those systems), then a ship traveling at 0.6c would measure 12 parsecs between them.
GSwift7
1 / 5 (1) Sep 06, 2011
Temple:

Cheers, you get a drink on me. NICE job. Relativistic physics is truely cool stuff. 5/5 and my vote for best comment of the day.
Ricochet
not rated yet Sep 07, 2011
More simply, it could be that the Kessel Run was a race up to a certain speed, or a timed race where the ship that travels the farthest in a set time is the winner.
Ricochet
5 / 5 (1) Sep 07, 2011
Given that this has nothing to do with actual science, I feel a Wikipedia reference is ok here...
http://en.wikiped...m_Falcon

As per the article:
On the A New Hope DVD audio commentary, Lucas comments that, in the Star Wars universe, traveling through hyperspace requires careful navigation to avoid stars, planets, asteroids, and other obstacles, and that since no long-distance journey can be made in a straight line, the "fastest" ship is the one that can plot the "most direct course", thereby traveling the least distance.

So, there's one of life's great mysteries solved...
Next up, The Shampoo Principle:
Why does it take so much less shampoo to wash your hair after the 1st wash?

And yes, someone actually named it that, and couldn't figure it out...