Cheating to create the perfect simulation: Physicists on the way to describe the inside of neutron stars

Jan 17, 2013
PD Dr. Axel Maas and colleagues from the Universities of Jena and Darmstadt (both Germany) have succeeded in simulating the strong atomic nuclear interactions to enable its calculability while at the same time preserving the typical characteristics of a neutron star. Credit: Photo: Jan-Peter Kasper/FSU

The planet Earth will die – if not before, then when the Sun collapses. This is going to happen in approximately seven billion years. In the universe however the death of suns and planets is an everyday occurance and our solar system partly consists of their remnants.

The end of stars – suns – rich in mass is often a neutron star. These "stars' liches" demonstrate a high density, in which atoms are extremely compressed. Such neutron stars are no bigger than a small town, but heavier than our sun, as physicist PD Dr. Axel Maas of the Jena University (Germany) points out. He adds: "The atomic nuclei are very densely packed." Compared to atoms, like water, the nuclei of neutron stars are as tightly packed as a bus with 1.000 passengers crowded together in comparison to a bus with only the driver on board. In these densely packed atomic nuclei, so-called "nuclear forces" are at work. They keep the neutron star together and are responsible for its "eternal life" – and for the last 35 years the strong nuclear interactions were amongst the greatest challenges of .

Together with colleagues from the Universities of Jena and Darmstadt (both Germany) Axel Maas has succeeded in simulating the strong atomic nuclear interactions to enable its calculability while at the same time preserving the typical characteristics of a neutron star. "It is the first theory for such a tight package," the Jena Physicist says. Previously simulations trying to specify the matter inside of neutron stars collapsed far too much in size and yielded the wrong properties time and again – even on the most . "These simulations didn't work because there are too many atomic nuclei," Maas explains the problem, whose solution the world of physics has come closer to due to the calculations of the Jena researchers. To get there, the scientists did so many calculations at the Loewe Center for Science Computing (CSC) in Frankfurt, that it would have taken a single PC approximately 2.500 years to do the same.

"We weren't able to solve the initial problem either," Axel Maas concedes, as algorithms are not (yet) powerful enough. However, the Jena physicist who had been researching this problem since 2007 and his colleagues "reached a new level of quality". They found a "modification of the theory for such a tight package", Maas says. And thus they enabled nuclear material to be simulated. Most characteristics of the neutron star are being preserved with the Jena method, but now they enabled its calculability.

The team accomplished this big step forward by intelligently modifying the and by solving the stacking problem of the atoms. That they were at the same time 'cheating a bit', the freely admit. However, Maas firmly believes: "We found the best possible shortcut". Now they know "what is relevant for the original simulation".

Now this new verifying method is available for numerous questions and theories about neutron stars and very dense packages. Maas already knows of first groups of scientists who are planning to use the Jena findings to work with them and to carry them further. The scientists involved are already in the process of enlarging the simulation and to verify the results: the results enabling scientists to understand the inside of eventually.

Explore further: Experiment with speeding ions verifies relativistic time dilation to new level of precision

More information: Axel Maas, Lorenz von Smekal, Björn Wellegehausen, Andreas Wipf: The phase diagram of a gauge theory with fermionic baryons, Physical Review D 86, 111901 (Rapid Communication) (2012). This article is available for free online: arxiv.org/abs/1203.5653

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rkolter
5 / 5 (6) Jan 18, 2013
The first paragraph of this article needs to be taken out back and shot.
cantdrive85
1 / 5 (5) Jan 18, 2013
The team accomplished this big step forward by intelligently modifying the nuclear forces and by solving the stacking problem of the atoms. That they were at the same time 'cheating a bit', the physicists freely admit. However, Maas firmly believes: "We found the best possible shortcut". Now they know "what is relevant for the original simulation".


Gotta love "science" and the faith (firmly believes?) it requires.
Modernmystic
3.7 / 5 (3) Jan 18, 2013
In these densely packed atomic nuclei, so-called "nuclear forces" are at work. They keep the neutron star together and are responsible for its "eternal life"


Call me crazy, but I thought it was gravity that kept a neutron star together. I didn't know neutrons were attractive to each other via the strong, weak, or EM forces.

Quite the contrary I thought if you shut off gravity "neutronium" would "explode". There would be nothing keeping neutrons that cozy....

Am I missing something (no sarcasm)?

Are they talking about the Palui exclusion principle and what's keeping it from COLLAPSING further? If so it's an odd way to parse the phrase isn't it?
antialias_physorg
5 / 5 (5) Jan 18, 2013
I didn't know neutrons were attractive to each other via the strong, weak, or EM forces.

Not so much EM, but strong nuclear force keeps nucleons together. That's why the nucleus of an atom doesn't fly apart (as it would otherwise, because all the positively charged protons in close proximity repel each other with great force)

Once the electrons are pushed into the protons to make neutrons in a neutron star collapse you have the strong nuclear force and gravity pulling this stuff together
(now unopposed by the EM force, although to be exact there is still some EM force because the neutron is composed of 1 up and 2 down quarks with charge 2/3 an -1/3 respectively - which gives the neutron itself some internal stability from collapsing even further)

Gotta love "science" and the faith (firmly believes?) it requires.

If you think science requires belief then you haven't understood what science is. At all.
Modernmystic
5 / 5 (2) Jan 18, 2013
Not so much EM, but strong nuclear force keeps nucleons together. That's why the nucleus of an atom doesn't fly apart (as it would otherwise, because all the positively charged protons in close proximity repel each other with great force)


Thanks for the info anti! I've been thinking about this stuff all wrong up until now. I didn't know neutrons would "stick" together if just left to their own devices without gravity.
antialias_physorg
5 / 5 (6) Jan 18, 2013
There's an interesting talk by Feynman (who was involved in the Manhatten project) in which he argues that we actually don't have 'nuclear' weapons but merely 'electrostatic' weapons.

The neutrons in a nucleus keep the nucleus stable by mingeling with the protons - due to the strong nuclear force between nucleons being stronger at that range than the electrostatic repulsion - and thereby keep the protons 'far enough apart' so that they stay in the nucleus.

When a U-235 decays it emits a neutron. This destabilizes the nucleus (because of the above: less neutrons to keep the protons apart). So the nucleus splits with great force driven by EM repulsion of the now too close protons that can overpower the strong nuclear force. This is the explosive energy of the bomb.

The strong nuclear force is actually a NEGATIVE contribution to the reaction because it wants to keep the nucleons together.
vacuum-mechanics
1 / 5 (4) Jan 18, 2013
"The atomic nuclei are very densely packed…. In these densely packed atomic nuclei, so-called "nuclear forces" are at work. They keep the neutron star together and are responsible for its "eternal life" – and for the last 35 years the strong nuclear interactions were amongst the greatest challenges of theoretical physics.

This seems to be the familiar conventional explanation; but the problem is that there is no explanation which tells us how the 'nuclear force' works! Maybe this physical view of the mechanism could help us to understand it.
http://www.vacuum...=4〈=en