'Pulsar in a box' reveals surprising picture of a neutron star's surroundings

October 11, 2018, NASA
Credit: NASA

An international team of scientists studying what amounts to a computer-simulated "pulsar in a box" are gaining a more detailed understanding of the complex, high-energy environment around spinning neutron stars, also called pulsars. The model traces the paths of charged particles in magnetic and electric fields near the neutron star, revealing behaviors that may help explain how pulsars emit gamma-ray and radio pulses with ultraprecise timing.

"Efforts to understand how pulsars do what they do began as soon as they were discovered in 1967, and we're still working on it," said Gabriele Brambilla, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and the University of Milan who led a study of the recent simulation. "Even with the computational power available today, tracking the physics of particles in the extreme environment of a is a considerable challenge."

A pulsar is the crushed core of a massive star that ran out of fuel, collapsed under its own weight and exploded as a supernova. Gravity forces more mass than the Sun's into a ball no wider than Manhattan Island in New York City while also revving up its rotation and strengthening its . Pulsars can spin thousands of times a second and wield the strongest magnetic fields known.

These characteristics also make pulsars powerful dynamos, with superstrong electric fields that can rip particles out of the surface and accelerate them into space.

NASA's Fermi Gamma-ray Space Telescope has detected gamma rays from 216 pulsars. Observations show that the high-energy emission occurs farther away from the neutron star than the radio pulses. But exactly where and how these signals are produced remains poorly known.

Various physical processes ensure that most of the particles around a pulsar are either electrons or their antimatter counterparts, positrons.

"Just a few hundred yards above a pulsar's magnetic pole, electrons pulled from the surface may have energies comparable to those reached by the most powerful particle accelerators on Earth," said Goddard's Alice Harding. "In 2009, Fermi discovered powerful gamma-ray flares from the Crab Nebula pulsar that indicate the presence of electrons with energies a thousand times greater."

Speedy electrons emit gamma rays, the highest-energy form of light, through a process called curvature radiation. A gamma-ray photon can, in turn, interact with the pulsar's magnetic in a way that transforms it into a pair of particles, an electron and a positron.

Explore a new “pulsar in a box” computer simulation that tracks the fate of electrons (blue) and their antimatter kin, positrons (red), as they interact with powerful magnetic and electric fields around a neutron star. Lighter tracks indicate higher particle energies. Each particle seen in this visualization actually represents trillions of electrons or positrons. Better knowledge of the particle environment around neutron stars will help astronomers understand how they produce precisely timed radio and gamma-ray pulses. Credit: NASA’s Goddard Space Flight Center

To trace the behavior and energies of these particles, Brambilla, Harding and their colleagues used a comparatively new type of pulsar model called a "particle in cell" (PIC) simulation. Goddard's Constantinos Kalapotharakos led the development of the project's computer code. In the last five years, the PIC method has been applied to similar astrophysical settings by teams at Princeton University in New Jersey and Columbia University in New York.

"The PIC technique lets us explore the pulsar from first principles. We start with a spinning, magnetized pulsar, inject electrons and positrons at the surface, and track how they interact with the fields and where they go," Kalapotharakos said. "The process is computationally intensive because the particle motions affect the electric and magnetic fields and the fields affect the particles, and everything is moving near the speed of light."

The simulation shows that most of the electrons tend to race outward from the magnetic poles. The positrons, on the other hand, mostly flow out at lower latitudes, forming a relatively thin structure called the current sheet. In fact, the highest-energy positrons here—less than 0.1 percent of the total—are capable of producing similar to those Fermi detects, confirming the results of earlier studies.

Some of these particles likely become boosted to tremendous energies at points within the current sheet where the magnetic field undergoes reconnection, a process that converts stored magnetic energy into heat and particle acceleration.

One population of medium-energy electrons showed truly odd behavior, scattering every which way—even back toward the pulsar.

The move with the magnetic field, which sweeps back and extends outward as the pulsar spins. Their rotational speed rises with increasing distance, but this can only go on so long because matter can't travel at the speed of light.

The distance where the plasma's rotational velocity would reach light speed is a feature astronomers call the light cylinder, and it marks a region of abrupt change. As the electrons approach it, they suddenly slow down and many scatter wildly. Others can slip past the light cylinder and out into space.

The simulation ran on the Discover supercomputer at NASA's Center for Climate Simulation at Goddard and the Pleiades supercomputer at NASA's Ames Research Center in Silicon Valley, California. The model actually tracks "macroparticles," each of which represents many trillions of or positrons. A paper describing the findings was published May 9 in The Astrophysical Journal.

"So far, we lack a comprehensive theory to explain all the observations we have from . That tells us we don't yet completely understand the origin, acceleration and other properties of the plasma environment around the pulsar," Brambilla said. "As PIC simulations grow in complexity, we can expect a clearer picture."

Explore further: The surprising environment of an enigmatic neutron star

More information: For more about NASA's Fermi mission, visit www.nasa.gov/fermi

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19 comments

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cantdrive85
2 / 5 (16) Oct 11, 2018
Their computer games using pseudoscientific claptrap are not going to explain anything that has to do with reality. Their "simulation" is in fact a simulated faerie tale of what is in fact a much simpler process similar to a strobe light.
Nik_2213
4.3 / 5 (11) Oct 11, 2018
@CD: Unlike a faerie tale, they can make falsifiable predictions. Go figure...
cantdrive85
2 / 5 (12) Oct 11, 2018
@CD: Unlike a faerie tale, they can make falsifiable predictions. Go figure...

Amusing, that's a swell thought but where is it? Only layers of ad hoc adjustments are added, falsification is never on the table.
jonesdave
3.3 / 5 (19) Oct 11, 2018
@CD: Unlike a faerie tale, they can make falsifiable predictions. Go figure...

Amusing, that's a swell thought but where is it? Only layers of ad hoc adjustments are added, falsification is never on the table.


Neutron stars are a proven fact. All they are doing is making a sim to see if the plasma environment predicted is actually matched by observations. Or, indeed, if observations that we don't currently have a handle on, can be explained by the sim. It's called science. It happens all the time.
Solon
2.1 / 5 (11) Oct 11, 2018
"Neutron stars are a proven fact."

Oy vey...
cantdrive85
2.5 / 5 (13) Oct 11, 2018
Neutron stars are a proven fact.

This statement displays a real proven fact, jonesdumb is an utter moron.
Whydening Gyre
4.6 / 5 (10) Oct 11, 2018
CD.
Why do you always start out with negative and denigrative commentary?
Surveillance_Egg_Unit
2.8 / 5 (9) Oct 11, 2018
CD.
Why does jonesdave always start out with negative and denigrative commentary?
says Whyde

Because that's what he does.
Surveillance_Egg_Unit
2.1 / 5 (7) Oct 11, 2018
"Neutron stars are a proven fact."

Oy vey...


Gesundheit!!
cantdrive85
2.2 / 5 (10) Oct 12, 2018
CD.
Why do you always start out with negative and denigrative commentary?

So you want to pretend that I haven't put up with negative and denigrative commentary for years?
dsylvan
3.7 / 5 (9) Oct 14, 2018
@CD
CD.
Why do you always start out with negative and denigrative commentary?

So you want to pretend that I haven't put up with negative and denigrative commentary for years?

It's what you live for--what makes commenting worth your while. Not the actual science.
jonesdave
3 / 5 (10) Oct 14, 2018
Neutron stars are a proven fact.

This statement displays a real proven fact, jonesdumb is an utter moron.


I'm sorry, woo boy? What were the GWs from a little while back? What was the EM from? Why did it all very well match with the predictions for what should happen in a neutron star merger? Good guesses, were they? Lol.
Besides, somebody that believes Earth used to orbit Saturn, (around its poles, no less), and that Venus got spat out of Jupiter, should have absolutely no problem with neutron stars. Eh?
If you think neutron stars are not a proven fact, show me the scientist who is saying that. Not braindead woo merchants; actual scientists.
cantdrive85
2.6 / 5 (10) Oct 14, 2018
Anything is possible with maths gymnastics.
barakn
3.3 / 5 (7) Oct 15, 2018
Physics matured from a qualitative science to a quantitative science centuries ago. Math is necessary to measure the relative ability of various hypotheses to explain observations, i.e. to identify which ones do better and which ones do worse. Complaints about "maths gymnastics" invariably come from people who performed poorly in math at school and are unnecessarily frightened and suspicious of it. The solution is to go back to school and learn more math, not loudly proclaim one's ignorance in every other post.
jonesdave
2.1 / 5 (7) Oct 15, 2018
Anything is possible with maths gymnastics.


Those were observations, you dummy. Try to keep up, thicko. You only have a problem with maths because nobody in your cult is proficient at it, and it has a habit of showing the crap you believe in to be impossible. Stick to mythology, woo boy.
cantdrive85
1.8 / 5 (5) Oct 15, 2018
"Physics is mathematical not because we know so much about the physical world, but because we know so little." Bertrand Russell

"Today's scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality." Nikola Tesla
jonesdave
2.1 / 5 (7) Oct 15, 2018
"Physics is mathematical not because we know so much about the physical world, but because we know so little." Bertrand Russell

"Today's scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality." Nikola Tesla


Couldn't give a sh!t woo boy. We are talking about observations here. Know what that word means, you dumb piece of crap? And it just so happens that the observations matched predictions. Whoda thunk it?
cantdrive85
2.6 / 5 (5) Oct 15, 2018
We are talking about observations here

Nope, computer games. Computer simulations is not an observation. And computer sims can look like anything you want them to look like given the garbage in.
jonesdave
2.1 / 5 (7) Oct 15, 2018
We are talking about observations here

Nope, computer games. Computer simulations is not an observation. And computer sims can look like anything you want them to look like given the garbage in.


No, thicko, you initially replied to my post, 23 hrs ago, about the detection of GWs and EM from a neutron star merger. Those are observations, you dumb fruitloop. Want the links to the numerous papers? Not that you'd understand them. I'll say it again, for the terminally stupid; neutron stars are a fact. End of story. And nobody is challenging that conclusion.

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