How Neutron Stars Get Their Kicks

mustermark writes: "Now we may know why neutron stars zip through space at 1000 times the speed of a normal star. Massive stars have been shown to collapse aspherically, and chunks blown off in this process may recoil the neutron-star remnant in the opposite direction."

Comments

Well, duh!

[Kris_J]

From the article;

supernovae are not symmetrical in shape

Of course they're not symmetrical, because stars aren't symmetrical. There's an article over at space.com that dicusses our own sun's "hills and dales". And, I mean, hello - sunspots, flares, magnetic storms, CMEs. Here's a bit of space.com's article;

The most sensitive measurement ever made of a star's shape shows that our sun is speckled with tiny hills and dales, much like the surface of the ocean, University of Hawaii researchers said.

The Dateline

[paulproteus]

I particularly enjoyed the dateline.

"Jun 19, 2000 - ROCHESTER, N.Y. -- When a massive star runs out of nuclear fuel something extraordinary happens in the space of a few seconds: The star's core collapses from a radius of 1,000 miles into a tight, dense ball."

Wow, all that happens here in Rochester?

Jeez. I really have to get over to the University of Rochester more often then!

Kind of cool!

[tie_guy_matt]

As the star collapses, if one side is less dense than the other gravity will cause the density gradient to increase. This insures that when it expels matter more matter is expelled on one side than the other. I guess it would be possible to have a star that's density is so balanced that no gravitational gradiant will be produced, but the odds of this happening is so insanely low that stars ALWAYS get a density gradient and therefore always get a kick when they are formed.

Understanding the mechanics of the universe is important because it increases our knowledge of science in general. It may not be clear right now how understanding something that happens thousands of light years away (and therefore took place thousands of years ago) may be useful. But one day it will be useful. After all at first studying the planets didn't seem that useful but Newton used planetary motion when he was fathering classical physics.

What about Binary Neutrons?

[krystal_blade]

I'm not sure how long ago it came up, but it was theorized that the high rate of speed came from a close binary system where one Nova'd.

A closely matched binary system would trade accretion until the soon to be Neutron was orbiting a further away, but rapidly falling towards the slightly denser soon to be Nova. If the quasi Neutron star was far enough away when big brother lost his top, the shockwave, and infalling matter would actually push it to "ludicrous speed".

If the quasi neutron star was too close... well, it would still move (if not destroyed) but its chances of growing into an adult Neutron.

Any Accretion pulled off of the nova'd star would be stripped while moving, and the star would begin it's decay into a Neutron.

krystal_blade

Enter the Collector

[krystal_blade]

The neutron star is basically the wiseguy of the universe. Small, compact, and BAD AS HELL...

So, with Cosmic Inflation, coupled with moderate interest levels, people are gonna start lookin for other means of entertainment. (Do you know how much it costs to get a supernova light show?) Plus, there's always the tickets to those special event horizons, that everyone seems so hyped up on. And lets not forget that since the discovery of the Cosmic Background Radiation, everyone wants a microwave.

Everyone's gotta PAY for that stuff, and some people are being super dense, and writing rubber checks their atomic structure can't cash. Eventually, all those star banks get pissed, and they send in Guido, the Neutron Star to clear things up. He's got the gravity for Repo jobs, and the speed to get things done quickly... He probably carries around one of those Accretion(tm) golf clubs too, just in case.

There's just no getting around the speed this guy needs to get his job done, since nothing travels faster than a bounced check. And you think those black holes got any money? Hell no... They sucked down both theirs, and a whole lotta other paychecks during "binge week". Give em Guido Neutrono... He'll bust their kneecaps.

krystal_blade

Other chunks...

[pvcf]

OK, this article left me with one question... If these neutron stars accelerate due to matter being blown off the star, and assuming that this matter being blow off is less than the mass of the star, the expelled matter would obtain an acceleration greater than the remainder of the star.

So, if the neutron star is going so fast, how fast is the stuff it's blowing off going?

More importantly, where is it going?

Oops, that's two questions isn't it? DOH!!! Three!

....Paul

Re:Other chunks...

[bubbaswank]

I also answered a bit of this below, but I thought I would elaborate here...

Very early on in a supernova remnant's life the ejected material is moving very fast, 10-20,000 km/s. Within a few hundred years most of it is decelerated to less than half that. By a few 1000 years the material is moving a few to several 100 km/s. By 10,000 years (or a few times that) the ejecta slows to about 10 km/s, which is the average random velocity of the interstellar medium. At this point the remnant blends with the ISM and vanishes.

It is mostly going outward. BUT much of it is not going exactly radially outward. In all remnants where this has been measured there exists a significant non-radial component to the velocity. This could be caused by the asymmetric explosion, or the interaction with the surrounding medium.

True, the ejecta move faster than the neutron star. This is due to conservation of momentum.

Re:motion of stars

[mmontour]

Since there aren't really any signs in the Universe that say "I am perfectly stationary, measure from me"

Actually, there is a pretty good one - the microwave background radiation.

There is a nice picture here which shows the relative temperature of this radiation as seen from earth. It is clearly red-shifted in one direction and blue-shifted in the opposite direction, indicating that the earth is moving rapidly (600 km/s) in the direction of the blue-shift. Some of this velocity is our motion around the sun, some is the sun's motion in our galaxy, but most of the velocity is common to our entire local group of galaxies.

If we were "at rest" in the universe, the microwave background would be uniform in all directions [more precisely, the dipole component would be zero; quadrupole and higher terms would still be present]. However, distant stars and galaxies would still be moving away from us due to the expansion of the universe.

This is already known, but interesting nonetheless

[bubbaswank]

This theory has been in place for a long time. It is a well known fact that neutron stars are often moving with high velocities. Many such objects have had their proper motions (angular velocities) measured. It is also known that supernova remnants (the guts of a star after it explodes at the end of its life) are not spherical. This is the topic of research that I work on. To answer a question above I have measured motions in supernova remnants that vary by over a factor of two. That is, one side may be moving at 5,000 km/s and the other may be moving at 2,000 km/s. One can also see much more rich structure in the kinematics of these complex objects. For instance, I have found material moving inwards! Now that certainly is not a spherical explosion!

Interesting Articles on Neutron Stars

[alexburke]

Just thought some of you might like a more in-depth look at neutron stars. I've been doing some reading on neutron stars in the last few days, so I hunted around in my browser's history and found the two articles I had been reading.

The first one, by New Scientist, is a neat article on stars and their hunger for the planets around them.

The second one, by Scientific American, is a bit technical, but it describes how the X-ray emissions from neutron stars are being used to estimate their size.

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