Physicists Measure the Skin of a Nucleus

ScienceNOW ^ | 2 March 2012 | Adrian Cho

[GeronL]

interesting.

[U-238]

It will tell us a lot about a neutron star.

[TXnMA]

Very interesting! Also, a nice change from discussions of sluts, etc...

[U-238]

This is cutting edge astrophysics stuff.

[HiTech RedNeck]

I wonder how scientists can conclude that the thickness of neutrons on the surface of a neutron star is the same as that on the surface of lead nuclei here on earth. Are neutrons unsquishable?

[Boogieman]

” Subtracting the known proton radius revealed a neutron skin 0.33 millionths of a nanometer thick, give or take about 50%”
...
“The PREX measurement suggests that the neutron skin of lead-208 is twice as thick as more-precise but model-dependent methods indicate.”

Hmm, so the measurement suggests it is twice as thick as previous measurements, but they estimate margin of error at 50%? Interesting stuff, but I can’t get too excited about the results with those numbers.

[U-238]

If you collapse a neutron star further it turns into a black hole.

[U-238]

What determines whether a star is going to be a neutron star or a black hole is the amount of mass the star.A star with mass greater than 3 times the Sun’s gets crushed into a single point, which we call a black hole

[Boogieman]

From what I understand, the neutrons themselves aren’t being compressed so much as the space between them gets smaller. The neutrons don’t physically push against each other, they resist the compression with something called degeneracy pressure. They can’t occupy the same space, so they will change states before that happens, which creates this pressure that resists the gravitational pressure.

[U-238]

You are correct.

[U-238]

But will electron degeneracy pressure will halt the gravitational collapse of a star if its mass is below the Chandrasekhar Limit?. A star exceeding this limit and without usable nuclear fuel will continue to collapse to form either a neutron star or black hole, because the degeneracy pressure provided by the electrons is weaker than the inward pull of gravity.

[count-your-change]

” There’s a possibility to set your skin a-tingling.”

50%, more or less, it does, it really does.

[SunkenCiv]

Thanks GeronL.

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[Boogieman]

“But will electron degeneracy pressure will halt the gravitational collapse of a star if its mass is below the Chandrasekhar Limit?”

At that point, you are asking the wrong guy :)

I’d suppose that if gravity can’t overcome the electron degeneracy pressure, the star would be stable, but I don’t know enough about how all the reactions at work in the star to say whether or not it would stay that way, just because the mass is below the limit to form a neutron star. It could still go supernova, couldn’t it?

[bigheadfred]

Also, a nice change from discussions of sluts, etc...and a lot of other things like the thickness of its crust, the response of its surface to explosions, et cetera...and black holes.

Thanks for the “string theory” ping, civ.

[MHGinTN]

Neutrons are the opposite of sluts don’tchaknow.

[allmost]

There is speculation of various intermediate degenerate star stages, quark stars for example. I think the recent interest in neutrino measurements may affect current models. Just a hunch.

[allmost]

Metrology at its finest.

[AFPhys]

Agreed: the result announced here is not something to get excited about.

However, the important part of this is that this experimental method promises to be able to produce a much better measurement of the neutron skin than previous methods. THAT is the point, and regardless of what that result proves to be, it will be a very important piece of information to know. The exciting thing here is the “proof of principle” that this experimental method is viable.

This data is important enough that if this team is unable to use this specific apparatus to produce sufficient accuracy, certainly there will be a drive to build a follow-on apparatus with sufficient stability to accomplish the task.