The Vela Pulsar

If you could see in X-rays, one of the brightest things you’d see in the night sky is the Vela pulsar. It was formed when a huge star’s core collapsed about 12,000 years ago.

The outer parts of the star shot off into space. Its core collapsed into a neutron star about twice the mass of our Sun—but just 20 kilometers in diameter! Today it’s spinning around 11.195 times every second. As it whips around, it spews out jets of charged particles moving at about 70% of the speed of light. These make X-rays and gamma rays.

The Chandra X-ray telescope made a closeup video of the Vela pulsar! It shows this jet is twisting around.

But the most interesting part of all this, to me, are the ‘glitches’ when the neutron star suddenly spins a bit faster. Let me tell you a bit about those.

First, I can’t resist showing you what happened to the star that exploded. It made this: the Vela Supernova Remnant. It’s so beautiful!

This photo was taken, not by a satellite in space, but by Harel Boren in the Kalahari Desert in Namibia!

Then, I can’t resist showing you a little movie of the Vela pulsar… slowed down:

This was made using the Fermi Gamma-Ray Space Telescope. The image frame is large: 30 degrees across. The background, which shows diffuse gamma-ray emission from the Milky Way, is shown about 15 times brighter than it actually is.

Then I can’t resist showing you a closeup photo of the Vela pulsar, taken in X-rays by the Chandra X-ray Observatory:

The bright dot in the middle is the neutron star itself, and you can see one of the jets poking out to the upper right, while the other is aimed toward us.

Now, about those glitches.

Since it’s putting out powerful jets, which carry angular momentum, we expect the Vela pulsar to slow down—and it does. But it does so in a funny way: every so often there’s a glitch where it speeds up for about 30 seconds! Then it returns to its speed before the glitch—gradually, in about 10 to 100 days.

What’s going on? A neutron star has 3 parts: the outer crust, inner crust, and core. The outer crust is a crystalline solid made of atoms squashed down to a ridiculous density: about 10¹¹ grams per cubic centimeter. But the inner crust contains neutron-rich nuclei floating in a superfluid made of neutrons!

Yes: while helium becomes superfluid and loses all viscosity due to quantum effects only when it’s really cold, highly compressed neutrons can be superfluid even at very high temperatures And the funny thing about a superfluid is that the curl of its flow is zero except along vortices which carry quantized angular momentum, coming in chunks of size ℏ.

Glitches must be caused by how the outer crust interacts with the inner crust. The outer crust slows down. The inner crust, being superfluid, does not. This can’t go on forever, since they rub against each other. So it seems that now and then a kind of crisis occurs: in a chain reaction, vast numbers of superfluid vortices suddenly transfer some angular momentum to the outer crust, speeding it up while reducing their angular momentum. It’s analogous to an avalanche.

So, we are seeing complicated quantum effects in a huge spinning star 1000 light years away!