A millisecond pulsar is a neutron star that is rotating about 600 to 700 times a second. Because of their strong magnetic fields, they produce strong beams of radio energy from the regions of their magnetic poles, and as they rotate these beams can point in our direction. As a result, we observe these neutron stars as radio bursts that pulse every 1 – 10 milliseconds. Hence their name.
Spirals
A while back I wrote about how general relativity predicts gravitational waves. While we haven’t yet observed gravity waves directly, we know they exist. That’s because gravitational waves carry energy away from their source, just as light waves carry light energy.
Glitch and Anti-Glitch
About a year ago in Nature astronomers reported evidence of an anti-glitch in the magnetar 1E 2259+586. You might remember from yesterday’s post that a magnetar is a neutron star with an extremely strong magnetic field. This particular magnetar is also a pulsar, meaning that the intense x-ray beams that stream from the magnetar’s polar region happen to be aligned so that we see it flash regularly. You can think of a pulsar as a kind of cosmic lighthouse, if you will.
Magnetars, Pulsars, and X-rays, Oh My!
One of the differences between astronomy and astrophysics is that astronomy is based upon observation, while astrophysics is about the underlying mechanism behind those observations. For this reason, many types of phenomena in the universe have multiple names depending on how we observe them. The reason for this is that typically astronomers start observing different phenomena, give them names, and then only later do astrophysicists figure out that they are different examples of the same thing. By then the names have already stuck.
Pico Arcseconds
One of the advantages of radio astronomy is that you can connect observations from radio telescopes thousands of miles apart. Done in the right way, this creates a radio interferometer that effectively makes a virtual telescope as big as the separation (baseline) of the individual telescopes. The bigger your telescope (or virtual telescope), the finer the detail of your image. When we talk about the detail level of an astronomical image, we usually talk about the angle of separation between two distinctly resolvable points. So a resolution of a tenth of a degree would mean you could resolve two points of light (such as stars) separated by at least that angle.
Little Green Men
In 1967 a PhD student named Jocelyn Bell detected a radio signal with an odd regularity. Patterns can be heard in all sorts of radio signals, but this particular signal was unusual in that it was a pulse with a period of 1.33 seconds. You can see this pattern in the figure above, and you can hear what the signal sounds like here.
Weeble Wobble
A magnetar is a neutron star with an extremely strong magnetic field, a billion times stronger than the strongest fields we can create on Earth. As a neutron star, magnetars also have very strong gravitational fields, with a surface gravity a hundred billion times that of Earth. Such a high gravity would seem to ensure that a magnetar is spherical, but a magnetar’s strong gravitational field could distort the star, making it more of an oblate spheroid. We’ve suspected that such a magnetic distortion could occur with magnetars, but now a research team seems to have found an example of this phenomenon.
Passing the Test
Recently popular-science websites have been buzzing with news of a new pulsar putting Einstein’s theory of gravity to its greatest test yet. In particular, some tout it as a test of alternatives to general relativity. While the attention this work has gotten in the press implies this is a new breakthrough, that’s not quite the case. So what’s the real deal on these latest findings?
Kick Me
Pulsars are neutron stars, formed when a large star explodes as a supernova. Because of this, one would expect a pulsar to lie within the surrounding supernova remnant, and to move at the same relative speed. But this is not the case with the Guitar Nebula. It seems that something must have caused the pulsar to move at great speed relative to the remnant. Given it a kick, as it were, hence the term pulsar kick (or neutron star kick). Given the mass of a neutron star (greater than that of our Sun) the only thing that could have provided such a kick would be the supernova itself.