Slashdot videos: Now with more Slashdot!

The article discusses this option, and actually finds it the most satisfying explanation. -

Most certainly a quite intriguing possibility.

What the heck are you talking about? If you have a positive relative energy before the encounter (which you must if you start not in orbit), you must dissipate energy in order to get captured into orbit (which requires a negative relative energy). The masses of the bodies involved do not change that simple physics.

You miss the point. They cannot be in orbit if they started out not in orbit UNLESS there is energy lost during the capturing. This is basic physics stemming for binding energies.

With planets, you can dissipate energy this with atmospheric drag, firing rockets (if you're a spacecraft), or three-body capture*. Only the last of these works with stars, and that's a dubious proposition since the millisecond pulsar would probably have been pretty close to its partner before the capture making it hard to strip during the encounter.

* In the interest of honesty, tides and gravity waves might do it, too, but in practice, their timescale for action is much too long to assist a capture.

You are correct that you need a dissipation mechanism to capture a pulsar into a new orbit.

For this system, assuming it started out in the dense stellar environment in a globular cluster, exchange encounters between multiple stars (3 or 4, i.e. single-binary or binary-binary) can provide the dissipation since the lowest mass stars (i.e. not the pulsar) tend to get energy boosts and are then ejected from the encounter. Alternatively, as you suggest, tides during a very close encounter can lead to a capture.

However, for this system, we have reasons for thinking that a triple system origin is a better explanation than an exchange encounter and subsequent ejection from a globular cluster (all this is described in the paper which will be available on the arXiv tomorrow night and which is on the Science website now).

Scott

For the triple scenario you never have to capture a pulsar. You only have to have the triple stellar system survive the supernova that created the neutron star (i.e. pulsars are neutron stars) and then subsequently, one of the other stars has to "recycle" the neutron star into a millisecond pulsar via accretion. The recycling process happens when a "normal" main-sequence star evolves into a red giant and dumps its outer envelope into a disk around a companion neutron star. When recycling is finished, you are left with a pulsar-white dwarf "binary" in a close-in orbit, and a main-sequence star orbiting both of those in a much larger orbit.

Scott

PS: Note that there is a another slightly different triple scenario that we mention in the paper where, continuing from above, the pulsar ablates away its white dwarf companion with a relativistic wind over a billion years or so and we are left with the pulsar main-sequence binary that we apparently see now.

Here, I know this is a little backward, but it's cool and it illustrates what is conserved. Try it yourself: http://isthis4real.com/orbit.xml [isthis4real.com]

It's also wrong. The creationist propaganda that comes with it is exactly why I get pissed off at creationists and ID people. They try to use flawed scientific arguments that sounds right to the uneducated.

It ignores gravitational interactions with other bodies in the solar system, ignores friction with the atmosphere (although it does include some type of friction when the two bodies are actually touching one another) when you start at ground level, and it doesn't allow you to move the "outer space" starting point.