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Anomalous Pulsar In Binary System Stymies Theorists
Science Daily has word of a millisecond pulsar in the wrong kind of binary system that has astronomers scratching their heads. According to current models of pulsar evolution, such a system should have no way to develop. The pulsar J1903+0327, which rotates 465 times per second, seems to be in a highly elongated orbit around a Sun-like star. Quoting: "Astronomers think most millisecond pulsars are sped up by material falling onto them from a companion star. This requires the pulsar to be in a tight orbit around its companion that becomes more and more circular with time. The orbits of some millisecond pulsars are the most perfect circles in the Universe, so the elongated orbit of the new pulsar is a mystery."
See what happens when real physicists write SF!
Perhaps the pulsar is closely paired with another small star and the pair has just be captured by a larger star. Wonders never cease!
This will be the iron clad proof of Creationism! Only (insert your favourite supreme being here) could have put such an anomaly there!
All hail (insert your favourite supreme being here)!
I don't think it runs Linux.
Author: Chris Wright
Date: Mon May 5 13:50:24 2008 -0700
added support for elongated orbit millisecond pulsars.
"Glory is fleeting, but obscurity is forever." - Napoleon Bonaparte
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.
I've been working on simulations of the 2.6.25.4 kernel running on neutron stars. Shortly after getting the 256-node Beowulf cluster simulation booted up, the cluster encounters severe gravitational disturbances. These interfere with network communications. I asked a physicist, and he started muttering something about event horizons and black holes. I think we are going to need a better patch.
Arg, no. No, no, and no.
Momentum is not energy. They are separate quantities and are conserved separately. The mass of the star is, as I stated earlier, irrelevant. When you have two bodies, the bind energy DOES NOT CHANGE during an interaction without some other dissipation. Gravity is a conservative force.
Look, I appreciate that you're throwing ideas out there, but this is pretty basic physics that we have a good handle on. If you don't believe me (which is fine!), look some of this stuff up for yourself.
Also, for the record, the star is less massive than the pulsar: the diagram of the orbits that I saw made it pretty clear that the star has the larger orbit.
I'm trying to figure out what other energy would apply. It's more just an honest question (my physics is obviously more of the terrestrial sort). Would something have to shed mass or slam into an orbiting body or something similar, in order to be bound?
ad logicam Claiming a proposition is false because it was presented as the conclusion of a fallacious argument.
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.