Rare Lone Neutron Star Found Nearby

F4_W_weasel sends us to the BBC for news of the eighth lone neutron star ever discovered. It has no associated supernova remnant, binary companion, or radio pulsations. It's in our stellar neighborhood, at most 1,000 light years away. The object emits all its radiation (as far as wa can detect with current instruments) in X rays. The object is called Calvera, after the bad guy in The Magnificent Seven — which is itself the collective nickname for the seven such objects previously known.

Re:Dragon's Egg

[fishdan]

I was hoping that it would have some weird tidal effect [wikipedia.org].

How certain are they about the radio noise?

[jd]

Let's face it, a pulsar shoots incredibly focussed beams of radiation from the poles and the poles alone. It is so incredibly focussed that even though all the object is doing is spinning off-axis by a small amount, we only see clearly-defined pulses. All it requires is that we're never inside that very narrow cone that gets a signal, and we would observe something from which we would never get any pulses.

There are also other variants of these objects - magnetars, for example - that are, if not well-known, then at least recognized and classified.

To decide this could be something totally new is an interesting decision but nothing in the press release is telling me why they have made that specific decision over, say, merely seeing a regular pulsar at too great an angle to ever see the pulses.

could be an off-axis pulsar

[renard]

As you say, jd, it could be an off-axis pulsar. (Note that we did do a search for radio pulsations, and none were seen.) The "off-axis pulsar" hypothesis is what we are banking on when we say it might be the closest neutron star to Earth (250 to 1000 light years). The current record-holder is 1RXSJ1856.5-3754, at 540 light years.

None of the known radio pulsars are closer to Earth than that.

Cheers,
renard / Derek Fox

Re:How certain are they about the radio noise?

[rerutledge]

Actually, the "new discovery" part is that we used a standard method to discover a specific class of neutron star -- the isolated, X-ray bright, radio dim class -- but found an object that, if we assumed it was a member of that class, would have placed it well outside the galactic plane. That offends theorists, mightily, since they are unlikely to be produced in SNe up there (no stars) and cool to quickly to travel there from the plane, unless this particular object is moving with a velocity much much greater than ever observed from a neutron star before (>5100 km/sec; 300 km/sec is more typical). We compared the NS with other classes we know; and it just doesn't fit well with those, with the exception of a radio pulsar whose beam does not cross our line of sight. If that is true, then Calvera's X-ray flux is such that it should be close by, perhaps the closest known neutron star. Other notes: supernovae remnants dissipate after about 10,000 years (not 10 Billion). Most of the neutron stars we've observed are not observed with their supernova remanent, but are instead radio pulsars wandering alone. I'll try to hang out a bit and field more questions.