Added 1 new A* page:Yep another 1 page lackadaisical Friday! On the plus side though next week should be pretty good for comic output since my gym will be closed for renovations--so I'll probably just sit around getting fat and drawing comics, wooo.|
There was an article making the rounds in the past day or so about an extra large magnetar. Magnetars are neutron stars that happen to have a large spin magnetic moment--having to do with quantum "spin" which is kind of a confusing thing--giving them a large magnetic charge, although this charge fades after a mere 10,000 years or so. Their magnetic field is measured in the range of gigateslas, or one billion teslas, one tesla being a magnetic force equivalent to what you get from a strong rare earth magnet.
It sounds impressive, but isn't all that much; while a magnetar's charge is enough to pull a human body apart at 1000 km, or to screw up your credit cards at about half the distance of the Moon to Earth (says Wikipedia), a neutron star, which is a super-dense remnant of a supernova--basically what happens when stars below about three solar masses go supernova: you end up with really dense matter (sometimes called "neutronium" which is a bit silly, but basically it's neutron-heavy stuff so dense that a teaspoonful would weigh something like five trillion kilograms :o) in an amount not quite sufficient to collapse into a singularity--is much more likely to do destructive things to you via gravity, radiation, or a pulsar beam or something. Still, you have to admit that "magnetar" and "gigatesla" are super-cool-sounding words.
Anyway, because magnetars don't last very long, there aren't very many known; this particular one, CXO J164710.2-455216, in the "super star cluster" Westerlund 1, somewhere between 12,000 and 16,000 light years from Earth, is the closest one known. The stars in the cluster--many of which are unusually large--are thought to have formed in a single big burst of star formation 4 or 5 million years ago, which makes them quite young; and since they all formed at the same time, and one already went and supernovaed into this magnetar, that means it must have been larger (since larger stars die faster) than any of the other stars still there, and I guess the largest of those is just about 40 solar masses.
image by NASA/CXC/UCLA/M.Muno et al. (source)
So the question was, why did a star of 40+ solar masses supernova into a neutron star instead of a black hole? You need a remnant of about 3 solar masses in order to collapse into a black hole, and it had been thought that a star of 20 solar masses or more would leave you with at least that much after its supernova--but somehow in this case, the supernova of what must have been a very large star left much less mass behind than expected, little enough that it couldn't collapse into a black hole. So one idea is that this star had a binary companion that helped strip away a lot of the mass.
Still, it isn't as though scientists have had a whole lot of opportunity to study actual supernova explosions, so who's to say that they don't just blow off way more material than current theories think they do? It had been thought that stars lost something like 75 to 90 percent of their material in a supernova, but maybe it's more like the 95 percent that the Westerlund 1 magnetar appears to have lost; or maybe mass loss in a supernova is way more unpredictable than nice convenient theoretical formulas would like.
Westerlund 1 is a pretty cool place. According to this new article, although it's hard to observe due to obscuring gas and dust, it's estimated to weigh in at about 100,000 solar masses, and all the stars in it are big ones: 30 to 40 solar masses. At a mere 6 light years across, it's as dense as areas typically much closer to the galactic core (like A*'s setting :). I liked this description in the article by lead researcher Ben Ritchie:
"If the Sun were located at the heart of this remarkable cluster, our night sky would be full of hundreds of stars as bright as the full Moon."
That's the type of environment I've been trying to portray in A* (here, for instance), and this is the first instance I can recall of a quote in plain English from an astronomer actually talking about it in quantifiable visual terms.
Here's a niftier photo of the cluster, taken in infrared light (the above photos were visible light and X-rays, respectively):
image by 2MASS/UMass/IPAC-Caltech/NASA/NSF (source)