Hungry Millisecond Pulsar Found Feeding 15
Gopher971 writes: "The latest joint discovery by the Hubble Telescope is a Millisecond Pulsar feeding off of it's companion Red Giant star. Scientists have long speculated on how Milli Pulsars formed and now have proof to back up their claims. See the UniSci link and The Irish Times link."
is that... no.... (Score:2, Interesting)
tee hee... tell me that "object" in the middle isnt a sperm, geez...
did disney make the pic or something?
Hmmm, blackhole (Score:2, Interesting)
Two theories (Score:5, Interesting)
Both say that the material will pile up on the surface until it reaches fusion temperatures and then start to burn.
One says that the burn will be fast and explosive, blowing all the rest of the new, degenerate and normal matter off of the surface. An extension of this idea suggests that the explosion, since it is very unlikely to be symmetrical and simultaneous all over the surface of the neutron star, will disrupt and break up the neutron star itself. We are talking about a big, nova or supernova class explosion here.
The other says that the fusion burn will be slow, intermittent or periodic, something more like a continuous series of neutron star sized burps and blow stuff off here and there and simply heat things up. The heat and radiation from the explosions slows the infall of matter, a form of negative feedback, so that the process is self throttling. Somewhere along the way, it might accumulate enough to collapse, otherwise the process just continues until the donor star "runs out of gas" and then everything calms down.
There are nuances to both depending on the rate of deposition, spin, size of the original neutron star, etc.
Mostly there's just not enough data to tell, perhaps both happen depending on the situation.
The first theory sounds incorrect (Score:2, Informative)
That sounds more like a certain theory for the collapse of white dwarfs under infalling matter. Supposedly this would always happen at the same mass and produce uniformly bright supernovae.
As I said, it's been awhle... (Score:1)
The other thing to be explained was the discovery of SN remnants that have no detectable NS at or near the center.
Obviously, both could be covered by the propelled version, but no one knows, AFAIK. Perhaps it was proposed simply as an attempt to cover all bases. If the NS is not there, it must have moved or been destroyed. OTOH, if the NS is here, and there is no nebulous remnant nearby, and there is no idea of how to destroy the remnant, then the NS must have moved.
If there has been more data gathered, better theories produced or simply better analysis of existing data and theory that has ruled out one of these options, that's fine by me. It has been a while since I studied or paid attention to this stuff.
Re:The first theory sounds incorrect (Score:1)
Re:Hmmm, blackhole (Score:2)
This pulsar is in a globular cluster, which probably contains a number of other neutron stars already. Sooner or later two of them are going to make close passes and get captured into a mutual orbit, which will then decay. When the two neutron stars merge they will likely collapse catastrophically into a black hole, with the added excitement of kilohertz gravitational waves thrown in.
Re:Hmmm, blackhole (Score:1)
For the same reason they don't care about shielding, they don't care about you, either.
And I'm still waiting for those gravitational waves to get observed. It would be so danmed cool to listen to the creation of a black hole that way...
Re:Hmmm, blackhole (Score:2)
Re:Hmmm, blackhole (Score:1)
Exactly. If you're close enough for the neutrinos to have any macroscopic effect, you're gonna be nothing but ionized H, O, N, C, etc. real soon (well, maybe in a few hours. The electromagnetic radiation can take a long time to reach the surface of a supernova, while the neutrinos get there at about the velocity of light). But the earlier poster warned about neutrinos after mentioning observing from a few light-years away, where the flux would be *far* too low to worry about.
Re:Hmmm, blackhole (Score:2)
Not very, I would guess. Neutron stars tend to have masses just at or near the Chandrasaker limit (actually, sometimes a bit lower, even). That's 1.4 solar masses. A neutron star becomes a black hole at between 2 and 3 solar masses (number uncertain). So that's a fair margin, particularly if you take the 3 solar mass limit.
Now, how much matter is transfered? If the neutron star is 1.4 solar masses, if it is typical size (10 km radius) and if the companion is 1 AU from the neutron star, you'd have to transfer about 2.5 X 10-5 solar masses to make a millsecond pulsar, I'm figuring. That's a tiny amount. The mass tranfer required goes like 1/r2 (until the mass transfered is a large fraction of the pulsar's inital mass, anyway). So even at 0.1 AU, it's still only 1/1000 of a solar mass. (0.1 AU = 10 solar radii, roughly) They'd almost have to be in physical contact to require enough mass transfer to push the neutron star over the black hole limit.
Globular Clusters! (Score:2, Informative)
here's a link to Globular Cluster NGC6397 [seds.org]
Can you find the pulsar? *grin*
Photo taken from the Hubble, circa 1994.