Starship Asterisk*

Wolf kotenberg wrote:
It is possible a very heavy neutron star just slammed into one that was not neutronized yet ?
Plain old mechanical collision at galactic speeds ?

http://en.wikipedia.org/wiki/Neutron_star wrote:
<<A typical neutron star has a mass between 1.35 and about 2.0 solar masses. In general, compact stars of less than 1.44 solar masses – the Chandrasekhar limit – are white dwarfs, and above 2 to 3 solar masses (the Tolman–Oppenheimer–Volkoff limit), a quark star might be created; however, this is uncertain. Gravitational collapse will usually occur on any compact star between 10 and 25 solar masses and produce a black hole.>>

bystander wrote:

Wikipedia: Type II Supernova wrote:A type II supernova … results from the rapid collapse and violent explosion of a massive star. …

When the mass of the inert core exceeds the Chandrasekhar limit of about 1.44 solar masses, electron degeneracy alone is no longer sufficient to counter gravity. A cataclysmic implosion takes place within seconds, … The collapse is halted by neutron degeneracy, causing the implosion to bounce outward. The energy of this expanding shock wave is sufficient to detach the surrounding stellar material, forming a supernova explosion, … Because of the underlying mechanism, the resulting variable star is also described as a core-collapse supernova.

I'm not sure I understand how this is induced by galactic interaction. Seems to me to be simply a property of massive stars. Unless you are saying the birth of these massive stars were caused by the interaction, but that's somewhat different than saying the supernova were induced by NGC 5195.

• 1) Massive stars have short lives.
  
  2) NGC 5195 has recently induced massive star formation which has lead to Type II Supernovae.

neufer wrote:Type II supernova in M51 were probably induced by NGC 5195:

Wikipedia: Type II Supernova wrote: A type II supernova … results from the rapid collapse and violent explosion of a massive star. …

When the mass of the inert core exceeds the Chandrasekhar limit of about 1.44 solar masses, electron degeneracy alone is no longer sufficient to counter gravity. A cataclysmic implosion takes place within seconds, … The collapse is halted by neutron degeneracy, causing the implosion to bounce outward. The energy of this expanding shock wave is sufficient to detach the surrounding stellar material, forming a supernova explosion, … Because of the underlying mechanism, the resulting variable star is also described as a core-collapse supernova.

http://en.wikipedia.org/wiki/Whirlpool_Galaxy wrote:
<<Recent simulations bear out that M51's spiral structure was caused by NGC 5195 passing through the main disk of M51 about 500 to 600 million years ago. In this model, NGC 5195 came from behind M51 through the disk towards the observer and made another disk crossing as recently as 50 to 100 Myrs ago until it is where we observe it to be now, slightly behind M51. Induced spiral structure in the larger galaxy isn't the only effect of the interaction. Significant compression of hydrogen gas occurs that leads to the development of starbirth regions. In pictures of M51 these show up as the bright blue 'knots' throughout the spiral arms.>>

rjtonnis wrote:What is the other light at about 5 o'clock from the supernova that is moving relative to the other light sources?

rguyg wrote:sh sh.. I was just told by aliens that 200 Supernova's occurred within ten years over 4 millon years ago in the Pin Wheel
I like the way we talk about what just happened; like this newly found Supernova. Just to think what's happened since..

BobStein-VisiBone wrote:Ah, true of observations from Earth. But observations of these same three supernovae from other points in the universe must definitely be separated on the order of 76,000 years. My point is that our viewpoint is a major factor in the oddity of this statistic.

Does anyone know when we started to be able to observe a supernova in M51? (Certainly not in Brahe's and Kepler's time. Their supernovae were in The Milky Way, correct?) If it was say 20 years ago then this may not be a statistical oddity, it may indicate a higher rate of supernova occurrence, at least in M51.

Chris Peterson wrote:The events are not separated in time by 760 years, but by 17 years.

Chris Peterson wrote: Three supernovas in a single galaxy in 17 years is a statistical oddity- but I think that's all it is. These things happen (consider the unlikelihood of Brahe's and Kepler's supernovas in 1572 and 1604). Supernovas can probably be considered as occurring according to Poisson statistics, and that means that every now and then you'll see something that we would call a "cluster", even though there is no causal connection between them.

BobStein-VisiBone wrote:So 3 supernova in 760+ years is no surge.

DLH wrote:I see only one image.

Guest wrote:Something that is common knowledge, but it always strikes me each time I see it. Like in this APOD, with its descriptions of the relatively recently photographed supernovas. As we read, it is as if this supernova, just photographed, just occurred, almost right before our very eyes, when actually, in fact, these supernovas happened about 31 million years ago, relative to the distance of M51, and to the speed of light.

The images are blinked to show the location of the exploded star.