What happens if two or three stars collide with each other?

The collision of another star with our sun would be a very effective way of ending all life on Earth. Fortunately stars are so far apart that the the chance of it happening in the life of the sun is very close to zero.

However in the densely packed cores of globular clusters the rate of collision is much higher, and there may be a collision somewhere in the milkyway once every 10000 years or so. Three way collisions don't happen (or are exceptionally unlikely) but would be similar to two two-star collisions.

The result varies depending on the size of the stars, their density, the relative velocity, and whether a collision is head on or not. Generally a denser star is likely to come out of a collision in better shape. So a red giant, could have most of its very rarified outer layers pulled off and the core escaping.

On the other hand, if two main sequence stars, like our sun, collide, they first compress each other. Some of the stellar envelope escapes perpendicular to the collision (think of jam being squeezed out of a sandwich). But within a few hours the two stars have mixed and merged, and a new, larger star formed.

The mixing adds lots more hydrogen to the core of the star, which causes it to rejuventate. The first evidence of stellar collisions is in globular clusters, in which there are some large blue stars that seem younger than all the other stars in the cluster (Blue stragglers)

A white dwarf and main sequence star collision is bad news for the star. The collision causes the core of the star to heat up and a massive release of thermonuclear energy. Plenty more than is needed to completely disrupt the star. The star is completely destroyed in the process. However the white dwarf is relatively unscathed.

White dwarf-white dwarf collisions can, depending on the size result in gravitational collapse to a neutron star.

The paper Stellar collisions, mergers and their consequences is a very readable summary.

solar system - How did Batygin estimate when Planet Nine was ejected?

Page 12 of Batygin & Brown (2016) says that a speculative formation scenario can be drawn from recent solar system formation simulations by Bromley & Kenyon and by Izidoro et al. These suggest that the core of a nascent ice giant may have been ejected very early in the solar system's history in order to explain the properties of the observed planets; the formation of Uranus and Neptune was probably accompanied by at least one other ice giant.

The source of the claim you mention is actually an article by Eric Hand in Science Magazine. He points out that possibly, to explain why this planet was ejected yet still remains part of the solar system in a much wider orbit, then you need it to have been slowed down by residual gas in the protosolar disk. So I assume the 10 million year is an (uncertain) upper limit on the dispersal of the disk and I would guess the 3 million year lower limit is just how long it takes to form a 10 Earth mass ice giant core at the distance of Neptune.

classification - Stars repartitions - Astronomy

I'm looking for the stars repartitions in percent, in the Harvard Classification (from O to M)

I have search every where but I found nothing. I'm not looking for exact values, but more generic values.

After that in each Classes I'm going to need the repartitions in the luminosity classes

If you have some link, or any lead to help, I'm gona take it

I'm working on a space Video games, and I'm gonna generate Solar system :)
I have done a first script whch generate good value, but not for us : http://global-chaos.fr/old/generator/

in ths frst generator we have simplfed the star classifcation, but we want to go on more realistic classification, and more diversty of star

nebula - Will new stars stop forming at some point of time?

Cosmic GDP has already crashed, as Peak Star was ~11 billion years ago.

According to Sobral et al's prediction, the future star production by mass will give only 5% of the stars in the universe today, "even if we wait forever." More theoretical predictions, such as this one, suggest that nebulae will run out of hydrogen on the order of $10^{13}$ years, while star formation will occasionally happen due to collision of brown dwarfs until somewhere on the order of $10^{14}$ years.

Of course, hydrogen itself may have a finite lifetime. The half-life of a proton is experimentally known to be longer than $10^{34}$ years, but it may still be quite finite.

Analysing the results of real-time PCR

You also probobably need to check if your samples haven't been contaminated with PCR reaction inhibitors, which is very common if you first extract your mRNA, digest remaining DNA and then run a PCR with a less then 10-fold dilution. You need at least a 200 times dilution to get rid of all the artifacts.

Once you've diluted your samples, place a repeats of successive dilutions of your target and baseline mRNA (200xdilution, 1000x dilution, 5000x dilution). Normally you will see a nice regular spacing between curves on your rtPCR plot. If you don't, something went wrong with the reaction.

More generally rtPCR is a pretty tricky experience, and if you want it to be 100% reliable, you've got a certain number of controls to perform. You can find a good and comprehensive guideline over here.

extra terrestrial - Could the KIC 8462852 (Alien megastructure star) be explained by orbiting gas clouds?

There are some theories to explain that. The following explanations, I took from wikipeda's article.

1. The star has a small companion red dwarf which just crossed its Oort cloud equivalent (at 885 UA). A passing star this close would surely cause havoc and serious disturbances to comets' orbits. This could result in a swarm of comets being thrown into the inner stellar system at once in highly excentric orbits. However, there are severe doubts about this.




2. It was also proposed that a planet with a very big ring system transits the star (or perhaps, nearly misses and just part of the rings transit the star). This is not unprecedent, and was already seen with another star.




3. Astronomer Jason Wright suggested that the star might be younger than it seems and it is still coalescing material around it.




4. Astronomer Bradley Schaefer presented just a few days ago (2016-01-13) a study where he concludes that the star dimmed roughly 20% from 1890 to 1989, and that this is unprecedent for a F-type star. So, there could be still more weird things going on than previously thought.




5. NASA Infrared Telescope Facility found similiarities with another star, Eta Corvi, which is undergoing a Late Heavy Bombardment.

Wikipedia's article also cites another possibility (which took some headlines around the world). But this is just some (unfortunately notable) sensacionalistic (un|pseudo)jornalistic claim that nobody can take seriously:

6. There is an advanced alien civilization building a giant device like a Dyson Sphere or something similarly big.

LocalFluff posted an answer suggesting another possibility:

7. 
   

   The anomalies correlate strictly with the telescope's orbital period and orientation and are obviously a man made artefact because of some unforeseen malfunction of the instrument, nothing astrophysical is involved.

   
   

So, the conclusion (at least my conclusion) is that we simply don't know yet what is happening and we need many follow up observations which will likely tell us a lot. Specially somewhere around May of 2017, when it is predicted that the strange megastructure transit should happen again.

I personally would guess that the close encounter with the red dwarf triggered a Late Heavy Bombardment. But this is only a guess from mine and I have no way to provide evidence for it.

the moon - Is extraterrestrial mining more difficult or impractical for bodies without plate tectonics?

I vaguely remember my dad talking about this.

Uranium and other heavy elements are dense. When the celestial body was molten (early in it's life) all the heavy elements sank to the core of the body. Now, with tectonics, the heavy elements are brought back up to the surface. This is why we can mine Uranium on Earth near the surface: the Uranium was brought back up due to convention current on Earth.
In conclusion, it's not worth it at all to mine on a non-tectonically active planet/moon

If anyone can extend this, please do.