galaxies colliding, NGC4013 (APOD 07 Feb 2008)

[memmd]

When two galaxies collide, as with today's NGC 4013 and the Tidal Stream, do the component stars ever crash together, and if so, what is the result? Obviously the stars are far apart even in dense galaxies, but star-star collisions must occur just statistically.

[emc]

hi memmd, Welcome to APOD!

http://apod.nasa.gov/apod/ap080207.html

A very interesting question...

8) I imagine it is many differences becoming a messy sameness until the samenesses are sorted back into some new differences (Hope you're not offended, I like your question and I like to try and be funny when I don't have a clue )

Hopefully someone else here knows the scientific answer

... and what about the planetary orbits?

[JohnD]

memmd,

If you google for "when galaxies collide" (use the quotes), you will find a wealth of articles about this.
In the vastness of space, the probability of stellar collisions is as near zero as makes no difference, but the gas and dust of two galaxies will definitely collide. Shock waves, compression zones and new star forming ensues. Our own galaxy is thought to have consumed others in the past, presumably smaller ones as two equally sized spiral galaxies form an elliptical.

John

[neufer]

When two galaxies collide, as with today's NGC 4013 and the Tidal Stream, do the component stars ever crash together, and if so, what is the result? Obviously the stars are far apart even in dense galaxies, but star-star collisions must occur just statistically.

With the width of stars at light minutes and the separation at light years there is a disconnect of the order of a million!

In terms of a collisional cross section area that disconnect is of the order of a million squared!!

Since a galaxy is tens of thousands of light years across each star has about ten thousand separate chances of hitting this small relative cross section (of one over a million squared) or ten chances in a billion.

If you took off on the Starship Enterprise at warp speed through the center of the galaxy your chances of hitting a star are about the same as the chances of you eye seeing the surface of a star ... or in other words it is the ratio of the brightness of the Milky Way to the brightness of the surface of the sun. (Olber's paradox)

Thus out of a galaxy of a 100 billion stars only about a thousand will engage a direct collision and unless one of those thousand stars is your sun this will be important only in terms of the gravitational radiation generated by the galactic collision.

[npsguy]

Quite a while ago I read where a scientist answered your question in this fashion. I am not sure the exact words but the jist was this:

"the odds of stars crashing together in two colliding Galaxies are the odds of two mosquitoes placed at opposite ends of the Grand Canyon eventually crashing into each other.... and forming an avocado."

[emc]

We may get a close hand look in about 3 billion years.

http://www.cita.utoronto.ca/~dubinski/tflops/

Don't be mislead by the first impression of the webpage title

[memmd]

Thank you for these comments. I did Google as suggested and initially found this site from Cornell if anyone is interested:
http://curious.astro.cornell.edu/questi ... number=382

I am sure the odds of star collision are very, very low, but considering the billions of stars over billions of years, it must have happened more than once.[/url]

[iamlucky13]

Great picture.

In the large version, I noticed quite a few other features that were either too small to resolve in the small version, or cropped off, including numerous distant galaxies and some colorful nebulae. In particular, I was fascinated by what appears to be a blue-ish reflection nebula at about 5 O'clock from NGC 4013.

At 1 O'clock, there is a small swept-looking blue and yellow feature. I wonder if it could be a younger version of NGC 4013, with star formation still rapidly occurring in the tidal stream?

[neufer]

Thank you for these comments. I did Google as suggested and initially found this site from Cornell if anyone is interested:
http://curious.astro.cornell.edu/questi ... number=382

I am sure the odds of star collision are very, very low, but considering the billions of stars over billions of years, it must have happened more than once.[/url]

Another aspect to consider about colliding galaxies:

http://antwrp.gsfc.nasa.gov/apod/ap060824.html

[auroradude]

With the dange of appearing simplistic: If the universe is infinate, wouldn't that mean that in the whole of the universe, no matter how slim the chances, the number of collisions between stars would also be infinate?

[auroradude]

ER, before you jump on me spelling, let me make that "infinite".

[iamlucky13]

Not necessarily. Mathematically, it is possible to add an infinite number of finite numbers, and end up with a sum that is finite.

For example, the series 1/n^2 (1 + 1/4 + 1/9 + 1/6 +...) if carried out to n=infinity only adds up to pi^2/6.

Also, the universe is not, according to the big bang theory, thought to be infinite.

[emc]

Also, the universe is not, according to the big bang theory, thought to be infinite.

Not that it is or isn't, but how do we prove the universe is finite since we are looking outwardly back in time and cannot 'see' the 4D origin?

[memmd]

As a very minor note, the site I noted is an answer to the same question I asked, but from a 7th Grade student. It's nice to know I am keeping up with a 12 year old.

[neufer]

Also, the universe is not, according to the big bang theory, thought to be infinite.

Not that it is or isn't, but how do we prove the universe is finite since we are looking outwardly back in time and cannot 'see' the 4D origin?

But we can 'see' the wrinkly plasma left over 380,000 years after the 4D origin:

http://antwrp.gsfc.nasa.gov/apod/ap061007.html
http://antwrp.gsfc.nasa.gov/apod/ap050925.html
http://antwrp.gsfc.nasa.gov/apod/ap060323.html
http://antwrp.gsfc.nasa.gov/apod/ap070827.html

[emc]

Thanks for the links! You are very helpful and patient!

So the wrinkly plasma proves the universe is finite?

[neufer]

Thanks for the links! You are very helpful and patient!

So the wrinkly plasma proves the universe is finite?

The universe that is visible to us in the electromagnetic spectrum is finite
(assuming there are no wormholes around through which one can actually travel to a different universe).

[emc]

The universe that is visible to us in the electromagnetic spectrum is finite.

What about the 4D origin that we can't see??? Is the 4D source inferred or somehow defined from the known physical spectrums?

(assuming there are no wormholes around through which one can actually travel to a different universe).

Well, there is a big hole according to WMAP

[emc]

Art, (hope I'm not being too presumptuous) (cool first name)

Seems my 4D source question may be answered in the "'Hole in the Universe' possible explanation" Asterisk thread... the 4D source is inferred if I understand enough of what I read. This was my initial understanding from my Asterisk conversation with another physicist in a different thread. In my question to you, I was looking for validation of my understanding of what scientists believe about the origin of the universe.

For me, the scientific belief in a 4D source is similar to belief in a supreme being, as neither can be seen or quantifiably measured and both exist (by faith) outside of time and space. At least for myself, this gives me more hope and adds to our common ground... which I think is very cool 8)