Colliding Galaxies (APOD 24 Oct 2006)

Fors · Post by **Fors** » Tue Oct 24, 2006 7:32 pm

Understanding that the primary interaction between colliding galaxies is gravitational, what effect would those interacting gravitational fields have on planets in a star system? Is it possible that the planetary orbits could be distorted, or even dispersed as a result of an encounter with a passing star or star system? And with the infusion of organic elements, could such a close encounter spur the development of life on a given planet with favorable surface and atmospheric conditions?

Martin · Post by **Martin** » Tue Oct 24, 2006 9:23 pm

What if two stars did collide?

I don't ever recall seeing a model or math showing the outcome of such an event. Has it ever been observed or thought to have happened?

Is there a name for this?

I know that it is highly unlikely but still it had to of happened at some point in the past or it could happen at some point in the future (given a lucky roll of the cosmic dice, eh)

Orca · Post by **Orca** » Tue Oct 24, 2006 11:57 pm

Perhaps if a dense region of one galaxy got close enough to a dense region of the second, there'd be some interaction. But I doubt there would be much for the majority of the stars in each respective galaxy. Though the overall structure of a galaxy sure does seem to get "stirred up." I imagine star formation is increased in areas where average density is driven up.

Martin...yeah, I imagine it has to happen eventually. I can't imagine what it would entail! I suppose it would depend on how massive the original stars were. I am sure that a large explosion would ensue...then I'd guess what follows would depend on how much matter was not thrown off and how much stayed behind.

iamlucky13 · Post by **iamlucky13** » Wed Oct 25, 2006 12:24 am

Unless the star got really close, perhaps 20 times the distance between the planet and it's parent star (0.25% as much gravitational influence assuming equal mass), probably not much would happen. But the more it's gravity influences both the planet and the star, the more things change. The planet would probably develop a more eccentric orbit (or a slimmer chance of rounding out an elliptical orbit). If they got close enough, the planet might be stolen away by the intruding star, or even ejected into open space.

According to an article I found, stars colliding might actually be relatively smooth compared to a supernova. It would heat up to a new equilibrium appropriate to it's new mass, and I suppose it would spike due to density increases and the subsequent increases in fusion caused by the evening out of kinetic energy by the two masses.

http://www.space.com/scienceastronomy/b ... 40414.html

Martin · Post by **Martin** » Wed Oct 25, 2006 1:11 am

Is there a name for such an event?

And what kind of process would both stars go through?

I understand that it is almost "not possible" but that does not make it impossible, right?

What would remain of the two stars?

If a collision were to be observed -is there anything that could be learned from it?

What about collisions from other types of stars? There could really be a large combination of different types of "unlikely" collisions -if u think about it. What secrets could they reveal?

I imagine collisions of this nature would be the rarest event possible?

Questions, questions and more questions!!!

Qev · Post by **Qev** » Wed Oct 25, 2006 3:17 am

I'm not sure if there's actually a specific name for collisions between stars other than 'stellar mergers'. It's supposed to be a pretty rare event, although it apparently happens in very populous areas such as inside globular clusters, leading to what are called 'blue stragglers'.

When two stars collide, it seems to 'rejuvinate' them, the merged star appearing brighter, bluer, and younger than the two progenitor stars. Which only makes sense, I suppose, considering the star has just doubled (or more) its original mass.

fwalchak · Post by **fwalchak** » Wed Oct 25, 2006 3:20 am

Like Martin I had the immediate thought: What happens when or if two stars actually collide? Has there been any research or documentation? I can't imagine that there hasn't been any, but I have not found anything with a (admittedly) cursory review of the literature.

BMAONE23 · Post by **BMAONE23** » Wed Oct 25, 2006 4:36 am

They could go through a similar process to the Earth Moon system where the larger mass star steals some material (hydrogen) from the smaller and produces a binary system, Or even if enough matter is relocated to one of the stars the remaining lesser could become a brown dwarf or possibly a "Hot Jupiter"

orin stepanek · Post by **orin stepanek** » Wed Oct 25, 2006 10:47 pm

Here's an interesting video on colliding stars!
http://www.space.com/php/video/player.p ... ars_collid
I hope this helps.

Orin

ckam · Post by **ckam** » Thu Oct 26, 2006 11:00 am

you know it was funny
they had ads before actual video played, where things started to disappear; I thought to myself yeah right that's what happens when stars collide...

Martin · Post by **Martin** » Thu Oct 26, 2006 5:45 pm

orin -Thank you that was extremely fascinating.

Martin · Post by **Martin** » Thu Oct 26, 2006 6:17 pm

Ok my next question is......

There are so many space pictures of stars, gas, comets and galaxies that I am beginning to wonder why is this: http://antwrp.gsfc.nasa.gov/apod/ap060824.html > the only picture I have seen in reference to DM.

Surely even with galaxies colliding there would be some same evidence present -right?

Where is the DM in the galaxies colliding APOD????? Or any other photo that has gas expanding/moving in space -where is the DM reaction????

astro_uk · Post by **astro_uk** » Thu Oct 26, 2006 7:59 pm

There are plenty of pictures of the hot gas that surrounds large elliptical galaxies or clusters of galaxies. The problem is that they just don't look very good. The resolution of the instruments used to measure them is so poor you just end up with smooth looking blobs. Though the temperature and density of the gas does tell you that there must be some DM present.

I may have a go at knocking up something like this if I can get my hands on the Xray data.

Martin · Post by **Martin** » Thu Oct 26, 2006 9:15 pm

I look forward to that Astro -Thank you for replying.

Is the bullet cluster that close that its resolution is that good?

astro_uk · Post by **astro_uk** » Fri Oct 27, 2006 11:25 am

Not really you can see that the X-ray data just looks like a smooth blob. The question is whether or not this is due to the gas actually being smooth, or because the intruments resolution is so low it tends to smooth things out.

You can see in the bullet cluster that you can't resolve any real bumps or wiggles in the X-Ray data that are anything near the size of the galaxies in the cluster.

Martin · Post by **Martin** » Fri Oct 27, 2006 5:02 pm

I see your point.

What puzzles me is the fact that you can clearly see “an interaction” in the bullet cluster despite the resolution quality. Why isn't there clearly an abundant quantity of “interactions” present in other clusters, nebulas and star forming regions within our own galaxy? Or are there?

I do find it strange that there are a lack of observations confirming DM when it could account for 90% of our universe.

Nereid · Post by **Nereid** » Tue Oct 31, 2006 1:45 pm

fwalchak wrote:Like Martin I had the immediate thought: What happens when or if two stars actually collide? Has there been any research or documentation? I can't imagine that there hasn't been any, but I have not found anything with a (admittedly) cursory review of the literature.

There's been quite a bit of research on what happens when two stars collide.

There is a good, popular review in the November 2002 issue of Scientific American (maybe your local library has a copy?)

Nereid · Post by **Nereid** » Tue Oct 31, 2006 1:47 pm

For those interested, this Hubblesite Fast Facts page has a scale bar and orientation arrows, for the APOD.