Colliding Stars

Frank · Post by **Frank** » Tue Sep 06, 2005 3:24 am

Is there any evidence of colliding stars in our galaxy or other galaxies?

If two stars collided head on would one or the other or both be completely destroyed?

makc · Post by **makc** » Tue Sep 06, 2005 7:07 am

this post was clearly inspired by the same apod as this, and, while it has no replies yet, it was asked 1st, plus its question is quite different, so I won't lock it.

in other words: don't be shy, go and answer it

EDIT - to Frank - meanwhile, check this out.

Empeda · Post by **Empeda** » Tue Sep 06, 2005 1:09 pm

The chances of it are remote at best.

The distances between stars are so great that when even when two galaxies are merging, it is still incredibly (I mean incredibly, statistically we're looking at a decimal point and a lot of noughts here) unlikely that two stars will collide.

As for what would happen - havn't the foggiest! But I suspect it would be a fairly awesome spectical....

William Roeder · Post by **William Roeder** » Tue Sep 06, 2005 2:58 pm

Stellar collision - Google Search returned Scientists witness massive explosion due to stellar collision

Empeda · Post by **Empeda** » Tue Sep 06, 2005 4:04 pm

That's a collision between two neutron stars, which are incredibly dense, and would merge as the result of a binary system producing them. As it happens, the data coming back from swift is suggesting that the Short duration GRBs are not caused by this.

Odegard · Post by **Odegard** » Wed Sep 07, 2005 2:59 am

Stars colliding is extremely rare due to two reasons: they are small compared to the interstellar distances, and they all move in the same general direction (in the galaxy).

For stars to collide you'd need a direct hit. If the stars pass each other real close they will probably (depending on the relative passing velocity) go into an orbit around a common center of gravity. This "spiral of death" could last almost forever, however, long before they collide one of the stars will definately have stolen mass from the outer layers of the other stars, reaching the supernova limit and explode. The exception would be extremely dense stars like a pair of neutron stars, a pair of black holes where it would be really hard to steal mass from your companion.

S. Bilderback · Post by **S. Bilderback** » Sat Sep 10, 2005 3:56 am

I would have to disagree - in a way. Near the center of galaxies stars are moving very fast in relatively close proximity interfering with each other's orbits. Collisions happen but are rarely observed, washed out by the intense energy of the galactic core and by outer atmospheres mutually being torn away.

I would love to see what the animation of two red giants colliding head-on, in cold space, would look like.

Empeda · Post by **Empeda** » Mon Sep 12, 2005 11:29 am

Not sure - even when there's a galactic collisions the chances of two stars colliding are remote - gases can be condensed and produce starburst galaxies - but the distances between the stars are far too massive to make stellar collisions likely...

Babyface81g · Post by **Babyface81g** » Mon Sep 12, 2005 4:52 pm

I would think that if one star is roughly the size of Jupiter and the other star is the size of Earth than if in case of collision one would swalow the other. Stars are mostly made of hydrogen and helium (hot gas). During collision it would give off some explosion but one star conquers over the other by intertwining.

BMAONE23 · Post by **BMAONE23** » Mon Sep 12, 2005 5:18 pm

[quote="S. Bilderback"]I would have to disagree - in a way. Near the center of galaxies stars are moving very fast in relatively close proximity interfering with each other's orbits. Collisions happen but are rarely observed, washed out by the intense energy of the galactic core and by outer atmospheres mutually being torn away.

Maybe this is the cause of all the intensity at the galactic center.
how does the distances between stars differ at(near) the center of the galaxy vs. out on the arms?

Empeda · Post by **Empeda** » Tue Sep 13, 2005 12:13 pm

The distances between stars is still far more massive then the areas of the stars themselves.

It is so unlikely that two stars would collide that it is almost negligable. What is more likeyl to happen (though still quite inprobable) is that two stars will interact gravitationally - forming a binary. Now if one star is more massive than the other, rather than 'pulling it in' a mass accretion process is more likely i.e. the larger star will start 'stealing' material from the other. This of course would effect the dynamics of each of the stars....

This can be helpful to us though - a white dwarf and star binary for example. If the white dwarf steals mass from its binary companion, it gains mass. If it's mass reaches more that 1.4 solar masses, it cannot support itself and will collapse to form a neutron star. This is known as a Type 1a Supernova, and will always emit the same amount of energy (since 1.4 solar masses is a 'critical mass'). Very useful = think standard candle! Easy to measure relative distances......

S. Bilderback · Post by **S. Bilderback** » Wed Sep 14, 2005 2:30 am

In theory, stars near the galactic center can be accelerate to 0.1 the speed of light as they are pulled toward a super massive black hole residing at the galactic center. Star density increases at some factor of 1/πR. Gaseous stars are torn apart under the forces creating supper-heated nebulae, I don't know what would happen to a neutron star, If they could hold their structure, the speed vs. density would reach a point where collisions would become probable.

The fastest moving star ever found is a neutron star on it's way out of the galaxy, the interaction to cause such a course change would have to be a near miss.

Empeda · Post by **Empeda** » Thu Sep 15, 2005 12:44 pm

Probably yes - would a large supernova, or even a hypernova, produce a big enough kick to accelerate the star - what do you think? I suppose another possibility is that it could have been kicked out of a three-star system?

makc · Post by **makc** » Thu Sep 15, 2005 3:44 pm

just wanted to inform everybody on ongoing related (though not exactly the same) discussion.

S. Bilderback · Post by **S. Bilderback** » Fri Sep 16, 2005 1:03 am

I believe it is much more likely that it was a gravitational slingshot than acceleration from an explosion. Also, its total kinetic energy tells me it involved more than one star system.

I hope it's not heading for us!

Empeda · Post by **Empeda** » Fri Sep 16, 2005 12:17 pm

Me too - we'd have to send Bruce Willis up to stop it if he's got a clean white vest.......

The only reason I suggested a kick was because it is a neutron star - though I suppose a close near-miss with something else of massive density would cause hell of a slingshot....

makc · Post by **makc** » Fri Sep 16, 2005 1:50 pm

Empeda wrote:...I suppose a close near-miss with something else of massive density would cause hell of a slingshot....

same as with capture thing I've mentioned few posts ago. Why won't misser (?) slow down back to its original speed after miss? gravity haven't gone anywhere, it should pull it back (or at least slow it down back) after the miss.

William Roeder · Post by **William Roeder** » Fri Sep 16, 2005 2:19 pm

It wouldn't because speed is not conserved only total momentum.

We slingshot probs around planets to get a speed increase to reach the outer planets. The large mass gets a minuscule change in direction/speed while the smaller mass gets a large change in both direction/speed.

That neutron star must have had a close encounter with something really massive. Perhaps the super-massive black hole at our galaxy center. 1-3 solar masses vs several billion

S. Bilderback · Post by **S. Bilderback** » Sat Sep 17, 2005 3:35 am

Well put!

makc · Post by **makc** » Tue Sep 20, 2005 6:12 am

No, not well at all

Check damn facts wrote:Since the orbit is symmetric about Jupiter, the angle that the spacecraft leave the SoI (Sphere of Influence - makc) of Jupiter is determined. As mention above, the magnitude of this velocity is the same as that with which the spacecraft entered.

S. Bilderback · Post by **S. Bilderback** » Tue Sep 20, 2005 12:16 pm

Please don't me make me do the math. We are not talking about an orbit, for example in the case of the Voyager probes, the probes robbed Jupiter of its orbital speed by using Jupiter's gravity to change voyager's angular path. In doing so, the probe spent more time accelerating towards the planet than it did decelerating while leaving. Jupiter slowed down - the probe sped up. If Voyager passed Jupiter from the leading side of the planet at the same angle, the probe would have slowed and Jupiter would increase its speed - gravitational braking.

makc · Post by **makc** » Tue Sep 20, 2005 1:36 pm

S. Bilderback wrote:Please don't me make me do the math.

...but, without math, whatever you have said aftewards is meaningless

eidt: here, it's almost exactly what you said, but explained. the speed value does not change relative to Jupiter, but to Sun, and so it cannot "gain" more than 2x speed of Jupiter relative to Sun, in principle. now, let's replace probe with "slingshoted" star, Jupiter with black hole in the center of Milky Way, and Sun... with itself. it follows that, relative to Sun, no star can gain more than 2x 250 km/s, and, relative to black hole itself, no "thrusting" occurs, only change in direction. so, what's behind 1100 km/s? more edit: and I'm not quite sure about "2x" part... shouldn't it be "1x"? now you have to see why I need some math.

BMAONE23 · Post by **BMAONE23** » Tue Sep 20, 2005 4:36 pm

I’m not educated in the mathematics of gravity, however; it is my opinion that different things affect the gravity of any given object. Specific gravity would be the attractiveness of all combined matter that any given object possesses (The heavier the elements, the stronger the relative gravity). For any matter contained therein, the affects of gravity would be slightly countered by kinetic energy as the body rotates. This would only act upon the matter contained within and upon the surface of that body (The inhabitants of Earth for example). The planet would then create a gravity well in the fabric of space that could only reach out so far and then have a nil effect on its surroundings. The same thing would apply to all bodies in space weather they are planets, proto-planets, moons, asteroids, comets, and even satellites and space probes. Because of their much smaller size, the latter would have a gravity well so small that they couldn’t perceptibly affect something the size of a planet (IMHO).
Standing on the earth, you can throw a baseball a few hundred feet. Standing on the moon, you could throw it a few hundred yards. Standing on a moderately sized asteroid, you could throw it into orbit. Standing on a small asteroid, you could throw it into space.

S. Bilderback · Post by **S. Bilderback** » Wed Sep 21, 2005 1:26 am

The math without understanding isn't much help, let me try and help show the "big picture".

Jupiter has a diameter of 142,984 km and a mass 318 X Earth, because of the large distance from the planet core (or center point of gravity) and the wide vector angles of gravitational pull (because of its large diameter), the gravitational pull for the Voyager probes was only 26Gs, the gravitational pull at the surface of the rock core is only 2.5Gs. If the mass of Jupiter was compressed the density of a neutron star the G force at the surface would be 318 G. If the Voyager probes used the slingshot acceleration and could get within a few meters of the gravitational center, the "robbed" K-energy acquired by the probe would be equal to the K-energy needed to keep the probe moving in a straight line and at the same speed. If you plug the numbers into the angular momentum equations you'll see how large the acceleration can be even to a neutron star's near approach to a super massive black hole.

makc · Post by **makc** » Wed Sep 21, 2005 6:43 am

dear friend, acceleration does not have anything to do with the issue at hand. acceleration acts both ways, it speeds probe up 1st and slows it down back (2nd). the only effect of acceleration is change in speed direction (as described in the link above, and illustrated below). and let me note that, without math, there is no room for understanding. let me also note that, in my idiot oppinion, it could take black hole pair to resolve this issue, or perhaps speed change might be a side-effect of frame dragging, but mere acceleration just does not cut it. there's no way you could drop a rock from ISS so that it would "near-miss" the earth and get "slingshoted" out of solar system.