# Astrophysics, star collision

• AUK 1138
In summary, the conversation discusses a homework problem involving the collision of Andromeda and the Milky Way galaxies. The problem asks for the time it would take for a star to collide with the sun, given the relative speed and distance between the two stars. The conversation also explores different approaches to solving the problem and discusses the concept of mean free path and the number of particles per unit volume. The question of whether a collision between a star and the sun is possible is also raised.
AUK 1138

## Homework Statement

The problem is assume Andromeda and the Milky Way are going to collide. the relative speed of them moving is 10^6m/s. assume each star has the radius of our sun (6.955*10^8m) the distance between each star is 3.1*10^18 m. how long will it take for a star to collide with the sun?

## Homework Equations

i believe it might solved with the mean free path with mean free time= lamda/v, lambda being 1 over the area of the object in question.

## The Attempt at a Solution

I've done a few things with this problem, first i divided the radius by the distance then divided by velocity, but that doesn't work due to the units. i tried the mean free path way, but then the distance isn't involved and it seems like it should be. the other thing i tried was to find the area of disc with radius of the distance and the subtracting the area of radius then use that for the mean free time. that seemed all right, but i still have a unit problem. also the answers have seemed low. only the first way provided an answer that i felt was correct, but again, unit problems.

i'm now thinking maybe i have to use 1/distance and then divide the radius by that then by velocity, but I'm not sure why.

What is the number of particles per unit volume in this problem? How can you use the distance between particles to compute that?

"How long" seems like a very odd question in this circumstance. Wouldn't "what's the probability be of a collision?" be a lot more meaningful question? You don't really think there would be a collision with the sun, do you?

voko said:
What is the number of particles per unit volume in this problem? How can you use the distance between particles to compute that?

i figure the number of particles is 4 per (3.1*10^18)^2.

and no, i don't expect there to be a collision with the sun and another star. that's one of the reasons i posted this question. it seems almost absurd. but it's a homework problem nonetheless.

any help is appreciated.

AUK 1138 said:
i figure the number of particles is 4 per (3.1*10^18)^2.

Why 4 and why (3.1*10^18)^2? The latter is not volume dimensionally.

i figure 4 due to assuming 1 star on every corner one a square. i assume one of my answers is right, but i don't know which.

A square does not have any volume. The mean free path is defined in terms of number of particles per volume. Imagine a star in space. How many stars do you have within a sphere of a certain radius? What is the volume of this sphere?

## 1. What is astrophysics?

Astrophysics is a branch of physics that focuses on studying the physical properties and behavior of objects and phenomena in the universe, including stars, galaxies, and other celestial bodies.

## 2. How do stars collide?

Stars can collide in a few different ways. One possibility is through a binary star system, where two stars orbit each other and eventually come close enough to collide. Another possibility is when a star passes through a dense gas cloud or another star's planetary system, causing gravitational disturbances that can lead to a collision.

## 3. What happens when stars collide?

When stars collide, the resulting impact can cause a release of energy in the form of light and heat. This can lead to the creation of new elements and can also cause the stars to change shape or even explode.

## 4. Can star collisions be observed?

Yes, star collisions can be observed using telescopes and other instruments. However, they are relatively rare events and can be difficult to detect due to their short duration and the vastness of space.

## 5. Are star collisions dangerous for Earth?

No, star collisions are not dangerous for Earth. The nearest star to Earth, the Sun, is too far away to be affected by any potential collisions. Additionally, the chances of a star collision happening near Earth are extremely low.

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