· As the universe expands, why don't galaxies get stretched out?

Answer 1

Even though gravity is the weakest known force, there is enough gravitational force from all the galaxy's mass to keep it together. It is the space-time fabric between the galaxies that is expanding.

Answer 2

The expansion of the Universe is just an approximate solution to the Einstein field equations for gravity. If all the matter were distributed uniformly, a uniform expansion of everything would be the solution. On large scales (bigger than clusters of galaxies) this approximation is quite accurate, and so the uniform expansion solution fits well.

On small scales (smaller than clusters of galaxies) the matter is not at all uniform. There are many deep potential wells. You can think of the solution for the space-time manifold as something like a uniformly inflating toy balloon, except that the balloon surface, on small scales, has many small "puckers" where the galaxies are. Within those "puckers", the dynamics acts pretty much like Newtonian gravity, and the manifold is not much affected by the overall expansion outside. In other words, the full and accurate solution to the Einstein field equations is quite complex, and not all of the manifold is expanding.

I'm not so sure about Lorenzo Steed's answer. It is true that the galaxies will slowly lose some of their mass as the energy of the stars radiates out into intergalactic space, but most of the mass will wind up in stellar "cinders" like white dwarfs that will persist for extremely long periods of time (10^30 years) and will maintain the potential well of the galaxies. To make a planet expand, you have to envoke somthing like the decay of baryons.

Answer 3

The galaxies are not expanding, just the space between them. The mass of the stars in a galaxy is enough for gravity to hold them together.

Answer 4

The galaxies themselves are held together by gravity. Recent research has suggested that there may be a super-massive black hole at the centre of each galaxy, with all its stars and their associated planets revolving around it. it is, however, the space between the galaxies that is expanding and, in a few billion years, it might be possible to look at the night sky and see almost no stars at all, as they will all be too far away. Don't worry, though. Our sun will swallow up the earth and all its inhabitants long before that happens!

Answer 5

Mostly these answers are correct - gravity is the big factor here. But, more correctly, as the energy of each galaxy decreases (meaning as entropy increases), the loss of energy (and its equivalent mass) will result in a reduction of the available gravitational force, so that each galaxy WILL expand, as each solar system will, as each planet from its primary will.

Answer 6

theyre all drawn towards the black hole at the center. a galaxy is like a huge solar system. the solar system isnt expanding so why should the galaxies. and theres hundreds of billions of stars in a galaxy that all pull on eachother, keeping it together. and then you also have dark matter to keep it all intact.

Answer 7

Each galaxy has a black hole in the middle which supplies the gravity for all the solar systems.

Answer 8

Yes they do. the galactic expansion is also a phenomenon in every galaxy, including ours. As we could see the spectrum of light from stars of our galaxy in its spiral arms we see the difference in Doppler shift namely the 'red shift' as different with different stars in different locations indicating the speed variation in its position with time axis to show the expansion of the galaxy itself, but we get to believe they are in one hold still, since what we see and understand today on the positions of the stars are tens of thousands of years old light emitted by them and the current status would arrive in next ten thousand to fifty thousand years later only!

Our solar system itself is floating like a speck of dust in one of the spiral arm of our milky way galaxy and positioned 30,000 light years away from its center in one end! In the center of the galaxy a huge cluster of millions of stars are in great explosion with unbelievable mass and energy release making the matter to expand too, which we could observe in its electromagnetic spectral line bandwidth variation as one millionth of a millimeter in a day's time, could give your the idea of how far we are away from the system to know things in the right way and to interpret the meaning for everyone to understand!

Answer 9

Because despite what astrophysicists say, there are forces at work in the universe that are still beyond our comprehension.
Beyond the observable universe, everyone is guessing--no one really even knows the true nature of gravity, so how can they begin to explain the phenomena of the universe??

Answer 10

Thats what BB fails to explain !I am not joking it is a serious answer please note.