Our galaxy the Milky Way is growing and predicted to expand into its neighbour Andromeda, say scientists.
Thankfully, the cosmic collision will not happen for about another four billion years.
The Milky Way, a barred spiral galaxy, is already huge with a diameter of about 100,000 light years. It is home to several hundred billion stars, including the sun which occupies an insignificant spot within one of its minor spiral arms.
At the outer edge of the main body of the galaxy, the galactic disc, new stars are still being created out of gas and dust. Computer simulations suggest that the new stars will slowly increase the size of the galaxy.
To check if this was right, scientists looked at other galaxies similar to the Milky Way using a number of ground-based and space telescopes.
They calculated that the Milky Way, and other galaxies like it, are growing at around 500 metres per second.
Spanish lead researcher Cristina Martinez-Lombilla, from the Astrophysical Institute of the Canaries in Tenerife, said: "The Milky Way is pretty big already. But our work shows that at least the visible part of it is slowly increasing in size, as stars form on the galactic outskirts.
"It won't be quick, but if you could travel forward in time and look at the galaxy in three billion years' time it would be about 5% bigger than today."
In about four billion years the Milky Way is predicted to collide and merge with its mighty neighbour, the Andromeda galaxy, she said.
Currently a safe 2.5 million light years away, the Andromeda galaxy is even larger than the Milky Way. Also a spiral galaxy, it is 110,000 light years across and contains an estimated one trillion stars.
The new research will be presented on Tuesday April 3, at the European Week of Astronomy and Space Science meeting in Liverpool.