When the astronomers - Rodrigo Ibata from the European Southern Observatory, Harvey Richer and Douglas Scott from the University of British Columbia in Canada, and Ronald Gilliland from the Space Telescope Science Institute in Baltimore - compared the two Hubble images, they noticed that five objects appeared to have moved, indicating that they are local to our galaxy. Two of them appear to be white dwarfs, while the other three require further observations.

White dwarfs are Earth-sized stars that have the masses similar to the mass of our Sun, which makes them extremely dense and compact. The possible white dwarfs seen by Hubble are very old - around 12 billion years of age. According to theoretical predictions, if all the missing mass in the galactic halo is made up of these white dwarfs, then four such stars should be seen in the Hubble Deep Field.