How many known galaxies are there?
There are more than 100 billion galaxies in the observable universe.., http://en.wikipedia.org/wiki/Galaxy Abell 2029 houses the largest known galaxy.., http://en.wikipedia.org/wiki/Abell_2029 The galaxy’s name is IC1101, a giant lenticular galaxy with a diameter of 5.6 to 6 million light-years, 80x Milky Way’s diameter.., I do not know if this was already surpassed by those monstrous spider-like galaxies lately… http://en.wikipedia.org/wiki/IC_1101 Another interesting galaxy: http://www.earthsky.
The Hubble Ultra Deep Field photo, made from a compilation of many photos taken over the course of 4 months in 2003-2004, is around 11 square arc minutes in size. For Hubble to photograph the entire sky at this scale, it would have to take approximately 13,000,000 different photos. In the Ultra Deep Field photo, scientists estimate at least 10,000 galaxies are visible. Multiply 10 thousand by 13 million and you get 130 billion. These are just the observable galaxies Hubble can see from Earth. It is believed that of the 30 members in our Local Group of galaxies, only 5 could be seen by Hubble at the same distance photographed in the Deep Field. This means we could multiply 130 billion by 6 to give us the total of all galaxies; spirals, ellipticals, irregulars, and most important, the dwarfs. The number is a possible 786 billion galaxies.
No-one is really sure exactly how many there are. Many millions probably. One thing that might be useful in answering this is a 2 year survey (the 2dF Galaxy Survey) which has just finished. So far they have surveyed 100, 000 galaxies to make a 3-D map of the universe, but their goal is 250,000! And that’s certainly not all of them that are out there. Look at the 2dF website for more on this. There are 4 million names in the NASA Extragalactic database! (NED) Although this is probably not everything either. It is estimated that there are as many as 200 billion galaxies in the observable universe, but we aren’t able to see all of them yet as our telescopes are not big enough. This number is interesting because it is similar in magnitude to the number of stars estimated to be in our Galaxy.
