Over 5,500 galaxies depicted in Hubble’s eXtreme Deep Field, including a galaxy formed only 450 million years after the Big Bang
Magnificent spiral galaxies similar in shape to our Milky Way and the neighboring Andromeda galaxy appear in this image, as do the large, fuzzy red galaxies where the formation of new stars has ceased. These red galaxies are the remnants of dramatic collisions between galaxies and are in their declining years. Peppered across the field are tiny, faint, more distant galaxies that were like the seedlings from which today’s magnificent galaxies grew. The history of galaxies — from soon after the first galaxies were born to the great galaxies of today, like our Milky Way — is laid out in this one remarkable image.
The universe is 13.7 billion years old, and the XDF reveals galaxies that span back 13.2 billion years in time. Most of the galaxies in the XDF are seen when they were young, small, and growing, often violently as they collided and merged together. The early universe was a time of dramatic birth for galaxies containing brilliant blue stars extraordinarily brighter than our sun. The light from those past events is just arriving at Earth now, and so the XDF is a “time tunnel into the distant past.” The youngest galaxy found in the XDF existed just 450 million years after the universe’s birth in the big bang.
How Many stars are in the universe?
Astronomers had estimated that the observable universe has between 100 billion – 200 billion galaxies. Our own Milky Way is home to around 300 billion stars, but it’s not representative of galaxies in general. The Milky Way is a titan compared to abundant but faint dwarf galaxies, and it in turn is dwarfed by rare giant elliptical galaxies, which can be 20 times more massive. By measuring the number and luminosity of observable galaxies, astronomers put current estimates of the total stellar population at roughly 70 billion trillion (7 x 1022).