Hubble eXtreme Deep Field

There Are At Least 10 Times More Galaxies In The Universe Than We Thought

The universe suddenly looks a lot more crowded.

Waaaaay back in 1995, the Hubble Deep Field images surprised the world by revealing how crammed the universe is with galaxies. At that time astronomers estimated there were about 200 billion galaxies in the universe. Recent estimates put that count closer to 2 trillion, at least 10 times as many galaxies as we thought. However, about 90% of the galaxies in the observable Universe are actually too faint and too far away to be seen or studied. Phil Plait explains:

Now, let me be clear. This doesn’t meant the Universe is ten times bigger than we thought, or there are ten times as many stars. I’ll explain — I mean, duh, it’s what I do — but to cut to the chase, what they found is that there are lots of teeny, faint galaxies very far away that have gone undetected. So instead of being in a smaller number of big galaxies, stars are divvied up into a bigger number of smaller ones.

And it doesn’t mean the Universe has 10 times more mass than we thought. The mass is the same, it’s just distributed differently than we thought. It’s like knowing there are 1 million people in a city, and finding out they live in 100,000 buildings when you thought they were only in 10,000. There are more buildings, but not more people

This discovery has also helped lead to explanations for Olbers’ paradox which states, “Why is the sky dark at night if the universe contains a multitude of stars?” NASA helps explain:

The team came to the conclusion that indeed there actually is such an abundance of galaxies that, in principle, every patch in the sky contains part of a galaxy. However, starlight from the galaxies is invisible to the human eye and most modern telescopes due to other known factors that reduce visible and ultraviolet light in the universe. Those factors are the reddening of light due to the expansion of space, the universe’s dynamic nature, and the absorption of light by intergalactic dust and gas. All combined, this keeps the night sky dark to our vision.

The sky is literally covered in galaxies! Mind boggling to be sure!

Youthful NGC 362 Globular Cluster

A Young Globular Cluster

Youthful NGC 362 Globular Cluster

Earlier this week NASA released this dazzling image of NGC 362. It is one of about 150 known globular clusters on the outskirts of our own galaxy, the Milky Way. Globular clusters are giant spheres that contain hundreds of thousands of stars and reside in the outskirts of galaxies. The ESA says NGC 362 is unusual:

By studying the different elements present within individual stars in NGC 362, astronomers discovered that the cluster boasts a surprisingly high metal content, indicating that it is younger than expected. Although most globular clusters are much older than the majority of stars in their host galaxy, NGC 362 bucks the trend, with an age lying between 10 and 11 billion years old. For reference, the age of the Milky Way is estimated to be above 13 billion years.

This image, in which you can view many of NGC 362’s individual stars, was taken by Hubble’s Advanced Camera for Surveys (ACS) If you want a new desktop image, here’s the 42 MB full-size original (it will automatically download).

Hubble eXtreme Deep Field

Hubble eXtreme Deep Field

Hubble eXtreme Deep Field
Image courtesy of NASA

NASA has recently released a new Deep Field image called eXtreme Deep Field (XDF) that improves on the older Ultra Deep Field (UDF) image. The XDF is the deepest image of the sky ever obtained and reveals the faintest and most distant galaxies ever seen. This image is a composite of nearly ten years worth of photographic exposures taken by the Hubble Space Telescope – over 2,000 photographs totaling 22.5 days worth of total exposure time. Nearly everything you see in the picture is a galaxy containing billions of stars.

The new full-color XDF image reaches much fainter galaxies and includes very deep exposures in red light from Hubble’s new infrared camera, enabling new studies of the earliest galaxies in the universe. The XDF contains about 5,500 galaxies even within its smaller field of view [than the UDF]. The faintest galaxies are one ten-billionth the brightness of what the human eye can see.

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.

Click on the image above for the gigantic 1.4MB image. And keep looking up.