Galaxies
https://www.newscientist.com/article/2158391-mystery-dark-matter-may-be-ordinary-neutrons-that-have-decayed/
The Milky way
- When confronted with the topic of stars and galaxies, a question that tantalizes most humans is, “Is there other intelligent life out there?” Let’s put some numbers to it—
- As many stars as there are in our galaxy (100 – 400 billion), there are roughly an equal number of galaxies in the observable universe
- so for every star in the colossal Milky Way, there’s a whole galaxy out there.
- All together, that comes out to the typically quoted range of between 1022 and 1024 total stars, which means that for every grain of sand on every beach on Earth, there are 10,000 stars out there.
10,000,000,000,000,000,000,000,000 = 1024
One hundred billion galaxies
- According to the best estimates of astronomers there are at least one hundred billion galaxies in the observable universe.
- They've counted the galaxies in a particular region, and multiplied this up to estimate the number for the whole universe.
The Hubble Ultra-Deep Field (HUDF) is an image of a small region of space in the constellation Fornax, containing an estimated 10,000 galaxies.
The original release was combined from Hubble Space Telescope data accumulated over a period from September 24, 2003, through to January 16, 2004.
Looking back approximately 13 billion years (between 400 and 800 million years after the Big Bang) it has been used to search for galaxies that existed at that time.
The HUDF image was taken in a section of the sky with a low density of bright stars in the near-field, allowing much better viewing of dimmer, more distant objects. ....
When combined with existing HUDF data, astronomers were able to identify a new list of potentially very distant galaxies.
Black holes
Most galaxies have at least one. In a few words - they can eat stars. We have billions of years before this type of demise.
A
We will be long gone by then.
B
The universe is unpredicable. Next year?
