Galaxies in the Universe
Some Useful Information about Our Universe
We know from studies of radioactivity of the Earth and Sun that our solar system probably formed about 4.5 billions years ago, which means that the Universe must be at least twice that old, because before our solar system formed, our Milky Way galaxy had to form, and that probably took several billions years by itself.
It would be reasonable to guess that the Universe is at least twice as old as our Sun and Earth. However, we can’t do radioactive dating on distant stars and galaxies. The best we can do is balance a lot of different measurements of the brightness and distance of stars and the red shifting of their light to come up with some ballpark figure. The oldest star clusters whose age we can estimate are about 12 to 15 billions years old. So it seems safe to estimate that the age of the Universe is at least 15 billion years old, but probably not more than 20 billion years old.
This matter is far from being settled by astrophysicists and cosmologists, so stay tuned. There could be radical new developments in the future.
We can observe only a portion of the entire universe. Because the universe is only about 14 billion years old, light has only had about 14 billion years to travel through it. Therefore, the most distant regions of the universe we can see are about 14 billion light-years away. This is the extent of the “observable universe,” but the entire universe is probably much larger. It could even extend infinitely in all directions.
Types of Galaxies
There are spiral galaxies, like Andromeda, and barred spirals — similar to spiral galaxies but containing a rectangular “bar” of material through their centers. There are ellipticals: spherical masses of stars, gas, and dust. There are lenticulars, which appear lens-shaped; and there are irregulars, relatively formless clouds of matter lacking organized structure. In the late 1930s, astronomers discovered examples of a new class, dwarf spheroidal galaxies, and later found so-called peculiar galaxies, which seem highly distorted.
Our Milky Way Galaxy
The Milky Way is the galaxy that contains our Solar System, with the name describing the galaxy’s appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye.
WASHINGTON — Space is vast, but it may not be so lonely after all: A study finds the Milky Way is teeming with billions of planets that are about the size of Earth, orbit stars just like our sun, and exist in the Goldilocks zone — not too hot and not too cold for life.
Astronomers using NASA data have calculated for the first time that in our galaxy alone, there are at least 8.8 billion stars with Earth-size planets in the habitable temperature zone. The study was published Monday in the journal Proceedings of the National Academy of Science. – http://www.nydailynews.com/news/national/8-8-billion-earth-like-planets-milky-study-article-1.1507171
A monochromatic image of the Andromeda Galaxy, our galactic neighbor, reveals the intricate details of its spiral arms, areas of swirling gas clouds near the galaxy’s center, and two satellite companions, M32 (above, left of the center of Andromeda), and NGC 205 (below the galaxy’s center).
The magnificent edge-on Sombrero Galaxy
One of the greatest edge-on galaxies in the sky, and the one most people say looks like a flying saucer, is the Sombrero Galaxy (M104) in Virgo. This galaxy consists of a large rotating disk with a prominent dust lane edging it, consumed by a glowing halo of gas and stars. It lies 10 million light-years away and is about 49,000 light-years across — half the size of the Milky Way.
NASA AND THE HUBBLE HERITAGE TEAM (AURA/STScI)
NGC 6744: A galaxy that looks like the Milky Way
The brilliant galaxy NGC 6744, which lies in the southern sky in Pavo, is a larger version of the Milky Way. This barred spiral stretches 175,000 light-years across — some 75 percent bigger than our home. Its structure, however, is similar to ours, with a core, a strong bar through its center, and radiating spiral arms filled with glowing stars and gas.
Hubble Telescope’s top ten greatest space photographs
28 million light years from Earth – was voted best picture taken by the Hubble telescope. The dimensions of the galaxy, officially called M104, are as spectacular as its appearance. It has 800 billion suns and is 50,000 light years across