A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. The word galaxy is derived from the Greek galaxias, literally “milky”, a reference to the Milky Way.
Diameter
approximately 3,000 to 300,000 light years
Most of the galaxies are 1,000 to 100,000 parsecs indiameter (approximately 3,000 to 300,000 light years) and are separated by distances on the order of millions of parsecs (or megaparsecs).
Different languages
In other languages galaxy
American English: galaxy /ˈgæləksi/Brazilian Portuguese: galáxia.Chinese: 星系European Spanish: galaxia.French: galaxie.German: Galaxis.Italian: galassia.Japanese: 星雲
Colors
Why are galaxies the colors that they are, like when we see them through telescopes they are blue, white, red, sometimes purple or a mixture of colors.
astronomer Charles Messier
The first galaxies were identified in the 17th Century by the French astronomer Charles Messier, although at the time he did not know what they were. Messier, who was a keen observer of comets, spotted a number of other fuzzy objects in the sky which he knew were not comets.
It is very difficult to count the number of stars in the Milky Way from our position inside the galaxy. Our best estimates tell us that the Milky Way is made up of approximately 100 billion stars. These stars form a large disk whose diameter is about 100,000 light years. Our Solar System is about 25,000 light years away from the center of our galaxy – we live in the suburbs of our galaxy.
One of the brightest galaxies in the night sky, Centaurus A, is well known for its distinct “S” shape. This shape is believed to be the result of a clash between a spiral and an elliptical galaxy about 100 million years ago.⠀
⠀
Now, for the first time, scientists have mapped out the invisible magnetic fields pulsing through Centaurus A using infrared light. The results show how the merging of the two original galaxies created a new, reshaped, and contorted galaxy that not only combined the two galaxies’ magnetic fields but amplified their forces.⠀
⠀
The large-scale magnetic fields, across 1,600 light-years, are parallel to the dust lanes seen in visible light and other wavelengths. However, the fields appear twisted and distorted near the middle. The twisting is a remnant of the spiral-shaped magnetic field from one of the original galaxies, while the active, supermassive black hole at its core adds to the distortions.⠀
⠀
I don’t want to alarm you, but there’s a massive galaxy heading our way and will collide with us in a few billion years. But aren’t most galaxies speeding away? Why is Andromeda on a collision course with the Milky Way?
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
I don’t want to freak you out, but you should be aware that there’s a gigantic galaxy with twice our mass headed right for us. Naw, I’m just kidding. I totally want to freak you out. The Andromeda galaxy is going to slam head first into the Milky Way like it doesn’t even have its eyes on the road.
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
This collision will tear the structure of our galaxy apart. The two galaxies will coalesce into a new, larger elliptical galaxy, and nothing will ever be the same again, including your insurance premiums.
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
And now that we know the disaster is inbound, all we can do is ask WHY? Why this is even happening? Isn’t the Universe expanding, with galaxies speeding away from us in all directions? Shouldn’t Andromeda be getting further away, and not closer?
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
Here’s the thing, the vast majority of galaxies are traveling away from us at tremendous speed. This was the big discovery by Edwin Hubble in 1929. The further away a galaxy is, the faster it’s moving away from us. The most recent calculation by NASA in 2013 put this amount at 70.4 kilometers per second per megaparsec. At a billion light-years away, the expansion of the Universe is carrying galaxies away from us at 22,000 km/s, or about 7% of the speed of light. At 100 million light-years away, that speed is only 2,200 km/s.
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
Andromeda is only 2.5 million light-years away. Which means that the expansion of the Universe is carrying it away at only 60 kilometers per second. This is clearly not fast enough for our purposes of not getting our living room stirred into the backyard pool. As the strength of gravity between the Milky Way and Andromeda is strong enough to overcome this expansive force. It’s like there’s an invisible gravity rope connecting the two galaxies together. Dragging us to our doom. Curse you, gravity doom rope!
It is very difficult to count the number of stars in the Milky Way from our position inside the galaxy. Our best estimates tell us that the Milky Way is made up of approximately 100 billion stars. These stars form a large disk whose diameter is about 100,000 light years. Our Solar System is about 25,000 light years away from the center of our galaxy – we live in the suburbs of our galaxy.
The small magellanic cloud (SMC) is a dwarf galaxy orbiting the Milky Way. It contains about 7 billion solar masses but it’s only visible from the southern hemisphere. It’s about 200,000 light years away.
I requested a remote observation from a telescope.live instrument in Chile. I then downloaded the monochrome images, stacked them, sharpened and adjusted them in Affinity Photo to produce this picture.
Two enormous galaxies captured by Hubble Space Telescope neighbor each other approximately 350 million light-years away.
The galaxy on the left is a lenticular galaxy, a galaxy type that sits between the more familiar elliptical and spiral varieties. The galaxy on the right, is a spiral galaxy facing side-on. These two galaxies, among thousands, are members of the Perseus galaxy cluster.
The Perseus galaxy cluster is one of the most massive objects known in the universe! This larger-than-life cluster is named after a major figure in Greek mythology – Perseus, a valiant warrior who possessed some powerful weapons – including the head of the Gorgon Medusa, which had the capability to turn everything to stone.
