The Milky Means is a barred spiral galaxy, one among lots of of billions within the observable universe. It is also our residence.
Like different galaxies, the Milky Means is an remoted assortment of stars and different materials certain collectively by their widespread gravity. Along with the 100 billion to 400 billion stars in our galaxy, the same variety of planets doubtless exist within the Milky Means — a few of them a part of photo voltaic programs and a few floating freely. Between the celebrities sit innumerable nebulas, that are clouds of gasoline and dirt. The overwhelming majority of the interstellar gasoline is hydrogen and helium.
Nonetheless, a number of strains of proof — most significantly, that materials within the galaxy orbits the middle far too shortly to be held collectively by the gravity of seen objects — recommend that many of the mass of the Milky Means is made up of some type of matter that doesn’t work together with gentle. Astronomers name this darkish matter, and its true nature shouldn’t be totally understood.
Who found the Milky Means?
From our vantage level on Earth, the Milky Means appears like a band of diffuse gentle that arcs throughout the nighttime sky. That is the place the English identify comes from: The Romans referred to as it Through Lactea and envisioned it as a band of spilled milk. Astronomers and philosophers debated the character of the Milky Means till Galileo Galilei first noticed it with a telescope and located that the sunshine of the Milky Means comes from innumerable distant stars. The celebs themselves are too distant to see all of them individually, however their mixed gentle provides the acquainted band.
Up till the early 1900’s, astronomers assumed that the Milky Means contained all the celebrities within the universe (both the Milky Means prolonged to fill your complete cosmos, or it was a finite measurement and surrounded by an infinite void). Nonetheless, within the early 1920’s, astronomer Edwin Hubble made detailed observations of the Andromeda Nebula, revealing that it was its personal “island” of stars — a galaxy in its personal proper — positioned tens of millions of light-years away from us, based on Britannica.
What does the Milky Means appear to be?
The Milky Means Galaxy is organized into spiral arms of big stars that illuminate interstellar gasoline and dirt. The solar is in a finger referred to as the Orion Spur. (Picture credit score: Hubble House Telescope)
The Milky Means is a comparatively skinny, flattened disk. This explains why it seems as a band in our sky. After we are wanting within the route of the disk, Earthlings see the mixed gentle of all the celebrities within the galaxy. After we look in a route away from the disk, we see solely the celebrities near our photo voltaic system.
The Milky Means has three principal components: the core, the disk and the halo.
The core is not spherical; it is elongated into the form of a bar wherever from 5,000 to twenty,000 light-years lengthy. As much as 1 / 4 of all the celebrities within the Milky Means reside within the core; the density of stars there may be as much as 1,000,000 occasions larger than it’s within the neighborhood of the solar, based on the House Telescope Science Institute. On the very middle of the galaxy sits Sagittarius A*, a supermassive black gap with a mass that is 4.1 million occasions that of the solar, based on the UCLA Galactic Heart Group.
The stellar disk of the Milky Means has a radius of 75,000 to 100,000 light-years, however it’s only about 1,000 light-years thick. Inside the disk sit a number of main spiral arms, based on NASA, the place the density of stars and gasoline is greater than common and star formation happens at a better price, making these arms stand out in visible observations.
Our photo voltaic system sits within the disk, about 27,000 light-years from the galactic middle, close to the interior rim of the Orion Arm.
Past the disk of the Milky Means is its halo, which is a spherical area with a radius of about 100,000 light-years. The halo accommodates outdated stars and globular clusters, all orbiting the galactic middle in random instructions. The darkish matter extends even farther, as much as 400,000 light-years from the middle, based on a research printed in 2019 within the journal Astronomy & Astrophysics.
The place is the Milky Means?
The Milky Means and the opposite members of our Native Group of galaxies. (Picture credit score: Ron Miller/Stocktrek Photos by way of Getty Photos)
The Milky Means has two main satellite tv for pc galaxies — the Massive and Small Magellanic Clouds — and dozens of smaller satellites. Our nearest neighbor is the Andromeda galaxy, positioned about 2.5 million light-years away. Along with Andromeda and about 80 smaller galaxies, the Milky Means is part of the Native Group, which is a gaggle of galaxies, about 10 million light-years throughout, certain collectively by their widespread gravity, based on Swinburne College.
The Native Group is one member of a bigger construction referred to as the Virgo Supercluster, which is surrounded by a number of nice intergalactic voids, based on Durham College. On the middle of this supercluster sits the Virgo Cluster, an enormous assortment of 1,000 to 2,000 galaxies about 54 million light-years away. The Virgo Supercluster itself is considered a element of a fair bigger construction referred to as the Laniakea Supercluster.
How massive is the Milky Means?
It is tough to estimate the true measurement of our galaxy, as a result of we stay inside it and all of the clouds of gasoline and dirt obscure our observations of it. Astronomers estimate that the overall mass of the Milky Means is round a trillion occasions the mass of the solar, based on NASA. Most of that mass, by far, is within the type of darkish matter; stars characterize round only one% of the mass of the galaxy, and interstellar gasoline accounts for less than 0.1%.
Is the Milky Means shifting?
Relative to the overall enlargement of area that pulls galaxies away from one another (on common), the Milky Means is shifting at roughly 391 miles per second (630 kilometers per second), scientists reported on the preprint server arXiv in 2005. Our galaxy is on a collision course with Andromeda, and our two galaxies will crash and start to merge in about 5 billion years.
Each the Milky Means and Andromeda are shifting collectively within the route of what is referred to as the Nice Attractor, the College of Hawaii Institute for Astronomy reported. The Nice Attractor is considered the middle of the Laniakea Supercluster. Nonetheless, observations of this area of the native universe are tough as a result of it lies previous the route of our galactic middle, which obscures our view.
—California Academy of Sciences has this nice academic video that lets college students tour the Milky Means.
—This Nationwide Geographic Guide “Visible Galaxy” has attractive photos of the Milky Means.
—Try these actions and assets in regards to the photo voltaic system and night time sky on the McDonald Observatory.