When you look up at the sky, all the stars you see belong to the Milky Way, the spiral galaxy to which we belong. The Milky Way is home to all the alien worlds that humans have ever discovered, and the billions of other planets that exist in the galaxy and that we do not yet know exist.
On a dark night, the Milky Way’s dance begins like a luminous ribbon in the sky. When the sky is dark enough and clear enough, away from light pollution, this ribbon is so intense that the stars and clouds of dust and gas illuminate our field of vision. These clouds are so prominent that the Australian aboriginal people interpret the shapes they take in the wind.
Our galactic home is one of the trillions of galaxies in the universe. Astronomers have been studying it for nearly a century, since Edwin Hubble discovered that our neighbor Andromeda was not a nebula, but a galaxy in its own right. Yet, men are still trying to unravel the secrets of the Milky Way, and to determine its place in the vastness of the universe.
Here are some facts you (probably) do not know about our galaxy, which is 13.6 billion years old.
THE MILKY WAY IS (OVERALL) FLAT
Our galaxy is about a hundred thousand light-years long and a thousand light-years wide. Inside this generally flat (albeit somewhat distorted) disk, the Sun and its planets are enveloped in clusters of gas and dust, more than 26,000 light years from the tumultuous heart of our galaxy. A wave of dust and stars envelops the galactic center.
THE EARTH IS 18 GALACTIC YEARS OLD
The solar system moves through interstellar space at a speed of 805,000 kilometers per hour. Even at this speed, it takes 250 million Earth years to circle the Milky Way. The last time our 4.5 billion-year-old planet was in the same position in the Milky Way, all five continents were still touching, dinosaurs had just appeared, mammals had yet to evolve, and the world’s greatest extinction mass of our planet’s history was falling into place.
A HUGE BLACK HOLE IS LOCATED AT THE CENTER OF OUR GALAXY
Sagittarius A, located in the center of the Milky Way, is a huge black hole whose mass is about 4 million times that of our sun. This object has never been observed directly – it is hidden by thick clouds of dust and gas. However, astronomers have been able to observe the orbit of stars and clouds near the center of the galaxy, and in this way calculate the mass of this hidden cosmic giant.
Huge black holes are said to have made their home in the heart of most galaxies, and some feed on surrounding matter so forcefully that they reject powerful radiation visible millions of light years away.
Discover an animation of the heart of the Milky Way unveiled at the last congress of the American Astronomical Union.
THE MILKY WAY IS NOT ETERNAL
In about 4 billion years, the Milky Way will collide with its closest neighbor, the Andromeda Galaxy. The two spiral galaxies are approaching each other at a speed of 402,000 kilometers per hour. When they make contact, it will not be as catastrophic as one might imagine – Earth will certainly survive this galactic shock, and only a few rare stars will actually be destroyed. The new mega-galaxy will offer intensely starry night skies.
OUR SUN IS JUST A STAR AMONG HUNDREDS OF BILLIONS
The Milky Way is home to a hundred billion stars. Maybe 300 or 400 billion. We do not yet know for sure how many stars make up our galaxy. Several of them are small, faint stars that are difficult to detect over great cosmic distances, especially when massive clouds obscure the horizon near Sagittarius A *. Astronomers have estimated the total number of stars in the Milky Way based on the mass and brightness of our galaxy, but it remains impossible to determine this number exactly.
WE ARE SURROUNDED BY A BLACK HALO
The Milky Way is nested in a cluster of dark matter much larger and more massive than the galaxy itself. In the late 1960s, astronomer Vera Rubin deduced the presence of dark matter in the periphery of galaxies by studying the speed of rotation of stars in spiral galaxies. She observed that the stars near the outskirts of Andromeda were moving at a speed that should have sent them to the far reaches of the universe. Yet they stayed in their orbit, which meant that some sort of cosmic glue held them together. This “glue”, we now know, is dark matter.
WE HAVE OLD STARS
More than 150 ancient groups of stars, some of which are among the oldest in the universe, also surround the Milky Way. Called globular clusters, these conglomerates of primordial stars live in the orbit of the Milky Way and its galactic center. Each of these clusters includes hundreds of thousands of stars. In addition, dozens of satellite galaxies accompany the Milky Way in its course; some are difficult to observe, but the Small Cloud and the Large Magellanic Cloud appear every evening in the southern hemisphere.
THE GALAXY IS AN ISLAND IN A CURRENT OF STARS
The Milky Way absorbs galaxies that come a little too close. Over time, scientists who have studied our galaxy have detected two dozen clusters of stars, afterglow of galaxies. These rivers of ghostly stars were formed when the very powerful gravity of the Milky Way dismantled the smallest galaxies. During the last Congress of the American Astronomical Union, a team from the Dark Energy Survey, an international program seeking to map hundreds of millions of galaxies in order to better understand the nature of dark energy, announced the detection 11 additional star currents, some of which bear Aboriginal names.
THE GALACTIC CENTER RELEASES HOT AIR
The Milky Way releases massive bubbles of extremely hot gas. Fermi bubbles are radiating “8” shaped structures located on either side of the galactic center of the Milky Way and oriented perpendicular to the galactic disk. Unknown until 2010, it is not clear exactly why these bubbles form and exist, but scientists believe they could be linked to the death of a star in the Sagittarius A region.
GAS CLOUDS LEAVE OUR GALAXY
Observed recently from the Green Bank Observatory, more than a hundred hydrogen clouds are making their way through the galaxy at a speed of 1.2 million kilometers per hour. Scientists studying the desert cloud explain that clouds can act as tracers for the process those results in Fermi bubbles.
