Every star you see in the night sky is part of the Milky Way Galaxy (although on a clear night, you can glimpse one or two galaxies that lie beyond the Milky Way). The Milky Way Galaxy, the galaxy to which our own star, the Sun, belongs, is a vast, disc-like, barred spiral of stars. It resembles the Andromeda Galaxy, also a barred spiral, which lies 2.25 million light years away, but which is significantly larger. Named after the misty band of stars in the night sky—actually our side-on view of one of its spiral arms—the Milky Way contains about 200 billion stars and measures about 100,000 light years across. In the Sun's region, the Galaxy spins at 250 km/sec (150 miles/sec), taking 240 million years to complete one full circle.

Side-on view

Seen from the side, the Milky Way Galaxy looks like a pair of fried eggs stuck together back-to-back. The “yolks” form the central bulge, while the “whites” form the spiral-shaped disc surrounding it.

Structure

The Milky Way Galaxy has a bulge at its centre where older, red stars are concentrated. The bulge is stretched out into a bar shape, so the Milky Way is classified as a barred spiral galaxy. At the centre of the Galaxy there is a supermassive black hole. 

​​​​​​​Four giant arms spiral out from the centre. They are: the Scutum-Centaurus Arm, the Perseus Arm, the Norma-Outer Arm and the Sagittarius Arm. (A fifth, smaller, arm or spur, the Orion Arm, lies between the Sagittarius and Perseus arms.) Younger blue stars are found in these arms, along with clouds of gas and dust, where new stars are forming. The Sun is situated on the Orion Arm, about 26,000 light years (roughly halfway out) from the Galaxy's centre. Here are mostly yellow and orange young-to-middle aged stars.
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Galactic centre

This image (left) of the centre of the Milky Way Galaxy, a "mosaic" of 370 separate observations made over the past 20 years by the Chandra X-ray space telescope, was published in May 2021.

​​​​​​​The image depicts billions of stars—and also reveals countless black holes, neutron stars and remnants of supernovae, all emitting X-rays, high-energy electromagnetic radiation. The white areas in the image are dense clusters of X-ray dots, each representing one of these sources of high energy. X-rays of different energies are shown in orange, green, blue and purple. “What we see in the picture is a violent or energetic ecosystem in our galaxy’s downtown,” said astronomer Daniel Wang, who produced the image from the data transmitted by the Chandra telescope.

Black holes

Dozens of black holes have been found in the Milky Way Galaxy—astronomers think there may be many millions of them. Most are stellar black holes, meaning they were formed from exploding stars, and have masses around 10 times that of the Sun. BH3, discovered in 2024, is the most massive stellar black hole yet found in the Milky Way. Its mass is estimated at 33 times that of the Sun. Sagittarius A*, the supermassive black hole at the centre of the Galaxy, is, however, of a different order. It formed not from an exploding star but from the collapse of vast clouds of dust and gas, and has the combined mass of four million Suns.