Our galaxy is the Milky Way.

On summer evenings, you can sometimes lift your eyes to the sky and see a diffuse glow, like a long strip of light in space: it's the Milky Way. But what is it?
A clear streak crosses the summer sky, almost like a milky trail. Indeed, that's why scientists called it the Milky Way!

But what is that strip? Easy: it's our galaxy.

The Milky Way is our galactic home.

A galaxy is a cluster of many stars held together by a primordial and very powerful force called gravitational pull. The glow you see along the Milky Way is generated by a cluster of these stars. But how many of them are there? Our Sun is just one of the 300 billion stars that make up the Milky Way. And around each of these 300 billion stars are often orbiting planets, like Earth and the other 7 planets (8 to be exact, if you include the dwarf planet Pluto) that make up our Solar System.

To make matters worse, there are an estimated 100 billion galaxies in the entire universe! Depending on their shape, galaxies fall into four categories:

Spiralling
Barrier spirals
Elliptical
Irregular

The Milky Way is in the shape of a closed spiral (i.e. a 'streak' of stars runs through its centre) and rotates: it takes the Sun 200 million years to circle the centre of the galaxy!

How did the name for our galaxy come about?

In Italy the galaxy is called Via Lattea, in English it's Milky Way... In short, we're all talking about milk. How did this happen?

The Europeans took the name from the Greek galaxias, which in turn comes from gala, galaktos, meaning milk. The Greeks chose this name after being inspired by one of their ancient myths.

Zeus, the father of the gods, fell in love with the mortal Alcmene. To seduce her, he transformed himself into her husband Amphitrion and from their union the legendary Hercules was born. To make his son fully divine (and therefore immortal), Zeus tried to bring the child close to the breast of Hera - wife of Zeus and queen of the gods - while she slept. He intended to nourish the child with the abundant milk of the gods. Hera, however, suddenly woke up and immediately pushed the baby away, causing the milk to splash into the sky. Well, according to the Greeks, these splashes of milk became the Milky Way.

The history of the Milky Way

Unlike other galaxies, ours has been without any loud incidents, at least nothing terrible has happened during humanity's lifetime. But, has the Milky Way always been a quiet galaxy? Not at all, at least according to a recent Australian study analysing the traces left in space by a colossal explosion that swept through the centre of our galaxy about 3.5 million years ago.

A team of researchers from the University of Sydney has discovered evidence of an apocalyptic 'explosion' that shook the centre of our galaxy. The wave from the impact was felt 200,000 light years away!

According to results presented in the Astrophysical Journal by a team led by Professor Joss Bland-Hawthorne of the ARC Australian Centre of Excellence for Whole-Sky Astrophysics in Three Dimensions (ASTRO 3D), not too long ago - at least astronomically speaking - the Milky Way was torn apart by a terrible explosion near a supermassive black hole at the heart of our galaxy.

The shock is thought to have been caused by the nuclear activity of a black hole - known as Sagittarius A* and more than four million times more massive than the Sun - which led to a very unusual phenomenon called a Seyfert flare.

This flash generated two gigantic 'cones of ionisation' which crossed the Milky Way, emitting radiation waves of such intensity that they were perceptible at distances of up to 200 000 light-years. The flash was so powerful that the shock waves are still identified as the so-called Magellanic Current, a stream of neutral hydrogen produced by the gravitational interaction between the Milky Way and the Magellanic clouds.

"The glow must have been like a beam of light," explains Professor Bland-Hawthorne, "Imagine you are in the dark and then suddenly someone turns on the lights for a moment...

Recently and long ago - everything is relative.

Scientists from ASTRO 3D and the University of Sydney were able to track the apocalyptic event by examining data from the Hubble Super Telescope, which showed that the explosion occurred relatively recently. After all, 3.5 million years is nothing to the universe, or even Earth. We are talking about a fairly recent timeline, because at that time, Australopithecines, who later became our ancestors, had already appeared on the planet.

According to Magma Guglielmo, a researcher at the University of Sydney and co-author of the study, these results "fundamentally change our view of the Milky Way".