Dust makes toddler galaxy look like a grown-up

Suppose you would find a toddler with a full-grown moustache. That would be weird, right? Astronomers have found something just as weird: a very young galaxy, not with a moustache, but with lots of dust. No one expected so much dust to form in the first few hundred million years of a galaxy’s life.

Most galaxies formed long, long ago, when the universe was less than a billion years old. So if you want to study a very young, new-born galaxy, you’ll have to look back in time. Luckily, that’s easy in astronomy. You only need to look very, very far away.

Dust makes toddler galaxy look like a grown-up

Using the Hubble Space Telescope, astronomers discovered an extremely faint smudge of light – probably a very remote galaxy. The European Very Large Telescope in Chile was able to measure the galaxy’s distance: 13.1 billion light-years. That means that the light of the galaxy takes 13.1 billion years to reach Earth. In other words: we see the galaxy as it was 13.1 billion years ago. We are looking back in time, to an era when the universe was only 700 million years old.

Back then, the galaxy can’t have been much older than a few hundred million years – much younger than ‘mature’ galaxies like our own Milky Way, which may be 13 billion years old. If we compare our Milky Way to a middle-aged man, the distant galaxy is a young toddler.

Surprisingly, ALMA observations of the toddler galaxy revealed the existence of large amounts of dust. The atoms in dust particles can only form in the interiors of stars. That means it takes time before a galaxy can become dusty. Stars have to form first. Then they need to reach the end of their lives and explode as supernovas. Only then will dust particles be able to grow.

So finding a very young galaxy that contains large amounts of dust is just as weird as finding a young toddler with a full-grown moustache. Never before have astronomers found so much dust in such a young galaxy. Apparently, the birth, evolution and death of massive stars and the subsequent growth of dust particles all happened extremely fast.

In the future, astronomers hope to study more of these young, distant galaxies with ALMA, to find out if they’re all as dusty as this one.

The young, dusty galaxy is known as A1689-zD1. It is located in the constellation Virgo the Virgin, at a distance of some 13.1 billion light-years. This is so far away that ALMA would not have been able to detect the galaxy at all, if its light hadn’t been amplified by gravitational lensing. The galaxy is located behind a large cluster of galaxies at a distance of ‘only’ 2.2 billion light-years, and the galaxy’s feeble light is distorted and amplified by the gravity of the cluster.
The ALMA observations of A1689-zD1 were analysed by Darach Watson and Lise Christensen of the University of Copenhagen in Denmark. Darach and Lise worked together with astronomers from the United Kingdom, France, Italy and Sweden. They published their results in the scientific journal Nature.