The Universe is becoming gradually cleaner as more and more cosmic dust is being mopped up by the formation of stars within galaxies, an international team of astronomers has revealed. Peering back 12 billion years using the Herschel space telescope to produce far-infrared images of the sky, the team led by researchers at Cardiff University has been able to observe the very early formation of galaxies and compare them to galaxies that have formed much more recently.

The results showed that stars were forming inside galaxies much faster in the past compared to today, and that this rapid star birth is using up more and more of the cosmic dust that is ubiquitous in the Universe.

Cosmic dust is comprised of tiny solid particles that are found everywhere in space between the stars. The dust and the gas in the universe is the raw material out of which stars and galaxies form.

Though this blanket of material is key to the formation of stars and galaxies, it also acts as a sponge, absorbing almost half of the light emitted by stellar objects and making them impossible to observe with standard optical telescopes.

With the launch of the Herschel space telescope in 2009, researchers were provided with the perfect tool for probing this hidden universe. Owing to a collection of sensitive instruments, mirrors and filters, the Herschel telescope had the capacity to detect the dust through the far-infrared emission it emits, revealing the existence of stars and galaxies hidden by the dust.

Professor Steve Eales, a co-leader of the project from Cardiff University's School of Physics and Astronomy, said: "We were surprised to find that we didn't need to look far in the past to see signs of galaxy evolution. Our results show that the reason for this evolution is that galaxies used to contain more dust and gas in the past, and the universe is gradually becoming cleaner as the dust is used up."