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Gassy galaxies were perfect star factories
Posted: 11 February 2010

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Large galaxies that were present in the first few billion years after the big bang were bloated on gas, resulting in a rash of star formation that outstripped the current rate at which stars are born in the Universe today by up to ten times.

On the left is a Hubble Space Telescope optical image of a spiral galaxy whose light has been travelling 8.3 billion years (at a redshift of 1.1). On the right is the same galaxy observed at millimetre wavelengths (false colour) showing carbon monoxide emission. Image: MPE/IRAM.

Astronomers have known that stars formed in far higher numbers in the early Universe, and that there was a greater abundance of massive stars in the past, but until now there has never been a satisfactory understanding of why this was the case. Were star factories simply more efficient in the past, or was gas much more plentiful? New observations made with ground-breaking sensitivity at the Plateau de Bure millimetre Interferometer in the French Alps – the most powerful millimetre interferometer in the world, linking six 15m radio telescopes – have mapped both the distribution and motion of molecular hydrogen gas clouds in galaxies as far away as 10.7 billion light years (a redshift of about 2.3). Previously this had only ever been achieved in brilliantly bright quasars (galaxies with extremely active cores); to observe cold gas in normal galaxies at such a distance “has opened the door for an entirely new avenue of studying the evolution of galaxies,” says Pierre Cox of the Institute for Radio Astronomy in the Millimetre Range (IRAM).

The Plateau de Bure millimetre interferometer. Image: IRAM.

The observations didn’t measure the cold hydrogen directly, but instead latched onto the easier-to-see emission lines from carbon monoxide molecules, which are also present within the clouds. Huge reservoirs of gas were detected, confirming that there was more gas in galaxies ten billion years ago than there is today. This gas is accumulated from cannibalisation of nearby dwarf galaxies and large amounts of intergalactic gas pulled in by the gravity of the dark matter haloes around the galaxies. The more gas there is, the more stars are born. Because stars much more massive than our Sun are only born in a ratio of one to several hundred lower mass stars, the greater star formation rate results in larger numbers of massive stars that will explode as supernovae.

“These findings provide us with clues and constraints for theoretical models that we will use to study the early phases of galaxy development in more detail,” says Andreas Burkert of the Excellence Cluster Universe at the Technische Universitaet Muenchen in Garching, Germany. “Eventually these results will help us understand the origin and the development of our Milky Way.”

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!


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