Infant galaxy found

Cosmic lens magnifies faint galactic building-block.

Astronomers have peered deep into space and time and spotted a baby galaxy. Their results suggest that the tiny star-forming region may have helped to build today’s Universe¹.

“We believe this is one of the galactic building-blocks that join together to make larger galaxies,” says Konrad Kuijken, of the Kapteyn Institute in Groningen, the Netherlands, a member of the team that found the object. The merging over time of galaxies born just after the Universe began is thought to have made large galaxies, such as our Milky Way.

“This is a significant step towards understanding galaxy formation,” says astronomer Rob Kennicutt of the University of Arizona in Tucson. More building-blocks must be found to get to the bottom of it, he says.

The international team had been on the trail of baby galaxies for over a year. Confirming their existence is no easy task. They are small, very far away and give out far less light than telescopes can detect.

To find this one, says Kuijken, “we had to make our own luck”. This meant exploiting a phenomenon predicted by Einstein’s general theory of relativity: gravitational lensing. The vast gravity of very massive objects such as galaxies bends and magnifies, light coming from behind them, much as a glass lens bends light in a telescope.

The team pointed the Hubble Space Telescope and the Hawaii-based Keck telescope towards one such gravitational lens – a massive cluster of nearby galaxies called Abell 2218.

After two lengthy exposures, the team found two faint red blobs representing the light from the baby galaxy magnified more than 30 times and split in two by the gravitational lens.

Concluding that they were looking at a baby galaxy, the discoverers, typically a reserved lot, “literally jumped up and down” with excitement, confesses team member Jean-Paul Kneib of the Mid-Pyrenees Observatory in Toulouse, France.

Measuring the wavelengths and brightness of its light, the team calculate that the baby galaxy is about 200 times smaller than our Galaxy and 13.4 billion light years away. Signatures in this 13.4-billion-year-old light also reveal that the infant was actively making new stars at that time – just 600 million years after the birth of the Universe.

Combined, these characteristics mean the object is most likely to be a galactic building-block. “It’s exactly like what our models predict,” says Kuijken.

Kuijken is hopeful that the team will find more such objects. “There are many other galaxy clusters in the sky,” he says, and behind some of these giant lenses may lurk more infant galaxies.

References

1. Name, A.B.Title. Astrophysical Journal Letters, in press (2001).