Lensing cluster Abell 383: The giant cluster of elliptical galaxies in the centre of this image contains so much dark matter mass that its gravity bends light. This means that for very distant galaxies in the background, the cluster’s gravitational field acts as a sort of magnifying glass, bending and concentrating the distant object’s light towards Hubble.
Credit: NASA, ESA, J. Richard (CRAL) and J.-P. Kneib (LAM). Acknowledgement: Marc Postman (STScI)
PARIS: A distant galaxy has been discovered whose stars were born unexpectedly early in cosmic history - just 200 million years after the Big Bang - a finding that challenges assumptions of how the Universe grew from infancy into childhood.
The researchers' evidence comes from a remote galaxy whose glimmer of light was teased open to reveal the presence of truly ancient stars. The oldest galaxy previously detected and confirmed was created some 480 million years after the Big Bang.
"This [finding] challenges theories of how soon galaxies formed and evolved in the first years of the Universe," said lead author Johan Richard from the Lyon Observatory in France. "It could even help solve the mystery of how the hydrogen fog that filled the early Universe was cleared."
A suburb chance alignment
To all appearances, the new finding could lay a claim on being the record-beater. But no such claims are being made because the discovery was made indirectly, rather than through direct observation, Richard said.
Richard's team spotted the galaxy in recent observations from the NASA/ESA Hubble Space Telescope, verified it with observations from the NASA Spitzer Space Telescope and measured its distance using W. M. Keck Observatory in Hawaii.
The distant galaxy was visible through a cluster of galaxies called Abell 383, whose powerful gravity bends the rays of light almost like a magnifying glass.
The chance alignment of the galaxy, the cluster and the Earth amplifies the light reaching us from this distant galaxy, allowing the astronomers to make detailed observations. Without this gravitational lens, the galaxy would have been too faint to be observed even with today's largest telescopes.
950 million years old
After spotting the galaxy in Hubble and Spitzer images, the team carried out spectroscopic observations with the Keck-II telescope in Hawaii.
Spectroscopy is the technique of breaking up light into its component colours. By analysing these spectra, the team was able to make detailed measurements of its redshift - the galaxy's redness and a telltale of age - and infer information about the properties of its component stars.
The galaxy's redshift is 6.027, which means we see it as it was when the Universe was around 950 million years old. This does not make it the most remote galaxy ever detected - several have been confirmed at redshifts of more than 8, and one has an estimated redshift of around 10 (heic1103), placing it 400 million years earlier.
Made of old, faint stars
However, hidden in the bundle of infrared data from Spitzer were signs that many stars in the galaxy were surprisingly old and relatively faint.
"When we looked at the spectra, two things were clear. The redshift placed it very early in cosmic history, as we expected. But the Spitzer infrared detection also indicated that the galaxy was made up of surprisingly old and relatively faint stars, said co-author Eiichi Egami from the University of Arizona, U.S.
"This told us that the galaxy was made up of stars already nearly 750 million years old - pushing back the epoch of its formation to about 200 million years after the Big Bang, much further than we had expected."
