Washington, May 13 : Astronomers have detected for the first time in the ultraviolet the carbon monoxide molecule in a galaxy located almost 11 billion light-years away, which has allowed them to obtain the most precise measurement of the cosmic temperature at such a remote epoch.
The team of astronomers aimed the UVES spectrograph on ESO's (European Southern Observatory's) Very Large Telescope for more than 8 hours at a well-hidden galaxy whose light has taken almost 11 billion years to reach us, that is about 80% of the age of the Universe.
The only way this galaxy can be seen is through the imprint its interstellar gas leaves on the spectrum of an even more remote quasar.
According to Raghunathan Srianand, who led the team making the observations, "Quasars are here only used as a beacon in the very distant Universe. Interstellar clouds of gas in galaxies, located between the quasars and us on the same line of sight, absorb parts of the light emitted by the quasars."
"The resulting spectrum consequently presents dark 'valleys' that can be attributed to well-known elements and possibly molecules," he explained.
The team was able to discover the presence of normal and deuterated molecular hydrogen (H2, HD) and carbon monoxide (CO) molecules in the interstellar medium of this remote galaxy.
"This is the first time that these three molecules have been detected in absorption in front of a quasar, a detection that has remained elusive for more than a quarter century," said Cedric Ledoux (ESO), member of the team.
Most importantly, the team was able to measure with the best ever precision the temperature of the cosmic background radiation in the remote Universe.
"Unlike other methods, measuring the temperature of the cosmic background using the CO molecule involves very few assumptions," said co-author Pasquier Noterdaeme.
If the Universe was formed in a 'Big Bang', as most astrophysicists infer, the glow of this primeval fireball should have been warmer in the past.
This is exactly what is found by the new measurements.
According to co-author Patrick Petitjean, "Given the current measured temperature of 2.725 K, one would expect that the temperature 11 billion years ago was about 9.3 K."
"Our unique set of VLT observations allows us to deduce a temperature of 9.15 K, plus or minus 0.7 K, in excellent agreement with the theory," he added.