A molecular thermometer for the distant universe

But most importantly, the team was able to measure with the best ever precision the temperature of the cosmic background radiation in the remote Universe [3]. “Unlike other methods, measuring the temperature of the cosmic background using the CO molecule involves very few assumptions,” declares 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. “Given the current measured temperature of 2.725 K, one would expect that the temperature 11 billion years ago was about 9.3 K,” says co-author Patrick Petitjean. “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.”

“We believe our analysis pioneers interstellar chemistry studies at high redshift and demonstrates that it is possible, together with the detection of other molecules such as HD or CH, to use interstellar chemistry to tackle important cosmological issues,” adds Srianand.

Notes

[1] The team is composed of Raghunathan Srianand
(IUCAA,
Pune, India), Pasquier Noterdaeme and Cédric Ledoux (ESO), and Patrick Petitjean (IAP, France). The same team already made the first measurement of the temperature of the cosmic microwave background radiation, at a time when the Universe was only about 2.5 billion years old, also using UVES on the VLT (see ESO 27/00). At that time, they could only measure a temperature in the range between 6 and 14 K.

[2] Quasars are extraordinarily luminous objects in the distant Universe, thought to be powered by supermassive black holes at the heart of galaxies. A single quasar could be a thousand times brighter than an entire galaxy of a hundred billion stars, and yet this remarkable amount of energy originates from a volume smaller than our Solar System.

[3] One of the fundamental predictions of the Hot Big Bang theory for the creation of the Universe is the existence of the Cosmic Microwave Background Radiation (CMBR). This relic radiation of the primeval fireball was discovered in 1964 by means of radio observations by American physicists Arno A. Penzias and Robert W. Wilson, who were rewarded with the Nobel Prize in 1978. Precision measurements by the COBE and WMAP satellites later showed that this ancient radiation fills the Universe, with a present-day temperature of slightly less than 3 degrees above absolute zero (2.725 K [Kelvin], or -270.4 °C). A particular prediction of the Big Bang theory is that the Universe cools when expanding, the temperature scaling with the dilution factor of the Universe (1 + redshift). At the redshift of the galaxy (2.41837), one would thus expect a temperature of 2.725 x (1 + 2.41837) = 9.315 K or -263.835 degree Celsius.