Sometimes astronomers & astrophysicists work at such gigantic, mind bending scales, in terms of distance & time, that you can’t help but be amazed at the new discoveries they keep making.
Case in point: a temperature check probe of the universe in its youngest phase, just 880 million years after Big Bang, made possible by observing the shadow cast by a cloud of cold water gas at about 13.8 billion light years from Earth’s.
This is our first aspect at the temperature of the universe, that scientists think it cools over-time as it expands & spreads, and This is another very useful data point in hunting the most mysterious of forces behind expansion: dark energy.
“This important milestone not only confirms expected cooling trend for a much earlier-epoch than previously been possible to measure, but could also have a direct-implications for nature of strong dark energy,” says astronomer Axel Weiss, from the Max Planck Institute for Radio Astronomy in Germany.
The key to how this was-done centers on contrast of temperatures. Using Northern Extended Millimeter Array telescope in France, astronomers focused on HFLS3 galaxy, known as the starburst galaxy due to the unusually high number of new stars that it is producing.
Light has taken so long to reach us from HFLS3 that we see it as if less than a billion years have passed since the existence of the Universe. What we also see is an big cloud of water vapor between us and the galaxy, a cloud that is colder than the cosmic micro-wave background radiation (CMB) that indicating the temperature of the universe.
The temperature difference between the cooler gas & CMB creates so-called absorption lines, and by examining these lines it is possible to determine the temperature of the CMB. It’s a rather complicated bit of astrophysics made possible by infrared light emitted by newborn stars in HFLS3.
The researchers calculate a CMB of between 256.8 to 243°C at the time period represented by HFLS3, which matches previous cosmological model predictions of the 20 Kelvin. This is an important confirmation of our modeling.
“Besides showing evidence of cooling, this discovery also shows us that the universe in its in-fancy had some very specific physical features that no longer exist today,” says astrophysicist Dominik Riechers of the University of Cologne in Germany.
“Very early, about 1.5 billion years after Big Bang, the cosmic microwave background was already too-cold for this effect to be observable. Thus we have a unique window of observation that only opens for a very young universe.
The results show that previous estimates of rate of temperature decrease as-it corresponding to the expansion are in the right zone. Trying to take that kind of reading now wouldn’t work: the CMB is too cold to produce the same temperature contrast.
Dark energy is believed to be driving the expansion of the universe, but observing it directly remains outside the scope of our current instruments. However, we can learn more by looking at its effects, including the rate at which the universe is expanding and the temperature drop of the CMB.
As usual, one piece of research begets many others. The research team is now looking for other cold-water clouds to which the same technique can be applied, with the aim of obtaining another reading within the first 1.5 billion years after Big Bang.
“Our team is already tracking this with NOEMA by studying the surroundings of other galaxies,” says astronomer Roberto Neri of the Radio Astronomie Millimétrique Institute in France.
“With the expected improvements in the accuracy of the larger sample studies of water clouds, It remains to be seen whether our current basic understanding of the expansion of the universe holds.
The research has been published in Nature.