The temperature of the universe just 880 million years after the Big Bang has been revealed, thanks to observation of the projected shadow of a cloud of cold water gas, located about 13.8 billion light-years from Earth. The study was carried out using an innovative technique for observing and measuring the temperature of the cosmic microwave background.
This finding, published in the journal Nature, supports the hypothesis that the universe is cooling — after the hot Big Bang, it would tend to cool down quickly. It may also have direct implications for the nature of mysterious dark energy.
For the study, astronomers observed the galaxy HFLS3, a starburst galaxy, that is, whose production of stars reaches unusual rates, using up its gas faster than predicted. Because it is located so far away, its light takes more than 13 billion years to reach us.
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That means astronomers are looking at HFLS3 as it was 880 million years after the Big Bang. However, there is a large cloud of water vapor between us and the galaxy, colder than the cosmic microwave background (CMB).
The CMB is a very old light, so old that it “lived” for much of the entire history of the expansion of the universe. During that time, the electromagnetic waves of this light stretched (because of the expansion) until they became microwaves. The CMB is an important tool for astronomers, and has now been used to calculate the temperature of the cosmos.
According to the new study, the temperature difference between the cooler gas and the CMB creates absorption lines in the electromagnetic spectrum captured by scientific instruments. These lines reveal the temperature of the CMB, calculated by the research team between -256.8 to -243 °C.
This temperature refers to the time period represented by HFLS3, that is, when the universe was 880 million years old. This fits with previous predictions of a cosmological model that predicted measurements close to these.
Astrophysicists don’t know what causes the universe to expand, but they attribute it to something called dark energy, some whose properties are still unknown. This makes it one of the main forces behind the evolution of cosmic expansion and the cooling of the universe. Based on the new study, the properties of dark energy remain consistent with those of the Einstein cosmological constant.
Now the team is gearing up to look for other clouds of water to map the cooling of the universe after the first 1.5 billion years of cosmic history. “With the expected improvements in the accuracy of studies of larger samples of water clouds,” said Roberto Neri, co-author of the research, “it remains to be seen whether our current basic understanding of the expansion of the Universe holds.”
