Scientists have figured out that the universe is getting hotter. The study, published in the Astrophysical Journal, examines its heat history over the past 10 billion years.
It turned out that the average temperature of gas in the Universe has increased 10 times over 10 billion years. To date, it has reached about 2 million degrees Kelvin, which is about 2 million degrees Celsius.
“As the universe develops, gravity unites dark matter and gas in space into galaxies and their clusters, causing resistance and heating of the gas,” explains I-Quan Chan, a research associate at the Ohio State University’s Center for Cosmology and Astronomical Particle Physics.
The scientists used a new method that allowed them to estimate the temperature of a gas far away on Earth (i.e., even further back in time). The readings were compared to temperatures closer to Earth (and at the present time). The results of the study confirmed that the universe is getting hotter over time due to the gravitational collapse of the cosmic structure, and it seems that the heating is only increasing.
To understand how the temperature of the universe changes over time, the researchers used data collected by two missions — Planck and the Sloan Digital Sky Survey.
Planck is an astronomical satellite of the European Space Agency (ESA) designed to study variations in the cosmic microwave background (relic radiation).
The Sloan Digital Sky Survey is a large-scale study of multispectral images and redshift spectra of stars and galaxies using the 2.5-meter wide-angle telescope at Apache Point Observatory in New Mexico.
Scientists pooled data from the two missions and estimated distances to hot gases in the vicinity and in the distance using redshift measurements. Astrophysicists use it to estimate the age of distant space objects. (“Redshift” got its name from the nature of the lengthening of the wavelengths of light. The further something is in the universe, the longer the length)
The observed light from objects in deep space is older than their light from those closer to Earth. This fact, together with a method for estimating temperature from light, allowed researchers to measure the average temperature of gases in the early universe – which are far from Earth – and compare them with the average temperature of nearby space objects today.
The researchers found that gases near-space objects located closer to Earth reach temperatures of about 2 million Kelvin. This is about 10 times the temperature of gases around objects farther in distance and in time.
According to Chang, the universe is heating up due to the natural formation of galaxies and structures. This is not related to warming on Earth.