The telescope tasked with creating the largest map of the universe in history has confirmed a harsh, if not surprising, truth. The truth is that nothing lasts forever, not even the cold November rain or the universe itself.
Using a vast catalog of observations from the European Space Agency’s (ESA) Euclid and Herschel Space Telescopes, a team of 175 researchers produced the most comprehensive reading of the temperature of the universe ever recorded. By studying the heat emitted by stardust in more than 2 million galaxies, the researchers found that galaxies have become slightly cooler and the rate of star formation has slowed over the past 10 billion years of the universe’s history.
According to the researchers, these small but distinct downward trends suggest that the universe’s peak period of growth is over. While the lifespan of the universe is still a mind-bogglingly long way off (recent estimates put it between 33 billion and 1 quintillion years, or 78 1s followed by 0s), the new discovery suggests that it’s all downhill from here in terms of the rate of star formation.
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3D map of the universe
In March, ESA’s recently launched Euclid telescope shared its first major data release, including observations of 26 million galaxies spanning more than 10.5 billion light-years beyond the universe. This was just the first step in the telescope’s mission to build the largest 3D map of the universe in history, with the ultimate goal of charting about 1.5 billion galaxies covering a third of the night sky.
For the new study, the researchers looked at the 2.6 million galaxies cataloged in Euclid’s original data release and combined them with archival observations from ESA’s Herschel Space Observatory, which was active from 2009 to 2013. Euclid’s onboard instruments were tuned to record visible light and near-infrared light, while Herschel’s instruments detected far-infrared light. Combining these datasets therefore allowed the team to study the heat emitted by stardust over a wide range of wavelengths, providing the most comprehensive measurement of galactic temperature ever measured.
“By combining the data and obtaining such a large sample of galaxies, we are able to perform the most statistically robust calculations to date,” lead study author Riley Hill, a postdoctoral fellow at UBC, said in a statement.
The researchers found that the average temperature of galaxies has decreased only slightly over the past 10 billion years, by just 10 Kelvin. Stars like the Sun shine at over a million Kelvin, but galaxies are made mostly of empty space, meaning their average temperature is much cooler. The researchers found that the average galactic temperature of the earliest galaxies observed in the new survey was about 35 degrees Celsius (-396 degrees Fahrenheit, or -238 degrees Celsius).
Although this is a small change, the researchers noted that the heating of stardust is directly correlated to star formation. Hotter galaxies tend to have higher rates of star formation because they contain more hot, massive stars. Similarly, galaxies with less star formation tend to be cooler on average. The team’s work further supports this correlation, proving that star formation is slowly declining throughout the universe.
dust to dust
Dust may be a pain to deal with on Earth, but it’s crucial to the life of a star. Stars form when clouds of gas and dust become so dense that they collapse under their own gravity, heating and rotating in the process. When one of these collapsed clumps becomes hot and dense enough, it triggers nuclear fusion in its core, forming a star. Eventually, after billions of years, when the star runs out of its nuclear fuel supply, it will explode as a supernova, scattering even more dust around it and allowing the next generation of stars to grow.
Galaxies can run out of star-forming material in a variety of ways. To name a few, we may see gas supplies cut off during galaxy mergers, or the explosion of supermassive black holes violently eject star-forming material into space. Eventually, galaxies that don’t have enough material to form stars will run out of fuel and are doomed to smolder.
The new results suggest that our universe is on track to disappear completely, but again, not for an immeasurably long period of time. Earth’s sun will run out of fuel and explode long before the Milky Way runs out, leaving even more massive objects like black holes to live on forever. Meanwhile, new research provides the most precise exploration yet of some of the key states of galaxies across the universe. Measurements will become essential to Euclid’s quest to build the ultimate map of our universe.
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