The Universe, long past retirement at an age of 13.8 billion years, appears to be gradually “dying.” New observations strongly indicate that galaxies, vast collections of billions of stars such as our Milky Way and neighbors Andromeda and Triangulum, generate much less energy than they used to across the wavelength spectrum, a clear trend revealing the fading cosmos.
Scientists with the Galaxy and Mass Assembly (GAMA) survey, led by Simon Driver of the International Centre for Radio Astronomy Research in Australia, extensively and thoroughly examined more than 200,000 galaxies. Driver and his colleagues presented the results of their analysis at the general assembly of the International Astronomical Union (IAU) in Honolulu, Hawaii, which came to a close last weekend. Their announcement coincided with their data release and the submission of their paper to the journal, Monthly Notices of the Royal Astronomical Society. The paper has not yet been peer-reviewed or published, but the authors’ main conclusions are unlikely to change.
“While most of the energy sloshing around in the Universe arose in the aftermath of the Big Bang, additional energy is constantly being generated by stars as they fuse elements like hydrogen and helium together,” Driver said. “This new energy is either absorbed by dust as it travels through the host galaxy, or escapes into intergalactic space and travels until it hits something, such as another star, a planet, or, very occasionally, a telescope mirror.”
Stars of all ages throughout this multitude of galaxies convert matter into energy (remember E=mc2?) in the form of radiation ranging from ultraviolet to optical to infrared wavelengths, and astronomers have long known that the total energy production of the universe has dropped by more than a factor of 1.5 since its peak about 2.25 billion years ago. But GAMA scientists, utilizing the Anglo-Australian Telescope at Siding Spring Observatory in eastern Australia, were the first to document the declining energy output so comprehensively over 21 wavebands.
Check out this fly-through of the volume mapped out by the GAMA survey, which is expected to be approximately representative of the rest of the “nearby” universe, with the galaxies’ images enlarged (video courtesy of ICRAR/GAMA/Will Parr, Mark Swinbank and Peder Norberg (Durham University) and Luke Davies (ICRAR)):
The GAMA astronomers’ results point toward the universe’s continued “gentle slide into old age,” as Driver put it, but there is no need to panic! The time-scales involve billions of years, and we humans have only been around for about 100,000th of the universe’s lifespan so far. (That’s like the incredibly short lifetime of mayflies relative to ours.) We should be careful to note that the scientists’ conclusions come from a statistical assessment of numerous and diverse galaxies, similar to the way pollsters or census takers evaluate a population by studying a large number of its members. Individual galaxies and their stars may be young or old, but the general population continues to age with no indication of deviations from the demographic trend, much like the gradual aging of people in Japan.
Filled with galaxies and much more dark matter and much much more empty space, the universe rapidly expands and pulls objects away from each other, countering gravitational forces. Old stars within galaxies provide the fuel for new stars to form, but eventually it becomes harder and harder to scrape enough fuel together to make those new stars and galaxies, and on average the aging universe becomes fainter and fainter. It’s as if potential parents become increasingly unlikely to meet with random encounters and many ultimately die alone.
The universe will eventually pass away, but long after our sun has exploded in its red giant phase and destroyed the Earth and long after the Milky Way and Andromeda collide. I think the universe—and humans—has many more good years left though.