The Universe is Slowly Dying

Galaxies dimming and aging.
This composite picture shows how a typical galaxy appears at different wavelengths in the GAMA survey. This huge project has measured the energy output of more than 200 000 galaxies and represents the most comprehensive assessment of the energy output of the nearby Universe. The results confirm that the energy produced in a section of the Universe today is only about half what it was two billion years ago and find that this fading is occurring across all wavelengths from the ultraviolet to the far infrared. ICRAR/GAMA and ESO

When you look up at the stars at night, it probably never enters your mind that all of the stars you see will be gone in a few millions or billions of years. That’s because more will take their place as clouds of gas and dust create new ones throughout the galaxy even as older stars die out. 

The humans of the future will see entirely different skies than we do. Star birth replenishes our Milky Way Galaxy – and most other galaxies – with new generations of stars. However, eventually, the “stuff” of star birth gets used up, and in the far, far distant future, the universe will be much, much dimmer than it is now. In essence, our 13.7-year-old universe is dying, very slowly.

How Do Astronomers Know This?

An international team of astronomers spent time studying more than 200,000 galaxies to understand how much energy they generate. It turns out that there’s far less energy being generated than in the past. To be precise, the energy being generated as galaxies and their stars radiate heat, light, and other wavelengths is about half of what it was two billion years ago. This fading-out is happening in all wavelengths of light—from the ultraviolet to the infrared.

Introducing GAMA

The Galaxy and Mass Assembly project (GAMA, for short) is a multi-wavelength survey of galaxies. (“Multi-wavelength” means that astronomers studied a range of light streaming from the galaxies.) It’s the largest survey ever done, and it involved many space and ground-based observatories from around the world to accomplish. The data from the survey includes measurements of the energy output of each galaxy in the survey in  21 wavelengths of light.

Much of the energy in the universe today is generated by stars as they fuse elements in their cores. Most stars fuse hydrogen to helium, and then helium to carbon, and so on. That process releases heat and light (both are forms of energy). As the light travels through the universe, it can be absorbed by objects such as clouds of dust either in the home galaxy or in the intergalactic medium.  The light that arrives at telescope mirrors and detectors can be analyzed. That analysis is how astronomers figured out the universe is slowly fading away.

The news about a fading universe is not exactly new news. It’s been known since the 1990s, but the survey was used to show just how extensive the fade-out is.  It’s like studying all the light from a city instead of just the illumination from a few city blocks, and then calculating how much light there is as a whole over time. 

The End of the Universe

The slow decline of the universe’s energy isn’t something that will be complete in our lifetimes. It will continue to fade out over billions of years. No one is quite sure how it will play out and exactly how the universe will look. However, we can imagine a scenario where star-making material in all the known galaxies is finally used up.  No more clouds of gas and dust will exist.

There will be stars, and they will shine brightly for tens of millions or billions of years. Then, they’ll die. As they do, they'll return their materials to space, but there won’t be enough hydrogen to combine with it to make new stars. The universe will get dimmer as it gets older, and eventually – if there are any humans still around – it will be invisible to our visible-light sensitive eyes. The universe will glow softly in infrared light, slowly cooling and dying until there’s nothing left to give off any heat or radiation.

Will it stop expanding? Will it contract?  What role will dark matter and dark energy play? Those are just a few of the many questions astronomers ponder as they continue to examine the universe for more signs of this cosmic “slowdown” into old age.