Astronomy 1 trillion years from now

Artist’s conception of the cosmic view a trillion years from now.

A trillion years from now, the sky will look very different. Will astronomers still be able to work out that the Big Bang happened?

ONE TRILLION YEARS FROM NOW, alien astronomers in our galaxy will have a difficult time figuring out how the universe began. They won’t have the evidence that we enjoy today.

Edwin Hubble made the first observations in support of the Big Bang model. He showed that galaxies are rushing away from each other due to the universe’s expansion.

More recently, astronomers discovered a pervasive afterglow from the Big Bang, known as the cosmic microwave background, left over from the universe’s white-hot beginning.

In a trillion years, when the universe is 100 times older than it is now, alien astronomers will have a very different view. The Milky Way will have merged with the Andromeda Galaxy to form the ‘Milkomeda Galaxy’. Many of its stars, including our Sun, will have burned out.

And the universe’s ever-accelerating expansion will send all other galaxies rushing beyond our “cosmic horizon,” sending them forever out of view.

The same expansion will cause the cosmic microwave background (CMB) to fade out, stretching the wavelength of CMB photons to become longer than the visible universe.

The universe will become dark and dull.

Artist's impression of a hypervelocity star.

Future astronomers will study hypervelocity stars to deduce the laws of the cosmos.

Shooting stars

Without the clues of the CMB and distant, receding galaxies, how will these far-future astronomers know the Big Bang happened?

According to Harvard theorist Avi Loeb, clever astronomers in the year 1 trillion CE could still infer the Big Bang and today’s leading cosmological theory, known as ‘lambda-cold dark matter’ or LCDM. They will have to use the most distant light source available to them—’hypervelocity’ stars flung from the centre of Milkomeda.

“We used to think that observational cosmology wouldn’t be feasible a trillion years from now,” said Loeb, who directs the Institute for Theory and Computation at the Harvard-Smithsonian Centre for Astrophysics.

“Now we know this won’t be the case. Hypervelocity stars will allow Milkomeda residents to learn about the cosmic expansion and reconstruct the past.”

About once every 100,000 years, a binary-star system wanders too close to the black hole at our galaxy’s centre and gets ripped apart. One star falls into the black hole while the other is flung outward at a speed greater than 1.5 million kilometres per hour—fast enough to be ejected from the galaxy entirely.

No need for faith

Finding these hypervelocity stars is more challenging than spotting a needle in a haystack, but future astronomers would have a good reason to hunt diligently. Once they get far enough from Milkomeda’s gravitational pull, these stars will get accelerated by the universe’s expansion.

Andromeda galaxy

Andromeda, the nearest big galaxy, will one day merge with our Milky Way.

Astronomers could measure that acceleration with technologies more advanced than we have today. This would provide a different line of evidence for an expanding universe, similar to Hubble’s discovery but more difficult due to the very small effect being measured.

By studying stars within Milkomeda, they could infer when the galaxy formed. Combining that information with the hypervelocity star measurements, they could calculate the age of the universe and key cosmological parameters like the value of the cosmological constant (the lambda in LCDM).

“Astronomers of the future won’t have to take the Big Bang on faith. With careful measurements and clever analysis, they can find the subtle evidence outlining the history of the universe,” said Loeb.

This research appears in a paper accepted for publication in the Journal of Cosmology and Astroparticle Physics.

Adapted from information issued by CfA. Artwork courtesy David A. Aguilar (CfA). Hypervelocity star artwork courtesy NASA, ESA, and A. Feild (STScI). Andromeda image courtesy Caltech.

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  1. Jonathan Nally says:

    Hi again Owen,
    I invited one of Australia’s leading cosmologists, Dr Tamara Davis, to give a response to your “what lies beyond what we can see?” question — see
    A big thank you to Tamara for tackling this for us, and particularly on a long weekend!

  2. Owen says:

    Hi Jonathan,
    If Milkomeda does indeed continue to exist, what of these burned-out embers, what could we expect to see so long after the galaxy ceases to regenerate new stars and all that once glittered has been reduced to these embers? How long might it take or rather, what could the galaxy’s life span be and then finally, what would be the end product of all these stars, after the embers have cooled, would Milkomeda be a vast, dark and lifeless graveyard of rocky material, perhaps similar in existence to the asteroid belt?
    Kind regards

  3. Jonathan Nally says:

    Hi Owen,
    I think the Milkomeda Galaxy would still be around, but it would comprise burned-out embers rather than lots of sparkly stars. As to how much universe is beyond our event horizon, that’s a great question, and I know just whom to ask to find out. I’ll post the answer when I get it.

  4. Owen says:

    Interesting views but of course in 1 trillion years, none of what currently exists in the universe will still exist and any such ‘Milkomeda Galaxy’ will have disappeared way long ago. However, what I’d really like to know is how much of the universe is already beyond our ‘cosmic horizon’ due to the expansion differential between Earth’s location and opposite areas of the universe where the expansion differential has long since exceeded light speed and therefore ‘invisible’ from Earth?

  5. norman black says:

    I believe that in 1 trillion years time a lot of what we are starting to take for granted will be proven flawed.Possibly ark matter,dark energy and maybe even the continued expansion of the universe.From a laymans point of view we seem to be falling into the trap of inventing things to give credence to our theories.