Scientists analyzed data obtained by NASA’s New Horizons mission to Pluto and the Kuiper Belt and their results were rather surprising – there are a lot fewer galaxies in the universe than previously thought.
It was previously stated that there are about 2 trillion galaxies in the universe but new research has revealed that there are hundreds of billions. That is still a huge number but much less than the original estimate.
If you look very far off into space, it is incredibly dark but not completely black as there are faint lights from very distant galaxies and stars. And studies of those very faint glows are what revealed to scientists that there aren’t as many galaxies gathered in the universe.
Marc Postman from the Space Telescope Science Institute in Baltimore, Maryland, and an author of the study, stated, “It’s an important number to know – how many galaxies are there?,” adding, “We simply don’t see the light from two trillion galaxies.”
As for their original estimate of two trillion galaxies, scientists came up with that number by using data from NASA’s Hubble Space Telescope and while the majority of galaxies were too far off and faint to be detected by the telescope, they used mathematical models to predict that 90% of galaxies were too far to be seen by the Hubble.
Postman went on to say, “While the cosmic microwave background tells us about the first 450,000 years after the big bang, the cosmic optical background tells us something about the sum total of all the stars that have ever formed since then.” “It puts a constraint on the total number of galaxies that have been created, and where they might be in time.”
Tod Lauer from NSF’s NOIRLab and another author of the study, weighed in by saying, “Take all the galaxies Hubble can see, double that number, and that’s what we see – but nothing more.”
The Hubble’s ability to observe distant galaxies was affected by light pollution from pieces of comets, asteroids, and small dust particles that are in our solar system. These small objects reflect the sunlight, making a glow (called zodiacal light) which made it hard for the telescope to completely observe the far areas into space.
Thankfully, the New Horizons spacecraft is far enough away from the zodiacal light that it was able to make more precise observations of the universe. In fact, when the spacecraft was at a distance of more than 4 billion miles away from Earth, it observed the universe at about 10 times darker than when the Hubble made its observations.
Lauer explained how exciting these observations were, “These kinds of measurements are exceedingly difficult. A lot of people have tried to do this for a long time.” “New Horizons provided us with a vantage point to measure the cosmic optical background better than anyone has been able to do it.”
After the scientists removed all of the excess glows from expected galaxies as well as the light from the stars in the Milky Way, they still had some leftover glows which could be from dwarf galaxies, diffuse halos of stars from galaxies, or rogue, intergalactic stars. Or there might possibly be even more undetected galaxies.
Their study can be read in full here.