The National Aeronautics and Space Administration’s latest mission has discovered there might be far fewer galaxies in the universe than initially thought.
Observations from NASA’s New Horizons mission to Pluto and to the Kuiper Belt revealed there are hundreds of billions of galaxies, not the 2 trillion originally believed, according to a news release Tuesday from Hubblesite.
Astronomers estimate the total number of galaxies by counting things that are visible in a Hubble deep field and multiplying them by the total area of the sky.
Some galaxies are too faint and distant to directly detect. But even though they can’t be counted, they still have a feeble glow.
“It’s an important number to know — how many galaxies are there?” said study author Marc Postman of the Space Telescope Science Institute in Baltimore.
“We simply don’t see the light from 2 trillion galaxies.”
That original estimate had come from observations by NASA’s Hubble Space Telescope, which used a mathematical model to conclude that 90 percent of the galaxies in the universe were beyond the telescope’s ability to see “visible light.”
The spacecraft provided the first close-up pictures of Pluto, and its position at the edge of the solar system allows it to see ambient sky 10 times darker than the Hubble does.
The observations were taken when the $720 million spacecraft was over 4 billion miles from Earth.
“These kinds of measurements are exceedingly difficult. A lot of people have tried to do this for a long time,” Lauer said.
“New Horizons provided us with a vantage point to measure the cosmic optical background better than anyone has been able to do it.”
The leftover glow in the universe could be an abundance of dwarf galaxies that are just beyond detectability or the diffuse halos of stars surrounding other galaxies, according to the news release.
Astronomers said they hope the James Webb Telescope, which had its launch delayed because of the coronavirus pandemic, could help clear up the mystery of why there are less than 50 percent fewer galaxies than originally thought.
The New Horizons spacecraft, meanwhile, has made several discoveries since its launch.
In June 2014, the spacecraft discovered the object Arrokoth, nicknamed Ultima Thule.
In May 2019, it found water and organic molecules on Arrokoth, which is located deep in the Kuiper Belt, beyond Neptune.
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