Astronomers were wrong about the number of galaxies in universe - study
What if the universe is a little darker than expected, with far fewer galaxy than had been previously estimated for years?
By Sarah Chemla, Jerusalem Post, January 14, 2021
Hubble mosaic image of the Sombrero galaxy (photo credit: REUTERS)
Can astronomers be so wrong about the number of galaxies in the universe?
What if the universe is a little darker than expected, counting way less galaxy than previously estimated for years?
It seems so, according to new data harvested by NASA's New Horizon spacecraft.
Leaving
the illuminated inner solar system is the best way to determine just
how many galaxies may exist in the unseen distance – which is exactly
what New Horizons did.
Indeed,
a previous measurement by the Hubble Space Telescope suggested there
were 2 trillion galaxies spread across the universe.
But the latest discovery counts only hundreds of billions of galaxies instead.
The new NASA mission estimated the number of galaxies to be half of what had previously been estimated for years, in a new study published in The Astrophysical Journal and presented Wednesday at the 237th meeting of the American Astronomical Society, this one virtual.
NASA's New Horizons mission flew by Pluto, located four billion miles
from Earth on the edge of our solar system, in both 2015 and 2019. It
looked across the vastness of black space, the study said, as the
spacecraft was at such a distance that the sky it surveyed was 10 times
darker than the darkest sky observed by Hubble.
"It's
an important number to know: How many galaxies are there?" study
co-author Marc Postman, a distinguished astronomer at the Space
Telescope Science Institute in Baltimore, said in a statement reported
by CNN. "We simply don't see the light from two trillion galaxies."
"Take all the galaxies Hubble
can see, double that number, and that's what we see – but nothing
more," said lead study author Tod Lauer, an astronomer at the National
Science Foundation's National Optical-Infrared Astronomy Research
Laboratory, in a statement.
Previously,
astronomers believed that 90% of the galaxies in the universe remained
hidden from Hubble's view. Hubble only orbits the Earth from a distance
of 340 miles, and it has to contend with light pollution from an effect
called zodiacal light as the earth is situated in a solar system
corner full of dust shed by asteroids and comets. Those dust particles
reflect sunlight, thereby creating zodiacal light.
The previous estimate of galaxies was determined by astronomers counting every galaxy visible in Hubble's deep field and multiplying it based on the total area of the sky.
The study explained that the background glow in the universe, called the cosmic optical background, is the visible light counterpart of the afterglow associated with the Big Bang, which is called the cosmic microwave background.
"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," Postman said. "It puts a constraint on the total number of galaxies that have been created, and where they might be in time."
"New Horizons provided us with a vantage point to measure the cosmic optical background better than anyone has been able to do it," Lauer said.
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