Our Galaxy Is Lonelier Than We Thought, New Horizons Shows

When you look up at the sky, all the stars you see are part of our galaxy, the Milky Way. And we know that our galaxy is just one of many in the universe.

It was previously believed that there were trillions of galaxies in the vast expanse of space, but new research using data from NASA’s New Horizons mission is calling that number into question. Now it seems that galaxies can number hundreds of billions, not trillions.

“It’s an important number to know – how many galaxies are there?” Marc Postman of the Space Telescope Science Institute in Baltimore, Maryland, a lead author on the study, said in a statement. “We just don’t see the light of two trillion galaxies.”

To find out how many galaxies there are, it is not possible to count them because there are so many and they are so far from us. Instead, the researchers estimate the total number of galaxies by studying how much weak background light penetrates the darkness of space. That glow was measured using data from the New Horizons mission in Pluto, which was used to estimate the number of faint galaxies that exist beyond our means of seeing with tools like the Hubble Space Telescope.

“Take all the galaxies Hubble can see, double that number, and we see that – but nothing more,” said Tod Lauer of NSF’s NOIRLab, a lead author on the study.

This photo shows a phenomenon known as the zodiac lights. At the bottom left, a glowing spot extends to the top right in the direction of Jupiter, the bright object to the left of the center. Zodiac lights are caused by sunlight reflecting off tiny particles of dust in the inner solar system – the crumbled remains of comets and asteroids. Attempts to use telescopes like Hubble to measure what the dark room is like have been thwarted by this ambient light. Z. Levay / STScI

The reason the background glow of distant galaxies is difficult to measure is because it is hindered by a phenomenon called zodiac light, where dust particles in our solar system reflect sunlight and create a glow in the sky.

The inner solar system our planet is in is full of light from these particles, which limits Hubble’s ability to see these faint galaxies. As New Horizons traveled to the outer solar system, it was able to look further out and examine the background light more clearly.

“This type of measurement is extremely difficult. A lot of people have tried to do this for a long time, ”said Lauer. “New Horizons gave us a vantage point to measure the cosmic optical background better than anyone has ever been able to.”

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