Our galaxy is lonelier than we thought, New Horizons data shows

By Georgina Torbet Published January 17, 2021

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

It was previously thought that there were trillions of galaxies out there in the vastness of space, but new research using data from NASA’s New Horizons mission questions that figure. Now, it seems that galaxies may number in the hundreds of billions, rather than the trillions.

Recommended Videos

“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 simply don’t see the light from two trillion galaxies.”

To figure out how many galaxies are out there, it’s not possible to count them because there are so many and they are so far away from us. So researchers instead estimate the total number of galaxies by looking at how much faint background light suffuses the darkness of space. That glow was measured using data from the New Horizons mission to Pluto, which was able to put an estimated cap on the number of faint galaxies that exist beyond the bounds of our ability to see using tools like the Hubble Space Telescope.

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

This photo shows a phenomenon known as zodiacal light. — This photo shows a phenomenon known as zodiacal light. At lower left, a glowing patch extends to the upper right in the direction of Jupiter, the bright object left of center. Zodiacal light is caused by sunlight reflecting off tiny dust particles in the inner solar system—the disintegrated remains of comets and asteroids. Attempts to measure how dark space is using telescopes like Hubble have been thwarted by this ambient glow. Z. Levay / STScI

The reason that measuring the background glow of distant galaxies is hard is that it is hampered by a phenomenon called zodiacal light, where dust particles in our solar system reflect sunlight and create a glow in the sky.

The inner solar system where our planet is located is full of light from these particles which limit 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 investigate the background glow more clearly.

“These kinds of measurements are exceedingly difficult. A lot of people have tried to do this for a long time,” said Lauer. “New Horizons provided us with a vantage point to measure the cosmic optical background better than anyone has been able to do it.”

Topics

Tech News

Georgina Torbet

Space Writer

Georgina has been the space writer at Digital Trends space writer for six years, covering human space exploration, planetary…

Space

Hubble revisits an irregular dwarf galaxy bursting with young stars

The dwarf galaxy NGC 1705 featured in this image from the NASA/ESA Hubble Space Telescope lies in the southern constellation Pictor, approximately 17 million light-years from Earth. NGC 1705 is a cosmic oddball – it is small, irregularly shaped, and has recently undergone a spate of star formation known as a starburst.

This week's image from the Hubble Space Telescope shows the quirky dwarf galaxy NGC 1705, an unusually shaped small galaxy located 17 million light-years away. Stars have formed in this galaxy across its entire lifetime, but the galaxy went through a very intensive period of star formation, called a starburst, approximately 30 million years ago. Many of the stars born during this period are now located around the central core or within the huge central star cluster.

This particular dwarf galaxy is an irregular shape, but it is still a useful object of study. Dwarf galaxies are thought to be some of the oldest galaxies, so studying them can help us learn about the early universe. This one was observed in order to learn about young stars.

Space

Hubble spots three galaxies pulled into an unusual shape

The subject of this image is a group of three galaxies, collectively known as NGC 7764A. They were imaged by the NASA/ESA Hubble Space Telescope, using both its Advanced Camera for Surveys and Wide Field Camera 3.

This week's image from the Hubble Space Telescope shows a group of three galaxies that are so close together that they have been given one collective name: NGC 7764A. When galaxies come close together, they can interact as their gravity affects one another, leading to them being pulled into different shapes or even, in extreme cases, merging together or destroying one of the galaxies.

"The two galaxies in the upper right of the image appear to be interacting with one another," the Hubble scientists explained in a statement. "The long trails of stars and gas extending from them give the impression that they have both just been struck at great speed, thrown into disarray by the bowling-ball-shaped galaxy to the lower left of the image. In reality, interactions between galaxies happen over very long time periods, and galaxies rarely collide head-on with one another. It is also unclear whether the galaxy to the lower left is interacting with the other two, although they are so relatively close in space that it seems possible that they are."

Space

Water could have been on Mars more recently than we thought

NASA’s Mars Reconnaissance Orbiter used its Context Camera to capture this image of Bosporos Planum, a location on Mars. The white specks are salt deposits found within a dry channel. The largest impact crater in the scene is nearly 1 mile (1.5 kilometers) across.

One of the biggest topics in Mars research right now is understanding the history of water on the planet. Scientists know that there was once abundant liquid water on its surface, though now all that water has disappeared and the planet is arid. The only remaining water on Mars's surface today is in the form of water ice near its poles or in deep canyons. To understand what happened to all the water which was present billions of years ago, researchers are trying to piece together a geological history of the planet.

Most researchers thought that the water on Mars evaporated around 3 billion years ago, but new research is questioning this figure. Recent data from NASA's Mars Reconnaissance Orbiter (MRO) suggests that there could have been water on Mars as recently as 2 billion years ago, meaning we may have to re-configure our understanding of the planet's history.