How Many Suns Exist In The Milky Way? It’s Complicated

Key Takeaways On How Many Suns Are in the Milky Way

• How many suns exist in the Milky Way depends on what your definition of a sun. According to astronomers, our sun is considered a main-sequence G star.
• To know how many suns are in the Milky Way, astronomers measure the light emitted by the galaxy. From these measurements, they estimate that no more than 10 percent of the stars in the galaxy are like our sun.
• Using the same measuring methods, astronomers can likely predict the number of suns in the universe. The number is so large that it can be difficult to understand. Carl Sagan once compared the number of stars in the universe to the number of grains of sand on all of Earth’s beaches, and again, about 10 percent or fewer would be similar to our sun.

The Milky Way galaxy alone contains billions of stars, though when branching out from our corner in the universe, NASA estimates the cosmos itself may contain up to one septillion stars, with 24 zeroes behind it. Among these, one of them is our sun.

Just how many other suns might populate this vast fabric of space, however, depends on how strict your definition is.

“Oftentimes, you’ll hear textbooks say our sun is like the quintessential average star,” says Christopher Palma, teaching professor of astronomy and astrophysics at Penn State University. “It’s in the middle of the mass range and temperature range. A lot of the properties of the sun are decidedly average.”

That makes our sun a main-sequence G star, burning through the hydrogen in its core. It sits near the center of a scale that runs from O, B, A, F, G, K, and M. By this criterion only, the simplest way to answer this question would be to ask how many main-sequence G stars there are.

Read More: 10 Facts You May Not Know About the Milky Way

How Many Suns Are In The Milky Way?

One way astronomers figure out how many stars exist in the Milky Way is by measuring light.

“We can often have really good estimates for the number of molecules in a beaker of water, for example. But in astronomy, we’re working with detecting light from things that are really far away, and that’s all we have to go on,” Palma says. “We see a blip of light, and we’re trying to figure out how much stuff is in that blip of light.”

Palma compares it to the light of a single LED versus a flashlight containing thousands of them: the flashlight would be a thousand times brighter than the light of a single LED. To extrapolate that to galaxies, astronomers work backwards.

“A typical galaxy like the Milky Way is giving off this much light. If a typical star is this bright, how many stars add up to the same amount of light that’s being emitted by the Milky Way?” Palma continues.

It’s easier to make those estimates when looking into distant galaxies, including Andromeda.

“We live about halfway out from the center of the galaxy, and we certainly can’t see the entire galaxy, because we’re in it,” says Kevin France, associate professor in the University of Colorado’s Department of Astrophysical and Planetary Sciences. “If you’re in a cloud, you cannot see the shape of the cloud because you can only see what’s right around you.”

Ultimately, judging by the light emitted by the Milky Way, there are hundreds of billions of stars contained in our galaxy, with a lower limit at around 100 billion — and among them, Palma adds, a few to ten percent are expected to be similar to our sun.

How Many Suns Exist In Space?

Astronomers can similarly estimate the number of stars in the whole universe. If the Milky Way is a typical galaxy, France says, astronomers could first estimate how many other Milky Ways populate our cosmic neighborhood.

“What’s the volume of this little corner of the universe we can see, compared to what we think the volume of the whole universe is?” France continues. “It’s sort of similar. You could basically multiply by that number and get the total number of stars.”

This total can be difficult to comprehend, an amount of zeroes trailing a number that few people ever encounter in life. Astronomer Carl Sagan famously compared the total number of stars in the universe to be roughly equivalent to the amount of grains of sand on all of Earth’s beaches. Similarly, around ten percent of them could be sun-like stars.

“Even though you’re never going to count them all individually, you can point your telescope at a patch of the sky and ask, ‘How many galaxies do I see in that patch of sky?’” Palma says. “Then you can do math to extrapolate to the whole universe.”

Read More: To Understand the Universe, Scientists Are Studying the Milky Way’s Cosmic Neighbors

Which Planet Has More Suns?

One might wonder how many of the billions of sun-like stars out there float adrift and alone in space, and how many are tethered to planets instead. Stars can exist in twin systems or even triplets, though an extra planet in the mix would not have a stable enough orbit to stay in the system.

Meanwhile, our solar system consists of eight planets attached to a single star — a configuration that is more common than multiple stars linked to a single planet.

“Typically, one star has multiple planets. We’ve found examples of other systems with seven planets. We have eight,” Palma says. “But we’re not able to see all of them right now.”

As for how many of those stars belong to planets that could actually support life, that’s even tougher to find. The reason it’s been so hard to detect them is because stars literally outshine planets, “by a factor of a billion,” according to Palma. If our sun is the blaring eye of a lighthouse, one can imagine Earth as the light of a firefly’s tail.

It’s possible, then, to quibble with current estimates of sun-like stars by asking how many are sun-like because they support life on planets. That’s where the simple answer becomes complicated, from G stars to Earth 2.0’s.

Moreover, astronomers are wondering the reverse: Must an Earth-like planet have a sun-like star attached to be Earth-like?

“That’s the million-dollar question,” France says.

Sun-like stars and Earth-like planets

How Earth-like planets come to be is a question France tackled in a recent study published in The Astronomical Journal.

Stars’ magnetic fields twist, kink, and break as they spin, generating massive amounts of radiation. As they slow down and age over time, the level and intensity of radiation changes as well. Too much high-energy radiation for too long can strip away a planet’s atmosphere, rendering it inhospitable.

“That means that the planets going around that star experience changes by that amount, too. If you have a really short period of time when you’re getting zapped by lots of high-energy radiation, maybe your atmosphere survives,” France says.

Understanding the relationship between the host star and its planet is key to determining what makes a second Earth.

“You can’t separate the planet from its star,” France says. “They’re linked.”

NASA’s upcoming Habitable Worlds Observatory, of which France is a part, aims to one day launch an instrument into space that can block out blinding starlight in order to catch the fireflies of accompanying planets. More precisely, France adds, that’s around 10 billion stellar photons blocked for every one planetary photon.

Once the observatory captures enough nearby stars, the counting begins: which of those sun-like stars have a planet in the ideal spot, and which of those planets have an atmospheric fingerprint that might indicate biology.

The technology is still developing, but it brings scientists closer to answering one of the oldest, million-dollar questions humans have asked: Are we alone?

“We live at a very lucky time when we’re on the cusp of technically being able to have the ability to start answering that question,” France says.

Read More: The JWST May Have Discovered the Milky Way’s Twin

Article Sources

Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article: