The Milky Way is only a fraction of a universe filled with an uncountable number of galaxies. But if we had to make an educated guess, how many galaxies are there in the universe?
That sounds like a simple question, but it’s not. The first problem is that even with our most powerful telescopes, we can only see a tiny fraction of the universe.
“The visible universe is the part of the universe from which light has had time to reach us,” the astronomer. When you are in Noeskewho is now a service officer at the European Space Agency, told Live Science.
The universe is 13.8 billion years, but the visible universe is more than 13.8 light years in all directions. That’s because the universe is expanding and light started at the beginning, when the universe was small.
“Now, the total size in each direction is about 46 billion bright years,” Noeske said.
It is much smaller than our smallest estimates of the universe. “We only see about 3% of the universe,” Pamela Gaysenior scientist at the Planetary Science Center, told Live Science.
Related: Why do constellations have different shapes?
The second problem is that there are so many galaxies that we can only make general estimates based on what we can see in small parts of the universe.
“You look at a small part of the sky, and you count everything in that small area and you multiply it by the size of the sky,” Gay said.
But still action is needed. “What are we explaining? [as] galaxy?” Noeske said: “We have massive galaxies that must be 10 times more” the mass of our galaxy, “and we have a lot of smaller galaxies. of the stars, from the lower galaxies 10 times the mass … down to the smaller galaxies.”
Sometimes, scientists need to define the minimum mass of a galaxy to make predictions possible.
“If we put a large scale and try to do this, like a million solar masses, we end up with an average number of galaxies in the universe from the beginning to today of about 1 in 2 trillion,” Noeske said. Scientists think that there were more galaxies earlier in the history of the universe than there are today, which is why galaxy estimates are time averages.
But those results are from Hubble [telescope] – The James Webb Space Telescope is beginning to report these results – close to Earth, deep within our own solar system, and far short of what they can see of all our objects. solar system that adds brightness to the sky,” Gay said. “We have one spacecraft with a camera that goes beyond all the debris in our planetary system, and that’s it. New Horizons spacecraft.”
Study of 2021 he used the camera on board New Horizons to measure the total amount of light in different parts of the sky and estimated how many galaxies would be needed to produce that much light.
“And suddenly, because they’re outside of all the light sources in our solar system, they realize that we don’t need as many galaxies as we thought,” Gay said. So, their estimates put us at, like, 200 billion, maybe even 100 billion galaxies in the visible universe.
He said: “So somewhere between 2 billion galaxies at the upper limit and 100 billion at the lower limit is the number of galaxies in our visible universe.
If you assume that it is 3% – at most – of our universe, you can multiply those galaxies to get the total number of galaxies in the universe. If we do not see more of the universe than we think, there will be a small number of galaxies.
But when we consider that we don’t know the size of the universe, those estimates are unclear. “If it’s an infinite universe, you’re going to have an infinite number of galaxies,” Gay said.
#galaxies #universe