The Milky Way is merely a tiny fragment within a vast universe teeming with countless galaxies. However, if we were to venture an informed estimate, approximately how many galaxies might be out there?
That appears to be an easy query, yet it’s far from straightforward. The primary issue is that despite having access to our strongest telescopes, we are still able to observe just a minuscule portion of the cosmos.
As per an astrophysicist, the observable universe refers solely to the portion from where light has managed to arrive at our location. Kai Noeske , who currently serves as an outreach officer at the European Space Agency, told Live Science.
The universe is 13.8 billion years old However, the observable universe extends over 13.8 billion light-years in all directions. This occurs due to the expansion of the universe; initially, when the cosmos were smaller, light had an earlier beginning.
Currently, the overall dimension in every direction is approximately 46 billion. light-years ," Noeske said.
That's significantly smaller than what we anticipated for the whole universe. As we understand it, 'We can observe only up to 3 percent of the universe,' Pamela Gay , a senior scientist at the Planetary Science Institute, told Live Science.
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The second issue is that due to the vast number of galaxies, we can only estimate the overall count by examining limited areas within the observable universe.
As Gay explained, you observe a tiny section of the heavens, tally all objects within that segment, and then extrapolate those findings across the entire sky.
However, this still necessitates a threshold. “How do we classify something as a galaxy?” asked Noeske. “We’ve got truly massive galaxies that must be at least ten times heavier than ours,” he noted, “and then there are numerous smaller galaxies, including those with lesser masses—about one-tenth that of our galaxy—and extending right down to dwarf galaxies.”
At times, researchers must establish a lower limit for a galaxy’s mass to enable accurate estimations.
"Noeske stated that if we establish a mass threshold and aim for it to be conservative, such as one million solar masses, then the estimated total number of galaxies from the early stages until now would be roughly between one and two trillion." Experts believe there were more galaxies present during the earlier periods of the universe compared to what exists currently, hence these estimations represent an averaged figure across different epochs.
However, those findings originate from the Hubble telescope—the James Webb Space Telescope is beginning to provide insights into these observations—which focus on regions close to Earth within our solar system and are constrained by everything in between. solar system That illuminates the sky," Gay stated. "We do possess one spaceship equipped with a camera that has managed to travel outside of all the debris within our solar system, and that’s the New Horizons spacecraft ."
A 2021 study utilized the onboard camera of New Horizons to gauge the overall quantity of light across different sections of space and then calculated the number of galaxies required to produce such luminosity.
“And then, as they find themselves beyond all the light sources within our solar system, they conclude that we might not require as many galaxies as previously believed,” Gay stated. “As a result, their calculations suggest there could be around 200 billion, perhaps even down to 100 billion, galaxies observable in the universe.”
"Somewhere between 2 trillion galaxies at the higher end and 100 billion galaxies at the lower end lies the estimated number of galaxies within our observable universe," she explained.
If you estimate that this accounts for approximately 3%, or possibly even less, of our universe, then you could scale up this galaxy count to determine the overall quantity of galaxies in the cosmos. Should our observable portion represent an even lesser fraction of the entire universe, the cumulative number of galaxies would consequently decrease as well.
However, since we lack knowledge about the actual dimensions of the universe, these calculations remain uncertain. "In the case of an infinitely vast universe, you would expect to find limitless galaxies," explained Gay.
