by Since it began sending data back to Earth in 2022, the James Webb Space Telescope (JWST) has had a major impact on astronomy, and one of its most revolutionary achievements has been observing some of the most distant galaxies. farthest ever seen. However, because light does not travel instantaneously — but moves about 300 million meters (985 million feet) per second in a vacuum — we see those galaxies not as they are today, but as they were billions of years ago.
In addition, our universe is estimated to be 13.8 billion years old. Therefore, we should assume that the most distant galaxy we could hope to see is no more than 13.8 billion light years away. (The distance light travels in a year is one light years). That point should be some sort of “cosmological field” — and no telescope should be able to see beyond that. And, since nothing can travel through space faster than c, that means a galaxy shouldn’t be more than 13.8 billion light years away, and the whole time could go a long way. applied to the Earth. Right?
Wrong. If only the universe were that simple.
“The cosmological horizon is the maximum distance from which information could be recovered,” Jake Helton, a University of Arizona astronomer who is part of the JWST Advanced Deep Extragalactic Survey (JADES) team told Space.com.
“There are a few different cosmological horizons,” Helton continued, “which have different definitions and depend on different cosmological quantities. The most relevant one here is the cosmological horizon, which is the maximum distance from which light could be having traveled to us over the years
the edge of the observable cosmos.”
Related: James Webb Space Telescope takes a look at the most distant galaxy ever seen (image)
In March 2024, JADES scientists announced that the powerful JADES-GS-z14-0 telescope had spotted the most distant and earliest human galaxy they had ever seen. The paradox, however, is that JADES-GS-z14-0 is located about 33.8 billion light-years away.
How can we see light from something so far away that the universe is not old enough to allow it to reach us? Doesn’t JADES-GS-z14-0’s position 33.8 billion light years away mean we see it as it was 33.8 billion years ago, which would definitely challenge estimating the age of the universe?
It’s not. Again, this is evidence that the universe has a way of drawing sensible and logical conclusions.
“How is it possible to see a distant galaxy like JADES-GS-z14-0, since it is more than 13.8 billion light years away and its light seems to take more time than the age of the universe for us achieve?” Helton asked rhetorically. “The answer is the expansion of the universe.”
See a galaxy older than time itself
If the universe sat still, it would take us 33.8 billion years to reach light from a galaxy 33.8 billion light years away, and that would be it. But, in the early 1900s, Edwin Hubble discovered that distant galaxies appeared to be receding from each other, and the further apart they were, the faster they were going. In other words, the universe is not static; it is expanding.
This was further complicated in 1998, as the 20th century drew to a close when two separate teams of astronomers noticed that not only is the universe expanding, but that expansion is also accelerating. The force responsible is a mystery, but the placeholder name was given “dark energy.”
There have been two major and distinct periods of expansion over the 13.8 billion year history of the universe. The first is an initial period of rapid cosmic inflation now commonly known as the “Big Bang.”
In this period of inflation the size of the cosmos increased by 10^26 (10 followed by 25 zeros). That is equivalent to your nail going from growing at 1 nanometer per second to a sudden growth of 10.6 light years (62). trillion a mile) long. At this time, the universe was dominated by energy, and this period is called the Age of greatest energy.
This was followed by an era dominated by matter starting 47,000 years after the Big Bang. Eventually, universal expansion caused the cosmos to cool enough to allow protons to form from quarks and gluons, and then protons to combine with electrons to form the first hydrogen atoms, which became the first stars and galaxies. During this period, the Big-Bang-driven expansion of the universe slowed to an end.
The most relevant era ended when the universe was just under 10 billion years old. At this time, the universe suddenly began to expand rapidly again. Moreover, that expansion became faster and faster and continues to accelerate even today. This third significant period of the universe is called the dark-energy era. That’s the era we’re in right now.
Thanks to these expansion periods of the universe, the light from JADES-GS-z14-0 has only been traveling to the JWST and Earth for 13.5 billion years, despite its source being much more distant than 13.5 billion light years. . That means the JWST sees JADES-GS-z14-0 as it was 300 million years after the Big Bang. Without the expansion of the universe, JADES-GS-z14-0 would still be about 13.5 billion light-years away, although it would still experience smaller local motions that could move it closer together or further farther from nearby galaxies. But such galactic movement would be nowhere near the kind that caused the expansion of the universe.
According to Helton, the cosmological horizon, or the “Photon Horizon,” is a sphere whose boundary is about 46.1 billion light-years away, a figure driven by the expansion of the universe. This is the actual horizon where we should not be able to “see” a galaxy. The galaxy JADES-GS-z14-0 is indeed within that horizon.
To avoid confusion, astronomers use two scales of distance measurement: a comoving distance that excludes the expansion of the universe as a factor and a proper distance that includes it. That means the collective motion distance of JADES-GS-z14-0 is 13.5 billion light years, and the proper distance is 33.8 billion light years.
However, JADES-GS-z14-0 and other distant and ancient galaxies will not always be visible.
It’s a very lucky time to have the James Webb Space Telescope
Since the JWST can see JADES-GS-z14-0, it means that it was once “causally connected” to Earth and our local Universe. That is, a signal from JADES-GS-z14-0 could be reached for us in the Milky Way, so a “cause” in this galaxy could have an “effect” to plot. of the day in our galaxy. in this modern era of the cosmos.
“Any observable galaxy has to be within the particle horizon and has to be causally connected to us at some point in the history of the universe,” Helton said.
However, this is no longer the case. Galaxies like JADES-GS-z14-0 and the other galaxies discovered by JADES are now so far away and being driven away from us so fast, thanks to dark energy, that no signal from them sent today could ever reach us . That’s because the horizons move photons away from us at the speed of light, but for Seriously distant objects, the space between the Milky Way and those galaxies is expanding faster than the speed of light.
That may seem unbelievable, because Albert Einstein’s theory of special relativity sets the speed of light as a universal speed limit. However, that is a rule for objects with mass in motion through space, not a rule for the fabric of space itself.
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In about 2 trillion years after Earth and humanity are long gone, the expansion of the universe means that whatever intelligent species replaces the Milky Way (if one ever does), it will not be able to contain any existing galaxies. over to see our local group. — which has a diameter of about 10 million light years.
It’s an exciting idea, and it means that humanity lives at a unique point in the history of the universe where the most distant galaxies are still in our view. We are able to know more about the universe and its origins than any intelligent life that follows us. Astronomers, including Helton, intend to use the JWST to fully exploit this cosmic privilege.
“Working with JWST and the JADES Collaboration has been incredible,” said Helton. “Writing papers about science with JWST, like the one I had recently
JADES-GS-z14-0, the experience was most rewarding and exciting
of my research life.”
