Imagine being able to see the very first stars igniting and the earliest galaxies starting to form – witnessing cosmic dawn hundreds of millions of years after the Big Bang. This profound view of the infant Universe has long been a dream for astronomers. Now, it‘s becoming reality thanks to the remarkable power of the James Webb Space Telescope.
Within just its first year of operations, Webb has already detected candidate galaxies dating to just 300-500 million years after the Universe‘s birth. I want to explain for you how this was achieved, why it matters so much for cosmology, and what we can hope to learn next from Webb about the early days of galaxy evolution.
The Mission of the James Webb Space Telescope
First, let‘s get familiar with this unprecedented telescope and its ambitious mission. The James Webb Space Telescope represents the culmination of over 20 years of development and the efforts of an international team of over 10,000 scientists, engineers and technicians.
With a massive 21-foot primary mirror and advanced infrared instrumentation, Webb is the largest and most complex space telescope ever built. It launched on December 25, 2021 and is now stationed nearly 1 million miles from Earth at a gravitationally stable point called L2.
Webb has a suite of objectives in its 5-10 year mission, but a primary goal is observing the distant, early universe – peering back to within a few hundred million years of the Big Bang. Specifically, Webb aims to:
- Detect the first stars and galaxies to understand cosmic origins
- Observe galaxy evolution and assembly over billions of years
- Study exoplanetary systems in new detail
- Revolutionize many other areas of astronomy
Now equipped with this amazing new tool, astronomers are thrilled to start probing the ultimate depths of the cosmos.
Observing the Ancient Universe Thanks to the Speed of Light
But how can Webb reveal the Universe as it was 13 billion years ago? The answer lies in the finite and constant speed of light. Light travels at 186,282 miles per second through space. This means that the ancient light from the most distant galaxies has taken billions of years to traverse the expanding cosmos and reach our telescopes.
We see these galaxies not as they are today, but as they appeared when that light began its long journey eons ago. In essence, telescopes like Webb allow us to look back in time and directly observe the early Universe as it evolves.
This works because even as space expands significantly over billions of years, the speed of light remains fixed. Measuring a distant galaxy‘s redshift – how much its light is stretched by expansion – tells us how long that light has traveled. Extremely high redshifts indicate ancient light from the early cosmos.
Analyzing this faint, highly redshifted light is incredibly challenging and requires Webb‘s unprecedented sensitivity and infrared vision. But it provides our window into cosmic dawn.
Peering Back 13 Billion Years with Webb‘s Deep Field Images
Soon after its instruments were calibrated, Webb conducted several Deep Field surveys that targeted small patches of seemingly empty sky. With Webb‘s ability to gather extremely faint light, these ultra-long exposures revealed thousands of previously unseen galaxies from the early universe.
Some of these galaxies were merely dots, but they had enormous redshifts indicating observations from over 13 billion years in the past. Each new deep field image contained new record holders for the most distant galaxy yet seen.
Webb‘s project to survey the Hubble Ultra Deep Field beginning in 2023 will reveal even more galaxies at the edge of observability. The longer Webb stares into the void, the more ancient objects it will detect stretching back over 13 billion years.
Measuring Redshift Reveals Lookback Time and Distance
But how do astronomers precisely determine these vast distances and cosmic lookback times? Let‘s take a closer look at redshift and what it signifies.
The Doppler effect causes waves from a moving source to become compressed or stretched out. For light, this shifts the wavelength towards the blue or red end of the spectrum. It‘s similar to how an ambulance siren changes pitch as it passes by.
As galaxies move away from us due to the Universe‘s expansion, their light is redshifted to longer wavelengths. The faster the galaxy recedes, the greater the redshift.
Extreme redshift means the light has been traveling for billions of years, giving it a time machine quality. Distant quasars have been observed by Webb with redshifts of over 7, meaning we see them as they were when the Universe was only 5% of its current age.
In addition to lookback time, redshift also indicates cosmological distance. The expansion rate, called the Hubble Constant, is around 67 km/s/Mpc. Combining this with redshift gives the distance a galaxy is now compared to where it was when the light was emitted.
For example, a high redshift of 10 corresponds to a lookback time of about 13 billion years and a current distance of about 32 billion lightyears!
Galaxy Candidates From Cosmic Dawn Discovered by Webb
Using its unmatched infrared vision and redshift measuring capability, Webb has now discovered candidate galaxies dating to only a few hundred million years after the Big Bang.
An international team used Webb‘s Near-Infrared Camera (NIRCam) and Spectrograph (NIRSpec) to analyze the light from four faint galaxy candidates called JADES-GS-z10-0, JADES-GS-z11-0, JADES-GS-z12-0 and JADES-GS-z13-0.
They used NIRCam‘s extraordinary sensitivity and stability to take continuous 9-28 hour exposures, gathering enough ancient light for analysis. NIRSpec‘s spectra provided precise redshift measurements indicating extreme distances – and thus extremely early epochs just 300-500 million years after cosmic origins.
The table below summarizes the galaxy candidates and their potentially remarkable ages:
|Galaxy||Redshift||Age of Universe|
|JADES-GS-z10-0||10.957||500 million years|
|JADES-GS-z11-0||11.247||400 million years|
|JADES-GS-z12-0||12.633||350 million years|
|JADES-GS-z13-0||13.183||300 million years|
Just consider – we may be seeing light that originally emitted when the Universe itself was only 300 million years old!
Understanding Galaxy Evolution Through Chemical Composition
Astronomers also determine a galaxy‘s age through its chemical composition. After the Big Bang, only the two simplest elements – hydrogen and helium – existed.
Heavier elements like oxygen, carbon, and iron are created later inside stars and supernovae. The earliest galaxies consisted of unenriched primordial gas.
The galaxy candidates from Webb show this primitive hydrogen-helium dominated spectrum. This matches predictions for some of the very first galaxies to form.
Observing these unchanged relics of cosmic dawn provides a direct window into the infant Universe as it looked soon after the Big Bang. Analyzing their properties and evolution will improve our cosmological models.
Significance of Observing the Earliest Galaxies
Seeing back to the period when the first galaxies ignited is tremendously significant for cosmology. Theories predict when the initial galaxies should form, but observations provide essential tests.
Finding and studying galaxies from cosmic dawn places tight constraints on different models of the early Universe. This helps rule out some ideas and refine others.
Understanding the first galaxies also sheds light on how fundamental astrophysical processes like star formation began. Observing the primordial Universe enhances our knowledge of physics, chemistry, and astronomy across the board.
There are still many open questions about these earliest epochs that Webb may help answer:
- How did the first stars and galaxies ignite?
- What were early galaxies made of and how did they evolve?
- How did the first heavy elements begin to enrich galaxies?
- What role did dark matter play?
- When did supermassive blackholes start appearing?
Peering across 13 billion years to the cosmos‘s childhood and watching the first galaxies grow up will reveal so much about our cosmic history.
Debate Over Candidates for Earliest Galaxies
However, some experts argue that Webb has not yet conclusively identified the very first galaxies. Its current deep field surveys cover only a tiny patch of sky, so may be missing earlier objects.
One study proposed that the telescope may have picked up light from Dark Stars instead. These hypothetical giants powered by dark matter could predate normal star formation.
Others contend that galaxies identified by Webb formed 150 million years later, still impressive but not quite as ancient. More data is needed to verify redshift distances and chemical makeup.
Over longer observations, Webb is sure to find galaxies from even earlier cosmic times. But this debate highlights the remaining uncertainty about objects right at the edge of observability.
What‘s Next for Webb‘s Exploration of the Early Universe
Although Webb‘s initial images are awe-inspiring, they represent only a tantalizing hint of what‘s to come over its 5-10 year mission.
Some of Webb‘s surveys slated for 2023 will be up to 100 times larger than previous deep fields. In particular, Webb‘s long-stare observations of the Hubble Ultra Deep Field will reveal incredibly ancient and distant galaxies, thanks to that area‘s minimial obscuring light.
Webb will also analyze gravitationally lensed galaxies to peer back over 13 billion years. And by stacking multiple high redshift galaxy spectra, it can study their chemical evolution as a whole.
The more Webb stares into the void, the more unseen galaxies will come into focus. Its unparalled sensitivity is steadily illuminating the early Universe and cosmic dawn. Webb is answering foundational questions about our origins while raising fascinating new mysteries.
Thanks to this engineering marvel, the infinite blackness of space is lighting up with visions from the Universe‘s infancy. We stand on the cusp of revealing creation itself and unveiling the very first stars, galaxies, and phenomena to emerge after the Big Bang. What an awe-inspiring time for astronomy.