The Most Important Image Ever Taken By NASA's Hubble Space Telescope
One peek into a small part of the sky, one giant leap back in time. This small patch of sky represents less than 1/100,000,000th of the volume of the Universe, but reveals nearly 1,000 galaxies that had never been seen before. This small fraction of the original Hubble Deep Field image is a huge part of how we learned what our Universe looks like.
Later this month, the Hubble Space Telescope will celebrate its 30th anniversary.
This photo of the Hubble Space telescope being deployed, on April 25. 1990, was taken by the IMAX Cargo Bay Camera (ICBC) mounted aboard the space shuttle Discovery. It has been operational for 30 years, and has not been serviced since 2009. With a 2.4-meter diameter mirror, it gathers as much light in 1 minute as a 160-mm (6.3″) telescope would require 3 hours and 45 minutes to gather.
More than any other observatory in history, Hubble revealed what the Universe looks like.
Looking back from the present day, we can see a ‘pencil beam’ view of the distant Universe. But a huge number of galaxies are still undiscovered, owing to the limitations of how we’re capable of looking. Hubble has taken us remarkably far, but there’s still farther to go.
When it was first launched, a problem with its mirror’s optics produced only flawed images.
The before-and-after difference between Hubble’s original view (left) with the mirror flaws, and the corrected images (right) after the proper optics were applied.
In late 1993, new flaw-correcting equipment was installed, along with an improved camera: WFPC2.
The Wide Field and Planetary Camera 2 (WFPC2) was Hubble’s workhorse camera for many years. It recorded images through a selection of 48 colour filters covering a spectral range from far-ultraviolet to visible and near-infrared wavelengths. The ‘heart’ of WFPC2 consisted of an L-shaped trio of wide-field sensors and a smaller, high resolution (Planetary) Camera placed at the square’s remaining corner.
The next year, scientists embarked on a risky observing campaign: the Hubble Deep Field.
When you collect just a single photon at a time, many of them will be hot pixels, cosmic rays, instrument noise, etc. But when you build up a high-enough signal-to-noise ratio, you can identify what actually is a real object, like a distant galaxy, and what’s just random noise.
They examined a region of sky that was seemingly empty: with no bright, nearby stars or galaxies.
The original target area selected for the Hubble Deep Field. This was out of the plane of the ecliptic, out of the galactic plane, and located in a region of space with only a small number of faint Milky Way stars and zero known galaxies beyond our own.
For ten consecutive days, across multiple wavelengths, Hubble observed the same patch of nothing, collecting one photon at a time.
The original Hubble deep field image, shown here, was taken by stacking dozens of images of an empty region of space and seeing what showed up. The answer was thousands of galaxies, revealing what our distant Universe looks like for the very first time. While for many of us, it feels like yesterday, this image is now over 25 years old.
When all the data was collected, this is what they saw.
A small section of the original Hubble Deep Field, featuring hundreds of easily distinguishable galaxies. The original Hubble Deep Field may have only covered a tiny region of the sky, but taught us that there were at least hundreds of billions of galaxies contained within the observable Universe. Today, superior data and analysis has placed that figure closer to ~2 trillion.
Where nothing was known previously, thousands of new, distant, faint galaxies were revealed.
Less than a year after the original Hubble Deep Field was produced, the same team chose a different region of the sky in the southern celestial hemisphere to construct a second Hubble Deep Field. The results were just as spectacular.
These Hubble Deep Field images revolutionized our view of the Universe.
Fewer galaxies are seen nearby and at great distances than at intermediate ones, but that’s due to a combination of galaxy mergers and evolution and also being unable to see the ultra-distant, ultra-faint galaxies themselves. Many different effects are at play when it comes to understanding how the light from the distant Universe gets redshifted.
Future observing campaigns and subsequent, superior instruments brought the Universe into greater focus.
This image showcases the massive, distant galaxy cluster Abell S1063. As part of the Hubble Frontier Fields program, this is one of six galaxy clusters to be imaged for a long time in many wavelengths at high resolution. The diffuse, bluish-white light shown here is actual intracluster starlight, captured for the first time. It traces out the location and density of dark matter more precisely than any other visual observation to date.
A small section of the GOODS-North field as viewed in ultraviolet light by the Hubble Deep UV (HDUV) Legacy Survey. The total mosaic represents 14 times the area-on-the-sky of the original, 2014 Hubble Ultraviolet Ultra Deep Field.
The Ultra-Deep and eXtreme Deep Fields surpassed the original Hubble Deep Field.
The Hubble eXtreme Deep Field (XDF) may have observed a region of sky just 1/32,000,000th of the total, but was able to uncover a whopping 5,500 galaxies within it: an estimated 10% of the total number of galaxies actually contained in this pencil-beam-style slice. The remaining 90% of galaxies are either too faint or too red or too obscured for Hubble to reveal. As time goes on, the total number of galaxies within this region will rise from ~55,000 up to approximately to ~130,000 as more of the Universe is revealed.
Even more distant and fainter secrets are out there.
The viewing area of Hubble (top left) as compared to the area that WFIRST will be able to view, at the same depth, in the same amount of time. The wide-field view of WFIRST will allow us to capture a greater number of distant supernovae than ever before, and will enable us to perform deep, wide surveys of galaxies on cosmic scales never probed before. It will bring a revolution in science, regardless of what it finds, and provide the best constraints on how dark energy evolves over cosmic time. If dark energy varies by more than 1% of the value it’s anticipated to have, WFIRST will find it.
Future missions, like WFIRST and LUVOIR, will reveal them.
A simulated view of the same part of the sky, with the same observing time, with both Hubble (L) and the initial architecture of LUVOIR (R). The difference is breathtaking, and represents what civilization-scale science can deliver.Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.
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