Travel the universe with Dr. Ethan Siegel as he answers the biggest questions of all
The Ultra-Deep and eXtreme Deep Fields have revealed the Universe as never before. Here’s what lies inside.
From 2003 through 2014, NASA’s Hubble Space Telescope observed the same tiny region across 7 different wavelength bands.
Although there are magnified, ultra-distant, very red and even infrared galaxies in the Ultra Deep Field and eXtreme Deep Field images, there are galaxies that are even more distant out there than what we’ve discovered in our deepest-to-date views. These galaxies will always remain visible to us, but appear as they were billions of years ago in cosmic time: very close to the Big Bang itself. (NASA, ESA, R. BOUWENS AND G. ILLINGWORTH (UC, SANTA CRUZ))
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. (HUDF09 AND HXDF12 TEAMS / E. SIEGEL (PROCESSING))
Here are 10 scientific revolutions hiding inside.
What appears at first glance to be a boring yellow blob is actually the most distant red dwarf star, UDF 2457, ever observed to exist within the Milky Way. Located 59,000 light-years away, more than twice the distance of the Sun from the galactic center, this is the most distant individual star known in the Milky Way’s disk. (HUBBLE SPACE TELESCOPE, STSCI, NASA, ESA)
1.) The Milky Way’s most distant red dwarf star ever seen: UDF 2457, located 59,000 light-years away.
This enormous spiral galaxy from the Ultra Deep Field image, UDF 423, is the brightest and largest (in terms of angular diameter) galaxy to be revealed in this deepest-ever view. Its light comes to us from 7.7 billion years ago, when the Universe was less than half of its present age. (HUBBLE SPACE TELESCOPE, STSCI, NASA, ESA)
2.) The largest, brightest deep galaxy, UDF 423: a giant spiral from 7.7 billion years ago.
The galaxy HUDF-JD2 is actually extremely close to UDF 423: serendipitously so. The nearer, larger galaxy acts as a gravitational lens, magnifying the more distant galaxy and enabling Hubble to pick it up where it would otherwise be too faint and distant for our current set of instruments. (NASA, ESA, AND S. BECKWITH (STSCI) AND THE HUDF TEAM)
3.) Ancient galaxy HUDF-JD2 appears just 0.9 billion years after the Big Bang, having already grown to 600 billion solar masses.
This faint red dot in the image, unceremoniously named UDFj-39546284, was initially thought to be an ultra-distant galaxy, but follow-up observations demonstrated how a combination of features misled us. It’s still very far away, but is not among the most distant galaxies in the Universe. (NASA, ESA, G. ILLINGWORTH (UNIVERSITY OF CALIFORNIA, SANTA CRUZ), R. BOUWENS (UNIVERSITY OF CALIFORNIA, SANTA CRUZ, AND LEIDEN UNIVERSITY) AND THE HUDF09 TEAM)
4.) Ultra-faint, red galaxy UDFj-39546284 initially fooled us: it’s an interloping galaxy mimicking a more distant one.
The galaxy UDFy-38135539 continues to be a source of controversy, as multiple spectroscopic measurements have yielded inconsistent results. We still do not know how far away it is, which means we cannot reliably count it among the most distant known galaxies. (NASA, ESA, G. ILLINGWORTH (UCO/LICK OBSERVATORY AND UNIVERSITY OF CALIFORNIA, SANTA CRUZ) AND THE HUDF09 TEAM)
5.) UDFy-38135539 is similarly controversial: its disputed distance measurements mean it could be another interloper.
Some of the most distant galaxies in the Universe are revealed by ultra-deep observations. the more distant a galaxy is, the younger, less evolved, smaller, and full of star-forming material it tends to be. Star formation reached a peak just 3 billion years after the Big Bang, and has fallen ever since. (R. WILLIAMS (STSCI), THE HUBBLE DEEP FIELD TEAM AND NASA)
6.) Star formation peaked some 11 billion years ago, having steadily fallen ever since.
A total of 36 interacting galaxies with tadpole-like appearances were extracted from the Hubble Ultra Deep Field to form this mosaic. Interacting galaxies in this fashion showcase galaxy mergers and evolution, which were far more common in the young Universe than they are today. (NASA, A. STRAUGHN, S. COHEN, AND R. WINDHORST (ARIZONA STATE UNIVERSITY), AND THE HUDF TEAM (SPACE TELESCOPE SCIENCE INSTITUTE))
7.) Dozens of cosmic tadpoles showed that interacting, merging galaxies are common in the young, evolving Universe.
The Hubble eXtreme Deep Field, the deepest image ever taken of the Universe, is just a tiny fraction of the angular size of the full Moon on the sky. If we wanted to fill up the sky with XDF images, it would require some 32 million of them. (NASA, ESA, AND Z. LEVAY (STSCI))
8.) The XDF’s deepest view ever found 5500 galaxies in a region covering just 1/32,000,000th of the sky.
Galaxies identified in the eXtreme Deep Field image can be broken up into nearby, distant, and ultra-distant components, with Hubble only revealing the galaxies it’s capable of seeing in its wavelength ranges and at its optical limits. All told, it reveals nearly 10% of the estimated galaxies in this region of sky: an enormous, but incomplete, number. (NASA, ESA, AND Z. LEVAY, F. SUMMERS (STSCI))
9.) 170 billion galaxies would be visible if Hubble could view the entire sky, which would require millions of years.
This tiny slice of the eXtreme Deep Field illustrates an important concept: if we count the number of galaxies in this image and extrapolate how many such similar images we’d need to cover the entire sky, we can get an estimate for how many galaxies would be revealed over the entire sky to Hubble’s eyes. The actual number of galaxies is significantly larger. (NASA, ESA, H. TEPLITZ AND M. RAFELSKI (IPAC/CALTECH), A. KOEKEMOER (STSCI), R. WINDHORST (ARIZONA STATE UNIVERSITY), AND Z. LEVAY (STSCI))
10.) It taught us 2 trillion total galaxies occupy the observable Universe, with Hubble’s limits unable to penetrate farther.
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.
