Travel the universe with Dr. Ethan Siegel as he answers the biggest questions of all
If you want to know what the Universe is like, you have to look at it in the right way.
Only by observing it can we know what the Universe is like.
The European Space Agency’s space-based Gaia mission has mapped out the three-dimensional positions and locations of more than one billion stars in our Milky Way galaxy: the most of all-time. However, even with all the features that observatories like this can identify in our Milky Way, much remains obscure to our eyes due to our limited perspective. (ESA/GAIA/DPAC, CC BY-SA 3.0 IGO)
The Eagle Nebula, famed for its ongoing star formation, contains a large number of Bok globules, or dark nebulae, which have not yet evaporated and are working to collapse and form new stars before they disappear entirely. While the external environment of these globules may be extremely hot, the interiors can be shielded from radiation and reach very low temperatures indeed. These globules, like most forms of dust and molecular gas, are quite efficient at blocking visible light. (ESA / HUBBLE & NASA)
But Hubble’s views are fundamentally limited in two ways.
Here, Hubble reveals the two interacting galaxies that form the pair Arp 194. There is an interstellar “star bridge” connecting the two galaxies, as gas collapses to form young, hot, luminous blue stars, similar to along the densest areas in each of the interacting galaxies. It is expected that these two galaxies will merge over the next billion or three years. (NASA, ESA, AND THE HUBBLE HERITAGE TEAM (STSCI/AURA))
First, this light can only reveal objects where intervening dust is absent.
The gas burning off in the Carina Nebula may be clumping into planet-like and planet-sized objects, but the luminosity and the ultraviolet radiation from the massive star driving the evaporation will certainly boil it all away before any clumps can grow into a star. The “clumps” that do remain will likely form failed stars and failed solar systems: a bevy of rogue planets. In visible light, we cannot observe what’s going on behind the light-blocking dust. (NASA, THE HUBBLE HERITAGE TEAM AND NOLAN R. WALBORN (STSCI), RODOLFO H. BARBA’ (LA PLATA OBSERVATORY, ARGENTINA), AND ADELINE CAULET (FRANCE))
Second, Hubble’s views are deep, but are extremely narrow-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. (HUDF09 AND HXDF12 TEAMS / E. SIEGEL (PROCESSING))
The streaks and arcs present in Abell 370, a distant galaxy cluster some 5–6 billion light years away, are some of the strongest evidence for gravitational lensing and dark matter that we have. The lensed galaxies are even more distant, with some of them making up the most distant galaxies ever seen. This Hubble mosaic, however, still only takes up a tiny fraction of a square degree on the sky. (NASA, ESA/HUBBLE, HST FRONTIER FIELDS)
Hubble excels at revealing “individual trees.”
A close-up of over 550,000 science related observations made by the Hubble Space Telescope. The locations and sizes of the observations made can all be seen here. Although they are located in many different places, the total sky coverage is minimal. Many of the observations are clustered in the galactic plane. (NADIEH BREMER / VISUAL CINNAMON)
This map shows data from the Sloan Digital Sky Survey, covering a much larger fraction of the sky than Hubble images can reveal. In this portion of the map, each dot represent its own galaxy, and there are more than one million dots total in this image. Very clearly, they are clumped and clustered together in a non-random way. (DANIEL EISENSTEIN AND THE SDSS-III COLLABORATION)
Only deep, wider-field views will suffice.
The top two panels show dark matter (L) and clumps dense enough to correspond to the formation of a galaxy (R) from a simulation by the Virgo consortium, while the bottom panel shows observational data from the (now-defunct) Herschel space telescope, an infrared telescope from the European Space Agency. In the bottom photo, each dot of light is its own galaxy; the feature revealed is known as the Lockman Hole. (VIRGO CONSORTIUM/A. AMBLARD/ESA (TOP AND MIDDLE); ESA / SPIRE CONSORTIUM / HERMES CONSORTIA (BOTTOM))
Infrared light — which is largely transparent to light-blocking dust — is ideal for this task.
NASA’s Spitzer Space Telescope began as an actively cooled observatory, taking near and far infrared observations of the deep Universe. When it ran out of coolant, it still took near-infrared observations, lasting more than 15 years until the mission came to an end. In many ways, its views are still the widest and deepest of the cosmos. (NASA/YOUTUBE)
In astronomy, there’s always a trade-off between the depth of your survey and your sky coverage. Hubble’s views, like the GOODS deep fields, can go to incredibly impressive depths, but only capture a small portion of the sky. Wider-field views tend to be shallower. Spitzer, via SEDS and the follow-up S-CANDELS surveys, goes deeper, on wider-fields, than any other observatory to date. (NASA/SPITZER/SEDS)
On large, cosmic scales, every point in these images represents its own galaxy.
In this portion of the COSMOS field, NASA’s Spitzer shows each galaxy as a single pixel. The non-random clustering of galaxies, which is evidence for the composition and gravitational history and evolution of our Universe, helps us conclude that most of the mass of the Universe is in the form of dark matter. (NASA/SPITZER/S-CANDELS; ASHBY ET AL. (2015))
This view of about 0.15 square degrees of space reveals many regions with large numbers of galaxies clustered together in clumps and filaments, with large gaps, or voids, separating them. This region of space is known as the ECDFS, as it images the same portion of the sky imaged previously by the Extended Chandra Deep Field South: a pioneering X-ray view of the same space. (NASA/SPITZER/S-CANDELS; ASHBY ET AL. (2015); Acknowledgment: Kai Noeske)
Quadrupling the original SEDS observing time, exposed galaxies trace the cosmic web.
This portion of the S-CANDELS survey reveals a portion of the Universe also imaged by the UKIDSS Ultra-Deep Survey (UDS), where a surprising number of galaxies can all be seen making row-like structures. These linear structures appear to be aligned along cosmic filaments, which represent regions overdense with dark matter and often linking larger galaxy clusters. (NASA/SPITZER/S-CANDELS; ASHBY ET AL. (2015))
Across 13 billion years of cosmic history, galaxies are clustered, rather than distributed randomly.
This region of the sky was also famously imaged by Hubble, as it contains the Hubble Deep Field-North. The Spitzer image, shown here as part of the S-CANDELS program, is also incredibly deep, but reveals light of much longer wavelengths than Hubble, and presents a much more greatly ‘zoomed out’ view. (NASA/SPITZER/S-CANDELS; ASHBY ET AL. (2015))
One of the last tests that will be performed on NASA’s James Webb is a final check of the mirror deployment sequence in full. With all environmental stress testing now out of the way, these last checks will hopefully be routine, paving the way for a successful 2021 launch. (NASA / JAMES WEBB SPACE TELESCOPE TEAM)
Perhaps the greatest achievement of the S-CANDELS research program, this view of the Extended Groth Strip is more than half a degree long on its long side: larger than the diameter of the apparent full Moon. Every pixel is a galaxy, and there are tens of thousands of bright pixels in this one image alone, despite the fact that most of it, like space, is dark. (NASA/SPITZER/S-CANDELS; ASHBY ET AL. (2015))
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.
