Hubble's Universe Unfiltered

  • March 4, 2016

    Episode 21: New Views of the Pillars of Creation

    by Frank Summers

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    New Views of the Pillars of Creation

    One of Hubble's most famous images was taken in 1995. The iconic "Pillars of Creation" shows the tall and beautiful gaseous pillar structures that can form inside star-forming regions. Within these dark clouds, stars are being born. Hubble kicked off its 25th anniversary year in 2015 with some images that used its improved cameras to revisit these beautiful pillars. This larger, higher resolution, and expanded wavelength examination uncovered new details, new features, and new perspectives on a classic image.  


    Hubble press release:



    • Most will remember that there was an initial flaw in Hubble's mirror that was corrected in 1993. After that repair mission, it took some time for the public to recognize just how amazing Hubble's views of the universe really were.  The 'Pillars of Creation' image, released in November 1995, was a watershed in that regard. The image was shown on television news and reproduced in newspapers and magazines everywhere. The widespread attention helped cerify Hubble's status to the public as the pre-eminent observatory of our time.

    • The "teapot" in Sagittarius is not the full constellation. It is a star pattern, called an "asterism," within the larger collection of connected stars that makes up the entire constellation. One can search online to see the full Sagittarius constellation as it depicts the archer. A similar asterism is the Big Dipper, which is a star pattern within the constellation of Ursa Major.

    • The visible and infared views of astronomical objects are generally similar enough that one can identify common structures between the views. When using other wavelengths, like X-rays or radio waves, it can be very hard to identify how the two different wavelength views correspond. Astronomers must record the exact sky coordinates of an image in order to be able to precisely compare against views by other telescopes and in other wavelengths.

    • In 2005, for Hubble's 15th anniversary, we released an image of another pillar in the Eagle Nebula. This pillar has a long, thin profile that earned it the nickname of a "stellar spire." As seen in this contextual image, the two pillar regions are near each other in the nebula and both point toward the same group of hot stars.


    Image notes

    Eagle Nebula Pillars (1995)
    Credit: NASA, ESA, STScI, J. Hester and P. Scowen (Arizona State University)

    Sagittarius Region
    Credit: A. Fujii

    Eagle Nebula
    Credit: Timber Rock Observatory,

    Eagle Nebula
    Credit: T.A. Rector (NRAO/AUI/NSF and NOAO/AURA/NSF) and B.A. Wolpa (NOAO/AURA/NSF)

    Eagle Nebula Pillars (2015)
    Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

    Eagle Nebula Pillars in Infrared (2015)
    Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

  • December 29, 2015

    How Hubble 'Sees' Gravity

    by Frank Summers

    [Note: This post is cross-posted on the Frontier Fields blog.]

    Gravity is the familiar force of nature responsible for the diverse motions of a baseball thrown high into the air, a planet orbiting a star, or a star orbiting within a galaxy. Astronomers have long observed such motions and deduced the amount of gravity, and therefore the amount of matter, present in the planet, star, or galaxy. When taken to the extreme, gravity can also create some intriguing visual effects that are well suited to Hubble’s high-resolution observations.

    Einstein’s general theory of relativity expresses how very large mass concentrations distort the space around them. Light passing through that distorted space is redirected, and can produce a variety of interesting imagery. The bending of light by gravity is similar to the bending of light by a glass lens, hence we call this effect “gravitational lensing.”

    The simplest type of gravitational lensing is called “point source” lensing. There is a single concentration of matter at the center, such as the dense core of a galaxy. The light of a distant galaxy is redirected around this core, often producing multiple images of the background galaxy (see the image above for an example). When the lensing approaches perfect symmetry, a complete or almost complete circle of light is produced, called an “Einstein ring.” Hubble observations have helped to greatly increase the number of Einstein rings known to astronomers.

    Galaxy Cluster Abell 2218

    Gravitational lensing in galaxy cluster Abell 2218

    More complex gravitational lensing arises in observations of massive clusters of galaxies. While the distribution of matter in a galaxy cluster generally does have a center, it is never perfectly circularly symmetric and is usually significantly lumpy. Background galaxies are lensed by the cluster with their images often appearing as short, thin “lensed arcs” around the outskirts of the cluster. Hubble’s images of galaxy clusters, such as Abell 2218 (above) and Abell 1689, showed the large number and detailed distribution of these lensed images throughout massive galaxy clusters.

    These lensed images also act as probes of the matter distribution in the galaxy cluster. Astronomers can measure the motions of the galaxies within a cluster to determine the total amount of matter in the cluster. The result indicates that most of the matter in a galaxy cluster is not in the visible galaxies, does not emit light, and is thus called “dark matter.” The distribution of lensed images reflects the distribution of all matter, both visible and dark. Hence, Hubble’s images of gravitational lensing have been used to create maps of dark matter in galaxy clusters.

    In turn, a map of the matter in a galaxy cluster helps provide better understanding and analysis of the gravitationally lensed images. A model of the matter distribution can help identify multiple images of the same galaxy or be used to predict where the most distant galaxies are likely to appear in a galaxy cluster image. Astronomers work back and forth between the gravitational lenses and the cluster matter distribution to improve our understanding of both.

    Three lensed images of a distant galaxy seen through a cluster of galaxies

    On top of it all, gravitational lenses extend Hubble’s view deeper into the universe. Very distant galaxies are very faint. Gravitational lensing not only distorts the image of a background galaxy, it can also amplify its light. Looking through a lensing galaxy cluster, Hubble can see fainter and more distant galaxies than otherwise possible. The Frontier Fields project has examined multiple galaxy clusters, measured their lensing and matter distribution, and identified a collection of these most distant galaxies.

    While the effects of normal gravity are measurable in the motions of objects, the effects of extreme gravity are visible in images of gravitational lensing. The diverse lensed images of crosses, rings, arcs, and more are both intriguing and informative. Gravitational lensing probes the distribution of matter in galaxies and clusters of galaxies, as well as enables observations of the distant universe. Hubble’s data will also provide a basis and guide for the future James Webb Space Telescope, whose infrared observations will push yet farther into the cosmos.

    A "smiley face" gravitational lens in a galaxy cluster

    The distorted imagery of gravitational lensing often is likened to the distorted reflections of funhouse mirrors, but don’t take that comparison too far. Hubble’s images of gravitational lensing provide a wide range of serious science.

  • October 3, 2015

    My Favorite Martian (Movie)

    by Frank Summers

    In 1982, I went to see the film "Blade Runner" without many expectations. It was just a sci-fi movie starring Harrison Ford, who, at the time, was known only for his role in "Star Wars." I came away enthralled with the depth of both the thought-provoking story and the detailed artistic vision. After recognizing that the director, Ridley Scott, had also done the 1979 film "Alien," he immediately rose to being a favorite. In subsequent years, the words "directed by Ridley Scott" were reason enough to go see a film.

    However, as an astronomer, I approached his new film "The Martian" with a bit of trepidation. While still in the category of science fiction, the story of an astronaut stranded on Mars is ripe for massive clashes against science fact. Previous astronauts on Mars stories have not thrilled me. Such movies generally pay homage to the scientific aspects by providing various reasonable justifications and using lots of jargon to make things sound technical and complicated. Then, in typical Holywood fashion, the movie veers off into something jarringly non-scientific to advance a storyline or provide a twist.  

    I am certainly not the type who tries to hold a work of fiction to the standards of reality. I truly bellieve in the audience's "willing suspension of disbelief" that is vital to capturing someone into a good yarn. I can suppress my analytic brain and forgive lots of small points that advance the narrative but really don't make sense. Even unexplained phenomena, used judiciously, can be quite enjoyable. However, as in the "Harry Potter" world, there are some unforgivable curses where basic facts, forces, or fallacies are ignored. These points can jolt my intellect and pull me straight out of the story.

    With that preface, let me say that "The Martian" did not disappoint. I watched the entire film staying inside the bubble of the narrative. The plot, characters, visuals, and direction kept me focused and empathetic, without startling my astronomical subconscious. That may not sound like high praise, but it is a rare experience for me on a film of this nature.

    Are there mistakes in the movie? Of course. Do they matter? Not much. I can discuss those points in another post (with proper spolier alerts). In this post, let me focus on the good stuff. Without giving away anything not already in the advertisements, here are three aspects I particularly liked.

    First, the computer graphics of Mars are wonderful. The views of what is really a rather bland and desolate planet are filled with warmth and majestic vistas. The mostly rock and dirt landscape of Mars was showcased in a wide variety of formations that gave it considerable grandeur. The scenes harken back to Scott's Monument Valley shots in "Thelma and Louise."

    Second, the fictional astronauts behave like real astronauts. I have interacted with a dozen or so astronauts, and observed some of them for long hours during the Hubble servicing missions. These people are part of our best and brightest. They are cool-under-pressure problem solvers who can attempt and accomplish audacious goals. Astronauts do have emotions and a sense of humor, and that is also captured in the film. But, overall, the characters exude proper competence, skill, and acumen, without soap-opera histrionics.

    Finally, the movie is a really good story, and is really well told. This tale has out-of-this-world dilemmas, strong and sympathetic characters, and action that is emotionally, intellectually, and visually engaging. Even before its release, I heard jokes comparing this movie to "Apollo 13." Now that I've seen it, I'd say the comparison is apt on many levels, and this film should garner similar acclaim and awards.

    Back in the year 2000, Neil Tyson and I started chatting about Ridley Scott's film "Gladiator." I gave that film perhaps the highest accolade by telling him nothing about it. I said something like "Don't read anything, just go see it with no expectations." I'm not sure I would go that far with "The Martian," but if the advertisements pique your interest, the film delivers on multiple fronts. I can heartily reccommend that folks see this picture, both as an astrophysicist and as a film enthusiast.