Hubble's Universe Unfiltered

  • September 16, 2016

    Thousands of Galaxies in the GOODS/ERS2 Field

    by Frank Summers

    Looking deeply into the cosmos with Hubble, astronomers can see all sorts of galaxies. Some are large and nearby, with the familiar spiral and elliptical shapes. Others are small and distant, with dotted, elongated, and/or irregular structures. This long exposure, from the Great Observatories Origins Deep Survey (GOODS), showcases the wide variation in galaxy shapes, sizes, and colors seen across the universe.

    One of the reasons this image is so colorful is that it goes beyond the wavelengths that the human eye can see (visible or optical light). This survey was also done in the shorter wavelength ultraviolet light, as well as the longer wavelength infrared light. Astronomers are studying these galaxies across all the wavelengths Hubble can observe in order to get a fuller picture and fuller understanding of their structures.

    The change of structures with distance is extremely important, as it also indicates how galaxies change over time. The light from a galaxy five billion light-years away has taken five billion years to traverse the intervening space, and thus we see that galaxy as it was five billion years ago. Looking out into space is also looking back into time.

    The history of galaxy development is contained in these images. Nearby galaxies show the familiar patterns of what I'll call adult galaxies. More distant galaxies are, on average, younger and show the development of galaxies through their teen years. The most distant galaxies seen by Hubble are the child galaxies, with very incomplete development and only the indications of their future potential. The GOODS survey and others have systematically imaged, categorized, and tracked the changes in galaxies over time to learn how our Milky Way and its brethren went from tiny stellar and gaseous clumps to vast galactic swarms.

    But the story is not written plainly in these images. The expansion of the universe stretches the light waves that travel across this expanding space. Hence, light that starts out as visible light can be stretched to infrared wavelengths by the time we observe it. Similarly, ultraviolet light can be stretched to visible light, or even beyond to infrared light. This cosmological redshift adds in a color shift for each galaxy according to its distance from us. The deconvolution of color information is an important consideration in comparing images and observed structures. It is also a major motivation for doing such multiwavelength studies.

    Finally, I'll note that cosmological redshift pushes the most distant galaxies outside of Hubble's reach. The light from the most distant galaxies, the baby galaxies if you will, has had their light redshifted so far into the infrared regime that Hubble cannot observe them. NASA's current infrared observatory, the Spitzer Space Telescope, does observe at those wavelengths, but lacks the angular resolution to discern such tiny sources. To see these galaxies requires a telescope with the same keen resolution of Hubble, and extending to the infrared wavelengths of Spitzer. That is the James Webb Space Telescope, which will launch in October 2018.

    Images like this can be mesmerizing for astronomers. The diversity of shapes and sizes and colors are cool to explore for most anyone. Now add on top of that an exploration of galaxy development across both space and time. The visual and intellectual adventure can be truly intoxicating.

    A high-resolution version (18 megapixels) of this image is available on the HubbleSite press release pages. Enjoy!

  • September 9, 2016

    News from the Universe, September 2016

    by Frank Summers

    Each month, I host the Public Lecture Series at the Space Telescope Science Institute in Baltimore, Maryland. Before introducing the main speaker, I present some Hubble discoveries and other astronomical findings and events called "News from the Universe".

    The stories I covered for the September 6, 2016 lecture are:

    -- An interesting SETI signal gets overblown on the internet

    -- Mission updates from Juno and Rosetta

    -- Dwarf galaxies found by their gas content



    Here are the description and links to the main speaker's presentation for the September 2016 Public Lecture Series:

    On the Trail of the Missing Galaxies: The Oldest Stars in the Neighborhood

    Tom Brown, Space Telescope Science Institute

    In the past decade, wide-field surveys have revealed a new class of ultra-faint dwarf galaxies orbiting the Milky Way and Andromeda. They are the least luminous, most dark-matter dominated, and least chemically-evolved galaxies known. These faint galaxies offer a new front in efforts to understand the missing satellite problem - the discrepancy that theory predicts many more satellite galaxies than the number of dwarf galaxies observed. As the best candidates for fossils from the early universe, the ultra-faint dwarfs are ideal places to test the physics of galaxy formation from that era. New data from the Keck Observatory and the Hubble Space Telescope provide evidence that reionization in the early universe suppressed star formation in the smallest seeds of galaxy formation, thus providing a possible explanation for the missing satellite problem.


    An archive of lecture webcasts back to 2005 is available at STScI Webcasting: STScI Public Lecture Series Archive.

    Most lectures since spring 2014 are also in a HubbleSiteChannel YouTube playlist: STScI Public Lecture Series Playlist.


  • July 21, 2016

    The Final Frontier of the Universe

    by Frank Summers

    [Note: this article is cross-posted on the Frontier Fields blog.]

    Fifty years ago, in 1966, the Star Trek television series debuted. Given the incredible longevity of the franchise, it seems remarkable that the original television series only lasted three seasons.

    Each episode famously began with the words “Space: the final frontier.” To me, those thoughts evoke an idea of staring into the night sky and yearning to know what is out there. They succinctly capture an innate desire for exploration, adventure, and understanding. Such passions are the same ones that drive astronomers to decipher the universe through science.

    While Captain Kirk and company could make a physical voyage into interstellar space, our technology has (so far) only taken humans to the Moon and sent our probes across the solar system. For the rest of the cosmos, we must embark on an intellectual journey. Telescopes like Hubble are the vehicles that bring the universe to us.

    To explore remote destinations, the Enterprise relied upon a faster-than-light warp drive. Astronomy, in turn, can take advantage of gravitational warps in space-time to boost the light of distant galaxies. Large clusters of galaxies are so massive that, under the dictates of general relativity, they warp the space around them. Light that travels through that warped space is redirected, distorted, and amplified by this “gravitational lensing.”

    Gravitational lensing enables Hubble to see fainter and more-distant galaxies than would otherwise be possible. It is the essential “warp factor” that motivates the Frontier Fields project, one of the largest Hubble observation programs ever. The “frontier” in the name of the project reflects that these images will push to the very limits of how deeply Hubble can see out into space.

    But is this the “final frontier” of astronomy? Not yet.

    Abell S1063 Parallel Field

    Abell S1063 Parallel Field - This deep galaxy image is of a random field located near the galaxy cluster Abell S1063. As part of the Frontier Fields Project, while one of Hubble's instruments was observing the cluster, another instrument observed this field in parallel. These deep fields provide invaluable images and statistics about galaxies stretching toward the edge of the observable universe.


    The expanding universe stretches the light that travels across it. Light from very distant galaxies travels across the expanding universe for so long that it becomes stretched beyond the visible and near-infrared wavelengths Hubble can detect. To see the most distant galaxies, one needs a space telescope with Hubble’s keen resolution, but at infrared wavelengths.

    In what may have been an homage to the Star Trek television series with Captain Picard, the project for such a telescope was originally called the “Next Generation Space Telescope.” Today we know it as the James Webb Space Telescope, and it is slated to launch in October 2018. Webb has a mirror 6.5 meters (21 feet) across, can observe wavelengths up to ten times longer than Hubble can observe, and is the mission that will detect and study the first appearances of galaxies in the universe.

    In the Star Trek adventures, Federation starships explore our galaxy, and much of that only within our local quadrant. Astronomical observatories do the same for scientific studies of planets, stars, and nebulae in our Milky Way; and go beyond to galaxies across millions and billions of light-years of space. Telescopes like Hubble and Webb carry that investigation yet further, past giant clusters of galaxies, and out to the deepest reaches of the cosmos. With deference to Gene Roddenberry, one might say “Space telescopes: the final frontier of the universe.”