Hubble's Universe Unfiltered

  • 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.”

  • June 3, 2016

    Caught in a Gravitational Whirlpool?

    by Frank Summers

    Gravitational lensing by a massive cluster of galaxies produces lots of streaks, arcs, and other distorted shapes. The images of distant galaxies have been transformed when their light passes through the warped space within the galaxy cluster.

    Astronomers know that these distant galaxies, if seen without the intervening cluster, could look like normal galaxies. Or, these galaxies might have strange shapes due to galaxy interactions. Also, since distant galaxies are seen as they were earlier in the universe, some are still developing their shapes.

    This lack of knowledge about the true shape of a galaxy that has been distorted by gravitational lensing makes interpreting their images more difficult. One way to comprehend the distortions is to run a simulation. Take a well-known galaxy, and simulate the distortions that its appearance would undergo via gravitational lensing.

    That process is demonstrated in the video below. The simulation imagines the Whirlpool Galaxy passing behind the massive galaxy cluster Abell 2744. Astronomers in the Frontier Fields project have studied Abell 2744 carefully and have a detailed mass map for the cluster. Using that mass distribution, they can calculate the lensing effects for the simulation. Note that this is just a demonstration of the image distortions due to gravitational lensing. In reality, galaxies don't pass behind clusters at such superluminal speeds, the Whirlpool would appear much smaller, and many other caveats.

    These demonstrations are useful in comprehending the types of image distortions one might see. The really hard task is, however, to take an observed distorted image and try to re-create the actual, undistorted image. I have seen that attempted a couple times with mixed results. Maybe I can find one of those attempts and write that up as another blog post.

    For a another perspective on this video, see this Frontier Fields blog post.