Hubble's Universe Unfiltered

  • 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.

  • May 6, 2016

    Episode 22: Celestial Fireworks

    by Frank Summers

    Download this episode

    Shownotes

    Celestial Fireworks

    To help commemorate Hubble's 25th anniversary in April 2015, our imaging team captured an amazing cluster of thousands of massive, hot, bright stars. The brilliance of the cluster inspired the metaphor of "celestial fireworks," celebrating decades of astronomical accomplishments. To make this beautiful image even more eye-popping, our visualization team processed it into a three-dimensional computer model and created a flight into the nebula. In this episode, Dr. Summers explores the spectacular image and reveals behind-the-scenes details of how the visualization was made.

     

    Hubble Press Release:

     

    Show Notes:

    • It is remarkable that the Hubble Space Telescope reached the 25 year milestone. However, that doesn't mean the telescope is "old." The five servicing missions to the telescope provided a continuing series of advances in both the observatory hardware and the scientific instruments. In addition, two decades of experience running the observatory have brought about vast improvements in efficiency and yield. In so many ways, Hubble has increased its capabilities over the years and gotten demonstrably better with age. Scientific productivity is perhaps the best measure of the vitality of a telescope, and on that measure Hubble is a robust as it has ever been.

     

    • A search for the Spitzer Space Telescope image of the nebula Gum 29 finds an object known as RCW 49. They are the same nebula. There are multiple catalogs of nebulae by different astronomers, at different observatories, at different times. Colin Stanley Gum published his study of 84 nebulae in 1955, while the team of Rodgers, Campbell, and Whiteoak (RCW) produced a catalog of 182 objects in 1960. Other catalogs of nebulae include those of Caldwell and Sharpless. A nebula can be referenced by any of these catalog names, or by the more well-known NGC catalog number if such an entry exists. Unfortunately, there is no one standard naming convention, and cross-referencing between catalogs is a standard feature in astronomy.

     

    • In many of our visualizations, the stars were handled as image cutouts. If there are just a few hundred stars in an image, the process of identifying the pixels associated with each star is not overly cumbersome. Software written for astronomical research addresses such tasks and can be applied to visualization. However, dense star clusters with many thousands of stars present a severe challenge with tremendous overlap amongst the stars. The point-spread function technique, described in the video, is also an adaptation of research software. Although developed specifically for star clusters, the process can be applied to any image.

     

    • The development of computer graphics software to support Hollywood movies has greatly benefited our work in scientific visualizations. Astronomy is not a large enough market for specialized visualization software to be particularly profitable. Instead, we use the software written for the billion-dollar film market, and adapt it to our purposes. The sophisticated tools for look development, virtual cameras, and image rendering help add a cinematic feel, while we can keep track of the scientific details and ensure the presentation is astronomically appropriate. We strive for a combination of accuracy and aesthetics.

     

    Image notes

    Zoom to Gum 29 (movie)

    Credit: NASA, ESA, G. Bacon, and Z. Levay (STScI)

    Acknowledgment: A. Fujii, the Digitized Sky Survey 2 (STScI/AURA, Palomar/Caltech, and UKSTU/AAO), ESO, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team 

     

    Nebula Gum 29

    Credit: ESO

     

    Nebula Gum 29, infrared

    Credit: NASA/JPL-Caltech/E. Churchwell (University of Wisconsin)

     

    Star Cluster Westerlund 2, x-ray

    Credit: NASA/CXC/Univ. de Liège/Y. Naze et al

     

    Nebula Gum 29 and Star Cluster Westerlund 2

    Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team 

     

    Flight to Star Cluster Westerlund 2 (movie)

    Credit: NASA, ESA, G. Bacon, L. Frattare, Z. Levay, and F. Summers (Viz3D Team, STScI), and J. Anderson (STScI) 

    Acknowledgment: The Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), the Westerlund 2 Science Team, and ESO

    Music courtesy of Associated Production Music (APM)

  • May 4, 2016

    May the Fourth Be With You

    by Frank Summers

    May 4th is celebrated as Star Wars Day across the internet. We who do "serious science" have always enjoyed the fictional universes of books and films, but the crossover to our work has generally been tangential.

    Not so this year! Last December, we jumped on the bandwagon and released an image with the headline "Hubble Sees the Force Awaken in a Newborn Star" (click on the accompanying thumbnail image to see it in detail). I like to refer to it as the "celestial lightsabers" image, as it bears a good resemblance to Darth Maul's double-bladed weapon. Hence, I can be fully justified in doing a Star Wars Day blog post about it.

    Examine the image for a while, and the big question one should ask is: How is it possible to get twin jets of material streaming at more than 100,000 miles an hour across over half a light-year of space?

    When a gas cloud collapses to form a star, the material condenses to the center and inevitably forms a disk. The disk is a simple result of the conservation of angular momentum, a.k.a. spin. The motions within a large cloud may have only a tiny bit of net spin, but when that material condenses, the spin is concentrated as well. A tiny spin across a long distance leads to a huge spin across a short distance. A disk around the newborn star is the result.

    In the inner edge of the disk, material falls onto the star. Not all of the infalling material is added to the star; some of it is expelled back outward. The directions perpendicular to the disk are the available paths for outflowing material. Hence, oppositely directed outflowing streams are to be expected.

    The remarkable feature is the thin collimation of those streams. The rapidly spinning disk contains ionized (electrically charged) material that carries along magnetic field lines. These magnetic fields become wrapped around the new star with twisting crossover points above and below the disk. Ionized material flowing along magnetic field lines can be ejected at high speed along two narrow openings in opposite directions.

    Herbig-Haro Object HH 47, observed by Hubble

    Herbig-Haro Object HH 47, as observed by Hubble

    The result is the twin jets seen in Herbig-Haro objects. The jets of HH 24 remain thinly coliimated for a long distance, creating the lightsaber resemblance. Many other HH objects, such as HH 47 pictured above, are more dispersed, puffier, and with large lobes at the end. These lobes indicate where the energy of the material is deposited into the interstellar gas. HH objects are relatively short-lived (thousands of years) and are moving at large enough speeds that Hubble has been able to measure the motion of HH clouds.

    A visualization with a 2D zoom and 3D flight to HH 24

    While I know of no scientific explanation of how a lightsaber is supposed to work in the Stars Wars universe, we have a pretty good idea of the physics behind the celestial lightsabers observed by Hubble. Star Wars Day becomes a great excuse to delve into Herbig-Haro objects. And that's part of what makes my job fun. Use the cool Hubble images to attract the public's attention, and then overlay a bit of scientific explanation. The universe is even more beautiful when you understand the forces behind it.

    Now, what do I do for Talk Like a Pirate Day? Arrr Arrr Lyrae variable stars, anyone?