Hubble's Universe Unfiltered

  • May 6, 2016

    Episode 22: Celestial Fireworks

    by Frank Summers

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    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?

  • March 11, 2016

    A Century Later, General Relativity Is Still Making Waves

    by Frank Summers

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

    In November 1915, Albert Einstein published a series of papers that laid out the ideas, equations, and some astronomical applications of the general theory of relativity. While Isaac Newton described gravity as a force between two massive bodies, Einstein's general relativity re-interprets gravity as a geometric distortion of space and time (see my previous blog post "Einstein's Crazy Idea").

    One example cited in those papers was that general relativity can explain the extra precession of Mercury's orbit that Newton's formulation does not explain. Another prediction, the bending of light as it passes a massive object, was tested and shown accurate less than four years later. This effect, called gravitational lensing, has been shown in tremendous detail by the Hubble Space Telescope (see my previous blog post "Visual 'Proof' of General Relativity"), and is one of the prime motivations behind the Frontier Fields project.

    Last year, scientists celebrated the centennial of general relativity, which has been a resounding success in diverse astronomical situations. However, there was one major prediction that had not yet been tested: gravitational waves.

    General relativity predicts that mass not only can create distortions in space-time, but also can create waves of those distortions propagating across space-time. In cosmology, the global expansion of space over time is a familiar concept. For a gravitational wave, space also stretches/shrinks, but that localized distortion moves across space at the speed of light.

    The Laser Interferometer Gravitational-Wave Observatory (LIGO) is one of the projects designed to observe the minute distortions of gravitational waves. It consists of two detectors, one in Hanford, Washington, and one in Livingston, Lousiana. Each detector has two perpendicular arms, consisting of ultra-high-vacuum chambers four kilometers (two and a half miles) in length.

    For the experiment, a laser light source is split and sent down and back each arm. By measuring how the laser light signals interfere with each other when recombined, extremely precise measurements of any change in distances can be made. The idea is that when a gravitational wave passes by, the minuscule stretch of one arm and shrink of the other will be observable.

    The signal observed in the LIGO event GW150914

    On September 14, 2015, both LIGO detectors observed an event (see the accompanying image). The pattern in the signal indicates that a series of gravitational waves passed through the detectors in about two-tenths of a second. It is extremely important that multiple detectors saw the same event so that local disturbances can be ruled out. Plus, the time delay between the detectors helps measure the speed of the waves.

    To analyze the event, the LIGO team used computer simulations. The shape and duration of the event waveform matched that expected for the merger of two black holes. The amplitude of the detection helped determine how far away the black-hole merger took place. The best fit is a merger of a 36-solar-mass black hole with a 29-solar-mass black hole to form a 62-solar-mass black hole, about 1.3 billion light-years away.

    The energetics of the merger are simply astounding. Recognizing that 36 + 29 = 65, one can see that three solar masses of material did not end up in the resulting black hole. Instead, it was converted in the energy that created the gravitational wave. Released in less than half a second, the peak wattage of the event was greater than the visible-light wattage from all the stars in the observable universe.

    And yet, when detected on Earth, the measured space distortion was smaller than the size of a proton. The reason it took a century to find gravitational waves is because one has to measure subatomic displacements. Gravity is demonstrably the weakest of the four fundamental forces. It takes a tremendous amount of energy to produce a gravitational wave that can be seen at cosmic distances.

    The title and abstract of the paper announcing the discovery of gravitational waves

    There are several major results from this observation. The detection shows, for the first time, that both black-hole mergers and gravitational waves exist. The time delay between detectors, and analysis of the signal at different frequencies, demonstrates that gravitational waves travel at the speed of light. All the results are consistent with the predictions of general relativity.

    This event marks the beginning of gravitational-wave astronomy. With more detectors coming online and planned improvements to current detectors, the field is burgeoning. Dozens to thousands of black-hole or neutron-star mergers, with more detail about each event, should be found in the next decade.

    More than a billion years ago, two black holes merged in a distant galaxy, emitted a tremendous amount of energy, and created a gravitational ripple moving across space. Recently, the LIGO project detected this almost-infinitesimal motion of space, a deviation much smaller than the size of an atom. With that amazing observation, the last major prediction of general relativity was verified. A century later, Einstein still rules.