Hubble's Universe Unfiltered

  • 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.

  • March 4, 2016

    Episode 21: New Views of the Pillars of Creation

    by Frank Summers

    Download this episode

    Shownotes

    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:

     

    Notes:

    • 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)
    http://hubblesite.org/newscenter/archive/releases/1995/44/image/a/


    Sagittarius Region
    Credit: A. Fujii
    http://hubblesite.org/newscenter/archive/releases/2005/12/image/h/


    Eagle Nebula
    Credit: Timber Rock Observatory, clearstarrynights.com
    http://clearstarrynights.com/PicPageFolder/M16-127.html


    Eagle Nebula
    Credit: T.A. Rector (NRAO/AUI/NSF and NOAO/AURA/NSF) and B.A. Wolpa (NOAO/AURA/NSF)
    https://www.noao.edu/image_gallery/html/im0725.html


    Eagle Nebula Pillars (2015)
    Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
    http://hubblesite.org/newscenter/archive/releases/2015/01/image/c/


    Eagle Nebula Pillars in Infrared (2015)
    Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
    http://hubblesite.org/newscenter/archive/releases/2015/01/image/g/