Hubble's Universe Unfiltered

  • March 5, 2015

    Twenty-Five Years of Hubble

    by Frank Summers

    The Hubble Space Telescope was launched into Earth orbit on April 24, 1990 aboard the Space Shuttle Discovery. While that event is a fond memory for many of us, it is now a quarter of a century, 25 years, in the past. When I give talks to schools, it is sobering to remember that Hubble was launched before any of the current elementary, high school, and college students were born. They have never known a time when there wasn't a Hubble. All their lives, the telescope has been a fixture and symbol of astronomy.

    For most scientific instruments, even ambitious and exceptional ones, their continued existence is scant cause for popular notice. Other billion dollar projects, say, particle accelerators, note the passage of milestones without significant fanfare. However, Hubble's images and discoveries have permeated into the global consciousness to the point that we feel a bit of public revelry is worthy. Throughout all of 2015, we will be celebrating Hubble's 25th anniversary.

    For my part, I have spent some significant time reviewing every Hubble press release ever created. Although I have been working on Hubble outreach for 14 years, I tried to take a fresh approach that would provide persepctive, context, and a flow of events across the decades. Most importantly, I wanted to identify the science story threads woven through the fabric of Hubble's many and diverse discoveries. There are so many great stories to tell. I'll be presenting some of them in this blog, and quite a number of other venues, over the coming weeks and months.

     

     

    Some of my perspective on Hubble's remarkable history is presented in my public lecture from January 13, 2015. Entitled "25 Years of Hubble", the talk winds its way across the important events, ground-breaking discoveries, and astounding imagery of what is perhaps the most important telescope ever. Join me -- and the rest of the Hubble team at the Space Telescope Science Intitute, at the Goddard Space Flight Center, across NASA, and at our European partner ESA -- in this presentation, and throughout 2015, for a celestial silver celebration.

  • February 26, 2015

    The Marvel of Gravitational Lensing

    by Frank Summers

    One of the coolest marvels in the universe is a phenomenon known as "gravitational lensing". Unlike many topics in astronomy, the images are not what makes it appealing. Gravitational lensing produces streaks, arcs, and other distorted views that are intriguing, but don't qualify for cosmic beauty pageants. What makes these images special is the intellectual understanding of how they are created, and the fact that they are even possible at all. The backstory takes an ordinary, everyday process, and transforms it to cosmic proportions.

    Most of us are familiar with the workings of a glass lens. If you have ever used a magnifying glass, you have seen how it changes the view of an object seen through it.

    The glass lens collects light across its surface, which is generally much larger than the pupil of a human eye. Hence, a lens can amplify brightness. In addition, the path of a light ray is bent when it passes through the glass lens. [To be specific, the path bends when the light crosses from air to glass, and again when it crosses back from glass to air.] This bending is called refraction, and the common lens shape will focus the light to a point. When we view that collected light, our view of the object can be bigger or smaller depending on the distances involved, both from the object to the lens and from the lens to our eyes. In summary, a glass lens can amplify and magnify the light from an object.

     

     

    Glass lenses, however, are not the only way that the path of light can be changed. Another way to redirect light comes from Einstein's theory of general relativity.

    My three word summary of general relativity is "mass warps space". The presence of a massive object, like a star, warps the space around it. When light crosses through warped space, it will change its direction. The result is that light which passes close enough to a massive object will be deflected. This deflection by mass is similar to refraction by glass.

     

     

    Clusters of galaxies are huge concentrations of mass, including both the normal matter we see in the visible light from galaxies and the unseen dark matter spread throughout. Many galaxy clusters are massive enough to produce noticeable deflections of the light passing through or near them. The immense gravity in the cluster can warp space to act like a lens that gathers, amplifies, and magnifies light. Such a gravitational lens will be lumpy, not smooth, and will generally create distorted images of background galaxies seen through them. Also, this lensing often produces multiple images of the same background galaxy, as light from that galaxy is re-directed toward us along multiple paths through the cluster.

     

     

    The simple idea of a glass lens becomes both cosmic and complex in gravitational lensing. Imagine a lens stretching millions of light-years across (many million million millions of miles). We don't need to construct such a lens, as nature has provided a good number of them through the warping of the fabric of space. These lenses allow us to see very distant galaxies in the universe, some of which could not otherwise be observed. That's the marvelous reality of galaxy clusters acting as gravitational lenses.

  • November 24, 2014

    A Black Hole Visits Baltimore

    by Frank Summers

    [NOTE: This post is the fourth in a four-part series. Previous posts are: 1) Einstein's Crazy Idea, 2) Visual "Proof" of Gravitational Lensing, and 3) Gravitational Lensing in Action. The same posts, slightly modified, also appear on the Frontier Fields blog.]

    For the final part of this series of blog posts, let's bring things back to Earth. The demonstration of a physical process will always seem a bit arcane when using unfamiliar objects as the example. Most folks don't have a working relationship with galaxies, let alone the strange varieties one gets in the distant universe. Instead of taking the viewer into the universe, it can be more intuitive to bring the cosmic phenomenon closer to home.

    Suppose that, say, a black hole decided to take a short vacation. Perhaps it got tired of the enormous responsibilities of being such a tremendous distortion of space-time. It needed a weekend off to cool its jets (absurdly geeky pun intended - sorry). Around Baltimore, where I work, the black hole might go down to the Inner Harbor, enjoy the sights and activities, indulge in a crab feast, and leave completely rejuvenated. Now, while I haven't yet tried to visualize a black hole eating crabs, and the concomitant singularity eruptions due to Old Bay seasoning, we can approximate what tourists might have seen during the visit.

    This scientific visualization presents a black hole of about the mass of Saturn passing through Baltimore's Inner Harbor. The initial view from Federal Hill shows the usual boats, shops, and office buildings along the water. As the black hole passes across the harbor, the view of the background buildings is distorted due to gravitational lensing. Light is redirected such that, in the region around the singularity, imagery is flipped top/bottom and left/right, with multiple views of the same object. This transformation of a familiar skyline scene can help one imagine the transformation of unfamiliar galaxies in the distant universe.

    Note: As in the previous simulated lensing image, a simplified, planar approach of gravitational lensing is used for this visualization. However, in this case, the foreground objects were not removed. The visual distortion of ship's masts on the near side of the harbor would not occur. We humbly ask your indulgences.

    While in graduate school, I had to solve problems using the complex collection of general relativity equations - but only a few times. And all of those instances were for problems with enough symmetry that things could be considerably simplified. I gained an appreciation for the essential character, and some of the beauty, of the mathematics behind it. However, as stated in the first post in this series, the whole concept still has a feeling of weirdness.

    Perhaps that notion would have dissipated had I specialized in relativity. Instead, as I developed into a scientific visualization specialist, I've gotten to revisit things from a public presentation, rather than research, perspective. The visual allure of gravitational lensing can attract an audience for topics typically mired in equations. It shows how a simple magnifying glass can have a truly cosmic analogue. It helps explore the perspective changing shift in gravity from Newton's force to Einstein's geometric re-interpretation. It opens the pathway to deeper philosophical thoughts about the fabric of space-time and the very underpinnings of our universe. Now, that's quite the opportunity for an outreach astrophysicist like me.

    In this case, weird is cool.