Hubble's Universe Unfiltered

  • March 12, 2015

    Revisiting a Legend

    by Frank Summers

    As discussed in a previous blog post, "Twenty-Five Years of Hubble," this year marks the silver anniversary of the Hubble Space Telescope. We have plans for a full year of festivities and kicked it off by revisiting a legend.

    One of our most famous images of all time is the 1995 view of three gaseous pillars in the Eagle Nebula nicknamed "The Pillars of Creation." The "creation" aspect derives from the fact that new stars are being born within the dark, dense clouds at the tops of the pillars. That greenish, irregularly shaped image (on the left in the montage image above) was taken with Hubble's Wide Field Planetary Camera 2 instrument that was installed during Servicing Mission 1 in 1993.

    An updated insturment, Wide Field Camera 3 (WFC3), was installed as a replacement during Servicing Mission 4 in 2009. Our first press release of the 25th anniversary year was a remarkable new WFC3 view of the same region. This new image (center in the montage) has twice the resolution, about six times the sky coverage, and more than twenty times the pixels of the previous version. The broader context and innumerable fine details combine to make a compelling updated portrait.

    Yet Hubble took it one step further. The greatly improved infrared-light sensitivity of WFC3 enabled a striking infrared image of the Eagle pillars (on the right in the montage). The longer wavelengths of infrared light can penetrate through much of the gas and dust clouds, bringing out both the nebula and a panoply of background stars in stark contrast. The pillars, seemingly solid dark columns in visible light, are revealed in infrared light as a combination of dense clouds and the shadows they cast.


    The contrast between Hubble's two new views is best seen in a cross-fade between the visible-light and the infrared-light images. The animated GIF displayed above has both images cropped to the same region. One can instantly pick out the visible gas that disappears in the infrared, as well as the bright infrared stars that have no visible counterparts.


    The pillars in the Eagle Nebula are the primary topic of this Hubble Hangout.


    There are so many interesting details to discuss in these images that it would fill a bunch of blog posts. Instead, let me point you to a Hubble Hangout that I did with Tony Darnell in late January. We call this series of hangouts "News from Hubble and Across the Universe." Usually, we cover three or four stories, but this time we spent the entire hour examining and comparing the Eagle pillar images. Have a look, as there are some rather intriguing and beautiful features to explore.

  • 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.