Zoom in on galaxies galore
Posted: Thursday, February 05, 2009 6:37 PM by Alan Boyle
K. Cook / LLNL / NASA / ESA |
Haunted by NGC 4921?
Click on the image for
a zoomable version.
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The Hubble Space Telescope's latest stunner is a pale ghost of a galaxy, floating amid its kindred spirits in the Coma Cluster. But wait ... there's more: If you take a closer look at the picture, you'll find thousands of other galaxies going far back into the depths of the universe.
This galaxy, known as NGC 4921, is part of a well-known cluster in the constellation Coma Berenices, 320 million light-years from Earth. More than a thousand galaxies huddle together, and most of them have been crunched together into elliptical shapes. NGC 4921 is one of the rare spirals still surviving - and in today's image advisory, the European Space Agency's Hubble team says it's a "rather unusual one."
NGC 4921 looks so ghostly because it's an "anemic spiral" - a galaxy where the process of star formation is much less intense than usual. Instead of the classic spiral arms, the galaxy contains pale swirls of dust, punctuated by bright young stars.
The space telescope's Advanced Camera for Surveys made a series of long, deep exposures documenting the galaxy as well as the surrounding area of sky - 80 exposures in all, which took up 27 hours of precious telescope time. All those exposures, in visible light and the near infrared, were combined to produce this picture, which reveals thousands of more remote galaxies.
You should be able to spot a variety of galactic shapes and colors in our HD View zoomable version of the image - including some lumpy raisins of light that are characteristic of galaxies on the far edge of the observable universe. You might have to click on the adaptive tone adjustment at upper right to get the contrast just right. If you don't want to download the HD View plug-in, you can look at the Hubble team's zoomable version, or this large-format JPEG.
Here's an annotated image that shows you what's what, and you'll definitely enjoy this "Hubblecast" video that tells the story behind NGC 4921.
There's another, sadder story behind this picture: The European Hubble team said the Coma Cluster imagery was originally collected by a team led by Lawrence Livermore National Laboratory's Kem Cook, as part of an effort to identify Cepheid variable stars in NGC 4921. Such stars can be used as "standard candles" to calibrate the distance to the galaxy, and indirectly yield information about the universe's expansion rate.
The team wasn't able to complete that project, however, because the Advanced Camera for Surveys gave out in 2007.
The good news is that Cook and his colleagues hope to return to the project once the camera is repaired. That's one of the items on the to-do list for NASA's final Hubble servicing mission, which is now scheduled for launch in May. If that repair job goes as expected, there might be some life left in this old galactic ghost after all.
For more stunners from Hubble, check out the European Space Agency's Hubble portal, the Space Telescope Science Institute's Hubblesite, and our own Space Gallery. And don't forget to cast your vote for your favorite future Hubble target.
