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Unknown object spotted by Hubble: Answers on a Postcard! September 15, 2008

Posted by Sarah in science.
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A very interesting paper was recently accepted for publication by the Astrophysical Journal and turned up on the preprint server astro-ph last week. A group of astronomers working on a program called the Supernova Cosmology Project report the discovery of an optical transient from images with the Hubble Space Telescope‘s Advanced Camera for Surveys. Now, it’s a pretty dangerous thing to announce that you may have found a new kind of astronomical object, but the authors seem to have worked hard to explain their observations, yet found no explanation for what the images showed.

Large imaging surveys, whereby large swathes of sky are imaged regularly over several days or weeks, are ideal for discovering new supernovae, in which massive stars end their lives in gigantic cosmic explosions. By comparing images taken at different times, astronomers can spot suddenly brightening stars that are the signatures of these cataclysmic events. This is precisely what happened in 2006, when a new bright object appeared in the camera’s field of view.

At first the point-like object looked like a supernova event, brightening over the course of around 100 days to supernova-like magnitudes at near-infrared wavelengths. But when the astronomers, as is usual with new supernova discoveries, turned the ground-based telescopes VLT, Keck and Subaru to the source to obtain further images and spectra to gain more information on the object’s composition and dynamics, they found the spectrum didn’t match that of any known supernova. Comparisons with databased spectra of other kinds of variable sources, QSO‘s or white dwarf stars yielded no results. They also ruled out a microlensing event, whereby a faint background object is suddenly and transiently ‘magnified’ by interlying dark matter.

We discussed this result in a journal club discussion last week, as I imagine did many astronomers round the world, and even some of our more cynical faculty members made some noises of approval. It’s a super interesting result that may genuinely have given us a new kind of object. Very cool! I’ll definitely be keeping an eye out further results on this.

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