Dissecting an Anemic Galaxy

The milky swirl seen here is NGC 4921, one of the very few spiral galaxies in the thousand-member Coma galaxy cluster about 320 million light-years away.


—Image courtesy NASA, ESA, K. Cook (Lawrence Livermore National Laboratory, USA)

The Hubble image, released today, is one of the deepest looks yet at this particular object, revealing a rich amount of new detail about a galaxy we’ve known of since the 1700s.

In addition to spotting some ghostly dwarf galaxies near the rim, Hubble picks up in sharp detail clusters of bluish dots that show where new stars are forming.

Astronomers consider this galaxy to be anemic, because its rate of star formation is unusually low. [A nice juxtaposition to yesterday’s news about a galaxy undergoing a period of hyper-starburst.]

But perhaps the coolest part of this picture is that’s actually a glass of proverbial lemonade, made when Hubble handed scientists at Lawrence Livermore National Lab one really big lemon.

Kem Cook and colleagues had been using the space telescope’s Advanced Camera for Surveys to search for what are known as Cepheid variable stars, a type of pulsating star that astronomers can use as a standard light source for telling how far away cosmic objects are from Earth.

But in early 2007 the ACS up and broke, leaving Cook’s data set incomplete.

Lucky for us, 80 of his images—50 taken with a yellow filter and 30 in near-infrared—could be combined to make the above snazzy snapshot.

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