I’m sure many avid astro fans out there are used to seeing pretty pictures of galaxies. You know the type. They’re usually coloured, dynamic and absolutely gorgeous. We have a few of these (usually) Hubble pictures on the wall in the office. I see them reblogged around on tumblr all the time because they are just so striking and can make you feel giddy. But these images are sometimes art over science, with arbitrary false colours, touch-ups and the like. Those galaxies are awesome in their own right, but they’re not what I work with.
Instead I’m dealing with images of distant galaxies. Not exactly Hubble Deep Field, but light from these galaxies can be millions and often billions of years old. Here’s an example of real data I’m working with from the HerMES collaboration (from the public data-set) taken with the Herschel Space Telescope. These are far-infrared images, rather than Hubble’s near-infrared/optical pictures, so the light that Herschel sees is invisible to humans.
As you can see, there are no colours! This is standard. We work with images black-on-white rather than how space really looks, with colour-on-black, as the data files these pictures are stored in represent no light at a pixel as zero and increase the number with brightness. The file-viewer I’m using here, Aladin, rescales the image to get the full grey-scale range.
So here’s some fun statistics. This box is 1.74 square degrees, representing a tiny 0.004% of the sky. In this box, at this resolution and at this wavelength there are roughly a thousand galaxies that we can pick out against the background noise with confidence (5-sigma certainty). There are loads of them hiding in the background, though. These galaxies are only a few pixels large on the image and the vast majority will never have an official name or pretty posters of them on tumblr because they’re just so distant and hard to image. So go ahead, pick one as your own and name it! You might as well!
Thanks for reading, and of course, a big hello to you new people. My ask box is always open :)
(PS, for those interested, this is part of the Lockman-SWIRE field in Herschel’s SPIRE instrument’s 250µm band. It’s part of the Herschel Multi-tiered Extragalactic Survey’s (HerMES) first data-release (DR1), released earlier this month. It and other fields can be found here. Read more about HerMES here.)