The Coma Cluster is a collection of 1000 galaxies around 320 million light-years from Earth.
First of all, apologies it’s taken me so long to produce a new image. I’ve had this sat on my harddrive for a while, but my day job has kept me too busy to do much with it!
Galaxies are tough for me to image for two main reasons. First is that they’re broadband targets, and so filters aren’t much use for combatting light pollution. You can read more about filters here. The answer, as it so often is for urban astrophographers, is long integration times! This image is 24 hours in total. You can read my tips for getting long integration times here.
The second challenge with galaxies is that they’re small. Ok, well actually galaxies are huge, but they’re also really far away, meaning they look tiny in the sky. There are some exceptions, like The Pinwheel Galaxy, but most galaxies are tiny pin-pricks even through my Askar 130PHQ telescope, despite its focal length of 1000mm. The answer here is galaxy clusters, where there are so many galaxies that you can fill the frame with them.The Coma Cluster contains more than 1000 galaxies, and I can identify 275 of these in my image. Not bad from the centre of a city!
There’s some interesting history to the Coma Cluster. Back in 1933, it was observed that the galaxies were moving faster than could be accounted for by their mutual force of gravity alone. It was suggested that mysterious “dark matter” — something that couldn’t be directly seen, but its effects observed — may be responsible. Nowadays we think that around 90% of the Coma Cluster’s mass is dark matter.
Here are the main galaxies that I managed to capture:
NGC 4907 is a barred spiral galaxy. You can definitely see its shape in the picture.
NGC 4895 is a lenticular galaxy, meaning it’s a large disc but with no spiral arms.
NGC 4848 was stripped of most of its gas as it passed through the Coma Cluster.
NGC 4921 is one of the few spiral galaxies in this region. It has unusually low rates of star formation.
NGC 4894 is a lenticular type. Another galaxy, even further away, can be seen through its faint outer region.
NGC 4911 is a spiral galaxy that’s being warped out of shape due to the gravity of other nearby galaxies.
NGC 4872 contains an active galactic nucleus, which is an area at the centre of the galaxy that’s giving out lots of energy. The source isn’t known for sure, but it could be a supermassive black hole.
And as for the two large circular objects… well they’re stars much closer than the galaxies, just coincidentally along our line of sight.
Imaging details
* 19 April to 21 May 2024
* Bristol, UK (Bortle 8)
* Telescope: Askar 130PHQ Flatfield Astrograph
* Camera: ZWO ASI 2600MC-PRO
* Mount: Sky-Watcher EQ6-R PRO
* Guide: William Optics 50mm Guidescope with 1.25″ RotoLock; ZWO ASI 120MM Mini
* Control: ASIAIR Plus
* Software: PixInsight, Lightroom
– PixInsight Pre-processing guide
* Filters:
– Optolong L-Quad Enhance (RGB) 288 x 300 seconds (24 hours)
Total exposure time: 24 hours
By Lee Pullen
Processing walkthrough
Example source data
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