Observing M87 from London

[London_David]

I have been testing Martin Meredith’s excellent new software tool Jocular and it happened that one of my favourite objects was available to see.

For me, M87 is one of the most exciting views in astronomy. It may be an almost featureless elliptical galaxy but it does have the relativistic jet.

 

It never fails to excite me that the small line from the core of the galaxy in the above image is a jet of plasma traveling at close to the speed of light and 5000 light years long. The total energy of the jet is estimated to be ten trillion (for fun that's 10,000,000,000,000) times the total energy produced by the Milky Way in 1 second. The size and speed of this structure is quite spectacular. It's so big and powerful, even at a distance of just over 50 Million light years (redshift of 0.004360 ± 0.000022) you can see it move (https://www.spacetelescope.org/videos/opo1332a/).

M87 is also one of the most massive galaxies known to exist. It has a diameter of 120,000 light years which is similar to the Milky Way. However, due to the elliptical shape, the galaxy has about 200 times the mass of the Milky Way. It has perhaps a trillion stars and more than 10,000 globular clusters.  

These images were made from a heavily light polluted Zone 2 London location with an ASI290mono and Skywatcher 150 PDS on an EQ3Pro mount. Due to the testing setup I was trying the observing workflow was a bit unusual. I used SharpCap on Windows 10 to capture and do some live stacking while saving each individual frame, and occasional stacked snapshot. Then I used Jocular to re-observe the data the next day. There are no flats, darks or bias used in any of these images.

I initially followed SharpCap’s Brain suggestion and tried 4s exposures at around about 120 Gain for a 10 minute observation. However, I wanted to take shorter exposures to see if I could see more detail. I then tried 212 frames of 0.5s at about 350 gain for 106s total integration (below) which clearly showed the Jet. However, since I was testing Jocular I wanted to try something more interesting.

 

212 frames at 0.5s for 106s total integration

 

I have been using an ultra short exposure workflow for EAA in SharpCap with exposure on DSOs of under 2s. So for M87 I captured about 20 minutes of data at 0.125s per exposure, leading to a total of 10936 images. 

I was trying to push Jocular as far as I could and it became clear that 11k images was definitely too slow to process in real time! This wasn’t a surprise.

However, it worked with a smaller sample of the first 264 x 0.125s giving a total integration of 33.125s.

 

264 frames at 0.125s for a total integration of 33.125s

I then tried with the first 800 x 0.125s giving a total integration time of 100s. This is cleaner and. I think a touch more detail given the extra minute of exposure, but I think I have clipped some information here (see the first image in the post, below is the inverted version).

800 frames of 0.125s with a total integration time of 100s

I look forward to trying it with the full data set in a new version of Jocular to see if there is any more detail. To get the best result it will require some filtering of the data first. SharpCap can live filter on FWHM during live stacking but since I captured everything, I know there is junk that blurs the image - I saw some transparent clouds come through on the images as I was watching. I also think I was probably too aggressive and should have raised the gain or increased the exposure time, but I knew that at the time and I wanted to see how fast I could go.

I have been experimenting with short exposure DSO observing since I started when I had terrible seeing (made worse by heat escaping from a house). I noticed very quickly that short exposures always had better FWHM than longer ones. So I found I could cut through bad seeing and dig out detail otherwise lost.

Recently I have also been following exaxe on CN (http://astrophoto17.eklablog.com) who has been creating great detailed AP images with this technique.

Either way, this was not a particularly careful run at observing the jet - it was more for experimentation. But I always find it impressive! 

This is what a high quality image of M87 looks like from Hubble: 

http://imgsrc.hubblesite.org/hvi/uploads/image_file/image_attachment/17738/full_tif.tif 

Interestingly, the jet axis is alined with the main East to North West axis of the Virgo Cluster.

For a broader sense of location, here is a diagram of the Virgo Supercluster from Wikipedia: https://commons.wikimedia.org/wiki/File:Earth's_Location_in_the_Universe.jpg

[Martin Meredith]

Amazing what you can get from near the centre of London. I always enjoy seeing results from challenging locations. It brings to mind Nytecam's feats (sadly missed) that got a lot of us started in this game. 

Thanks for testing Jocular to destruction too! I should say that it isn't really designed for 100s of subs, let alone 1000s! I am currently adding support for fractional binning and perhaps dynamic ROI (i.e. undoable/reselectable regions) to help out anyone with a larger megapixel count as this makes a huge difference to usability. 

Martin

[Mike JW]

Hi David, As a new member I am gradually exploring what other folk are doing. Impressed with what you achieve from London.  Thoroughly enjoyed reading your info on M87. My recent visit to M87 did not capture the jet - must try again. (use a C9/Ultrastar).

Mike

[Mike JW]

Hi David,

Took another look at M87 last night with the C9/Ultrastar. I tried a stack of 5 x 3 seconds. First image is cropped t o the relevant part. Second image is cropped and enlarged. Thanks for your post and inspiration. Now must spend reading up again about M87.

All the best

Mike

 

 

 

 

 

 

 

 

 

[AKB]

Super write up,  both re. M87 itself and the acquisition options.  Another one to add to the observing list!

Thanks.

Tony.

[Mike JW]

Thanks Tony.  David's post prompted me to review  my previous attempt, in particular to reduce down the time for each sub and hey presto it worked out. Mike

[London_David]

@Mike JW good shots - great that you can clearly see it in just 15s.

@Martin Meredith Thanks. I think 11k subs (even if it is only 20 minutes observation time) is going to be an edge case for use on Jocular! Also, while the subs help with background noise, ultimately there’s actually not a lot of difference in the amount of detail here for a lot more hassle. I think if I had filtered FWHM as they came in on SharpCap it might have been better. I still might revisit the data to filter at a later date. The lucky imaging is less effective if you don’t drop the unlucky shots!

The ROI feature I think will be fantastic for usability  and speed. Especially if you are trying to eek out any small detail in something like this, quick ROI recomputes would allow you to experiment and dig into the data faster and focus on the observing bit.

Thanks @AKB

It was @Astrojedi here and on CN originally inspired me to investigate the object with EAA since he managed to get some great images from San Diego. He has posted shots from his C8:

https://www.cloudynights.com/topic/567930-m87-relativistic-jet-and-other-galaxies-using-short-exposures/

You can clearly see detail in the thickness of the jet in the CN post of 30s (2s x 15). I think seeing must be the real key for detail on this object (seeing is my guess - if anyone else knows the physics better I’d love to know) - which is why I’m interested in testing the DSO lucky imaging method. It may also be that I need a larger aperture to see any more detail.

I’m in the process of upgrading, so I’ll be returning to see if I can find more detail with my 6” and later when I switch to 10”.

I just got the new mount (CEM60) and I’m hoping there will be a clear nights over the weekend to try again to try some alternative exposure/gain options to see if I can see any detail. 

Of course, the new equipment probably that means cloud cover for the next six weeks. 

[Mike JW]

Thanks David for the link. I agree seeing will help and I assume aperture. I note astrojedi was using 25 sec subs. Mike

[London_David]

That's true on the SGL post. However, on the CN post with the ASI290 he switched to 2s subs and got more detail.

On the night I was observing, the SharpCap Brian recommended 4s exposures for 10 minutes to get the best result. I went off-piste because I wanted to test large sub numbers on Jocular. I'm hoping I might get a chance this weekend to re-run the SharpCap test and see what it suggests if I restrict exposures in the too at 0.5s or shorter and then filter the stacking - perhaps quite aggressively - by FWHM. 

[Mike JW]

Hi David, I took another look at M87 last night, trying 5 second, 25 second subs, 1x1, 2x2, linear and arcsinh stacking on what was a damp and unsteady night. There was no obvious approach that was best. They all worked equally well and clearly showed the jet.  All tried at f4.4.  Mike