Polar rings or diffraction spikes?

by Alpha_Aurigae

The past couple of days I found three lightcurves of Hubble galaxies, with features that look like jets or polar rings. It has been suggested in one of the discussions the features are diffraction spikes, and I tend to agree. Here they are:

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AGZ0000mdv

Posted September 23, 2014 9:36 AM

by Alpha_Aurigae

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AGZ0000jxm

Posted September 23, 2014 9:37 AM

by Alpha_Aurigae

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AGZ0000519

Posted September 23, 2014 9:39 AM

by Alpha_Aurigae

And yet another one:

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AGZ0000zfl

Posted September 23, 2014 12:30 PM

by Alpha_Aurigae

Number 5:

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AGZ0000613

Posted September 23, 2014 12:41 PM

by Alpha_Aurigae

Looks like number 6:

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AGZ000108q

Posted September 23, 2014 12:51 PM

by Alpha_Aurigae

Capella05 sent me this text from the the Hubble/ESA website:

" Why do stars have a cross-shaped distortion in most Hubble images? Why do galaxies not? The cross shape visible on bright objects (such as stars) in Hubble images is a form of distortion that is visible in all telescopes that use a mirror rather than a lens to focus light rays. The crosses, known as diffraction spikes, are caused by the light’s path being disturbed slightly as it passes by the cross-shaped struts that support the telescope’s secondary mirror. It is only noticeable for bright objects where a lot of light is concentrated on one spot, such as stars. Darker, more spread-out objects like nebulae or galaxies do not show visible levels of this distortion."

My personal opinion - which is not scientifically based - is that the features in the previous 6 galaxies are diffraction spikes. It is very obvious in the 6th image. I don't expect I will find more of these features in Hubble galaxies. Maybe a scientist could have a look at these images I posted here?

Posted September 23, 2014 1:16 PM

by Alpha_Aurigae

Number 7 even:

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AGZ0000b6y

Posted September 23, 2014 1:42 PM

by JeanTate in response to Alpha Aurigae's comment.

Cool! 😃

The case that the second one (AGZ0000jxm) is a diffspike is particularly clear; there's a nearby bright star with diffspikes, one pair of which is aligned with that of the galaxy (at eyeball-level anyway).

If there were a way to zoom-out for the other three fields, and find stars with diffspikes, that'd be further evidence consistent with the diffspike hypothesis.

That the diffspikes show at all says a lot about Hubble's superb optics (and being above the atmosphere); it also strongly points to the nuclei of these galaxies being point sources, so likely AGNs.

Posted September 23, 2014 2:49 PM

by Alpha_Aurigae

Thanks Jean 😃

Posted September 23, 2014 2:56 PM

by JeanTate in response to Alpha Aurigae's comment.

Crossing posts ...

If you can clearly see two pairs, and they are (eyeball-level) 'compass points' (i.e. intersect at 90 degrees), that's yet more evidence for them being diffspikes. So too is that each pair seems to be a copy of the other, just rotated (i.e. similar brightness, which falls off from the center the same way). Of course, galaxy structure can make these comparisons more difficult, especially if you're just eyeballing.

The last one - #7, AGZ0000b6y (and to some extent AGZ0000zfl) - show another feature expected of bright point sources, hints of Airy rings. You can see these clearly in the star in #2 (AGZ0000jxm) - it's at the right edge; they're green and red colored rings (there are blue rings too, but not so easily seen).

Veterans of the GZ forum may recall seeing something similar before ...

Posted September 23, 2014 2:58 PM

by Alpha_Aurigae

Number 8:

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AGZ00009g1