# What is this object visible in the Chandra image of the Cartwheel galaxy that isn't visible in JWST image?

In the below images I aligned an image from Chandra of the Cartwheel galaxy over the image from JWST. The first is the Chandra image pasted on top, fully opaque. The second is just the JWST image, and the third is the Chandra image over the JWST image with transparency so they blend together. I put yellow boxes around some of the purple blob features where there is a corresponding feature in the JWST image, and then I put a green box (upper left most box) around the purple blob in the Chandra image which has no associated visible feature in the JWST image.

I guess what we are seeing is something which is emitting a lot of X-rays, but not a lot of infrared? Does this tell us anything interesting in particular?

• lens flare? (humor)
– uhoh
Aug 3, 2022 at 22:10

I did a SIMBAD search around the coordinates of the Cartwheel Galaxy and found multiple X-ray sources, reported in Gao et al. (2003) and Wolter & Trinchieri (2004):

The ones you've boxed are likely background active galactic nuclei (AGN); supermassive black holes accreting gas which is then heated to $$\sim 10^6\,\mathrm{K}$$, thereby emitting X-rays. The one in the green box indeed doesn't have any optical/infrared counterpart; it is listed in both references as "J003743.1-334142/3" (referring to the coordinates), but not discussed. With an X-ray count rate of 0.23 ± 0.07 per kilosecond, it's not very bright. It could perhaps be a particular dusty AGN, but I don't know.

But you also see several X-ray sources along the "rim" of the Cartwheel. Those might be X-ray binaries: Binary stellar systems where one companion is a compact stellar remnant — a neutron star or a black hole — accreting mass from the other companion. A large fraction of the mass energy of the accreted gas is released as X-rays.

The authors also mention supernova remnants as a possibility, and argue that, if they're X-ray binaries, they must be high-mass X-ray binaries, not low-mass.

The Cartwheel Galaxy has its peculiar shape from a relatively recent drive-by of a galaxy 3 arcminutes northeast of this field of view (usually called "G3"). This event has initiated star formation which has lit up the rim and spawned massive stars, consistent with the presence of several X-ray binaries.

• Yes, and that's rather obvious and sensible for most of them - the trick is what about the one in the green box? There appears to be no obvious galaxy counterpart in the other images, which suggests either it's a ludicrously potent source (the galaxy is very far away and/or small and yet it's flaring up with all the intensity of one of the sources in the noticeable galaxies), or else it's from something strange that leaves no optical counterpart. Aug 4, 2022 at 8:55
• @The_Sympathizer Ah, I missed the part about the green box, sorry. Yeah it's listed in both references (as "J003743.1-334142/3"), but not discussed.
– pela
Aug 4, 2022 at 10:44
• It seems quite possible that there is a Active galactic nucleus that is visible in X rays, but not in the visible or IR, at this length of exposure. I haven't looked, but the Cartwheel galaxy is not a particular dim object, so this won't have been a "deep field" image. There are doubtless hundreds of background galaxies that are not visible in this image. Aug 4, 2022 at 10:46
• @James K: Which would push toward the "super powerful" explanation, then. Would that make it, indeed, considerably more potent than the ones that are visible in the infrared and also glowing with X-rays? Aug 4, 2022 at 18:29