Centered on the invisible black hole called Sagittarius A*, infrared light from the Spitzer and WISE missions provides us a glimpse into what otherwise appears visually as a dark band in the constellation of Sagittarius. As you can see, it's a busy place bustling with star formation evidenced by glowing nebulas.
Because there is no separation between nearer and more distant structures, it's quite confusing. Imagine taking an x-ray of your body looking down from the top of your head with all your bones together on a single, flat plane. We can guess that larger structures are generally closer to us and the smaller ones are generally farther in the distance, but it's not always true, so it's best to take any interpretations about spatial positioning with a grain of salt. We know with our skeletal x-ray that our teeth are attached to our skull, but we don't have that advantage with our infrared view of the galaxy.
Still, it is tempting to make some general observations. Notice that there seems to be a lot of grayish-colored dust and gas sweeping outward from the center to the right side of the frame. Are we looking at the central part of an arm of our galaxy sweeping outward and toward us? Is the left side of the image the opposing arm receding in the other direction? Maybe. It does seem like some maps illustrating the Milky Way match up with this guess.
Some notes on the processing:
Once again I have made use of two Spitzer bands MIPS1/24μm and IRAC4/8μm for the red and blue channels, respectively. WISE's W3/12μm takes the green channel. Because the W3 and the MIPS1 data are so much less crisp than the IRAC4 data, I've used the IRAC4 data as a luminance layer in Photoshop. There's a bit of complexity in how I applied it. The green channel was also more strongly affected than the red channel.
One of the challenges of combining Spitzer and WISE data is that WISE imagery is at a much lower resolution. This causes some unsightly green glows around many of the stars. To deal with it this time I used a combination of a "Minimum" filter applied to the greenest areas. What this does is kind of shrink the spread of the star so it's more contained. Later on I also applied a channel mixer on some remaining green halos to nearly eliminate the glow. I think it worked really well without compromising the image quality in other ways too much.
Nov. 25 2016: I updated this image. Improvements should only be visible at around 100% zoom on the full size image. Overall image from lower zoom levels wasn't affected much.
Red: Spitzer/MIPS1 (24μm)
Green: WISE/W3 (12μm)
Blue: Spitzer/IRAC4 (8μm)
North is NOT up. It is around 60° counter-clockwise from up.
Tags: Sagittarius WISE Spitzer GLIMPSE infrared dust gas Milky Way black hole center nucleus Sgr A* Sagittarius A*
Spitzer, WISE, MeerKAT
The MeerKAT mosaic was released recently, giving me a chance to finally combine the Spitzer/WISE infrared mosaic with MeerKAT's radio data. MeerKAT data are overlaid in white.
Annotations from arxiv.org/abs/2201.10541
White overlay: SARAO/MeerKAT (1.28 GHz)
Red: Spitzer/MIPS1 (24μm)
Green: WISE/W3 (12μm)
Blue: Spitzer/IRAC4 (8μm)
North is NOT up. It is around 60° counter-clockwise from up.
Tags: infrared radio spitzer wise meerkat milky way sag a* sagittarius center
The world is wrong... and I am tired
This is a view using FITS file mosaics generously provided courtesy of Susan Stolovy, with attribution to Rick Arendt and Solange Ramirez for their work in producing the final mosaics. Her team used a processing technique that alleviated some of the saturation issues arising in some of the brighter parts of the mosaic that one might find in the mosaics provided by the Spitzer archive.
My take is not necessarily much different than what's already been done, but it is quite a bit less saturated than what you can find on the Spitzer website, and just a bit more of those wispy dust and gas formations can be made out. Anyway, it's nice to work with some data where someone else has already done most of the work.
For reference, here is a link to the original version using the same wavelengths on the Spitzer website: www.spitzer.caltech.edu/images/1540-ssc2006-02a-A-Cauldro...
Screen: 8.0 µm (IRAC4)
Red: 5.8 µm (IRAC3)
Green: 4.5 µm (IRAC2)
Blue: 3.6 µm (IRAC1)
The image is presented in galactic coordinates, with north up in that regard.
Tags: Milky Way Spitzer infrared dust gas Sgr A* center core nucleus IRAC
This nebula near the top left edge of the widefield Milky Way mosaic caught my eye. It looks different from most of the other nebulas, because its emissions are so strongly in the MIPS1 channel with very little or none appearing in the other two. So in my other image, it appears extremely red. For this version, I have processed it in a way that makes it easier to see by having it screen over the green and blue channels a bit.
Anyway, one thing I have been struggling with for infrared imagery is how to interpret the various bands. Is it dust? Is it gas? What kind of dust? What kind of gas? Trying to learn more about this nebula, I came across this paper which helps me understand why it's been difficult. If I've understood it correctly, the authors looked at the emissions of known objects and compared them to the WISE W3 and W4 bands to see what matches up. In particular, the W4 band is closely associated with Hα emission for certain objects like this one, and the W4 band is very close to Spitzer's MIPS1 band presented here, so I'm satisfied to say this could probably also a Hα emission nebula.
The curling, looping appearance is unfamiliar to me. I don't know if those are actual loops or if they just look like loops from here. Note that the star itself, WR102, is nearly invisible in this image.
Pale Orange: Spitzer/MIPS1 (24μm)
Green: WISE/W3 (12μm)
Blue: Spitzer/IRAC4 (8μm)
North is NOT up. It is 58.7° counter-clockwise from up.
Tags: WR102 Wolf-Rayet nebula infrared Spitzer WISE star