In 1993, during Hubble's Servicing Mission 1, corrective optics were installed to correct a flaw, known as spherical aberration, in the telescope’s mirror. The mirror had been ground too flat due to a faulty measurement device.
A before and after of the core of NGC 4321 show the dramatic improvement in image quality between the original Wide Field and Planetary Camera (WFPC) and the Wide Field and Planetary Camera 2 (WFPC2) installed during the servicing mission.
At left is the original, wider WFPC image taken in 1993 before the spherical aberration in Hubble’s mirror was corrected. The galaxy appears blurry because its light cannot be brought into a single focus. This is especially apparent in the orange foreground star below center which has clear image artifacts.
At right is a NGC 4321 image from Hubble's Wide Field Camera 3, installed during the last servicing mission to Hubble in 2009.
A wider view of NGC 4321 from the 1.5 m Danish telescope at the ESO La Silla Observatory in Chile.
It has two companion galaxies, NGC 4323 and NGC 4328, located in the upper left and upper right of center. Gravitational interactions with these small companion galaxies may be responsible for NGC 4321’s particularly well-defined spiral arms.
In this Spitzer infrared image of NGC 4321, the spiral arms are filled with green-colored dust, which are lit by the surrounding stars. The glow from the hottest dust is shown in red, giving the star-forming nuclear ring a reddish-white tinge. Stars are blue.
Its two small companion galaxies appear as fuzzy blue blobs on the upper left and center. These lenticular galaxies have very little dust, so they lack the red and green glow seen in their larger neighbor.
The Spitzer and JWST images of NGC 4321 are taken at similar infrared wavelengths. JWST has a narrower field of view, so we see a tight crop of the center of the galaxy.
JWST has a much larger mirror, allowing us to resolve finer details. This is true not only in the central part of the galaxy, where we see small structures in the galaxy’s inner star-forming ring, but also in the network of dust filaments, overlapping shells, and bubbles in the spiral arms only hinted at with Spitzer.
This ALMA image of NGC 4321 shows the location of cold gas in the galaxy, using carbon monoxide to trace the locations of molecular clouds in the galaxy’s bar and spiral arms.
While observations with earlier generations of radio telescopes were able to provide some details about the nature of cold, dense clouds where stars form, ALMA has both the sensitivity and fine-scale resolution at millimeter wavelengths to study them in great detail.
The first image is a visible (VLT), infrared (Spitzer), and X-ray light (Chandra) composite. The second is just X-rays.
The bright area in the center shows X-rays from gas interacting with the galaxy’s supermassive black hole.
The other bright points are black holes or neutron stars in the galaxy, or supermassive black holes in background galaxies. The point at the bottom right is likely a stellar-mass black hole created by supernova SN 1979C.
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