HEIC: A Mysterious Old Spiral (NGC 524)

[bystander]

A Mysterious Old Spiral
ESA/HEIC Hubble Picture of the Week | 2013 Jul 22

---

This striking cosmic whirl is the centre of galaxy NGC 524, as seen with the NASA/ESA Hubble Space Telescope. This galaxy is located in the constellation of Pisces, some 90 million light-years from Earth.

NGC 524 is a lenticular galaxy. Lenticular galaxies are believed to be an intermediate state in galactic evolution — they are neither elliptical nor spiral. Spirals are middle-aged galaxies with vast, pinwheeling arms that contain millions of stars. Along with these stars are large clouds of gas and dust that, when dense enough, are the nurseries where new stars are born. When all the gas is either depleted or lost into space, the arms gradually fade away and the spiral shape begins to weaken. At the end of this process, what remains is a lenticular galaxy — a bright disc full of old, red stars surrounded by what little gas and dust the galaxy has managed to cling on to.

This image shows the shape of NGC 524 in detail, formed by the remaining gas surrounding the galaxy’s central bulge. Observations of this galaxy have revealed that it maintains some spiral-like motion, explaining its intricate structure.

A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Judy Schmidt.

Credit: ESA/Hubble & NASA
Acknowledgement: Judy Schmidt

Zoomable Image

<< Previous ESA/HEIC Hubble POTW

[geckzilla]

I wonder how they decide who to acknowledge? I remember for this one in particular at least one person found and submitted the same picture before I did.

[bystander]

I found three others. Yours had the most views and was the most similar to their processing.

[Ann]

Congratulations on having your processing of this galaxy chosen by HEIC, geckzilla.

NGC 524 is definitely an interesting galaxy (but then, most galaxies are). NGC 524 is fascinatingly similar to NGC 2787. Both galaxies are lenticular galaxies. Both have numerous thin dust lanes encircling their nuclei. Both are very red as galaxies go, which appears to be a common trait among lenticulars. Their B-V indexes appear to be even redder than the B-V colors of ellipticals, or at least I get that impression when I routinely check the colors of galaxies of various types.

So the B-V index of NGC 524 is 1.050, according to my software, and its U-B index is 0.600. That is really red. Fascinatingly, NGC 2787 is even redder, with B-V and U-B indexes of 1.060 and 0.670.

For comparison, we may look at the colors of giant elliptical galaxies M84, M86 and M87. Their B-V indexes are 0.980, 0.930 and 0.960, all just a tad bluer than the B-V indexes of NGC 524 and NGC 2787.

But the U-B indexes of these elliptical galaxies are generally redder than the U-B colors of lenticulars NGC 524 and 2787. The U-B indexes of M84, M86 and M87 are 0.700, 0.655 and 0.740.

A possible explanation for these colors is that the lenticulars contain a small population of young or moderately young blue stars, whose "blue contribution", however, is smaller than the "reddening contribution" of dust in the lenticulars. But the moderately young stars have light curves that peak in the ultraviolet part of the spectrum, so that their "ultraviolet contribution" is greater than their "blue contribution". Ellipticals, by contrast, generally lack both dust and young stars. Therefore the lenticulars are often redder in B-V than ellipticals, but often bluer in U-B than ellipticals.

In any case, it is not hard to believe that the dust arcs around the nuclei of NGC 1316 and NGC 2787 could be the remnants of these galaxies' spiral past.

Ann

[owlice]

http://www.nasa.gov/content/goddard/hub ... ld-spiral/

Yay, Judy!!