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M100: A Grand Design Spiral Galaxy

Explanation: Majestic on a truly cosmic scale, M100 is appropriately known as a grand design spiral galaxy. It is a large galaxy of over 100 billion stars with well-defined spiral arms that is similar to our own Milky Way Galaxy. One of the brightest members of the Virgo Cluster of galaxies, M100 (alias NGC 4321) is 56 million light-years distant toward the constellation of Berenice's Hair (Coma Berenices). This Hubble Space Telescope image of M100 was taken recently with the Wide Field Camera 3 and accentuates bright blue star clusters and intricate winding dust lanes which are hallmarks of this class of galaxies. Studies of variable stars in M100 have played an important role in determining the size and age of the Universe.

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M100 is one of my favourite galaxies, and I'm very glad that Hubble has re-visited it!

An interesting thing about M100 is the extremely bright blue ring surrounding the even brighter yellow center. When you look closely at this nuclear ring, however, it doesn't resolve well into individual stars. My interpretation is that the nuclear ring of M100 is a post-starburst feature, which is to say that it used to be even brighter. Just think how brilliant it must have been in its prime!

(Of course... another possibility is that this ring has experienced "one small starburst after another" which has left huge numbers of bluish and "sort of bright" stars behind.)

Another interesting thing about M100 is that it is about to turn into a barred spiral. (Some astronomers may say that it is barred already.) Well, you can't really see the bar, and there is no yellow brightening stretching more or less straight across the bulge. (In some barred spiral galaxies, the bar is so dominant that it is the bulge.

But the two dark dust lanes of M100 winding their way from the "spiral disk" all the way into the nucleus are a dead giveaway that we are dealing with a barred galaxy, or at least a barred-galaxy-to-be. The brilliant nuclear ring is very typical of barred spiral galaxies, too.

So maybe M100 is showing us the transitional stage from non-barred to barred spiral galaxies!

Ann

Cepheid stars of M 100 have contributed to determine
Cosmic distances and the expansion speed of the
Universe