Revisiting the Whirlpool

The entire universe in blog form
Feb. 2 2010 7:00 AM

Revisiting the Whirlpool

One of the closest and most spectacular galaxies in the sky is M51, the Whirlpool. A grand design face-on spiral with a small, irregular companion, it's so bright and big that it's a favorite target for amateurs. So you just know when you point Hubble at it, what you get is nothing short of jaw-dropping heart-aching beauty.

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

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[Click to galactify.]

This image, using the Hubble Advanced Camera for Surveys, was originally released in 2005, but was recently reprocessed by the phenomenal astrophotographer Robert Gendler. And yeah, you absolutely want to click that link to see the work Robert has done. He's incredible.

I could go on and on about the galaxy, the glorious spiral arms, the red glow of nebular star birth factories, the odd companion that apparently has drawn out that long tidal tail of stars from the spiral, and so on... but you've read that stuff here before.

Instead, while looking this image up, I found the behind-the-scenes story on how they observed it that I think will interest you, my BABloggees. Extra cool is the page showing the galaxy observations in different colors, and you can see just what a big spiral looks like when you use different filters:

hst_m51_filters

You can see the ACS field of view, and the final version on the left. The different observations are listed (each frame is clickable to embiggen on that page, which lets you explore the galaxy on your own). The filters are labeled on the top of each image: B (blue), V (visual, or really yellow), I (near-infrared), and Hα + [NII], the reddish light given off by hot hydrogen clouds laced with nitrogen. That last bit is where stars are being born, and traces the spiral arms very well. The I-band shows very warm dust as well as stars, so it looks smoother since all that stuff is rather smoothly distributed in the galaxy. The B-band has hot stars in it, so again shows where stars are being born; blue stars don't live very long, and can barely escape their gas cloud nurseries before blowing up as supernovae.

When you put these all together you get the majesty of a spiral galaxy, a city of stars much like our own Milky Way. I've seen M51 myself with binoculars and through countless telescopes at star parties, and while it doesn't look as glorious as it does here -- of course -- just knowing what's going on in the galaxy and what it really does look like through the big guns is enough to thrill. It may look blurry and fuzzy through a small telescope, but our brains are big enough to encompass all those light years, and to understand what it is we're seeing.

Image Credit: NASA, Hubble Heritage Team, (STScI/AURA), ESA, S. Beckwith (STScI). Additional Processing: Robert Gendler

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