Round And Round The Spiral Goes

The core region of the Whirlpool Galaxy in Canes Venatici looks so dynamic it seems to swirl before your eyes. Credit: NASA/ESA

What better analog for a hypnotic spiral than the center of the Whirlpool Galaxy. If we could speed up time and watch it spin before our eyes, we might be induced into a trancelike state and transported 31 million light years to the galaxy itself. It probably wouldn’t hurt to have the help of a hypnotist just to be sure we got there and back safely.

The Whirlpool Galaxy, also known as M51 in Charles Messier’s catalog of deep sky objects, is Canes Venatici’s claim to fame. Messier discovered the galaxy on October 13, 1773, but it wasn’t until 1845 when Lord Rosse of Ireland used a 72-inch telescope that it was recognized as a spiral. His drawing, at right, resembles modern photographs. Not only does it show the main galaxy but also the smaller interacting companion galaxy NGC 5195.

At the time, most astronomers thought M51 and other galaxies were nebulas or gas clouds inside our own Milky Way. Lord Rosse thought otherwise. He believed the nebulas were composed of countless faint stars which most telescopes at the time simply could not resolve. Not until the early 1920s did astronomers nail down the distances to the spiral "nebulae" as they were called. Only then did we realize that galaxies like the Whirlpool were very much like our own Milky Way but far, far away.

Without a doubt, M51 is the most famous object within the borders of Canes Venatici the Hunting Dogs, a constellation we got acquainted with in yesterday’s blog. The little companion galaxy actually lies behind the big one, but millions of years ago it passed through M51’s disk disturbing the gas clouds and initiating the formation of those remarkable spiral arms.

M51 and its companion NGC 5195. Hot pink hydrogen gas clouds swaddle newborn stars and star clusters and outline the galaxy’s spiral arms. Lord Rosse called the pair of galaxies the "Question Mark". Credit: NASA/ESA

Amateur astronomers love to get wrapped up in those arms which are some of the easiest to see in a telescope. Suggestions of the whorls are visible in a 4-inch scope, and certainly with a 6-inch you can discern several short arcs under a dark sky. On spring nights, when the galaxy is high above the glow of light pollution and haze, the arms are one of the most beautiful sights in the sky through a large amateur scope (12-16 inches). Unlike many spiral galaxies, the arms begin to resemble their appearance in photographs but in a misty way like coils of fog. NGC 5195, dwarf galaxy, appear as a small, bright glow at the end of one of M51’s spiral arms.

With the moon’s departure from the evening sky and the return of darkness, we’ll soon have the opportunity to find this famous double galaxy with binoculars. It’s not hard to spot because you start at an easy place, the end of the handle of the Big Dipper. Use yesterday’s chart to help you find the Big Dipper, and then point your binoculars at Alkaid, the end star in the handle. A short distance above and to the left you’ll spot a fainter but obvious star and directly above it a small puff of light. That’s the galaxy! Find it and you’ll be looking across more than 30 million light years of space.

Starting with the Dipper’s handle you’ll find the Whirlpool Galaxy
about one binocular field of view (white circle) above and left of
the handle’s end star. Created with Chris Marriott’s
SkyMap software

The Whirlpool’s true size is something like 100,000 light years in diameter very similar to our own Milky Way. And like the Milky Way, the galaxy harbors a black hole in its deepest of cores. M51’s black hole has a mass of one million stars like the sun and hides behind an "X" of interstellar dust.

"X" marks the spot of the M51’s hidden black hole. The hole resides behind the intersection of two dark lanes of light-absorbing dust seen in silhouette against the galaxy’s starry core. Credit: NASA/ESA

One last item. If you haven’t already seen the movie of the massive solar eruption on April 19 recorded as a video by the new Solar Dynamics Explorer telescope, please click HERE and watch for yourself. Be patient — it’s a big download but worth playing over and over and over.

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