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Starts With A Bang

Messier Monday: A Star-Forming Spiral, M61

Washed out by the full Moon on any other night, the lunar eclipse makes this one visible tonight!

“All is well, provided the light returns and the eclipse does not become endless night. Dawn and resurrection are synonymous. The reappearance of the light is the same as the survival of the soul.” –Victor Hugo

We first started Messier Monday back in 2012, where each week we highlight one of the 110 deep-sky wonders that make up the Messier catalogue, the first accurate, large collection of star clusters, galaxies and nebulae all visible with a small, inexpensive telescope. I’d never showcase today’s Messier object under normal circumstances, as a full Moon would make a nearby galaxy virtually undetectable thanks to light pollution, but tonight’s lunar eclipse — for about 78 minutes, at any rate — will change all of that.

Image credit: Al Kelly of Johnson Space Center Astronomical Society, via http://www.kellysky.net/jscas_messiers_draft_10x11.jpg.

Shortly after sunset at this time of year, the Virgo cluster — the densest nearby collection of galaxies for hundreds of millions of light-years — rises in the sky, presenting thousands of constituent galaxies for our viewing pleasure, including 15 Messier objects. The full Moon hovers nearby, making these galaxies lousy targets for tonight. The full Moon alone is some 400 times brighter than the rest of the night sky combined. The entire night sky without a Moon (or any light pollution) in it would look like a “1” on the scale below; a full Moon is enough to ruin that and turn it into an “8,” even with no other sources of light pollution.

Image credit: Stellarium.

But during a total lunar eclipse, the Moon will not only be significantly less bright than it normally is, it will even be outshone by Mars, which shines at its absolute brightest during last week and this one. And if you look up with your telescope in the region of the Virgo cluster during the eclipse tonight, you’ll be treated to a galactic treat in Messier 61 that will, in fact, be invisible both before and after the eclipse’s duration. Here’s how to find it.

Image credit: me, using the free software Stellarium, via http://stellarium.org/.

As always, if you can find the Big Dipper, you can follow the “arc” of its handle to Arcturus, the brightest star in the northern hemisphere, and then “speed on” to Spica. The full Moon — whether it’s eclipsed or not — will be hovering right next to Spica, just a degree or two away at most tonight. And nearby is the planet Mars, which reached opposition just six days ago. When the eclipse reaches its maximum amount, Mars will likely outshine the eclipsed Moon, paving the way to view Messier 61, something you can find by navigating from Spica towards Denebola, the second brightest star in the constellation of Leo.

Image credit: me, using the free software Stellarium, via http://stellarium.org/.

If you continue on from Spica towards Denebola, you’ll run into Mars first, then the bright and prominent Porrima, and then another much less prominent naked-eye star that’s visible just below the blue box above: 16 Virginis. If you can spot this star in a telescope and navigate northwards just about a degree-and-a-half, you’ll run right into Messier 61, tonight’s treat.

Image credit: me, using the free software Stellarium, via http://stellarium.org/.

In 1779, there was a comet right in this very region of the sky, and Charles Messier could have found this nebula; he observed it before anyone else. In fact, you may remember that the original purpose of the Messier catalogue was to help skygazers avoid confusing these fixed, deep-sky objects with potential comets, yet that’s exactly what Messier did here! He mistook M61 for a comet, and instead credit for this object’s discovery goes to Barnabus Oriani, who beat Messier to the punch by a mere six days. But 235 years later, it still appears, all but unchanged from how Messier viewed it.

Image credit: Bethany and Amanda VanStavern at NOAO, via https://www.noao.edu/outreach/aop/observers/observer63.html.

Similar in size to the Milky Way at 100,000 light-years in diameter, this prominent barred spiral galaxy has a number of features that make it rather unusual among Virgo cluster galaxies. For starters, it’s incredibly rich in gas. Most galaxies that are part of a dense cluster like this have had their gas stripped away over time, and resemble something like last week’s galaxy, Messier 58. This gas is evident when we look at two places: the spiral arms and the central core.

Image credit: Adam Block/NOAO/AURA/NSF.

In a gas-rich galaxy, the spiral arms will be littered with star forming regions — visible in pink due to their ionized hydrogen gas — and also with very young, bright blue stars. Well, this is obviously present here, and it could also be intensified by likely gravitational interactions with two nearby, smaller galaxies as well.

But if we move in towards the center, we find something even more fascinating.

Image credit: © Mel Martin 2014 via http://www.azdeepskies.com/hyperion_images/messier-61.html.

The center of this galaxy is active, emitting high-energy radiation and undergoing a starburst, where somewhere around 100,000 new stars are all forming at once in here! There may even be a second, smaller bar in the very core of this object, causing the starburst to be even more intense. If we look in the infrared, we can see the new, star-forming gas shining more brilliantly than anyplace else in the galaxy.

Image credits: NASA/Spitzer in 24 microns (main), via http://www.jb.man.ac.uk/news/2012/Spitzer/; inset is a 3-band composite by Médéric Boquien using NASA/JPL-Caltech Spitzer data.

Although there is a supermassive black hole at the center, it’s likely small, estimated to be about 5 million solar masses, or comparable to our own. (Remember, some galaxies have central black holes a thousand times as massive!)

Image credit: Hunter Wilson, Wikimedia Commons user Hewholooks.

But another telltale sign of this galaxy’s activity is the very large number of supernovae that have been spotted in it: it boasts of six in the last 100 years, leaving it tied for the most found in any Messier object! The most recent one went off just a few years ago in 2008, which is amazing considering our Milky Way has exactly zero occur in it over the same timespan.

Image credit: ESA/Hubble & NASA
Acknowledgements: G. Chapdelaine, L. Limatola, and R. Gendler.

As is almost always the case, the most spectacular view of this galaxy comes from the Hubble Space Telescope, where the spiral arms stand out brightly against the dusty foreground, and bright blue stars highlight the most recent bursts of new star formation.

ESA/Hubble & NASA
Acknowledgements: G. Chapdelaine, L. Limatola, and R. Gendler.

Unlike many other Messier objects, this one will continue forming hot, young stars for the indefinite future, and should remain a supernova factory for thousands of years! Enjoy your skies tonight, and enjoy the galactic sights that are so rare during a full Moon if your skies allow it!

Enjoy all our previous Messier Mondays here:

And come back next week for yet another! Happy skywatching!


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