M81, up close and personal

Bad Astronomy
The entire universe in blog form
May 29 2007 9:27 AM

M81, up close and personal

What is it about grand design spiral galaxies? Is it their symmetry, their grace, the sweeping majesty of the spiral arms?

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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Beats me. But they sure are pretty!

The image above is a new release from Hubble, and shows the lovely M81, a spiral galaxy just 12 million light years away. That's close, as cosmic neighborhoods go; only a handful of big galaxies are closer. This means that M81 is pretty well studied, and Hubble images can be very detailed. In fact, in this observation, individual stars in M81 can be seen! Click it to get higher-res version, including, if you dare, a 23,000 x 15,000 pixel version that tips the scale at 700 Mb!

M81 is interesting. Despite its beautiful symmetry, it had a close encounter with another, somewhat smaller galaxy named M82 about 300 million years ago. They are still fairly close together:

They are about a degree apart, and easily spotted together by northern hemisphere observers using binoculars -- some sharp-eyed folks can even see them with their unaided eyes, in fact. If you look at M82 (click it for a bigger image) you can see that it's a mess. When galaxies pass each other, clouds of gas and dust can be disturbed or collide, which then triggers star formation. M82 is called a "starburst galaxy" because of the vast number of stars being born in it. The weird reddish tendrils are actually gas streamers being blown out by the most massive and luminous of the newly formed stars in the galaxy.

M81 holds a special place for me, too. Back in 1993, a star in the galaxy blew up, and it was named SN1993j (the 10th supernova seen that year). I was in grad school, and we took some students out to the 1-meter 'scope to take a look. I had looked up what the core of the galaxy looked like so I'd be familiar with it when I saw it. Near the core are two bright stars -- actually stars in our Galaxy -- seen superposed on the more distant spiral. But when I looked through the eyepiece, I saw a third star, about equal in brightness, and I knew right away it was the supernova.

I can still remember the awe I felt, the thrill, hunched over the eyepiece of the telescope. I had spent two weeks up in that same dome getting my Masters degree observations, but that was using a CCD, an electronic detector which saved images directly to a hard drive. This was different. I was seeing the supernova directly, myself. The photons I was seeing left that galaxy 12 million years previously, traveled across intergalactic space, were reflected by a mirror, and sent shooting into my own eye. Somehow, those packets of energy -- so weak individually that they couldn't ruffle a mosquito's wing -- were then converted into electric impulses by my eye and brain, and transformed once again into the sense of the numinous.

When those photons left that galaxy, there were no beings on Earth capable of understanding them. But during the intervening eons, our brains and eyes evolved, our imagination grew, and we became a species that can not only look up and wonder, but collect the feeble information that had previously fallen unheeded onto the ground and turn it into understanding.

Maybe that's not what everyone sees when they look at the image of M81, but it's what I see. And maybe, now, when you look at it, you can get a taste of it too.

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