Splendor and the Dust

When I glanced through the rear-view mirror, the Jeep’s back window looked like it was in a car-wash, except that instead of water it was flooded with tawny dust, dust that shot upward in standing waves from the window’s bottom and fanned out, tumbled down, replaced instantly with more dust boiling up in a continuous opaque flow.
Mat Hutchings, who had met me at I-80’s Tooele exit, waited until my dust had largely filtered to the ground or drifted off before he followed me in. He drove cautiously, parking far enough from my site that his dust wasn’t a bother, and began putting together his tall, 16-inch-diameter Dobsonian telescope.

[Mat Hutchings at his Dobsonian telescope, morning of Sept. 27, 2011, at Lakeside, Tooele County, UT. Photo by Joe Bauman]
The place was Lakeside, about an hour’s drive from Salt Lake City on I-80, a five-mile jaunt to the right on a small paved road, then only a few tenths of a mile on the dust road. This material covered the vehicle’s back like strange dry snow. A few minutes after I started setting up my scope, my sneakers and lower pant legs were covered.
I visited Lakeside three nights during the new-moon period: Sept. 24-25 alone; Sept. 26-27 with Hutchings, whose wonderful scope he had built himself, including grinding the mirror; and Sept. 28-29, when I found Jo and Allen Grahn already present with their Dobsonian out of its trailer and set up. Later that night Rev. Michael A. van Opstall of the University of Utah Math Department came too, only to leave shortly afterward when his allergies flared.
The dust got the better of me too, the third night. Bending to work on some equipment on the ground, I inhaled so much of the silt that I went into an extravagance of violent coughing and gagging. The Grahns said that they thought they’d have to run over and resuscitate me. Luckily, it ended quickly.
That same night I was walking through the brush in the dark and I heard a crunch and felt a sharp stab in my left sole. After I hobbled back to my observing table I found that I’d stepped on a sharp stick that penetrated the sneaker but not the skin. It was shaped like a sharpened stake and I needed a pair of pliers to extract it.
Although I hugely enjoyed all these friends, the most delightful night was when Hutchings was there because my scope was on its best behavior, allowing me time to chat, stare at the fathomless Milky Way, look through the binoculars on his homemade mount and peer through the Dob. I saw several stunning objects I had never glimpsed before, including the wispy Veil Nebula.
The three nights were still and clear, though the first two were cold. Blazing Jupiter dominated the arch of the heavens, while the Pleiades floated almost as high. A little after 1 a.m. we saw the constellation Orion rise on the eastern horizon, the three stars of the belt pointing straight up. By the time I looked again at 2:30 or 3, the great Orion Nebula was easily visible. The starlight was bright enough for walks without using a flashlight.
Tracing the boxy shape of Pegasus, I wondered again how anyone could see a flying horse in that constellation. It looks more like a squarish octopus. Same with nearby Cassiopeia — that’s no princess, just a sprawling crooked W.
A main focus the morning of Sept. 27 was a galaxy in Pegasus designated NGC7217. It’s an exceptionally tight spiral, without protruding arms, without a central bar structure, whose outer region forms a bright ring. The galaxy is an isolated one, not part of any group, distance calculated at just over 60 million light-years away. When I finished imaging it at 6 a.m. it was less than 13 degrees above the horizon, so low that it was blurred in some exposures.
It was awe-inspiring to find the galaxy and watch its images come onto the laptop screen, a slightly oval, faint, fuzzy disk with its brighter ring. Showing it to Mat, I traced the ring with my fingertip.

[NGC7217 in an image taken the morning of Sept. 27, 2011, at Lakeside, Tooele County, UT. For a larger version, click HERE. Photo by Joe Bauman]

*****
Recent studies by Russian astronomers show that NGC7217 is a strange galaxy. Nearly face-on, it boasts a complex structure with a bulge and star-forming rings.
The most recent paper is “Large Scale Nested Stellar Disks in NGC7217,” accepted on March 7, 2011, by the Monthly Notices of the Royal Astronomical Society, London. Its authors are Olga K. Sil’chenko, Igor V. Chilingarian, Natalia Ya. Sotnikova and Victor L. Afanasiev. Analyzing spectroscopic observations by a 6-meter (nearly 20-feet) diameter telescope operated by the Russian Academy of Sciences, they obtained detailed readings of the movements of the galaxy’s stars and gases. The Hubble Space Telescope also provided data.
Besides the star-forming rings, NGC7217 has a gas disk around the nucleus that is sharply inclined to the plane of the galaxy. Startlingly, the stars of the inner area rotate in the opposite direction to the rest of the galaxy.
Dominating the galaxy’s middle is a bulge about 1,300 light-years to 4,000 light-years from the center; next comes an inner disk from about 5,000 light-years to 13,000 light-years from the center; and finally an outer disk extending from about 15,500 light-years to almost 29,000 light-years from the center.
The bulge is old, with stars aged from 10 billion to 13 billion years. The thin inner star disk — only 650 light-years to 2,300 light-years deep — is the home of intermediate age stars dating back about 5 billion years, according to the paper. However, the outer disk may be up to almost 10,000 light-years thick and is dominated by young stars around 2 billion years old.
The explanation apparently is that the galaxy underwent two mergers with satellites galaxies; alternatively, only one satellite merger took place and material flung out by that collision eventually was drawn back into NGC7217, making in effect two absorption events.
Different orbits by the colliding objects resulted in star disks moving in opposite directions. According to the report, “The encounter on a retrograde orbit resulted in the formation of the inner polar disk, while the outer star-forming ring and the outer disk thickening were consistent with a minor merger on a prograde orbit.”
I contacted Sl’chenko to see whether I understood the paper, and emailed the photo. On the staffs of the Sternberg Astronomical Institute of Moscow State University and the Isaac Newton Institute of Chile, Moscow Branch, she quickly responded.
“Indeed, the galaxy NGC7217 have the rings of collisional nature (and your image of NGC7217 reveals the outer one very well), and the inner and outer disks have the stars of different ages,” she replied.
These disks “experienced their main star formation in different epochs related probably with different merger events.”
*****
Following three nights at Lakeside, even after a couple of hundred miles of freeway travel, dust remained piled on the rear bumper.

[The dust of Lakeside on our Jeep’s rear bumper, after three round trips from Salt Lake City. Photo by Joe Bauman]

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