Supernova!

Thirty-one million years ago, in a star-forming region of an outer arm in what we know as the Whirlpool Galaxy, a supergiant yellow star exploded. Around May 30, light from the explosion reached our neck of the Milky Way Galaxy. A French amateur astronomer, Amde Riou, detected the supernova on May 31.

Before the cataclysm, the vast star, estimated at 18 to 24 times the mass of our sun, had been so dim from our vantage point that it could only be seen by powerful instruments like the Hubble Space Telescope. But the violent blast set it blazing so brightly that it was — and remains — as easily visible through moderate-size backyard telescopes as many stars in our own Milky Way Galaxy.

Several of our galaxy’s stars that happen to line up in front of the Whirlpool are dimmer than the supernova taking place those many millions of light-years away. According to latest reports, the supernova has faded slightly but remains visible to amateur astronomers. The galaxy is located close to the last star in the Big Dipper’s handle.

The Whirlpool Galaxy is called that because it is a dramatic spiral, looking as if it were whirling with vast waves of stars and dust. Its technical name is Messier 51 (M51), and the new supernova is dubbed SN 2011dh in M51. Spectral analyses indicate it is a Type IIb supernova — one that may have resulted in the formation of a black hole.

Meanwhile, superheated debris from the explosion is hurling through space at 2,000 miles per second. Any nearby planets were destroyed; civilizations may have burned in a flash.

I wanted to photograph the supernova. I had taken views of the last such explosion in M51 just under six years ago, and didn’t want to miss this. But it required four arduous nights before I succeeded.

*** June 3, relying on the National Weather Service prediction for “mostly clear” weather, I drive to the site local astronomers call Lakeside, in Tooele County. By nearly 10:30 the sky is completely clouded over, not a star showing, and I give up. Later, after the difficult process of breaking down my scope and packing it at night, while I am driving back, I notice the clouds are clearing.

*** Night of June 4-5, back at Lakeside, the gears will not turn on my brand-new focuser. Trying to adjust it, I take off a couple of crucial screws and a part falls to the ground and breaks. I can’t get one of the screws back on. I continue trying to use the focuser, duct-taping the piece onto the telescope; that doesn’t work. The night is clear but dew falls copiously and in the morning everything is soaked, with water on my folding table and my equipment. It’s as if I’d left everything out in the rain. On June 6, I use superglue to repair the focuser. In our well-lighted home it’s a cinch to get the screw back on. This time it operates well; I discover the reason the gears wouldn’t turn is that an electrical connection had to be pulled out slightly.

*** Night of June 7-8: I set up at the Stansbury Park Observatory Complex (SPOC), Tooele County, owned by the Salt Lake Astronomical Society, of which I am a member. Not only can I not get my software to find the focus automatically, as it would if I knew how to make it, but I accidentally throw the telescope off balance and it won’t track accurately or point at a target.
Patrick Wiggins, a NASA solar system ambassador to Utah and secretary-treasurer of the astronomy club, drops around before dawn and aims my scope at M51. After he leaves I move it to a bright star to improve the focus — and can’t find the galaxy again. Heavy dew covers the folding table.

*** Night of June 9-10, I return to SPOC. This time I balance the telescope properly. I still can’t make the focuser work automatically but quit trying and simply focus by using a cardboard Bahtinov mask I made last September. The moon is bright and high, leaving only two hours between moonset and dawn. Sometimes, while ancient photons stream through the telescope, I huddle in one of the observatory’s buildings, pulling a blanket around myself because it’s so cold. At daybreak I realize the equipment, including the main telescope and guide scope lenses, are lightly bathed in dew. But by then I have the images I need.

[View I took of M51 from Stansbury Park, Tooele County, on the morning of June 10, 2011. Exposure through my LX200GPS 12″ telescope was 70 minutes — 45 minutes without a filter (luminosity), 5 minutes with a red filter, 10 minutes with green filter and 10 minutes with a blue filter. Each exposure was broken into 5-minute segments called subexposures. I used an f/6.3 reducer.]

M51 is too far away for my telescope to resolve ordinary stars. The view shows numerous blue clumps, which are not stars but gigantic nebulas where young stars are forming. Every star we can see in this image — except one — is a foreground star in our galaxy. The exception is Supernova 2011dh, indicated by the straight lines. For a larger version without the markings, click HERE.

One of my five-minute luminosity exposures was ruined by something zipping through the frame. This happened about 3 a.m. I assume it was a meteorite, asteroid or satellite.

[Five-minute exposure of M51 with something flying through the view. This was taken about 3 a.m. on June 10, 2011. The fact that the object shows a single straight line rules out an aircraft’s running lights.]

A Type II supernova happens when a large young star burns up all its available fuel. The energy produced by nuclear fusion pushing outward isn’t strong enough to counter the gravity of the rest of the star pulling inward, triggering a collapse quickly followed by an explosion.

Stars begin life as giant balls of hydrogen, and their nuclear fires fuse hydrogen atoms into helium. A massive star will convert helium to carbon at its core; as nuclear reactions continue, carbon also is fused.

A NASA WEBSITE explains that when a star at least 10 times as massive as the sun exhausts the helium in its core, “the nuclear burning cycle continues. The carbon core contracts further and reaches high enough temperature to burn carbon to oxygen, neon, silicon, sulfur and finally to iron. Iron is the most stable form of nuclear matter and there is no energy to be gained by burning it to any heavier element. Without any source of heat to balance the gravity, the iron core collapses until it reaches nuclear densities. This high density core resists further collapse causing the infalling matter to ‘bounce’ off the core.

“This sudden core bounce (which includes the release of energetic neutrinos from the core) produces a supernova explosion. For one brilliant month, a single star burns brighter than a whole galaxy of a billion stars.”

NASA’s Goddard Space Flight Center says a supernova explosion is equivalent to the power that would be released by “a few octillion nuclear warheads.”

The Weizmann Institute of Science in Rehovot, Israel, noted on June 6, “The star hurls its outer layers into space, and a new ‘bright star’ appears in the night sky where none was seen before. Just such a new star was observed in the night sky between May 31 and June 1 in a spiral arm of our galaxy’s close neighbor, M51.”

Extreme heat and pressures during the explosion cause elements to fuse, transforming into new elements beyond the iron that was generated in the star’s core. “In addition to making elements,” says the Goddard Space Flight Center, supernovas “scatter the elements that are made by both the star and supernova out into the interstellar medium. These are the elements that make up stars, planets and everything on Earth, including our bodies.”

When part of a vast star’s outer atmosphere blows into space, the core and other material may continue to implode, collapsing into a single point of unbelievable mass, a concentration of gravity known as a black hole.

M51 and a smaller galaxy called NGC5195 are locked in a cosmic square dance that seems destined to merge them. Eons back, gravity drew them close to perform a little do-si-do. While NGC5195 passes behind, tidal forces pull one arm of M51 out at a strange angle; in my astrophoto, the smaller galaxy is at top and the sprung arm reaches beyond the main mass of M51. Light from NGC5195 glows through the end of the larger galaxy’s arm, illuminating its dust and gas lanes.
Scientists say a supernova can be expected about once every century in a typical spiral galaxy. NGC5195 had one in 1945. But M51 sustained these titanic explosions three times in the past 17 years: in 1994, 2005 and 2011.
The Weizmann Institute believes, “The high occurrence in M51 can be explained by its interaction with another, very close galaxy [NGC5195], which causes the process of massive star formation to accelerate, thus increasing the rate of collapse and explosion, as well.”
Supernova 2011dh must be drawing attention to itself whenever its light reaches an inhabited planet. In M51, a galaxy over 60,000 light-years across, that happened more than 30 million years ago. For other galaxies, notice of this giant explosion arrived millions of years later. It will show up in galaxies farther away millions of years from now.
Just as I waited for moisture-laden clouds to clear, an astronomer on a planet in another galaxy may have waited for ammonia clouds to part in order to get a glimpse of the eruption in the Whirlpool.

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