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This year’s (astronomy) fireworks came early

The galaxy Messier 101, as seen the morning of June 27, 2020, from the vicinity of Vernon, Tooele County. Individual stars in this view are in the foreground, part of the Milky Way Galaxy. But the star-forming regions, the bright central core and spiral arms are parts of M101.
Joe Bauman

Editor’s note: A version of this has been previously published on the author’s website.

The big fireworks display came early for me this year. On the predawn morning of June 27, an intricate glowing pinwheel hung high above in the darkness as I watched from a safe social distance — 21 million light-years.

I was making astrophotos a few miles from Vernon, Tooele County, in a grassy clearing with logs and a child’s forgotten toy truck left beside a rock fireplace. The night was mostly clear. The Wasatch Front’s light pollution created a glow to the northeast, not interfering with my goals. An annoying stiff breeze kicked up from time to time, shaking the telescope and rendering many pictures unusable. The unstable atmosphere set star twinkling, yet the Milky Way arched serenely overhead, most prominently toward the south. The site was dark enough that rifts in our galaxy’s wide band were easy to see.

The target was M101 because it’s large, bright and one of the famous spring galaxies, and because I had never photographed it before. If I’d known how lovely it is, I would have gone for it years earlier. The pinwheel is easiest to see in April. By late June it was high enough for photography only about three and a half hours during the short night.

M101 is a large, sprawling, lopsided galaxy nicknamed the Pinwheel Galaxy, for obvious reasons. It’s like a fireworks pinwheel hanging in the Ursa Major constellation, better known as the Big Dipper. A modest telescope will show it as a patch close to the Big Dipper. The outside of the elbow in the Dipper handle points almost to the galaxy. Lopsidedness is sometimes seen in a galaxy that underwent or is undergoing a close encounter with a fellow galaxy.

According to those at NASA’s Goddard Space Flight Center, in Greenbelt, Maryland, the M101 spiral is 170,000 light-years across, compared with our galaxy’s breadth of 100,000 light-years. According to information at Goddard on www.nasa.gov:

“M101 is estimated to contain at least one trillion stars. The galaxy’s spiral arms are sprinkled with large regions of star-forming nebulas. These nebulas are areas of intense star formation within giant molecular hydrogen clouds. Brilliant, young clusters of hot, blue, newborn stars trace out the spiral arms.”

Several of the bright regions show up in the photo above.

On Aug. 24, 2011, Peter Nugent of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory in Berkeley, California, discovered an extremely rare supernova — the indication was in data “pouring in” from an automated telescope called the Palomar Transit Facility, a release from the lab reported later that year. The news release on newscenter.lbl.gov is headed “Closest Type Ia Supernova Solves a Cosmic Mystery.”

The triggering of a Type Ia is more complicated than the supernova that marks the death of an ordinary massive star, designated Type II. A Type II explodes because the star has run out of fuel and collapses in on itself. In a Type Ia, according to reports from Goddard at imagine.gsfc.nasa.gov “a carbon-oxygen white star is accreting matter from a companion.” Goddard says what sort of companion is involved is “hotly debated.” (The 2011 discovery, however, apparently could help define the companion.)

Researchers from the Space Flight Center add, “In a popular scenario, so much mass piles up on the white dwarf that its core reaches a critical density …. (that is) enough to result in an uncontrolled fusion of carbon and oxygen, thus detonating the star.”

A white dwarf is the remnant of a star like our sun at the end of its existence. The sun will eventually become a red giant, puffing off its atmosphere and glowing as a planetary nebula. When the nebula cools and dissipates, the remnant is a white dwarf — a blazing-hot core that may glow for many billions of years. Goddard experts write on imagine.gsfc.nasa.gov that a typical white dwarf is half as massive as the sun but the size of a planet, and 200,000 times as dense as Earth. Theoretically, it will become a black dwarf, a cinder remnant — assuming something peculiar, like a supernova, doesn’t interfere.

Not only was the supernova nearby compared with other recent Type Ia explosions, but it was photographed in the earliest hours of its eruption. Berkeley Lab’s report quoted Nugent, “We caught the supernova just 11 hours after it exploded, so soon that we were later able to calculate the actual moment of the explosion to within 20 minutes. Our early observations confirmed some assumptions about the physics of Type Ia supernovae, and we ruled out a number of possible models. But with this close-up look, we also found things nobody had dreamed of.”

According to those at the Berkeley Lab, by studying the light curve as the supernova brightened, the spectra of elements ejected, whether or not material was flying onto a massive companion star and causing secondary flares and by examining the speed of the ejecta, the team discovered that the progenitor star was a white dwarf, that the companion wasn’t much larger than our Sun and that the white dwarf’s surface was clumpy, with oxygen not evenly distributed.

Type Ia supernovas don’t create black holes. The white dwarf blows up and is reduced to ash. The explosion sends the companion star flying. As Goddard experts explain at svs.gsfc.nasa.gov/10532, “With its partner destroyed, the normal star careens into space. ... Because they explode with similar brightness and can be seen across the universe, Type Ia supernovae provide astronomers with information about the distant cosmos.”

By judging how distance has dimmed the Type Ia blast, astronomers can calculate how far away its host galaxy is.

Of course, when I observed M101, all signs of the supernova had died away long before. Instead, I pictured a serene-looking magnificent spiral with blue star-forming regions and red areas where massive red stars shine. It gave no hint of the violent explosions it can generate.

But unexpected blasts did light up the night. While I was working at the impromptu observatory, a bright meteor caught my eye. It streaked lower in the atmosphere, exploded with an exceptional flare, and continued to burn, not as bright, as it raced toward the horizon.

Joe Bauman, a former Deseret News science reporter, writes an astronomy blog at the-nightly-news.com and is an avid amateur astronomer. His email is joe@the-nightly-news.com.