Editor's note: A version of this was published on the author's website.
Patrick Wiggins has done it again! At 2:49 a.m., Jan. 14, the Tooele County amateur astronomer photographed a field of stars and galaxies in the area of Ursa Minor (the Little Dipper) — and caught his fifth supernova.
From his home observatory, Wiggins, who is a member of the Salt Lake Astronomical Society and is a public outreach educator at the University of Utah Department of Physics and Astronomy, searches the galaxies night after night for the explosions. His latest makes an astonishing three in eight months.
This one, which he discovered four years to the day after his first, is hosted by the barred spiral galaxy NGC 6217. It's in the galaxy's sparsely populated outskirts. A physicist notes that galaxies can have disks that extend beyond their obvious collections of stars, gases and clusters — a fact borne out by radio studies, he said.
But this exploding star is so far outside what we can easily see of the galaxy that it looks like it's floating by itself in space.
That's the impression Wiggins had when he first glimpsed the dot on the photograph, a dot that was not there when he imaged the same field in 2014. It was so far from the main galaxy that it didn't seem part of it. After 3 that morning, he posted the following on a Facebook discussion page maintained by the Salt Lake Astronomical Society, SLAS Talk:
"Anyone imaging tonight?
"I came across 'something' earlier tonight next to NGC 6217 and I’ve no idea what it is.
"I’ve been watching it for nearly an hour and it’s not moving.
"And I can find no known minor planets that are that bright in that position.
"If it were in the galaxy rather than next to it I’d be thinking supernova but it appears to be far outside the galaxy.
"Anyone here happen to be imaging that area tonight?"
Wiggins reported the discovery to the International Astronomical Union, which sent out notifications to star-watchers around the world. Soon two other observatories had picked up the distant flare of the exploding star. By Jan. 15, it was confirmed as a Type II supernova in the early stages of demolition. Given the designation SN 2018gj, it's a Type II supernova, one that results from a star core's violent collapse.
According to the NASA/IPAC Extragalactic database maintained by the California Institute of Technology, the host galaxy is about 59 million light-years or 59.7 million light-years distant, meaning the star blew up nearly 60 million years ago. NGC 6217 is an estimated 30,000 light-years across; light from a supernova blast on one edge of the galaxy would take 30,000 years to reach the other, traveling 186,000 miles a second.
Light from the supernova flashed through space for almost 60 million years before landing in Wiggins' 14-inch telescope.
A supernova is the most violent explosion known, marking the death of a bloated red supergiant star at least eight times the size of our sun. When its fuel runs out and iron remains in the core, the star collapses.
NASA's Goddard Space Flight Center explains: "In less than a second, the star begins the final phase of gravitational collapse. The core temperature rises to over 100 billion degrees as the iron atoms are crushed together. The repulsive force between the nuclei is overcome by the force of gravity. So the core compresses but then recoils. The energy of the recoil is transferred to the envelope of the star, which then explodes and produces a shock wave, which we see as a supernova explosion."
Stars less than eight times the mass of the sun do not produce supernovas. Larger ones that explode form either a neutron star or a black hole. Black holes are thought to form from supernovas of stars at least 25 times the mass of the sun, according to scientists working with the Hubble Space Telescope.1 comment on this story
Black holes are among the strangest objects, with gravity so immense that nothing escapes. What's at the center of a black hole? The most likely theory is that nothing is inside, just a point in space carrying astonishing mass.
No news from the cosmos yet on whether Wiggins' supernova produced a black hole.
Wiggins is the only Utahn this chronicler knows about who has discovered a supernova. To have brought five of them to the attention of the world's observers is a wonderful service to science. It's no surprise that the Earth Science Picture of the Day, produced by the Universities Space Research Association, highlighted his latest as the photo and story of the day.