Amateur Astronomer Records Stellar Beacon 80 Million Light Years Distant

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Supernova 2016gkg, a Type II, Core Collapse Supernova (indicated by red bars) in the galaxy NGC 613, located about 80 million light years from Earth in the constellation Sculptor. (Image by C. Kilpatrick, UC Santa Cruz, and Carnegie Institute for Science, Las Campanas Observatory, Chile)

Victor Buso at the rooftop observatory that houses his 0.4 meter telescope, the setup that captured the first-light images of a supernova.

On February 21st, in a heretofore unprecedented accomplishment, an amateur astronomer has recorded the “First Light” of a dying star over 80 million light years distant. As described in the Nature article, the first point of contact for the supernova’s photons after traveling 80 million years, a point in the distant past 15 million years before the dinosaurs met their demise, was Victor Buso’s 0.4 meter (16″) diameter telescope! This was the first such discovery for Buso of Rosario, Argentina, an amateur astronomer who was serendipitously testing a new digital camera setup to image objects of interest through his 0.4 meter telescope.

Victor Buso’s first light discovery image of SN2016gkg.

Up until now, no astronomer using any modern telescope has ever observed the shock breakout of a supernova; yes, we’ve observed thousands of supernovae, some near and some far, but never have we observed them in the optical (visible) part of the spectrum at “Shock Breakout”, the moment when the explosion caused by the rapidly imploding stellar core rebounds against the dying star’s quantum degenerate nickel-iron inner core, propagating back outward at supersonic speeds, obliterating the star and everything within 10 light years. For a moment in time, in that singular event, the luminosity of the dying star exceeds that of the entire host galaxy!

The Supernova remnant SNR 1987a, the aftermath of one of the brightest stellar explosions since the invention of the telescope more than 400 years ago. Image credit: NASA/ESA Hubble Space Telescope.

SN1987a, a supernova that occurred in the Large Cloud of Magellan, was the closest and most widely studied supernova thus far in the modern era, bringing to bear the considerable power of the world’s great observatories and the Hubble Space Telescope. In the case of SN1987a, although we obtained a “before and after” sequence of images, we didn’t actually observe the event as it was happening at “shock breakout”.

There are two general types of supernovae, Type I and Type II.

The progenitor star that leads to a Type I supernova is generally a white dwarf, the parasitic companion in a binary star system consisting of the white dwarf and a normal star such as our sun. White dwarfs are the end-states for stars such as our sun up to and including stars with approximately 3 times its mass. If the white dwarf in this parasitic binary system orbits too close to the companion star, its powerful gravity draws material from the companion onto the white dwarf’s surface. When a very specific mass is reached, about 1.4 solar masses,  known as the Chandrasekhar mass (named in honor of the Indian physicist and Nobel Laureate Subrahmanyan Chandrasekhar), a runaway thermonuclear fusion reaction begins resulting in the violent obliteration of the star and a Type Ia supernova.

The progenitor star resulting in a Type II supernova is a star in excess of 8 solar masses that has reached its nuclear dead-end, the end state in the star’s evolutionary life cycle where heavy-element nucleosynthesis has gone as far as it can, having produced a nickel-iron core, a state where no additional energy can be derived from nuclear fusion reactions in the core and thus, the loss of any outward support. The core implodes at about 20% the speed of light, rebounding against the dying star’s quantum degenerate nickel-iron inner core, propagating back outward at supersonic speeds, obliterating the star and everything within 10 light years. SN2016gkg was such a supernova as was SN1987a and the famous Crab Nebula.

Victor Buso’s four image, first-light discovery sequence of SN2016gkg, a Type II, core-collapse supernova that occurred in NGC-613, a the spiral galaxy 80 million light years distant

As stated by Dr. Alexi Filippenko of UC, Berkeley who followed up Buso’s discovery of SN2016gkg with observations at the Lick and Keck observatories that proved critical to a detailed analysis of the explosion, “Professional astronomers have long been searching for such an event”; said Filippenko: “Observations of stars in the first moments they begin exploding provide information that cannot be directly obtained in any other way”. For Victor Buso, according to Filippenko, “it’s like winning the cosmic lottery“.

Fortuitously, Victor examined the images immediately and noticed a faint point of light quickly brightening near the end of one of the galaxy’s spiral arms, a point of light that was not visible in his first set of images.

Astronomer Melina Bersten and her colleagues at the Instituto de Astrofísica de La Plata in Argentina soon learned of the serendipitous discovery and realized that Buso had caught an exceedingly rare event, part of the first hour after light emerges from a massive exploding star, a rare moment like no other in the evolutionary life cycle of the star. During this time, critically singular information is obtained, such as the duration and rise of the light curve and the spectra of the light, an aspect of the observation that will allow us to determine what type of supernova it is and the composition of the rapidly expanding shell of gas. Bersten estimated Buso’s chances of such a discovery, his first supernova, at one in 10 million or perhaps even as low as one in 100 million.

 

NGC-613, as imaged by the Hubble Space Telescope with Victor Buso’s discovery images of SN2016gkg, is featured on NASA’s Astronomy Picture of the Day for February 28 of this year.


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