Astronomers have been waiting centuries to see a supernova in our own galaxy, but watch thousands a year elsewhere in the universe. Most, however, are billions of light-years away, so in 2018 when an explosion was seen a mere 70 million light-years away the Hubble telescope paid attention. Now NASA has released a timelapse of nearly a year of observations so we can watch it in all its glory.
OK, 70 million light-years is an unimaginable distance by human standards; so vast that when the explosion occurred dinosaurs were still dominating the Earth. Yet in the vastness of the cosmos, it's really quite close. The galaxy NGC 2525, where the event occurred, was among the first to be discovered way back in 1791 when William Herschel was making some of the first records of what we now know to be cities of stars beyond our own galaxy. It's closeness and beautiful structure makes it a favorite for amateur astronomers.
The event, known as SN2018gv, gained an extra allocation of Hubble's precious time because it was a Type Ia supernova, the product of a white dwarf drawing so much material off a neighboring star it passed the critical mass threshold to blow up. Type Ias are consistent in their intrinsic peak brightness, an astonishing 5 billion times that of the Sun. Consequently, by measuring their light, we can calculate the distance to their host galaxy.
That's not necessary for NGC 2525, whose distance has already been measured through other means, but is absolutely essential for our ability to quantify the span of space to much further galaxies. By observing the rise and fall of a supernova in a galaxy with a precisely known distance, we can improve our calibration of the events at the edge of our capacity to observe.
Professor Adam Riess of Johns Hopkins University shared the 2011 Nobel Prize for physics for his use of Type Ia supernovas to show the expansion of the universe is accelerating. Distant galaxies are moving away from us not only more rapidly than closer ones, but even faster than if the rate of expansion was constant. This discovery, completely counter to the assumptions of the time, has caused a revolution in cosmology as it can only be explained by the presence of dark energy.
“No Earthly fireworks display can compete with this supernova, captured in its fading glory by the Hubble Space Telescope," Reiss said in a statement.
Although Reiss's measurements were precise enough to prove expansion, they still had a substantial margin of error, and detailed observations of events like SN2018gv can improve that. In 2019 Reiss co-authored a paper refining the measurements to within 2 percent but hopes to use the data from SN108gv to make the error bars even narrower.
The rest of us get to just sit back and enjoy the view.