Free Astronomy Magazine May-June 2021

39 MAY-JUNE 2021 ASTRO PUBLISHING the explosion site at an average speed of 3.2 million kilometers per hour. At that speed, you could travel to the Moon and back in 15 minutes. Researchers have studied the Hub- ble archive looking for visible-light images of the supernova remnant and they have analysed the data to calculate a more accurate estimate of the age and centre of the super- nova blast. According to their new estimates, light from this blast arrived at Earth 1700 years ago, during the decline of the Roman Empire. This super- nova would only have been visible to inhabitants of Earth’s southern hemisphere. Unfortunately, there are no known records of this titanic event. Earlier studies proposed ex- plosion dates of 2,000 and 1,000 years ago, but this new analysis is believed to be more robust. To pinpoint when the explosion oc- curred, researchers studied the tad- pole-shaped, oxygen-rich clumps of ejecta flung out by this supernova blast. Ionised oxygen is an excellent tracer because it glows brightest in visible light. By using Hubble’s pow- erful resolution to identify the 22 fastest moving ejecta clumps, or knots, the researchers determined that these targets were the least likely to have been slowed down by passage through interstellar mate- rial. They then traced the knots’ mo- tion backward until the ejecta co- alesced at one point, identifying the explosion site. Once that was known, they could calculate how F eatured in this Hubble image is an expanding, gaseous corpse — a supernova remnant — known as 1E 0102.2-7219. It is the remnant of a star that exploded long ago in the Small Magellanic Cloud, a satellite galaxy of our Milky Way located roughly 200,000 light-years away. [NASA, ESA, and J. Banovetz and D. Milisavljevic (Purdue University)] million kilometres per hour from the centre of the explosion to have arrived at its current position. The suspected neutron star was identi- fied in observations with the Euro- pean Southern Observatory’s Very Large Telescope in Chile, in combi- nation with data from NASA’s Chan- dra X-ray Observatory. ! long it took the speedy knots to travel from the explosion centre to their current location. Hubble also measured the speed of a suspected neutron star — the crushed core of the doomed star — that was ejected from the blast. Based on the researchers’ estimates, itmust be moving at more than 3