The Tycho supernova remnant by NASA’s Chandray Observatory

It was the astronomical event of the last millennium, second only to the discoveries in this millennium of extrasolar planets, or exoplanets, as they are also called. Let’s recap the chained events.

In the year 1054, on the approximate date of July 4, Chinese annals recorded “an invited star” in the heavens. It was as bright as Venus; coming to rival in brightness its first cousin, Tycho Brahe’s supernova of 1572, which reached an apparent magnitude close to -4. Both were visible to the naked eye; as well as its other relative, that of Kepler in 1604, which rose to -2.5. Efforts to locate the remains of the last two observed from Europe have been unsuccessful. The first – detected in China and Japan – luckily has records of its location in the sky, which is why it bequeathed us the location of today’s Crab Nebula – its remnant, with a central pulsar – which is still expanding in Taurus. , near the horns of the classic asterism and is observable with small instruments.

We had to wait 383 years to be the protagonists again of a cataclysmic stellar event visible to the naked eye, and no less than 933 years for a similar one also visible from our hemisphere! Telescopic supernovae are continuously recorded in different distant galaxies, but their brightness does not make them directly accessible to the human eye, nor – almost always – to small telescopes.

From Chile we were informed on February 25 or 26, 1987 (we cannot specify the exact day now, after so much time), that the Canadian astronomer Ian Shelton, in a plate taken around midnight on the 23rd, at the Observatory of « Las Campanas”, had registered a supernova in the Larger Magellanic Cloud, of approximately sixth magnitude.

The star called Sanduleak – 69,202 of that neighboring galaxy, a member of a triple system, with an apparent brightness of 12.24, had exploded as a supernova! (Poor hypothetical beings from the planets of her two companions!).

The events unfolded in a remarkable way. Taking the plate of discovery, Ian Shelton, who would not be a professional astronomer, would have had a problem with the telescope. For this reason, he suspended the routine undertaken of programmed photographs, to proceed to develop the plate on the spot, thus discovering almost instantly the aforementioned supernova.

He immediately communicated the news to his superiors, who, in addition to sending the corresponding telegram to the International Astronomy Union, would have ordered the transfer without delay to the place of some Canadian astronomers who were in La Serena.

Less than an hour after the obligatory informative tour, the Canadian moved about twenty meters to another telescope in Las Campanas, which had a photometer attached.

The young Argentine astronomer Dr. Emilio Lapasset was working there, engaged in a program of photometric determinations. He immediately requested his collaboration, which he enthusiastically offered without limitation.

Thus, this astronomer, today Director of the Córdoba Observatory, participated in the discovery by carrying out, during the rest of the night, a series of UBV determinations of the new star, which luckily had been discovered very early in its evolution.

They took δ Doradus as a reference star. In the first photometry carried out that morning, the supernova had a visual magnitude of 4.837; in the second, 4,824, to continue increasing in brightness with the passing of the hours. Corresponding work on these determinations was published by both actors in the Astronomical Journal (Shelton and Lapasset 1993).

The peculiar behavior of the supernova and its early detection allowed scientists to fully study the phenomenon; causing the theoretical models of supernovae in force at the time to be substantially modified; a consequential momentous event.

The historical participation of this Argentine astronomer in the opportunity is practically unknown today

The “Las Campanas” observatory in Chile is one of the most prestigious and advanced international research centers, located on the hill of that name, in the middle of the Atacama desert. It is in a place near the observatory located in «La Silla». A place of exceptional transparency, it is attended by researchers from all over the world, and its permanent plant has Argentine astronomers.

It comes to mind for its expressive synthesis, the chronicle of the historical event, already made by one of its protagonists, who in turn provided us with a reproduction of the plate taken by Ian Shelton, which we cannot fail to share due to its great value: