It was the brightest supernova for nearly 400 years when it lit up the southern hemisphere’s sky in February 1987. Supernova 1987A — the explosion of a blue giant star in a nearby small galaxy known as the Large Magellanic Cloud — astounded the astronomical community. It gave them an unprecedented opportunity to observe a star explosion in real time using modern instruments and telescopes. But something was missing. After the supernova faded, astronomers expected to find a neutron star (a collapsing extremely dense stellar core made largely of neutrons) remaining in the core of the explosion. They saw nothing.
For 34 years, astronomers have been searching, unsuccessfully, for the missing neutron star. Various theories arose. She might not have had time to form it yet. Or, perhaps the mass of the blue giant was larger than expected, and the supernova created a black hole in place of a neutron star. Perhaps the neutron star was hidden, obscured by the dust of the explosion. If the missing star ever existed, it’s really hard to see.
But perseverance is paying off. Astronomers may have finally found it.
The first hint comes from the Atacama Large Millimeter / Sub-Millimeter Array (ALMA) in Chile. last summer. The radio telescope observed a hot «spot» inside the core of the supernova. The “point” itself is not a neutron star, but a hot mass of dust and gas that may hide behind a neutron star: After all, something is providing heat. But to confirm the existence of a neutron star, more observations are needed.
With the results of promising ALMA radio signals in hand, a team of researchers followed up by observing the supernova at X-ray wavelengths, using data from two different NASA spacecraft: the Chandra X-ray Observatory and the Nuclear Spectroscopic Telescope (Nostar) group. Their findings are published in The Astrophysical Journal this month. What they found is an X-ray emission near the core of the supernova explosion, with two possible explanations.
First, the emission could be the result of the acceleration of the blast shock wave. This shock wave theory cannot be completely ruled out, but the evidence appears to point to a second, more likely explanation — the Stellar Wind Nebula.
Pulsars are a type of rapidly rotating energetic neutron star, and the radiation flashes outward like a lighthouse as it rotates. Pulsars can sometimes create high-speed winds that blow outward and create nebulae, in the form of charged particles and magnetic fields. This is what the researchers think they see.
Chandra and NuSTAR data support the discovery of ALMA from last year. Somewhere inside Supernova 1987A there is a young pulsar. It may take a decade or more before the core of the supernova disappears enough to directly observe a pulsar, but for the first time in 30 years, astronomers can be quite confident in its existence.
The discovery is exciting. «To be able to basically watch a pulsar star from birth would be unprecedented,» Salvatore Orlando saidOne of the researchers involved in the discovery. «It could be a once-in-a-lifetime opportunity to study the evolution of a small pulsar.»
So, with a 30-year-old puzzle solved, and a lot of new science to be done in the coming years and decades, Supernova 1987A promises to preserve our attention. After all, it is the closest and brightest supernova we will ever see.
Unless the Betelgeuse explodes …