It was the brightest supernova in nearly 400 years when it ignited the air of the southern hemisphere in February 1987. Supernova 1987A – the explosion of a blue supergiant star in the nearby mini-galaxy known as the Great Magellanic Cloud – stunned the astronomical community. This gave them an unprecedented opportunity to observe an exploding star in real time with modern instruments and telescopes. But something was missing. After the supernova faded, astronomers expected to find a neutron star (a hyper-dense, collapsed stronger, consisting mainly of neutrons) in the heart of the explosion. They saw nothing.
In the 34 years that followed, astronomers searched unsuccessfully for the missing neutron star. Several theories have emerged. Maybe it has not yet had time to form. Or maybe the mass of the blue supergiant was larger than expected, and the supernova created a black hole instead of a neutron star. Maybe the neutron star was hidden, obscured by dust from the explosion. If the missing star was there at all, it was really hard to see.
But perseverance pays off. Astronomers may have finally found it.
The first tip came this summer from the Atacama Large Millimeter / Submillimeter Array (ALMA) in Chile. The radio telescope observed a hot ‘spot’ in the core of the supernova. The ‘spot’ itself is not a neutron star, but rather a heated mass of dust and gas that can hide the neutron star behind it: after all, something provides the heat. But to confirm the presence of a neutron star, further observations are needed.
With ALMA’s promising radio signal results in hand, a team of researchers observed the supernova in X-ray wavelengths using data from two different NASA spacecraft: the Chandra X-Ray Observatory and the Nuclear Spectroscopic Telescope Array (NuSTAR). Their results will be 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.
Astronomico di Palermo / Salvatore Orlando
First, the emission may be due to particles accelerated by the shock wave of the explosion. This shock wave theory can not be completely ruled out, but the evidence seems to point to a second, more probable explanation – a Pulsar wind nebula.
Pulsars are a kind of energetic neutron star that rotates fast, and flashes like a lighthouse like a lighthouse to the outside. Pulsars can sometimes create rapid winds that blow outward and create nebulae formed by charged particles and magnetic fields. This is what the researchers think they see.
The Chandra and NuSTAR data support last year’s ALMA detection. Somewhere in the middle of Supernova 1987A lies a young pulsar. It may take a decade or more before the core of the supernova clears up enough to observe the pulsar directly, but for the first time in thirty years, astronomers can reasonably trust that it is there.
The discovery is exciting. “To be able to see a pulsar since its birth would be unprecedented,” said Salvatore Orlando, one of the researchers involved in the detection. “This may be a once-in-a-lifetime opportunity to study the development of a baby pulsar.”
So, with a 30-year-old mystery solved and a lot of new science to do in the years and decades to come, Supernova 1987A promises to keep our attention. After all, it is the closest and brightest supernova we will ever see.
Unless Betelgeuse explodes …
(Betelgeuse is unlikely to explode anytime soon)
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