It was the brightest supernova in nearly 400 years when it lit the skies of the southern hemisphere in February 1987. Supernova 1987A – the explosion of a blue supergiant star in the nearby mini-galaxy known as the Large Magellanic Cloud – amazed the astronomical community. It offered 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 stellar core, made largely of neutrons) left-over at the heart of the explosion. They saw nothing.
In the 34 years since, astronomers have been searching, unsuccessfully, for the missing neutron star. Various theories arose. Perhaps it hadn’t had time to form yet. Or perhaps the blue supergiant’s mass was larger than expected, and the supernova created a black hole instead of a neutron star. Perhaps 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 persistence pays off. Astronomers may have finally found it.
The first hint came from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile last summer. The radio telescope observed a hot ‘blob’ within the core of the supernova. The ‘blob’ itself is not a neutron star, but rather a heated mass of dust and gas which may hide the neutron star behind it: after all, something is providing the heat. But to confirm the presence of a neutron star would require further observations.
With ALMA’s promising radio signal results in hand, a team of researchers followed up by observing 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 are being published in the Astrophysical Journal this month. What they’ve found is an X-Ray emission near the core of the supernova explosion, with two possible explanations.
Supernova 1987A with a pulsar wind nebula at its center. Credit: Chandra (X-ray): NASA/CXC/Univ. di Palermo/E. Greco; Illustration: INAF-Osservatorio
Astronomico di Palermo/Salvatore Orlando
First, the emission could be the result of particles being accelerated by the explosion’s shock wave. This shock wave theory cannot be ruled out entirely, but the evidence seems to point to a second, more likely explanation – a Pulsar Wind Nebula.
Pulsars are a type of energetic neutron star that rotate rapidly, flashing radiation outwards like a lighthouse as they spin. Pulsars can sometimes create high-speed winds which blow outwards and create nebulae, shaped by charged particles and magnetic fields. This is what the researchers think they are seeing.
The Chandra and NuSTAR data support the ALMA detection from last year. Somewhere within the center of Supernova 1987A lies a young pulsar. It may be a decade or more before the core of the supernova clears out enough to observe the pulsar directly, but for the first time in 30 years, astronomers can be fairly confident that it is there.
Supernova 1987A, as seen by NuSTAR and Chandra. Credit: Chandra (X-ray): NASA/CXC/Univ. di Palermo/E. Greco; Illustration: INAF-Osservatorio Astronomico di Palermo/Salvatore Orlando; NuSTAR (X-ray): NASA/JPL-CalTech
The discovery is exciting. “Being able to watch a pulsar essentially since its birth would be unprecedented,” said Salvatore Orlando, one of the researchers involved in the detection. “It might be a once-in-a-lifetime opportunity to study the development of a baby pulsar.”
So with a 30-year-old mystery solved, and plenty of new science to do in the years and decades ahead, Supernova 1987A promises to keep our attention. After all, it’s the closest and brightest supernova we’ll ever see.
Unless Betelgeuse explodes…
(Betelgeuse is not likely to explode anytime soon)
- Reclusive Neutron Star May Have Been Found in Famous Supernova. Chandra X-Ray Observatory.
- Emanuele Greco et al. “Indication of a Pulsar Wind Nebula in the hard X-ray emission from SN 1987A.” Arxiv Preprint.
- “ALMA Finds Possible Sign of Neutron Star in Supernova 1987A.” NRAO.
- Dany Page et al. “NS 1987A in SN 1987A.” The Astrophysical Journal.