Evidence grows for pulsar at the heart of famed supernova remnant

An artist’s impression of a pulsar wind nebula at the heart of the SN 1987A supernova remnant. Image: Chandra (X-ray): NASA/CXC/Univ. di Palermo/E. Greco; Illustration: INAF-Osservatorio Astronomico di Palermo/Salvatore Orlando

On 24 February 1987, a star exploded in the Large Magellanic Cloud, the first supernova visible to the unaided eye in nearly 400 years. Known as SN 1987A, the spectacular blast generated world-wide interest as astronomers scrambled to study the aftermath of the explosion some 170,000 light years from Earth.

Now, more than three decades after the fact, astronomers may have finally found signs of the collapsed remnant of the doomed star in multiple observations suggesting the presence of a “pulsar wind nebula” made up of charged particles and magnetic fields generated by a spinning neutron star.

That intriguing possibility is supported by data collected last year by the Atacama Large Millimetre/submillimetre Array, more recent observations by NASA’s Chandra X-ray Observatory and previously unpublished results from the Nuclear Spectroscopic Telescope Array, or NuSTAR.

Expanding rings of debris mark the spot where a star exploded in the Large Magellanic Cloud in 1987. Recent observations suggest the presence of a pulsar in the heart of the supernova remnant. Image: Hubble Space Telescope/P. Challis (CfA)

“For 34 years, astronomers have been sifting through the stellar debris of SN 1987A to find the neutron star we expect to be there,” said Emanuele Greco of the University of Palermo in Italy, leader of a study published by The Astrophysical Journal. “There have been lots of hints that have turned out to be dead ends, but we think our latest results could be different.”

When a massive star runs out of nuclear fuel, fusions reactions stop, the core collapses and the star’s outer layers are blown into space in a cataclysmic explosion. Depending on the original mass, the core can either be crushed into a city-size neutron star or, in extreme cases, all the way into a black hole.

Spinning neutron stars are known as pulsars, some of which produce high-speed winds of debris that travel at nearly the speed of light – a pulsar wind nebula. Using data from Chandra and NuSTAR, the researchers observed low-energy X-rays smashing into surrounding material, along with evidence from NuSTAR of higher-energy particles.

Such X-rays could be produced by particles accelerated to extreme energies by the supernova blast wave. A pulsar is not required. But the Chandra and NuSTAR data, along with observations reported last year from the Atacama Large Millimetre/submillimetre Array, support the presence of a pulsar wind nebula.

The center of the SN 1987A remnant is still obscured by gas and dust. But the researchers were able to model how that material would absorb X-rays at different energies, giving them, in effect, a glimpse of the central regions of SN 1987A without the intervening material.

If the researchers are correct in assuming the presence of a pulsar, models predict the obscuring material near the center of the remnant will disperse over the next decade or so, eventually allowing pulsar emissions to emerge.

“Astronomers have wondered if not enough time has passed for a pulsar to form, or even if SN 1987A created a black hole,” said co-author Marco Miceli, also from the University of Palermo. “This has been an ongoing mystery for a few decades and we are very excited to bring new information to the table with this result.”