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Reclusive neutron star may have been found in famous supernova

On the left, data from NASA’s Chandra X-ray Observatory shows part of the remains of an exploded star known as the 1987A supernova. On the right, an illustration of what may be in the center of the supernova remnant, a structure known as the “pulsar wind nebula”. Credit: NASA / CXC

What remains of the star that exploded just outside our galaxy in 1987?

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The debris has obscured scientists’ perspective, but two of NASA’s x-ray telescopes have revealed new clues.

Since astronomers captured a star’s luminous explosion on February 24, 1987, researchers have searched for the crushed stellar core that should have been left behind. A group of astronomers using data from NASA space missions and ground telescopes may finally have found them.

As the first supernova visible to the naked eye in about 400 years, Supernova 1987A (or SN 1987A for short) created great excitement among scientists and quickly became one of the most studied objects in the sky.

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The supernova is located in the Large Magellanic Cloud, a small companion galaxy to our own Milky Way, just 170,000 light years from Earth.

As astronomers watched debris explode outside the site of the detonation, they also searched for what should have remained of the star’s core: a neutron star.

Data from NASA’s Chandra X-ray Observatory and unpublished data from NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR), in combination with data from the ground-based Atacama Large Millimeter Array (ALMA) year latest, now present a fascinating collection of evidence for the presence of the neutron star at the center of SN 1987A.

“For 34 years, astronomers have sifted through stellar debris from SN 1987A to find the neutron star we expect to find there,” said study leader Emanuele Greco, University of Palermo in Italy. “There were a lot of clues that turned out to be dead ends, but we think our latest results may be different. ”

This computer model from an article by Orlando and colleagues shows the rest in 2017, incorporating data taken by Chandra, ESA’s XMM-Newton, and Japan’s Advanced Satellite for Cosmology and Astrophysics (ASCA). Credit: INAF-Osservatorio Astronomico di Palermo / Salvatore Orlando

When a star explodes, it collapses on itself before the outer layers are thrown into space. Compression of the core turns it into an extraordinarily dense object, with the Sun’s mass squeezed into an object about 10 miles in diameter. These objects have been called neutron stars because they are made almost exclusively of densely concentrated neutrons. They are extreme physics laboratories that cannot be replicated here on Earth.

Fast-spinning, highly magnetized neutron stars, called pulsars, produce a beam of lighthouse-like radiation that astronomers detect as pulses as its rotation sweeps the beam across the sky. There is a subset of pulsars that produce winds from their surfaces – sometimes at the speed of light – that create complex structures of charged particles and magnetic fields known as “pulsar wind nebulae”.

Together with Chandra and NuSTAR, the team found relatively low energy x-rays from SN 1987A debris crashing into surrounding material.

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The team also found evidence of high-energy particles using NuSTAR’s ability to detect more energetic x-rays.

Supernova 1987A exploded over 30 years ago and is still surrounded by debris.

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The energetic environment was imaged by NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR (shown in blue) and the Chandra X-ray Observatory (shown in red), which has finer resolution. Credit: NASA / CXC

There are two probable explanations for this energetic X-ray emission: either a pulsar wind nebula, or particles accelerated to high energies by the blast wave of the explosion. This latter effect does not require the presence of a pulsar and occurs over much greater distances from the center of the explosion.

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The latest x-ray study supports the case of the pulsar wind nebula – meaning the neutron star has to be there – arguing on two fronts against the blast wave acceleration scenario. First, the brightness of the higher energy x-rays remained roughly the same between 2012 and 2014, while the radio emission detected with the Australian Telescope Compact Array increased. This defeats expectations for the shockwave scenario. Next, the authors estimate that it would take nearly 400 years to accelerate electrons to the highest energies seen in the NuSTAR data, which are more than 10 times older than the age of the rest.

“Astronomers wondered if it hadn’t passed long enough for a pulsar to form, or even if SN 1987A had created a black hole,” said co-author Marco Miceli, also of the ‘University of Palermo. “It has been a constant mystery for a few decades, and we are very happy to bring new information with this result. ”

Chandra and NuSTAR data also support a 2020 result from ALMA which provided possible evidence for the structure of a pulsar wind nebula in the millimeter wavelength band. Although this “drop” has other potential explanations, its identification as a pulsar wind nebula could be corroborated by the new radiographic data. This is further evidence that supports the idea that there is still a neutron star.

If it is indeed a pulsar at the center of SN 1987A, it would be the youngest ever.

“Being able to watch a pulsar primarily from birth would be unprecedented,” said co-author Salvatore Orlando of the Palermo Astronomical Observatory, a research center of the National Institute of Astrophysics (INAF) in Italy. “This could be a unique opportunity to study the development of a baby pulsar. ”

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The center of SN 1987A is surrounded by gas and dust.

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The authors used state-of-the-art simulations to understand how this material would absorb x-rays at different energies, allowing a more precise interpretation of the x-ray spectrum, that is, the amount of x-rays at different energies. This allows them to estimate what the spectrum of the central regions of SN 1987A is without the obscuring material.

As is often the case, more data is needed to strengthen the case of the Pulsar Wind Nebula. An increase in radio waves accompanied by a relatively high energy X-ray increase in future observations would defeat this idea. On the other hand, if astronomers observe a decrease in high-energy X-rays, then the presence of a pulsar wind nebula will be corroborated.

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The stellar debris surrounding the pulsar plays an important role in strongly absorbing its low-energy X-ray emission, which makes it undetectable at present.

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The model predicts that this material will disperse over the next few years, which will reduce its absorbency. Thus, the pulsar emission should emerge in about 10 years, revealing the existence of the neutron star.

An article describing these results is published this week in

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The astrophysical journal, and a pre-print is available online.

Kes 75 – Milky Way’s youngest pulsar reveals secrets of star’s disappearance

More information:
Indication of a pulsar wind nebula in the hard X-ray emission of SN 1987A, arXiv: 2101.09029 [astro-ph.HE]

Citation: A reclusive neutron star may have been found in the famous supernova (February 23, 2021) retrieved on February 23, 2021 from

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