A pulsar that emits the energy of ten million Suns

Image of the M82 galaxy with at its center, also magnified, the M82 X-2 pulsar (Image NASA/JPL-Caltech/SAO/NOAO)
Image of the M82 galaxy with at its center, also magnified, the M82 X-2 pulsar (Image NASA/JPL-Caltech/SAO/NOAO)

NASA’s NuSTAR (Nuclear Spectroscopic Telescope Array) Space Telescope allowed to discover a pulsar with a brightness never seen before. In an article published in the journal “Nature”, the international team led by Matteo Bachetti, who now works at INAF’s Astronomical Observatory of Cagliari and at the time at the Institut de Recherche en Astrophysique et Planetologie in Toulouse, France, illustrates the research that led to the discovery of this pulsar that emits energy ten million times that of the Sun.

This discovery is helping astronomers better understand the strong X-ray sources called Ultraluminous X-ray sources (ULX). So far, these sources have been attributed to black holes so the discovery of a pulsing ULX in the galaxy M82, about 12 million light years from Earth, was a great surprise.

Matteo Bachetti stated that he and his colleagues thought that the pulses came from another source because they are typical of the pulsar. These neutron stars are the extremely dense remnants of a star after it has exploded in a supernova. The term pulsar means “pulsating star” exactly because of their pulsations, which instead are absent in black holes.

Initially, the astronomers were observing a supernova in the galaxy M82 when they noticed the X-ray pulse from the source that was named M82 X-2. The Chandra X-ray Observatory and Swift, two other NASA’s space telescopes were also aimed at M82 for the same reason and their observations confirmed that M82 X-2 is a pulsar.

Combining the observations from different telescopes can be crucial to understand the nature of space objects, especially if they are as exotic as M82 X-2. In this case, different space telescopes allowed to make observations in various wavelengths but also the rate of pulsation of 1.37 seconds.

One element that’s really extraordinary is energy emitted by this neutron star, equivalent to that of ten million suns. It’s ten times the energy emitted by other X-ray emitting pulsars, making M82 X-2 really exceptional and hard to understand. In fact, an object of that type shouldn’t be able to emit so much energy.

It’s possible that this pulsar is nourished like a big black hole, meaning that there could be a considerable amount of matter in its vicinity that is swallowed and falling toward the star it heats up and emits X-rays of this intensity. To solve the mystery of the origin of such a high emission, astronomers intend to make further observations with NuSTAR, Chandra and Swift, also to investigate the nature of other sources of the ULX type.

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