Does a magnetar have an atmosphere? What we saw from the first observation of X-ray polarized light | sorae Portal of the universe


A star with a mass greater than 8 times that of the Sun will explode as a supernova at the end of its life, and the core will degenerate and become “neutron star”, a dense and compact object with a diameter of more than 10 km. As the name suggests, neutron stars have an average of neutrons (※1) , but the exact composition from the surface to the inside is believed to be different. specially,On the outer surface is an atmosphere made up of ordinary atoms, a leftover from when the star was a star.It is estimated that

*1…A neutron is one of the particles that together with a proton make up an atomic nucleus. A neutron star is, on average, almost entirely a cluster of high-density neutrons.

Assuming the neutron star has an atmosphere, the X-rays emitted by the neutron star are affected by the atmosphere and become polarized. (※2) has been theoretically shown to have an effect on However, such polarization of X-rays has never been observed before.

*2…When electromagnetic waves such as visible light and X-rays are viewed as “waves”, the fact that the vibration directions of the waves align in a certain plane is called “polarized light”.

A research team, including Roberto Taverna of the University of Padua, said:magnetar“One of”4U0142+61” has been studied. Magnetars are a class of neutron stars with remarkably strong magnetic fields and are known to emit occasional bursts of energy. However, there are many unclear points about why magnetars have such strong magnetic fields and how they emit energy, and research is still ongoing. 4U 0142+61 has been the subject of long-term searches because it is a relatively nearby magnetar, about 13,000 light-years from Earth.

Taverna et al., The X-ray Observation Satellite”IXPE extensionWe analyzed the observation data of “ 4U 0142+61 and investigated whether there is polarization for each X-ray energy. As a result, we were able to measure the X-ray polarization in neutron star radiation for the first time.

The degree of polarization of the observed X-rays varies with energy, for example values ​​for linearly polarized light range from 2 to 8 keV. (※3) 13.5±0.8% at 2~4keV, 15.0±1.0% at 5.5~8keV, 35.2±7.1% at 5.5~8keV and below detection sensitivity at 4~5keV. On the other hand, the polarization angle has been shown to change abruptly at 90 degrees between 4 and 5 keV.

*3: eV is a unit called “electron volt”. 1eV = 1.602 x 10^-19J, and is used as a unit to express energy in the world of elementary particles such as X-rays = photons.

Based on these values, it is estimated that most of the X-rays emitted by 4U 0142+61 are emitted from solid surfaces near the equator, and some of them are influenced by the surrounding strong magnetic field.

Unexpectedly, from the X-ray emission data of 4U 0142+61 obtained this time,No clear atmospheric presence was shown. This is an important point.

One possibility is that the atmosphere existing on the magnetar’s surface cannot maintain a gaseous state under the very strong magnetic field and condenses. This happens because (roughly speaking) the properties of matter made up of ordinary atoms are determined by the state of the electrons outside the atoms. Since electrons, which are electrically charged particles, react to magnetic fields, there is a possibility that the electrons undergo a change of state that causes the gas to solidify under the very strong magnetic field of the magnetar.

Our observations are just one example, and we can’t settle the debate about whether magnetars and neutron stars have atmospheres. It is possible that the presence or absence of an atmosphere differs between a magnetar, which has a strong magnetic field, and a neutron star, which, although weaker than a magnetar, has a magnetic field that is orders of magnitude stronger than that of ordinary celestial bodies. However, the present study was very successful as it was possible to determine the presence or absence of a neutron star’s atmosphere from actual observational data. Because magnetars and other neutron stars have different magnetic field strengths, the presence of an atmosphere can depend on the strength of the magnetic field. Future research results are awaited.

connection:NASA’s observation satellite has captured X-rays of the youngest ‘magnetar’ in the history of observation


Text: Riri Ayae

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