the kilonova behind GW170817 continues to shine in X and we...

Since the year 2015, we have entered the era of gravitational astronomy. It was prepared by many pioneers since the 1960s, some of whom are fortunately still with us and who have been awarded two Nobel prizes of physique, to know Kip Thorne and Roger Penrose.

We are still only at the beginning of the discoveries with this astronomy whose main objects of study are the black holes and the neutron stars. The first contain secrets in the field of the most fundamental physics, that of quantum gravity in connection with the very young field of quantum information. The latter have implications for the chemical evolution of galaxies and the origin of certain elements like gold nuclei and they are also great laboratories for the nuclear physics, elementary particles and many other things when these stars are also pulsars.

One can in particular explain with collisions of neutron stars a cosmic phenomenon which had remained enigmatic for decades, that of the famous gamma-ray bursts, the gamma-ray bursts (GRB) in English. These fantastic flashs of photons gamma releasing a energy prodigious were first discovered in the late 1960s thanks to the military Vela satellites, launched to monitor possible atomic tests in theatmosphere or space – in violation of past agreements that prohibited them.

Kilonovae, emitters of gravitational, gamma and X waves

The bursts gamma come in two forms, short and long. Short GRBs – that is, those lasting a few seconds at most, as opposed to long bursts lasting longer – are interpreted as kilonovae manifestations resulting from collisions of neutron stars in a binary system.

It is not difficult to understand the origin of the term “kilonova” when we know that these cosmic catastrophes are about 1,000 times brighter than a nova caused by a recurrent thermonuclear explosion on the surface of a white dwarf accreting matter, while a supernova is about 100 times brighter than a kilonova. Candidates for the title of kilonova have been detected since the beginning of the 2000s and in particular in 2013. But it was not until the rise of gravitational astronomy and the detection in 2017 of the source. G.W. 170817, by Link and Virgo, to conclude that we had really observed for the first time a kilonova, and that the associated short gamma-ray burst, GRB 170817A, detected by both the Fermi and Integral satellites, was indeed the product of a collision between two neutron stars. The gravitational waves measured by the two detectors had indeed made it possible to locate the collision on the celestial vault where the gamma counterpart had been found.

The kilonova was also a source of X-rays. The evolution of its curve light in this area of electromagnetic waves could have been followed by the famous instrument dedicated to astronomy X and bearing the diminutive of another Nobel Prize in physics who distinguished himself in the field ofastrophysics relativistic, the satellite Chandra from Nasa.

The theory of kilonovae needs to be reviewed

But now an international team of researchers, led by theastronomer from the University of Maryland, Eleonora Troja, just announced via a publication of an article in Monthly Notices of the Royal Astronomical Society, which can be found in free access on arXiv, that something is wrong with the kilonova models developed so far, according to Chandra’s data for GW170817.

Son regard has repeatedly focused on the galaxy NGC 4993 hence the gravitational signal of the collision of neutron stars, detected on Terre on August 17, 2017, left about 130 million years ago. It is indeed the distance in light years that separates the Milky Way of this lenticular galaxy located in the constellation of the’Hydra, initially discovered by the German-British astronomer William Herschel, March 26, 1789.

However, if the intensity of the X radiation emitted from the occurrence of GW170817 has indeed decreased over time, this decrease is much slower than expected. Chandra still sees them when they should have stopped. This is indeed what Eleonora Troja explains in a press release from the University of Maryland: ” We are entering a new phase in our understanding of neutron stars. We really don’t know what to expect from here on out as all of our models predicted the end of the emissions of x-rays and we were surprised to see them 1,000 days after the collision was detected. It may take years to find an explanation for what is happening, but our research opens the way door to many possibilities ».