(Paris) With 2.3 million degrees for an existence of only 841 years, the neutron star J0205 is too cold to fit a large number of models explaining the cooling of these unique bodies of cosmic fauna, according to a study by Spanish astronomers.
A neutron star is the remnant of a massive star exploding at the end of its life. If this effect exceeds a certain mass, it turns into a black hole. Below, it becomes a neutron star, such as PSR J0205+6449, its full name.
An enormously dense object, equivalent to 1.4 suns, compressed into a sphere 20 to 30 kilometers in diameter. Its rotation of fifteen revolutions per second generates a strong magnetic field, accompanied by the emission of X-rays.
This rotating cosmic fragment carries “unique information about the properties of matter and its behavior under extreme conditions of density and magnetic fields,” notes the study published Thursday in the journal Nature astronomy.
Conditions that cannot be replicated in the laboratory, and for which physicists have created models, are called equations of state. It makes it possible to describe the processes that occur in the core of these stars, in cases where the nuclei of atoms disintegrate and their components behave in strange ways.
By reviewing the catalog of the XMM-Newton and Chandra space telescopes, dedicated to discovering neutron stars, the team of Spanish astronomers identified three that stand out from the rest.
“On paper, their temperature is very high, but it is unusually cold for their young age,” D sums up to AFP.s Alessio Marino, co-author of the study and a member of the Barcelona Institute of Space Sciences. And not just a little, because it's at least half the height of neutron stars of the same age.
500 billion degrees
Michaela Oertel, director of research at the National Center for Scientific Research at the Strasbourg Observatory and a specialist in this field, explains that a star is usually born “at a temperature of about 500 billion degrees Celsius, and after only a few minutes, its temperature drops to less than 10 billion degrees.” These objects are embedded. This temperature will drop sharply with age, after a million years.
In this case, astronomers have calculated cooling curves by age, allowing them to be compared to neutron stars. They identified this era by observing the cloud left over from the original explosion that witnessed the birth of stars.
According to their calculations, the youngest, J0205, is 841 years old. This is a date confirmed by historical accounts of sky watchers in the Middle Ages.
The other two are 7,700 years old and range between 2,500 and 5,000 years old, with temperatures of 1.9 and 4.6 million degrees, respectively. At least twice the size of contemporary neutron stars.
However, “the cooling of a star is really sensitive to its internal composition,” particularly the ratio of neutrons compared to protons, according to Michaela Ortel, who was not involved in the study.
The researcher therefore welcomes the “very interesting” work, because it limits the number of models applicable to stars of a given mass.
In this case, the study concluded that for the neutron stars under consideration, these models must include a rapid cooling mechanism, linked to the star's composition.
The interest of this work is in fundamental physics, to help understand the particularly strong interaction, one of the fundamental forces that govern matter in the infinitely small. But also astrophysics, so it's infinitely large.
Since then, as MI Ortel: “We now know that neutron star mergers are the main source of heavy elements on Earth,” such as gold or platinum.
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