The researchers found that three neutron starsborn in the fire of other exploding stars, they cooled surprisingly quickly, bringing us closer to understanding the exotic nature of the matter at the cores of these extreme objects.
The discovery was made by a Spanish team led by Alessio Marino of the Institute of Space Sciences (ICE–CSIC) in Barcelona, ​​using European and American space telescopes that work with X-ray light.
A neutron star is the collapsed core of a massive star that has disappeared supernovaand can contain up to almost three times as much the mass of our sun in a spherical volume only about 6.8 miles (11 kilometers) in diameter. All that matter packed into such a small area means that neutron stars are among the densest concentrations of matter in the known universe, second only to black holes. To make this statement more comparable, consider how a tablespoon of neutron star material would be comparable to the mass of Mount Everest.
This extreme nature also means that the physics that govern the interiors of neutron stars remains unclear. These objects are called neutron stars to begin with because their matter has been crushed to such an extent that it is negatively charged electrons and positively charged protons come together and overcome the electrostatic force between them to create an object full of neutral neutrons. Deeper in the core of a neutron star, matter can be crushed to an even greater extent, forming exotic, never-before-seen particles such as the hypothetical hyperons. Scientists believe that or the neutrons themselves could rip apart in a neutron star to create a soup universemost basic particles: quarks.
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What happens inside a neutron star is governed by the neutron star’s equation of state. Think of it as a guide that determines the internal structure and composition of a neutron star based on things like its mass, temperature, magnetic field and so on. The problem is that scientists have literally hundreds of possibilities for what this equation of state could be. Because we cannot replicate to Earth conditions inside a neutron star, testing which model is the right one depends very much on how they fit what the astronomical observations tell us.
But now the discovery of three neutron stars with significantly lower surface temperatures compared to other neutron stars of similar age has provided a big clue that has allowed researchers to rule out three-quarters of the possible neutron star equation of state models in one. stroke. Two of the neutron stars are pulsars, which are fast-spinning neutron stars that shoot radio jets at us. The third neutron star, in the supernova remnant Vela Jr, does not exhibit pulsar behavior, but this may be because its radio jets are not pointing in our direction.
Neutron stars have been detected at X-ray wavelengths European Space Agency‘with The XMM-Newton telescope and NASA‘with the Chandra X-ray Observatory.
“The excellent sensitivity of XMM-Newton and Chandra made it possible not only to detect these neutron stars, but also to collect enough light to determine their temperatures and other properties,” said Camille Diez, XMM-Newton scientist at European Space. agency, in a statement.
The hotter a neutron star is, the more energetic its X-rays are, and the X-ray energy of these three neutron stars tells us that they’re pretty chilly as neutron stars go. We say “cool,” but neutron stars are still exceptionally hot, with temperatures ranging from 1.9 million to 4.6 million degrees Celsius (3.4 million to 8.3 million degrees Fahrenheit). However, for their young age, which ranges from 840 years to 7,700 years based on the size and expansion rate of the supernova remnants around them, they are considered exceptionally cool. Neutron stars are born at temperatures of hundreds of billions or even trillions of degrees, and as they cool, other neutron stars of a similar age have temperatures twice as high—sometimes even higher.
Neutron stars can cool by two mechanisms. One is thermal radiation from their surfaces, which allows thermal energy to escape into the cold space. Next is neutrino emission that steals energy from the neutron star’s core and is thought to be responsible for the rapid cooling of this particular trio of neutron stars.
However, how fast neutron stars can cool due to these mechanisms depends on the equation of state.
“The young age and low surface temperature of these three neutron stars can only be explained by invoking a rapid cooling mechanism,” said one of the researchers Nanda Rea from the Institute of Space Sciences and the Institute of Space Studies in Catalonia. declaration. “Because enhanced cooling can only be activated by certain equations of state, this allows us to rule out a significant portion of possible models.”
And they didn’t; the team estimates that three-quarters of all possible models can be ignored after this result. Scientists were able to determine this by calculating cold curves, which are basically graphs that show how neutron stars cool with respect to time. The shape of the curve is highly dependent on neutron star properties such as mass and magnetic field strength, so using machine learning the team calculated a range of parameters that best describe each cooling curve and then compared them to the potential. state equations, to see which ones still match and which ones might be thrown out because they have no chance of matching the data.
This process narrowed down the range of possible equations of state, but the findings are not limited to neutron characterization stars. It represents the behavior of matter on subatomic scales under intense pressure, extreme temperature and crushing gravity quantum effects too. Scientists currently lack a quantum theory of gravityand the equation of state for neutron stars could therefore put us on the path to quantum effects and highgravitation physics finally together as a single theory.
The findings are described in a paper published June 20 in the journal Nature Astronomy.