Scientists have discovered that three neutron starsborn in the fires of other exploding stars, have cooled surprisingly quickly, bringing us closer to understanding the exotic nature of the matter at the heart 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 operating with X-ray light.
A neutron star is the collapsed core of a massive star that has disappeared supernovaand can hold up to almost three times the mass of our sun in a spherical volume approximately 11 kilometers in diameter. All this matter compacted 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 relevant, consider how a tablespoon of neutron star material would compare to the mass of Mount Everest.
This extreme nature also means that the physics governing the interiors of neutron stars remains murky. These objects are called neutron stars because their matter has been crushed to such a degree that it is negatively charged. electrons and positively charged protons crash together, overcoming the electrostatic force between them to form an object filled with just neutral neutrons. Deeper in the heart of a neutron star, matter can be crushed even further, forming exotic and novel particles such as hypothetical hyperons. Perhaps, scientists think, neutrons themselves could be burst in a neutron star, creating a soup of the universeThe most fundamental particles of: 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 textbook that determines the internal structure and composition of a neutron star based on factors such as its mass, temperature, magnetic field And so on. The problem is that scientists have literally hundreds of options for what that equation of state could be. Since we cannot replicate on Earth conditions inside a neutron star, testing which model is correct depends heavily on whether they match what astronomical observations tell us.
However, the discovery of three neutron stars with significantly lower surface temperatures than other neutron stars of the same age provided an important clue, allowing researchers to rule out three-quarters of the possible models for the equation. state of neutron stars in one shot. stroke. Two of the neutron stars are pulsars, which are rapidly rotating neutron stars that send beams of radio jets towards us. The third neutron star, in the Vela Jr supernova remnant, does not exhibit pulsar behavior, but that may simply be because its radio jets are not pointing in our direction.
Neutron stars have been detected at X-ray wavelengths by the European Space AgencyIt is XMM-Newton telescope And NASAIt is Chandra X-ray Observatory.
“The superb 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 XMM-Newton scientist Camille Diez at the European Space Institute. Agency, in a press release.
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 are pretty cool as far as neutron stars go. We say “cold,” 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, ranging from 840 to 7,700 years, depending on the size and expansion speed of the supernova remnants surrounding them, they are considered extremely cold. Neutron stars are born with temperatures of hundreds of billions or even billions of degrees, and even as they cool, other neutron stars of similar ages have temperatures twice as high, sometimes even hotter.
Neutron stars can cool via two mechanisms. The first is the thermal radiation of their surfaces which allows thermal energy to escape into the cold of the space. The other is neutrino emission, which steals energy from the core of a neutron star, and is believed to be responsible for the rapid cooling of this particular trio of neutron stars.
However, the rate at which neutron stars can cool through these mechanisms depends on the equation of state.
“The young age and cold surface temperature of these three neutron stars can only be explained by invoking a rapid cooling mechanism,” said one of the researchers, Nanda Rea, of the Institute of Science. and the Institute of Space Studies of Catalonia. statement. “As enhanced cooling can only be enabled by certain equations of state, this allows us to rule out a significant portion of possible models.”
And didn’t they just do it? the team estimates that three-quarters of all possible models can be ignored after this result. The researchers were able to determine this by calculating cooling curves, which are essentially graphs showing how neutron stars cool relative to their ambient temperature. time. The shape of the curve depends strongly on neutron star properties such as mass and magnetic field strength. So, using machine learning, the team calculated the range of parameters that best describe each cooling curve, then matched them to the potential. equations of state, seeing which ones still matched and which ones could be discarded because they had no chance of matching the data.
This process reduced the range of possible equations of state, but the results are not limited to the simple characterization of neutrons. stars. The behavior of matter at subatomic scales under intense pressure, extreme temperatures, and overwhelming gravity introduces quantum the effects too. Scientists currently lack a quantum theory of gravityand an equation of state for neutron stars could therefore put us on the path to the emergence of quantum effects and high technologies.gravity physics finally united in a single theory.
The results are described in an article published June 20 in the journal Nature Astronomy.