Tour: NASA's Chandra Peers Into Densest and Weirdest Stars

Astronomers have taken an important step toward understanding some of the densest and strangest objects in the Universe by using NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton. These results show that the interiors of neutron stars may contain a special type of ultra-dense matter that does not exist anywhere else in the universe.

Neutron stars are the dense cores that can form after massive stars collapse. They are so dense that a teaspoon of their matter weighs about a trillion pounds.

The team in this new study analyzed previously released data from neutron stars to determine the so-called equation of state. This refers to the basic properties of the neutron stars including the pressures and temperatures in different parts of their interiors.

The authors used machine learning, a type of artificial intelligence, to compare the data to different equations of state. Their results imply that a significant fraction of the equations of state — the ones that do not include the capability for rapid cooling at higher masses — can be ruled out.

The researchers capitalized on some neutron stars in the study being located in supernova remnants, including 3C 58. Since astronomers have age estimates of the supernova remnants, they also have the ages of the neutron stars that were created during the explosions that created both the remnants and the neutron stars. The astronomers found that the neutron star in 3C58 and two others were much cooler than the rest of the neutron stars in the study.

The team thinks that part of the explanation for the rapid cooling is that these neutron stars are more massive than most of the rest. Because more massive neutron stars have more particles, special processes that cause neutron stars to cool more rapidly might be triggered.

One possibility for what is inside these neutron stars is a type of radioactive decay near their centers where neutrinos — low mass particles that easily travel through matter — carry away much of the energy and heat, causing rapid cooling. Another possibility is that there are types of exotic matter found in the centers of these more rapidly cooling neutron stars.

These are objects that seem to just get more interesting the more scientists look at them!