Protons Have Surprising Influence On Neutron Stars

Posted: Aug 16 2018, 11:15am CDT | by , Updated: Aug 16 2018, 11:18am CDT , in Latest Science News


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Protons have Surprising Influence on Neutron Stars
Credit: MIT

New study says that protons may have an outsize influence on the properties of neutron stars and other similar objects

Neutron stars are the smallest and densest objects in the universe. They are actually the stellar remnants that come from the gravitational collapse of extremely massive stars. Neutron stars, as the name suggests, are made up almost entirely of neutrons, a neutral subatomic particles. These stars also contain positively charged particles called protons but these particles account for just 5 percent of a neutron star.

Protons and neutrons make up the nucleus of an atom and can form a pair if they are close enough to each other. The pairs are held together by powerful nuclear forces. Such “short-range correlations,” highly influence the properties of a given atomic nucleus. However, the interaction between these two subatomic particles is far less well understood.

To better understand the process, researchers looked into proton and neutron pairs in atoms of carbon, aluminum, iron and lead with a progressively higher ratio of neutrons to protons. Researchers found that the presence of more neutrons increase the probability that a proton would form an energetic pair. But the likelihood that a neutron would pair up stayed about the same. It shows that protons or positively charged particles may have a disproportionally large impact on the properties of neutron stars and other objects with high densities of neutrons.

“We think that when you have a neutron-rich nucleus, on average, the protons move faster than the neutrons, so in some sense, protons carry the action,” said study co-author Or Hen from MIT. “We can only imagine what might happen in even more neutron-dense objects like neutron stars. Even though protons are the minority in the star, we think the minority rules. Protons seem to be very active, and we think they might determine several properties of the star.”

MIT researchers based their study on data collected by CLAS, a particle accelerator and detector in Jefferson Laboratory in Virginia. They only used archived data for signs of short-range correlations obtained from an experiment in 2004. In that experiment, researchers fired beams of electrons at carbon, aluminum, iron, and lead atoms and observed how particles produced in nuclear interactions travel through each atom’s respective volume. Each of the four types of atoms had different ratios of neutrons to protons in their nuclei, with carbon having the fewest neutrons and lead having the most. Researchers investigated whether the probability of this pairing changed as the ratio of neutrons to protons increased.

“We wanted to start from a symmetric nucleus and see, as we add more neutrons, how things evolve,” said Hen. “We would never get to the symmetries of neutron stars here on Earth, but we could at least see some trend and understand from that, what could be going on in the star.”

Researchers found that as the number of neutrons in an atom’s nucleus increased, the probability of protons having paired up with a neutron also increased significantly, while the same did not go for neutrons. The trend, however, may extend to the behavior of neutron stars.

“All these properties then affect how two neutron stars merge together, which we think is one of the main processes in the universe that create nuclei heavier than iron, such as gold,” said Hen. “Now that we know the small fraction of protons in the star are very highly correlated, we will have to rethink how (neutron stars) behave.”

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<a href="/latest_stories/all/all/47" rel="author">Hira Bashir</a>
The latest discoveries in science are the passion of Hira Bashir (). With years of experience, she is able to spot the most interesting new achievements of scientists around the world and cover them in easy to understand reporting.




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