Science, Tech, Math › Science Neutron Stars and Pulsars: Creation and Properties Share Flipboard Email Print This image of the crab nebula depicts the X-ray emission from the central pulsar of the region. Image Credit: NASA Science Astronomy Stars, Planets, and Galaxies An Introduction to Astronomy Important Astronomers Solar System Space Exploration Chemistry Biology Physics Geology Weather & Climate By John P. Millis, Ph.D Professor of Physics and Astronomy Ph.D., Physics and Astronomy, Purdue University B.S., Physics, Purdue University John P. Millis, Ph.D. is a professor of physics and astronomy at Anderson University. He conducts research at the VERITAS gamma-ray observatory in southern Arizona. our editorial process John P. Millis, Ph.D Updated November 15, 2017 What happens when giant stars explode? They create supernovae, which are some of the most dynamic events in the universe. These stellar conflagrations create such intense explosions that the light they emit can outshine entire galaxies. However, they also create something much weirder from the leftover: neutron stars. The Creation of Neutron Stars A neutron star is a really dense, compact ball of neutrons. So, how does a massive star go from being a shining object to a quivering, highly magnetic and dense neutron star? It's all in how stars live their lives. Stars spend most of their lives on what is known as the main sequence. The main sequence begins when the star ignites nuclear fusion in its core. It ends once the star has exhausted the hydrogen in its core and begins fusing heavier elements. It's All About Mass Once a star leaves the main sequence it will follow a particular path that is pre-ordained by its mass. Mass is the amount of material the star contains. Stars that have more than eight solar masses (one solar mass is equivalent to the mass of our Sun) will leave the main sequence and go through several phases as they continue to fuse elements up to iron. Once the fusion ceases in a star's core, it starts to contract, or fall in on itself, due to the immense gravity of the outer layers. The outer part of the star "falls" onto the core and rebounds to create a massive explosion called a Type II supernova. Depending on the mass of the core itself, it will either become a neutron star or black hole. If the mass of the core is between 1.4 and 3.0 solar masses the core will only become a neutron star. The protons in the core collide with very high-energy electrons and create neutrons. The core stiffens and sends shock waves through the material that is falling onto it. The outer material of the star is then driven out into the surrounding medium creating the supernova. If the leftover core material is greater than three solar masses, there's a good chance that it will continue to compress until it forms a black hole. Properties of Neutron Stars Neutron stars are difficult objects to study and understand. They emit light across a broad part of the electromagnetic spectrum—the various wavelengths of light—and seem to vary quite a bit from star to star. However, the very fact that each neutron star appears to exhibit different properties can help astronomers understand what drives them. Perhaps the greatest barrier to studying neutron stars is that they are incredibly dense, so dense that a 14-ounce can of neutron star material would have as much mass as our Moon. Astronomers have no way of modeling that kind of density here on Earth. Therefore it's difficult to understand the physics of what is going on. This is why studying the light from these stars is so important because it gives us clues as to what is going on inside the star. Some scientists claim that the cores are dominated by a pool of free quarks—the fundamental building blocks of matter. Others contend that the cores are filled with some other type of exotic particle like pions. Neutron stars also have intense magnetic fields. And it is these fields that are partially responsible for creating the X-rays and gamma rays that are seen from these objects. As electrons accelerate around and along the magnetic field lines they emit radiation (light) in wavelengths from optical (light we can see with our eyes) to very high energy gamma-rays. Pulsars Astronomers suspect that all neutron stars rotate and do so quite rapidly. As a result, some observations of neutron stars yield a "pulsed" emission signature. So neutron stars are often referred to as PULSating stARS (or PULSARS), but differ from other stars that have variable emission. The pulsation from neutron stars is due to their rotation, where as other stars that pulsate (such as cephid stars) pulsate as the star expands and contracts. Neutron stars, pulsars, and black holes are some of the most exotic stellar objects in the universe. Understanding them is only part of learning about the physics of giant stars and how they are born, live, and die. Edited by Carolyn Collins Petersen.