Description: BYU Professors Neilsen and Hirschmann are conducting theoretical research on interacting deep space objects, like neutron stars and black holes, and simulating the impact they can have on a galactic scale.
- Sponsor: NASA
- Principal Investigator: David Neilsen
- Co-PI: Eric Hirschmann
David Neilsen and Eric Hirschmann, two Associate Professors at BYU, are collaborating with Indiana University to research black holes and neutron stars. Dr. Neilsen has worked in the fields of numerical relativity, fluid dynamics, and relativistic astrophysics for over 15 years, and Dr. Hirschmann specializes in general relativity, nonlinear field theories, and computational physics. The focus of the project is to develop and use a computer platform with the capacity to simulate scenarios of merging neutron stars, as well as neutron stars with black holes. Additionally, the team has developed materials that solve several Einstein and relative MHD equations. (MHD stands for Magnetohydrodynamics, which comes from the Greek forms of “magneto” for magnetic fields, “hydro” for plasmas, liquid metals, et al., and “dynamics” for movement and power.) Over time, they hope these highly-coded simulations will consistently play-out, which will help solidify many theories and laws of physics.
Neutron stars are the remaining debris from a supernova star explosion. This stellar outburst sends a shock wave of material and light into the surrounding space, and what remains may become a new formation – a neutron star. In this neutron star, the protons and electrons (atomic particles) are pressed so tightly, they basically melt into each other to form neutrons— hence the name. Some neutron stars are two or three times the mass of our sun, but condensed into a radius of 10-20 kilometers (the sun has a radius of nearly 700,000 kilometers). Therefore, these objects are extremely dense and compact, with an overwhelming gravitational pull. It is hypothesized that in order to escape the gravitational attraction of these neutron stars, an object would have to be moving between a third and half the speed of light!
Neutron stars, and especially those in binary systems, can be very informative to scientists. “Binary” indicates that there are two objects— typically stars— that share a system and are close enough for their gravities to interact. Because these objects are close, calculations can be made of their orbits, which can lead to better estimates of mass, radius, and density than if they existed in their own system.
Around 5% of all discovered neutron stars are in a binary system, and about half of all visible systems contain multiple stars. Black holes are not easily observable, with only a handful being firmly identified, but it is estimated that within the Milky Way galaxy, there are about 100 million, contrasting the estimated 100 billion stars. Therefore, the event of merging/collapsing objects becomes more valid and a good investment for study.
Dr. Neilsen’s team is running detailed simulations of these merging events, coding in various types of astrophysical environments. Of note is their inclusion of stars’ and black holes’ magnetic fields, which past research has often overlooked. Also, they are extensively looking at the disk-like structures that gather around the merged objects (which this team calls accretion tori). For the future, they are developing codes that can calculate a single magnetized neutron star.
Their current results show two types of merging between two neutron stars: one scenario shows a quick collapse of the two stars, producing a black hole. In the other scenario, the merged stars initially form one star with a new rotation, and then later collapses into a black hole. Establishing consistent simulations will lead to firmer predictions and deeper-understood observations. While the research is still ongoing, it is reiterated that new technologies have the potential to resolve huge questions of nuclear and astronomical physics.
This information is essential in understanding the structure, formation, population and movement within our universe. These findings will support the science in projects like the upcoming LISA mission. LISA (the Laser Interferometer Space Antenna) is a team project between NASA (National Aeronautics and Space Administration) and ESA (the European Space Agency) to create a way to detect the thousands of black holes and binaries in our stellar neighborhood. Other ongoing NASA missions that will also be impacted by this research include: the GRB probe Swift, the gamma ray observatory Fermi, the space telescope Hubble, and the X-ray observatory Chandra.