Expanding our Knowledge of Pulsars and Magnetars Prof Nanda Rea of the ERC MAGNESIA Project is taking a fresh look at the pulsar population, including highly magnetised neutron stars called Magnetars, to understand how many there are, how they evolve and how we can use pulsars for technologies that will benefit us. Simulation representing all the pulsars. Credit: Nanda Rea
As one of the most extreme objects in the Universe, highly magnetised neutron stars known as magnetars are almost impossible to imagine. About 20 kilometres in diameter, they have a density equating to about a billion tonnes for an area the size of a sugar cube, and spin at phenomenal rates. They have a hard iron lattice exterior and inside them, the protons and electrons have crushed into neutrons. Their huge magnetic-field instabilities trigger emissions of electromagnetic radiation, like X-rays and gamma rays. They are thought to be also related to phenomena like Gamma-Ray Bursts (GRBs) and Fast Radio Bursts (FRBs). Discovered in the late ’70s via their powerful gamma-ray flares, we now know they share similarities with other pulsars in many ways. There is a lot that is not known about the pulsar population, and exact reach of the magnetars, and that’s why a team of researchers for the EU project, MAGNESIA, are tasked with collecting more data and information on what they are, simulate how many of them there are and how they can be of use to us.
A New Era of Discovery Magnetars differ from standard neutron stars as they have a much higher magnetism. Due to their incredible magnetised state, movement and density, they tend to erupt, quake and crack on the surface as they spin, releasing spectacular bursts of energy. They emit and flare when they spin, making them highly visible reference points in the void. “There are a lot of different kinds of neutron stars,” explained Prof. Rea. “However, they
are all formed the same way, have the same equation of state, that’s what we think for now. They form from supernova explosions when a very massive star ends its life. At a certain point inside, it reaches the iron limit, then it explodes, and the core becomes compact. We observe some differences in neutron stars when compared, for example, they don’t all emit in the same way. This indicates that some process happened or there are parameters at birth or in their evolution, so something
occurs to make a star extraordinarily bright, or alternatively very faint.” These differences in neutron stars have traditionally made them easy to miss. As the scientific community grasps more of an understanding of them and importantly, how they differ, new instrumentation is being developed to detect them more accurately. With advances, in the last 10 years, there have been thousands of discoveries, yet it’s becoming apparent this is only the beginning of the search in a lively Universe. Magnetars, the most magnetic extremes of the population, have become a source of many recent scientific revelations. For example, Fast Radio Bursts (FRBs), were powerful radio flashes or pulses, that were first seen in radio surveys around 2007 and when the first one was observed it was a complete mystery – it was even proposed early on that it could be signalling from ‘little green men’. It was a very bright signal, equal to the release of three days of the Sun’s output in a mere millisecond. The scientific community responded to solve the mystery and built radio sky-monitoring instruments to see if there were similar signals and subsequently discovered there were thousands. Only few years ago it was realised for the first time that magnetars and FRBs were related to each other. Furthermore, it was well known that magnetar flares were possibly related to other transient events like Gamma-
Ray Bursts (GRBs). With these new connections understood the hunt was on to discover more. “We use data from X-ray satellites, gamma ray satellites and radio telescopes mainly to detect more of them”, said Prof. Rea.
Map of the Stars One of the aims of the project is to create a census and model the distribution of the neutron stars, to essentially create a map of these galactic objects to understand how many exist and their population properties at birth. “We aim to predict the properties and numbers of these, in our galaxy and beyond and even those we cannot see for various reasons, such as if they are too faint to be observed, or they are behind the galactic centre.” One of the main goals is to know how big the population of these stars is, with the different magnetic fields they have at birth, and the different rotations and properties. The project is looking at the evolution of neutron stars, a subject that is arguably more related to nuclear physics than astrophysics. To do this, the team have to simulate a neutron star field evolution to fully understand its lifecycle and the variables that define it. Further, they are aiming to predict how many of them there are, how old they are and to reveal what their magnetic fields look like when they are older. The only way to do this is by devising accurate simulations, with new techniques such as machine learning.
Credit: Tomasz Nowakowski, Astrowatch.net
“With current standard instrumentation, we can observe only about three thousand pulsars, and a few tens of magnetars, and we expect there to be around ten million of them in total, so what we observe is really the tip of an iceberg. You need to know the physics of how those sources emit and how they are evolving in time.” In an innovative approach to the challenge, the latest knowledge of 3D magnetic field evolution, numerical modelling, nuclear physics and flaring rates is combined and fed into a computer model, in turn making it easier to create a realistic representation of the pulsar population. Graphic simulations are created with a computer, and machine learning is used for testing the outcomes and results.
Spin-off Technology Whilst developing a better understanding of these stars and uncovering their whereabouts is exciting fuel for our knowledge of the Universe, the unique nature of pulsars also means they have a practical use that could help us reimagine Global Positioning Systems (GPS) and even help us navigate in deep space.
“ The idea is that each of these sources has its own signal which is unique like someone’s DNA. They can be so bright that wherever you are in space, you can detect them and use them as a reference.”
Credit: Shackleton Books/ Gallego Bros
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www.euresearcher.com
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Magnesia The magnetar census and impact of highly magnetic neutron stars on the explosive and transient Universe
The MAGNESIA group organizing the COST Action PHAROS Annual Meeting in Rome in 2022.
Project Objectives
Neutron stars, or pulsars, are amongst the most extreme stars, wielding the largest magnetic fields of any known object in the Universe. The most magnetic ones are called magnetars. These stars are thought to be the source of the most luminous transients, such as the super-luminous supernovae, gamma-ray bursts, fast radio bursts, or magnetar giant flares. Several giant flares have been detected within the Milky Way. However, scientists lack a complete census of the pulsar and magnetar population. The EU-funded MAGNESIA project is developing the first pulsar population model using Machine Learning techniques. The new model will take into account neutron star 3D magnetic field simulations and observational constraints from all multiband data archives.
Project Funding
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement ID: 817661
Project Partners
https://www.ice.csic.es/ercmagnesia/group-members/whilst
Contact Details
Project Coordinator, Professor Nanda Rea Head of the Astrophysics and Planetary Department Institute of Space Sciences (ICE-CSIC, IEEC) T: +34 937 37 97 88 E: rea@ice.csic.es W: www.ice.csic.es Professor Nanda Rea
Nanda Rea is a Professor of the Spanish National Research Council (CSIC) at the Institute of Space Sciences (ICE) in Barcelona, Spain. Nanda Rea was part of the ESA Astronomy Working Group that advises the ESA director on proposals for new space missions, and a member of the ESA Athena Science Study Team. She has won numerous awards and served in over 40 committees, many of them as Chair. In 2018 she obtained an ERC Consolidator grant from H2020 to work on the Galactic neutron star population and its connection with the transient Universe.
Working with the European Space Agency (ESA) and two industrial companies on the PODIUM Project, Prof. Rea is helping with the creation of new innovations that could change how we use certain types of technology, forever. “The idea is that each of these sources has its own signal which is unique like someone’s DNA. They can be so bright that wherever you are in space, you can detect them and use them as a reference. Wherever you are in the galaxy you can recognise a sort of map of these and know which ones are closest to you and which are the ones furthest, so you can calculate your own position.” A test of this practical use came in 2018, when an instrument about the size of a washing machine was put in the International Space Station (ISS). It was an X-ray counter which looked at X-ray energies and had software to track pulsars and use these timing signals to calculate the precise position of the ISS in space, as it moved at 24,000 km per hr. The device worked perfectly. ESA has since been investing in research to make this technology smaller to fit into any satellites, and eventually, it is hoped in a far future, to be small enough to be fitted in smartphones.
“We now have a prototype of an instrument which instead of being the size of a washing machine is more like the size of a microwave, which is very compact. We might not need to send strings of satellites to orbit in the future to enable the use of GPS. Many countries cannot afford to send up all these satellites, so relying on a pulsar in the sky instead is an attractive alternative. Also, if we ever want to leave the solar system and explore deep space, this is one way to be able to navigate back without being lost.” The practical applications of this positioning technology are exciting for engineers and innovators, and these are merely the beginnings of broad studies of pulsars in general. The everbuilding map and understanding of these objects and other unusual signals being detected will increase over time. As a relatively new field, it’s no surprise that discoveries are happening regularly and seem destined to continue to do so. “We are recently finding very bright and slowly periodic radio signals in the sky and they are probably not regular pulsars, we just don’t know, because there is nothing comparable that produces these kinds of emissions. There are still these ongoing open mysteries and so there is much still to discover.”
Magnetars figure. Credit: ICRAR
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