When a star explodes, it collapses before the outer layer explodes into space. The compression of the core turns it into a very dense object, while the mass of the sun is compressed into an object only about 10 miles wide. These objects are called neutron stars because they are made almost entirely of densely packed neutrons. They are laboratories of extreme physics and cannot be replicated on earth.
A rapidly rotating and highly magnetized neutron star is called a pulsar, which produces a beam of radiation similar to a lighthouse. When astronomers rotate it across the sky, astronomers will detect it as a pulse. Some pulsars generate wind from their surface, sometimes at a speed close to the speed of light, forming a complex structure of charged particles and magnetic fields, called “pulse wind nebulae.”
Through Chandra and NuSTAR, the research team discovered that relatively low-energy X-rays from SN 1987A fragments hit the surrounding material. The team also used NuSTAR’s ability to detect more high-energy X-rays to find evidence of high-energy particles.
There are two possible explanations for this high-energy X-ray emission: a pulsar nebula, or explosive waves that accelerate particles to high energy. The latter effect does not require pulsars and will occur at greater distances from the center of the explosion.
The latest X-ray research has provided support for the pulsar nebula by demonstrating two aspects of the explosion sound wave acceleration scheme, which means that neutron stars must exist. First, between 2012 and 2014, the brightness of high-energy X-rays remained almost the same, while the radio emissions detected by the Australian telescope’s compact array increased. This violated expectations for the explosion wave scenario. Next, the authors estimate that it will take about 400 years to accelerate the electron to the highest energy seen in the NuSTAR data, and the energy of the NuSTAR data is more than 10 times the age of the remaining atoms.
“Astronomers want to know if there is not enough time to form a pulsar, or even SN 1987A caused a black hole,” said co-author Marco Miceli from the University of Palermo. “This has been a mystery for decades, and we are very happy to bring new information to the table and achieve such results.”
Chandra and NuSTAR data also support ALMA’s 2020 results, which provide possible evidence for the structure of the millimeter wave band pulsar nebula. Although there are other possible explanations for this “spot”, new X-ray data can confirm that it is a pulsar nebula. This more evidence supports the idea of leaving neutron stars.
If it is indeed the pulsar at the center of SN 1987A, it will be the youngest pulsar in history.
“It is unprecedented to be able to observe pulsars in essence,” said Salvatore Orlando, co-author of the Palermo Observatory, a research institute at the National Institute of Astrophysics (INAF) in Italy. “It may be a golden opportunity to study the development of baby pulsars.”
The center of SN 1987A is surrounded by gas and dust. The author uses the most advanced simulation method to understand how this material absorbs X-rays of different energies, so that the X-ray spectrum can be explained more accurately, that is, the number of X-rays at different energies. This allowed them to estimate the spectrum of the central region of SN 1987A without obstructing materials.
Normally, more data is needed to enhance the advantages of pulsars. In future observations, the increase in radio waves and the increase in relatively high-energy X-rays will contradict this view. On the other hand, if astronomers observe a reduction in high-energy X-rays, they will confirm the existence of a pulsar nebula.
The stellar debris around the pulsar plays an important role by absorbing a large amount of its lower-energy X-ray radiation and cannot be detected at present. The model predicts that this material will diffuse in the next few years, which will reduce its absorption capacity. Therefore, the pulsar emission is expected to appear about 10 years later, which reveals the existence of neutron stars.
A paper describing these results will be published in the Astrophysical Journal this week, and preprints are available online. The other authors of the paper are Barbara Olmi and Fabrizio Bocchino, also from INAF-Palermo. Shigehiro Nagataki and Masaomi Ono of the Big Bang Laboratory of Riken Astrophysics, Japan; Akira Dohi of Kyushu University, Japan, and Giovanni Peres of Palermo University.
NASA’s Marshall Space Flight Center manages the Chandra program. The Chandra X-ray Center of the Smithsonian Astrophysical Observatory controls science in Cambridge, Massachusetts and flight operations in Burlington, Massachusetts.
NuSTAR is a small explorer mission led by the California Institute of Technology (Caltech), managed by the Jet Propulsion Laboratory of the National Aeronautics and Space Administration (NASA), and used by the agency’s scientific mission committee in Washington. NuSTAR was developed in cooperation with the Technical University of Denmark and the Italian Space Agency (ASI). The spacecraft was manufactured by Orbital Sciences, based in Dulles, Virginia (now part of Northrop Grumman). NuSTAR’s mission operations center is located at the University of California, Berkeley, and the official data archive is located at NASA’s High Energy Astrophysics Science Archive Research Center. ASI provides mission ground stations and mirror archives. JPL is a division of California Institute of Technology.