The Identification of a Neutron Star from a Supernova
In 1987, a massive star explosion occurred in a nearby galaxy. The star, up to 20 times more massive than our Sun, exploded with such force that it was visible to the naked eye from Earth’s southern hemisphere for weeks. After years of research and analysis, scientists have now confirmed the descendant of this supernova – a neutron star.
Discovering Evidence of a Neutron Star
Two instruments on the James Webb Space Telescope (JWST) have been pivotal in this discovery. Observing the supernova at infrared wavelengths, these instruments detected chemical evidence involving argon and sulfur atoms. This evidence suggested that the newborn neutron star was hidden behind debris leftover from the explosion. The findings were announced by scientists on a Thursday, without specifying the exact date.
These types of supernovae explosions can create either a black hole or a neutron star. In this case, the observations made by Webb have helped solve the puzzle surrounding this particular supernova.
Tracking Supernovae and Their Aftermath
“After tracking supernovae and searching for a compact object for more than three decades, it is exciting to finally find the missing evidence for a neutron star, thanks to JWST,” said astrophysics professor Claes Fransson of Stockholm University, lead author of the study published in the journal Science.
Study co-author Patrick Kavanagh, a lecturer in experimental physics at the University of Maynooth in Ireland, described neutron stars as “the immensely dense compact remnants of the explosion of a massive star.” He explained that their density is equivalent to compressing the entire mass of the sun into the size of a city. “They’re so dense that a spoonful of a neutron star can weigh a mountain,” he added.
About Supernova 1987A
The supernova in question, named 1987A, occurred 160,000 light-years from Earth in the Large Magellanic Cloud, a dwarf galaxy in the neighborhood of our Milky Way. The star had a relatively short lifetime of about 20 million years due to its large mass, significantly less than our Sun.
Light from the explosion reached Earth on February 24, 1987, a day after a supernova explosion of neutrinos was detected. Neutrinos are subatomic particles produced in huge quantities when the core of a large star collapses. This was the first time since 1604 that a supernova was visible to the naked eye.
The Aftermath of a Supernova
Stars at least eight to ten times more massive than the Sun end their lives in supernovae, scattering much of their matter into space after their core collapses. Despite being catastrophic, these explosions are the main sources of the chemical elements, including carbon, oxygen, silicon and iron, that make life possible.
The remaining matter can form either a neutron star or a black hole, depending on the size of the collapsed star. A black hole is an object whose gravitational pull is so strong that even light cannot escape.
Confirming the Existence of a Neutron Star
In the case of supernova 1987A, the size of the star and the duration of the neutrino burst suggested that the remnant was a neutron star. However, until now, there was no direct evidence to confirm this.
“Direct evidence for any of these exotic objects has never been found so soon after a supernova explosion, until now,” said Kavanagh.
Using Webb’s instruments, scientists detected argon and sulfur atoms that had their outer electrons stripped, or “ionized.” By studying different scenarios, they determined that these atoms could have remained there in that state only with ultraviolet and X-ray radiation from the neutron star.
Next Steps
Scientists are now working to determine what type of neutron star it is: a fast-rotating type called a pulsar with a strong magnetic field, or a more subdued one with a weak magnetic field.
This discovery is another great achievement by Webb, which began operations in 2022.
