Cosmic puzzle solved: Scientists confirm star formed after Supernova explosion

By James Gamble via SWNS

A Supernova explosion nearly 40 years ago formed a neutron star instead of a black hole, suggests a new study.

An international research team believes they now have conclusive proof that the Supernova 1987A explosion 37 years ago formed a neutron star - the densest matter in the known universe.

Using highly sophisticated space telescopes, astronomers finally discovered evidence of a central source of radiation behind the obscuring space dust resulting from the huge explosion.

The discovery marks the first time in history scientists have been successful in probing the center of a supernova to find what has been left behind.

Supernovae are the spectacular and colossal explosions of stars up to 10 times the mass of our own Sun.

They are the main sources of the chemical elements such as carbon, oxygen, silicon, and iron that make life possible.

The collapsed core of these exploding stars can result in much smaller neutron stars, composed of the densest matter in the known universe, or black holes.

Supernova 1987A, located in a neighboring dwarf galaxy called the Large Magellanic Cloud, was the nearest, brightest supernova seen in the night sky in 400 years.

Exploding on February 23, 1987, at a distance of 160,000 light years, it was the closest supernova since the last naked-eye supernova observed by German astronomer Johannes Kepler back in 1604.

The 1987 supernova could be seen with the naked eye from Earth for several months before it faded.

It's the most studied and best-observed supernova ever and, more importantly, it's the only supernova to have been detected via its neutrinos.

These unimaginably small sub-atomic particles were produced in the supernova and detected on Earth the day before it was seen, indicating that a neutron star must have formed.

However, it has not been known until now whether the neutron star persisted or collapsed into a black hole, as the star has been obscured by dust that formed after the explosion.

In their new study, published in the journal Science, researchers from across the world used two instruments on NASA's James Webb Space Telescope (JWST) to observe the supernova at infrared wavelengths.

The telescope, which orbits the Sun a million miles away from the Earth, found evidence of heavy argon and sulfur atoms, the outer electrons of which had been stripped off - or 'ionized' - close to where the star explosion occurred.

The researchers modeled various scenarios and found that these atoms could only have been ionized by ultra-violet and X-ray radiation from an incredibly hot, cooling neutron star, or else from the winds of relativistic particles accelerated by a rapidly rotating neutron star and interacting with surrounding supernova material.

If the former scenario is true, the surface of the neutron star would be around a million degrees, having cooled down from 100 billion degrees or so at the moment of formation at the core of the collapse more than 30 years ago.

Professor Mike Barlow, a co-author of the study from the University College London's Physics & Astronomy department, explained: "Our detection with James Webb’s spectrometers of strong ionized argon and sulfur emission lines from the very center of the nebula that surrounds Supernova 1987A is direct evidence of the presence of a central source of ionizing radiation.

"Our data can only be fitted with a neutron star as the power source of that ionizing radiation.

“This radiation can be emitted from the million-degree surface of the hot neutron star, as well as by a pulsar wind nebula that could have been created if the neutron star is rapidly spinning and dragging charged particles around it.

“The mystery over whether a neutron star is hiding in the dust has lasted for more than 30 years and it is exciting that we have solved it.

“Supernovae are the main sources of chemical elements that make life possible – so we want to get our models of them right.

"There is no other object like the neutron star in Supernova 1987A, so close to us and having formed so recently.

"Because the material surrounding it is expanding, we will see more of it as time goes on.”

Professor Claes Fransson, the lead author of the study from Sweden's Stockholm University, added: “Thanks to the superb spatial resolution and excellent instruments on JWST we have, for the first time, been able to probe the center of the supernova and what was created there.

“We now know that there is a compact source of ionizing radiation, most likely by a neutron star.

"We have been looking for this from the time of the explosion, but had to wait for JWST to be able to verify the predictions.”

Dr. Patrick Kavanagh, another author of the study from Maynooth University in Ireland, described the discovery, the likes of which have never been seen before, as 'special'.

“It was so exciting looking at the JWST observations of SN 1987A for the first time," he said.

"As we checked the MIRI and NIRSpec data, the very bright emission from argon at the center of SN 1987A jumped out.

"We knew immediately that this was something special that could finally answer the question of the nature of the compact object."

Models from the research team, which included scientists from the UK, US and all across Europe and Scandinavia, indicate that heavy argon and sulfur atoms are produced in great abundance due to nucleosynthesis inside massive stars immediately before they explode.

While most of the mass of the exploding star is now expanding at up to 10,000km per second and is distributed over a large volume, the ionized argon and sulfur atoms were observed at close to the center where the explosion occurred.

The ultraviolet and X-ray radiation which is thought to have ionised the atoms was predicted in 1992 to be a unique signature of a newly created neutron star.

These ionized atoms were detected by James Webb’s MIRI and NIRSpec instruments using a technique called spectroscopy, where light is dispersed into a spectrum, enabling astronomers to measure light at different wavelengths to determine an object’s physical properties, including its chemical composition.

Professor Josefin Larsson, another co-author from the Royal Institute of Technology in Sweden, said: “This supernova keeps offering us surprises.

"Nobody had predicted that the compact object would be detected through a super strong emission line from argon, so it's kind of amusing that that’s how we found it in the JWST.”