In the fall of 1967, John Archibald Wheeler, a great Princeton quantum physicist, gave a lecture at a pulsator at a conference arguing that we should consider the center of the pulsar as a gravitationally completely collapsed object. He noted that one cannot keep saying a “gravitationally completely collapsed object” over and over again. So we need a shorter descriptive phrase. “What about the black hole?” someone in the audience asked and gave birth to the name of one of the most paradoxical objects in the universe.
Ahead of 2020, two teams of astronomers looking for the missing compact object to form in the remnants of the 1987A Supernova double-blast explosion led them to wonder if a black hole had collapsed instead of a neutron star. Based on observations from the Atacama Large Millimeter / submillimeter Array (ALMA) and a theoretical follow-up study, a compelling case of a 33-year mystery emerged. Scientists provide a new perspective on the argument that a neutron star is hidden deep in the remnants of an exploded star – the youngest neutron star ever known.
Because particles known as neutrinos were discovered on Earth on February 23, 1987, astronomers expected a neutron star to form in the collapsed center of the star. When scientists found no evidence for the star, they began to wonder if it could be Wheeler’s “gravitationally completely collapsed object.” For decades, the scientific community has been impatiently waiting for a signal from this object, which is hidden behind a very dense cloud of dust.
“Blob” in the core of SN 1987A
Observations from the ALMA radio telescope recently provided the first indication of a missing neutron star after the explosion. The high-resolution images revealed a hot drop in the dust core of the SN 1987A, which is brighter than its surroundings and coincides with the suspicion of the location of a neutron star.
“We were very surprised to see this warm blob formed by a dense cloud of dust in the rest of the supernova,” said Mikako Matsuura of Cardiff University and a member of the team that found the blob with ALMA. “There must be something in the cloud that heats the dust and makes it radiant. Therefore, we have suggested that a neutron star is hiding inside a cloud of dust. “
The high-resolution ALMA images above revealed a hot drop in the dusty core of the 1987A Supernova (insert), which could be the location of a missing neutron star. The red color shows dust and cold gas in the middle of the remnant of the supernova, taken at radio wavelengths with ALMA. The shades of green and blue reveal where a propagating shock wave from an exploded star collides with a ring of material around the supernova. Green represents the glow of visible light captured by NASA’s Hubble Space Telescope. The blue color reveals the hottest gas and is based on data from NASA’s Chandra X-ray Observatory. The ring was originally made to glow with a flash of light from the original explosion. In the following years, the annular material became much brighter when it was hit by a shock wave of explosion.
Although Matsuura and her team were excited about this result, they thought about the brightness of the block. “We thought the neutron star might be too bright to exist, but then Dany Page.” [an astrophysicist at the National Autonomous University of Mexico] and his team published a study that suggested that a neutron star could indeed be so bright because it is so young, ”Matsuura said.
“When I became a supernova, I was halfway there, when I became a supernova,” Page said, “it was one of the biggest events in my life that forced me to change the course of my career to try to solve this mystery. It was like a modern holy grail. “
“Despite the supreme complexity of the supernova explosion and the extreme conditions inside the neutron star, the detection of hot dust dust confirms several predictions,” Page and his Team, published today in The Astrophysical Journal, strongly support the ALMA team’s proposal that the neutron star the star drives a dust ball.
Forecasts – location and temperature
These predictions were the location and temperature of the neutron star. According to computer models, the supernova explosion “launched” a neutron star from its birthplace at hundreds of kilometers per second (tens of times faster than the fastest rocket). The block is exactly where astronomers think the neutron star will be today. And the temperature of the neutron star, which was supposed to be around 5 million degrees Celsius, provides enough energy to explain the brightness of the drop.
“Probably not Pulsar”
“The power of the pulsar depends on the speed of rotation and the strength of the magnetic field, which should have very precisely tuned values to match the observations, while the thermal energy emitted by the hot surface of a young neutron star is naturally appropriate,” said Page, suggesting that Contrary to current expectations, a neutron star – and a 25 km wide, extremely hot sphere of ultra-dense substances – is probably not a pulsar. A teaspoon of his material would weigh more than all the buildings in New York combined. Because it can only be 33 years old, it would be the youngest neutron star ever found. The second youngest neutron star we know of is in the remnant of the supernova Cassiopeia A and is 330 years old.
“The neutron star is behaving exactly as we expected,” added James Lattimer of Stony Brook University in New York and a member of Page’s research team. The lattimer also closely monitored SN 1987A and published predictions of the supernova neutrino signal before SN 1987A, which subsequently matched the observations. “These neutrinos suggest that the black hole never formed, and moreover, it seems difficult for the black hole to explain the observed brightness of the drop. We compared all the possibilities and came to the conclusion that the most likely explanation is a hot neutron star. “
Waiting for dust balance
Only a direct image of a neutron star would provide definitive proof that it exists, but astronomers may have to wait decades before the dust and gas in the rest of the supernova become transparent.
Although many telescopes have taken SN 1987A images, none of them have been able to observe their core with the same accuracy as ALMA. Previous (3-D) observations with ALMA have already shown the types of molecules found in the rest of the supernova and confirmed that they produced huge amounts of dust.
“This discovery is based on years of ALMA observations that show an increasingly detailed core of the supernova through continuous improvements in telescope and data processing,” said Remy Indebetouw of the National Radio Observatory and the University of Virginia, who was part of the ALMA imaging team.
Sources: ALMA observation “blob”: “Images of ALMA dust and high angle molecules in Ejecta SN 1987A”, author P. Cigan et al., The Astrophysical Journal. https://doi.org/10.3847/1538-4357/ab4b46
Theoretical study favoring a neutron star: “NS 1987A in SN 1987A”, by D. Page et al., The Astrophysical Journal. https://doi.org/10.3847/1538-4357/ab93c2
Daily galaxy, Max Goldberg, through NRAO
Image credits: Chandra X-Ray Observatory top of the page and insert ALMA (ESO / NAOJ / NRAO), P. Cigan and R. Indebetouw; NRAO / AUI / NSF, B. Saxton; NASA / ESA