In the fall of 1967, Princeton’s great quantum physicist, John Archibald Wheeler, gave a lecture on pulsars at a conference, arguing that we should consider the possibility that the center of a pulsar is a gravitationally completely collapsed object. He noted that one could not go on to say “gravitationally completely collapsed object” over and over again. That we needed a shorter descriptive sentence. “What about black hole?” asked someone in the audience, giving birth to the name of one of the most paradoxical objects in the universe.
Fast forward to 2020, two teams of astronomers searching for a missing compact object that should have formed in the remnants of the two light-year-wide explosion of Supernova 1987A, which led them to wonder if instead of a neutron star had collapsed into a black hole. A compelling case in the 33-year-old mystery has been made based on observations of the Atacama Large Millimeter / Submillimeter Array (ALMA) and a theoretical follow-up study. The scientists provide new insight into the argument that a neutron star hides deep inside the remnants of the exploded star – the youngest neutron star to date.
Lack of evidence
Because particles known as neutrinos were detected on Earth on February 23, 1987, astronomers expected a neutron star to form in the collapsed center of the star. But when scientists could not find any evidence for that star, they began to wonder if it might be Wheeler’s “gravity completely collapsing object.” For decades, the scientific community has been eagerly awaiting a signal from this object that has been hiding behind a very thick cloud of dust.
“Blob” at the core of SN 1987A
Recently, observations from the ALMA radio telescope gave the first indication of the missing neutron star after the explosion. Extreme high-resolution images revealed a hot “block” in the dusty core of SN 1987A, which is brighter than its surroundings and matches the suspected location of the neutron star.
“We were very surprised to see this hot brick made of a thick cloud of dust in the supernova remnant,” said Mikako Matsuura of Cardiff University and a team member who found the blob with ALMA. “There must be something in the cloud that has heated the dust and made it shine. Therefore, we suggested that there was a neutron star hidden inside the dust cloud. “
Extreme high-resolution ALMA images above revealed the hot “block” of the dusty core of Supernova 1987A (insertion), which could be the location of the missing neutron star. The red color shows dust and cold gas in the center of the supernova remnant, taken at radio wavelengths with ALMA. The shades of green and blue reveal where the expanding shock wave from the exploded star collides with a ring of material around the supernova. The 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 from the flash of the original explosion. Over the course of subsequent years, the ring material is significantly lightened as the shock wave of the explosion slams into it.
Although Matsuura and her team were excited about this result, they wondered about the brightness of the globe. “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 indicated that the neutron star can really be so bright because it is so very young, ”Matsuura said.
“I was halfway through my PhD when the supernova happened,” Page said, “it was one of the biggest events of my life that made me change the course of my career to try to solve this mystery. . It was like a modern holy grail. “
“Despite the overall complexity of a supernova explosion and the extreme conditions prevailing inside a neutron star, the detection of a hot block of dust is a confirmation of several predictions,” Page explained in the theoretical study of Page and his team, which was published today in The Astrophysical Journal, which strongly supports the proposal made by the ALMA team that a neutron star drive the lump of dust.
Predictions – Location and temperature
These predictions were the location and temperature of the neutron star. According to supernova computer models, the explosion “kicked away” the neutron star from its birthplace at a speed of hundreds of kilometers per second (tens of times faster than the fastest rocket). The block is exactly where astronomers think the neutron star would be today. And the temperature of the neutron star, which was predicted to be around 5 million degrees Celsius, provides enough energy to explain the brightness of the planet.
“Probably not a Pulsar”
“The strength of a pulse depends on how fast it spins and on its magnetic field strength, both of which must have very finely tuned values to match observations, while the thermal energy emitted from the hot surface of the young neutron star naturally matches data. said Page, suggesting that contrary to popular expectations, the neutron star is a 25 km wide, extremely hot sphere of ultra-dense matter. – probably not a pulsar. A teaspoon of its material would weigh more than all the buildings in New York City 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 located in the supernova remnant 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. Lattimer has also followed SN 1987A closely after publishing before SN 1987A predictions of a supernova’s neutrino signal that subsequently matched observations. “These neutrinos indicated that a black hole was never formed, and it also seems difficult for a black hole to explain the observed brightness of the globe. We compared all possibilities and concluded that a hot neutron star is the most likely explanation. “
Waiting for the dust to settle
Only a direct image of the neutron star would provide clear proof that it exists, but for that, astronomers may have to wait a few more decades until the dust and gas in the supernova remnant become more transparent.
Although many telescopes have made images of SN 1987A, none of them have been able to observe its core with such high precision as ALMA. Previous (3-D) observations with ALMA already showed the types of molecules found in the supernova remnant and confirmed that it produced large amounts of dust.
“This discovery is based on many years of ALMA observations that show the core of the supernova in more and more detail thanks to the continued improvements of the telescope and data processing,” said Remy Indebetouw of the National Radio Astronomy Observatory and University of Virginia, which has been part of ALMA imaging team.
Sources: ALMA observation of the “gap”: “ALMA images with high angular resolution of dust and molecules in SN 1987A Ejecta”, by 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, via NRAO
Image credits: Chandra X-Ray Observatory at the top of the page and deployed ALMA (ESO / NAOJ / NRAO), P. Cigan and R. Indebetouw; NRAO / AUI / NSF, B. Saxton; NASA / ESA