In the fall of 1967, Princeton’s great quantum physicist, John Archibald Wheeler, gave a lecture on pulsars at a conference in which he argued that we should consider the possibility that the center of a pulsar is a gravitationally completely collapsed object. He pointed out that one could not say “gravitationally completely collapsed object” over and over again. That we needed a shorter descriptive phrase. “How about black hole?” asked someone in the audience and gave birth to the name of one of the most paradoxical objects in the universe.
Fast coils until 2020, two teams of astronomers looking for a missing compact object that should have formed in the remnants of the two-light-wide explosion of Supernova 1987A, which made them wonder if instead of a neutron star it had collapsed into a black hole. A convincing 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 remains of the exploded star – the youngest neutron star known so far.
Evidence is missing
Since 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. But when scientists could not find any evidence for that star, they began to wonder if it could be Wheeler’s “gravitationally completely collapsed 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” in Core of SN 1987A
Recently, observations from the ALMA radio telescope gave the first indication of the missing neutron star after the explosion. Extremely high-resolution images revealed a hot “lump” 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 the hot lump made of a thick cloud of dust in the supernova remnants,” said Mikako Matsuura of Cardiff University and a member of the team that found the lump with ALMA. “There must be something in the cloud that has warmed up the dust and made it shine. This is why we suggested that there is a neutron star hiding in dust clouds. “
Extreme high-resolution ALMA images above revealed the hot “lump” in the dusty core of Supernova 1987A (deposit), which may be the site of the missing neutron star. The red color shows dust and cold gas in the middle 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 material ring 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 initially made to glow from the flash of light from the original explosion. In subsequent years, the ring material has brightened considerably when the shock wave of the explosion melts into it.
Although Matsuura and her team were happy with this result, they wondered about the brightness of the lump. “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 young, ”said Matsuura.
“I was halfway through my doctorate 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 highest complexity of a supernova explosion and the extreme conditions prevailing inside a neutron star, the discovery of a hot lump of dust is a confirmation of several predictions,” Page explained in the theoretical study of Page and his team published today in The Astrophysical Journal, which strongly supports the proposal from the ALMA team that a neutron star drift on the dust skull.
The forecasts – Location and temperature
These predictions were the location and temperature of the neutron star. According to supernova computer models, the explosion “kicked” the neutron star from its birthplace at a speed of hundreds of kilometers per second (tens of times faster than the fastest rocket). The lump is exactly where astronomers believe the neutron star to be today. And the temperature of the neutron star, which was predicted to be about 5 million degrees Celsius, provides enough energy to explain the brightness of the lump.
“Probably not a Pulsar”
“The power of a pulse depends on how fast it spins and on its magnetic field strength, both of which must have very fine-tuned values to match the observations, while the heat energy emitted from the hot surface of the young neutron star naturally matches the data,” said Page. Contrary to popular expectations, the neutron star – a 25 km wide, extremely hot ball of ultra-dense matter – is not likely to be a pulsar. A teaspoon of its material would weigh more than all the buildings in New York City combined. Since it can only be 33 years old, it would be the youngest neutron star ever found. The second youngest neutron star we know is located in 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. Lattimer has also followed SN 1987A closely after publishing before SN 1987A predictions about a supernova’s neutrino signal that then matched the observations. These neutrinos suggested that a black hole was never formed, and in addition, it seems difficult for a black hole to explain the observed brightness of the lump. We compared all possibilities and concluded that a hot neutron star is the most likely explanation. “
Waiting for the dust to escape
Only a direct image of the neutron star would give definitive proof that it exists, but for that astronomers may have to wait a few decades until the dust and gas in the supernova remnants become more transparent.
Although many telescopes have taken 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 present in the supernova remnant and confirmed that it produced enormous 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 in the telescope and data processing,” said Remy Indebetouw of the National Radio Astronomy Observatory and the University of Virginia, which has been part of ALMA. -avbildningsteamet.
Sources: ALMA Observation of the “Lump”: “High Angle Resolution ALMA Images 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 that favors 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 posts ALMA (ESO / NAOJ / NRAO), P. Cigan and R. Indebetouw; NRAO / AUI / NSF, B. Saxton; NASA / ESA