Free Astronomy Magazine September-October 2020

22 SEPTEMBER-OCTOBER 2020 SPACE CHRONICLES my career to try to solve this mys- tery. It was like a modern holy grail.” The theoretical study by Page and his team, published in The Astro- physical Journal, strongly supports the suggestion made by the ALMA team that a neutron star is powering the dust blob. “In spite of the supreme complexity of a supernova explosion and the ex- treme conditions reigning in the in- terior of a neutron star, the detec- tion of a warm blob of dust is a con- firmation of several predictions,” Page explained. These predictions were the location and the tempera- ture of the neutron star. According to supernova computer models, the explosion has “kicked away” the neutron star from its birthplace with a speed of hundreds of kilometers per second (tens of times faster than the fastest rocket). The blob is exactly at the place where with ALMA. “There has to be some- thing in the cloud that has heated up the dust and which makes it shine. That’s why we suggested that there is a neutron star hiding inside the dust cloud.” Even though Matsuura and her team were excited about this result, they wondered about the brightness of the blob. “We thought that the neutron star might be too bright to exist, but then Dany Page and his team published a study that indi- cated that the neutron star can in- deed be this bright because it is so very young,” said Matsuura. Dany Page is an astrophysicist at the National Autonomous University of Mexico, who has been studying SN 1987A from the start. “I was halfway through my PhD when the super- nova happened,” he said, “it was one of the biggest events in my life that made me change the course of astronomers think the neutron star would be today. And the tempera- ture of the neutron star, which was predicted to be around 5 million de- grees Celsius, provides enough en- ergy to explain the brightness of the blob. Contrary to common expectations, the neutron star is likely not a pulsar. “A pulsar’s power depends on how fast it spins and on its magnetic field strength, both of which would need to have very finely tuned values to match the observations,” said Page, “while the thermal energy emitted by the hot surface of the young neu- tron star naturally fits the data.” “The neutron star behaves exactly like we expected,” added James Lat- timer of Stony Brook University in New York, and a member of Page’s research team. Lattimer has also fol- lowed SN 1987A closely, having pub- lished prior to SN 1987A predictions of a supernova’s neutrino signal that subsequently matched the observa- tions. “Those neutrinos suggested that a black hole never formed, and moreover it seems difficult for a black hole to explain the observed brightness of the blob. We com- pared all possibilities and concluded that a hot neutron star is the most likely explanation.” This neutron star is a 25 km wide, ex- tremely hot ball of ultra-dense mat- ter. A teaspoon of its material would weigh more than all the buildings within New York City combined. Be- cause it can only be 33 years old, it would be the youngest neutron star ever found. The second youngest neutron star that we know of is lo- cated in the supernova remnant Cas- siopeia A and is 330 years old. Only a direct picture of the neutron star would give definite proof that it exists, but for that astronomers may need to wait a few more decades until the dust and gas in the supernova remnant become more transparent. ! T his colorful, multiwavelength image of the intricate remains of Supernova 1987A is produced with data from three different observatories. The red color shows dust and cold gas in the center of the supernova remnant, taken at radio wavelengths with ALMA. The green and blue hues reveal where the expanding shock wave from the exploded star is colliding with a ring of mate- rial around the supernova. The green represents the glow of visible light, cap- tured by NASA’s Hubble Space Telescope. The blue color reveals the hottest gas and is based on data from NASA’s Chandra X-ray Observa- tory. The ring was initially made to glow by the flash of light from the original explosion. Over subse- quent years the ring material has brightened considerably as the ex- plosion’s shock wave slams into it. [ALMA (ESO/NAOJ/NRAO), P. Cigan and R. Indebetouw; NRAO/AUI/ NSF, B. Saxton; NASA/ESA]