1987 жылғы SN 1987A жұлдыз жарылысы

1987 supernova event in the constellation Dorado

SN 1987A was a type II supernova in the Large Magellanic Cloud, a dwarf satellite galaxy of the Milky Way. It occurred approximately from Earth and was the closest observed supernova since Kepler's Supernova in 1604. Light and neutrinos from the explosion reached Earth on February 23, 1987 and was designated "SN 1987A" as the first supernova discovered that year. Its brightness peaked in May of that year, with an apparent magnitude of about 3. It was the first supernova that modern astronomers were able to study in great detail, and its observations have provided much insight into core collapse supernovae. SN 1987A provided the first opportunity to confirm by direct observation the radioactive source of the energy for visible light emissions, by detecting predicted gamma ray line radiation from two of its abundant radioactive nuclei. This proved the radioactive nature of the long duration post explosion glow of supernovae. In 2019, indirect evidence for the presence of a collapsed neutron star within the remnants of SN 1987A was discovered using the Atacama Large Millimeter Array telescope. Further evidence was subsequently uncovered in 2021 through observations conducted by the Chandra and NuSTAR X ray telescopes. In 2024, NASA's James Webb Space Telescope provided groundbreaking observations that further illuminated the enigmatic processes at play within SN 1987A's remnants.

SN 1987A was discovered independently by Ian Shelton and Oscar Duhalde at the Las Campanas Observatory in Chile on February 24, 1987, and within the same 24 hours by Albert Jones in New Zealand. Later investigations found photographs showing the supernova brightening rapidly early on February 23.

Four days after the event was recorded, the progenitor star was tentatively identified as Sanduleak −69 202 (Sk 69 202), a blue supergiant. After the supernova faded, that identification was definitively confirmed, as Sk −69 202 had disappeared. The possibility of a blue supergiant producing a supernova was considered surprising, and the confirmation led to further research which identified an earlier supernova with a blue supergiant progenitor. Some models of SN 1987A's progenitor attributed the blue color largely to its chemical composition rather than its evolutionary stage, particularly the low levels of heavy elements. There was some speculation that the star might have merged with a companion star before the supernova. However, it is now widely understood that blue supergiants are natural progenitors of some supernovae, although there is still speculation that the evolution of such stars could require mass loss involving a binary companion.

Approximately two to three hours before the visible light from SN 1987A reached Earth, a burst of neutrinos was observed at three neutrino observatories. This was likely due to neutrino emission which occurs simultaneously with core collapse, but before visible light is emitted as the shock wave reaches the stellar surface. At 07:35 UT, 12 antineutrinos were detected by Kamiokande II, 8 by IMB, and 5 by Baksan in a burst lasting less than 13 seconds. Approximately three hours earlier, the Mont Blanc liquid scintillator detected a five neutrino burst, but this is generally not believed to be associated with SN 1987A. The observations are also consistent with the models' estimates of a total neutrino count of 1058 with a total energy of 1046 joules, i. e. a mean value of some dozens of MeV per neutrino. Billions of neutrinos passed through a square centimeter on Earth. The neutrino measurements allowed upper bounds on neutrino mass and charge, as well as the number of flavors of neutrinos and other properties.

The three bright rings around SN 1987A that were visible after a few months in images by the Hubble Space Telescope are material from the stellar wind of the progenitor. These rings were ionized by the ultraviolet flash from the supernova explosion, and consequently began emitting in various emission lines. These rings did not "turn on" until several months after the supernova and the process can be very accurately studied through spectroscopy. The rings are large enough that their angular size can be measured accurately: the inner ring is 0.808 arcseconds in radius. The time light traveled to light up the inner ring gives its radius of 0.66 (ly) light years. Using this as the base of a right angle triangle and the angular size as seen from the Earth for the local angle, one can use basic trigonometry to calculate the distance to SN 1987A, which is about 168,000 light years. The material from the explosion is catching up with the material expelled during both its red and blue supergiant phases and heating it, so we observe ring structures about the star. Around 2001, the expanding (>7000 km/s) supernova ejecta collided with the inner ring. This caused its heating and the generation of x rays—the x ray flux from the ring increased by a factor of three between 2001 and 2009. A part of the x ray radiation, which is absorbed by the dense ejecta close to the center, is responsible for a comparable increase in the optical flux from the supernova remnant in 2001–2009. This increase of the brightness of the remnant reversed the trend observed before 2001, when the optical flux was decreasing due to the decaying of 44Ti isotope. using images from the Hubble Space Telescope and the Very Large Telescope taken between 1994 and 2014, shows that the emissions from the clumps of matter making up the rings are fading as the clumps are destroyed by the shock wave. It is predicted the ring would fade away between 2020 and 2030. These findings are also supported by the results of a three dimensional hydrodynamic model which describes the interaction of the blast wave with the circumstellar nebula. In 2018, radio observations from the interaction between the circumstellar ring of dust and the shockwave has confirmed the shockwave has now left the circumstellar material. It also shows that the speed of the shockwave, which slowed down to 2,300 km/s while interacting with the dust in the ring, has now re accelerated to 3,600 km/s.

Soon after the SN 1987A outburst, three major groups embarked in a photometric monitoring of the supernova: the South African Astronomical Observatory (SAAO), the Cerro Tololo Inter American Observatory (CTIO), and the European Southern Observatory (ESO). In particular, the ESO team reported an infrared excess which became apparent beginning less than one month after the explosion (March 11, 1987). Three possible interpretations for it were discussed in this work: the infrared echo hypothesis was discarded, and thermal emission from dust that could have condensed in the ejecta was favoured (in which case the estimated temperature at that epoch was ~ 1250 K, and the dust mass was approximately ). The possibility that the IR excess could be produced by optically thick free free emission seemed unlikely because the luminosity in UV photons needed to keep the envelope ionized was much larger than what was available, but it was not ruled out in view of the eventuality of electron scattering, which had not been considered. However, none of these three groups had sufficiently convincing proofs to claim for a dusty ejecta on the basis of an IR excess alone. An independent Australian team advanced several argument in favour of an echo interpretation. This seemingly straightforward interpretation of the nature of the IR emission was challenged by the ESO group and definitively ruled out after presenting optical evidence for the presence of dust in the SN ejecta. To discriminate between the two interpretations, they considered the implication of the presence of an echoing dust cloud on the optical light curve, and on the existence of diffuse optical emission around the SN. They concluded that the expected optical echo from the cloud should be resolvable, and could be very bright with an integrated visual brightness of magnitude 10.3 around day 650. However, further optical observations, as expressed in SN light curve, showed no inflection in the light curve at the predicted level. Finally, the ESO team presented a convincing clumpy model for dust condensation in the ejecta. Although it had been thought more than 50 years ago that dust could form in the ejecta of a core collapse supernova, which in particular could explain the origin of the dust seen in young galaxies, that was the first time that such a condensation was observed. If SN 1987A is a typical representative of its class then the derived mass of the warm dust formed in the debris of core collapse supernovae is not sufficient to account for all the dust observed in the early universe. However, a much larger reservoir of ~0.25 solar mass of colder dust (at ~26 K) in the ejecta of SN 1987A was found with the Hershel infrared space telescope in 2011 and confirmed with the Atacama Large Millimeter Array (ALMA) in 2014.