SN 1987A was a
type II supernova
A Type II supernova (plural: ''supernovae'' or ''supernovas'') results from the rapid collapse and violent explosion of a massive star. A star must have at least 8 times, but no more than 40 to 50 times, the mass of the Sun () to undergo this ...
in the
Large Magellanic Cloud
The Large Magellanic Cloud (LMC), or Nubecula Major, is a satellite galaxy of the Milky Way. At a distance of around 50 kiloparsecs (≈160,000 light-years), the LMC is the second- or third-closest galaxy to the Milky Way, after the ...
, a dwarf
satellite galaxy
A satellite galaxy is a smaller companion galaxy that travels on bound orbits within the gravitational potential of a more massive and luminous host galaxy (also known as the primary galaxy). Satellite galaxies and their constituents are bound ...
of the
Milky Way
The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...
. It occurred approximately from
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
and was the closest observed supernova since
Kepler's Supernova
SN 1604, also known as Kepler's Supernova, Kepler's Nova or Kepler's Star, was a Type Ia supernova that occurred in the Milky Way, in the constellation Ophiuchus. Appearing in 1604, it is the most recent supernova in the Milky Way galaxy to have ...
. 1987A's light reached Earth on February 23, 1987, and as the earliest supernova discovered that year, was labeled "1987A". Its brightness peaked in May, with an
apparent magnitude
Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...
of about 3.
It was the first supernova that modern
astronomer
An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, natural satellite, moons, comets and galaxy, g ...
s were able to study in great detail, and its observations have provided much insight into
core-collapse supernova
A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when a ...
e.
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.
For over thirty years, the expected collapsed neutron star could not be found, but in 2019, indirect evidence for its presence was found with the
Atacama Large Millimeter Array
The Atacama Large Millimeter/submillimeter Array (ALMA) is an astronomical interferometer of 66 radio telescopes in the Atacama Desert of northern Chile, which observe electromagnetic radiation at millimeter and submillimeter wavelengths. The a ...
telescope, with further evidence found in 2021 using the Chandra and NuSTAR X-ray telescopes.
Discovery
![Large](https://upload.wikimedia.org/wikipedia/commons/9/94/Large.mc.arp.750pix.jpg)
SN 1987A was discovered independently by
Ian Shelton
Ian Keith Shelton (born 30 March 1957) is a Canadian astronomer who discovered SN 1987A, the first modern supernova close and bright enough to be visible to the naked eye.
Born in Winnipeg, Manitoba, Canada, Shelton received his B.Sc. in 1979 fro ...
and
Oscar Duhalde
Oscar, OSCAR, or The Oscar may refer to:
People
* Oscar (given name), an Irish- and English-language name also used in other languages; the article includes the names Oskar, Oskari, Oszkár, Óscar, and other forms.
* Oscar (Irish mythology) ...
at the
Las Campanas Observatory
Las Campanas Observatory (LCO) is an astronomical observatory owned and operated by the Carnegie Institution for Science (CIS). It is in the southern Atacama Desert of Chile in the Atacama Region approximately northeast of the city of La Serena. ...
in
Chile
Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...
on February 24, 1987, and within the same 24 hours by
Albert Jones Albert Jones may refer to:
* Albert Beckford Jones (born 1958), American businessman
* Albert Edward Jones (1878–1954), English silversmith and designer
* Albert F. A. L. Jones (1920–2013), New Zealand astronomer
* Albert F. Jones (1858–1920 ...
in
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
.
[
]
Later investigations found photographs showing the supernova brightening rapidly early on February 23.
[
] On March 4–12, 1987, it was observed from space by
Astron Astron may refer to:
* Mitsubishi Astron engine
* ASTRON, the Dutch foundation for astronomy research, operating the Westerbork Synthesis Radio Telescope and LOFAR
* Astron (comics), a fictional character, a member of the Marvel Comics group The Et ...
, the largest
ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
space telescope
A space telescope or space observatory is a telescope in outer space used to observe astronomical objects. Suggested by Lyman Spitzer in 1946, the first operational telescopes were the American Orbiting Astronomical Observatory, OAO-2 launched ...
of that time.
Progenitor
left, The remnant of SN 1987A There was some speculation that the star might have merged with a Binary star, 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.
[
]
Neutrino emissions
Approximately two to three hours before the visible light from SN 1987A reached Earth, a burst of neutrinos was observed at three neutrino detector, neutrino observatories. This was likely due to Supernova neutrinos, neutrino emission, which occurs simultaneously with core collapse, but before visible light is emitted. Visible light is transmitted only after the shock wave reaches the stellar surface. At 07:35
UT,
Kamiokande II
The is a neutrino and gravitational waves laboratory located underground in the Mozumi mine of the Kamioka Mining and Smelting Co. near the Kamioka section of the city of Hida in Gifu Prefecture, Japan. A set of groundbreaking neutrino experi ...
detected 12
antineutrino
A neutrino ( ; denoted by the Greek letter ) is a fermion (an elementary particle with spin of ) that interacts only via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass is ...
s;
IMB, 8 antineutrinos; and
Baksan, 5 antineutrinos; in a burst lasting less than 13 seconds. Approximately three hours earlier, the
Mont Blanc
Mont Blanc (french: Mont Blanc ; it, Monte Bianco , both meaning "white mountain") is the highest mountain in the Alps and Western Europe, rising above sea level. It is the second-most prominent mountain in Europe, after Mount Elbrus, and i ...
liquid scintillator detected a five-neutrino burst, but this is generally not believed to be associated with SN 1987A.
[
The Kamiokande II detection, which at 12 neutrinos had the largest sample population, showed the neutrinos arriving in two distinct pulses. The first pulse started at 07:35:35 and comprised 9 neutrinos, all of which arrived over a period of 1.915 seconds. A second pulse of three neutrinos arrived between 9.219 and 12.439 seconds after the first neutrino was detected, for a pulse duration of 3.220 seconds.
Although only 25 neutrinos were detected during the event, it was a significant increase from the previously observed background level. This was the first time neutrinos known to be emitted from a supernova had been observed directly, which marked the beginning of ]neutrino astronomy
Neutrino astronomy is the branch of astronomy that observes astronomical objects with neutrino detectors in special observatories. Neutrinos are created as a result of certain types of radioactive decay, nuclear reactions such as those that take ...
. The observations were consistent with theoretical supernova models in which 99% of the energy of the collapse is radiated away in the form of neutrinos. 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.
The neutrino measurements allowed upper bounds on neutrino mass and charge, as well as the number of flavors of neutrinos and other properties.[ For example, the data show that within 5% confidence, the rest mass of the electron neutrino is at most 16 eV/c2, 1/30,000 the mass of an electron. The data suggest that the total number of neutrino flavors is at most 8 but other observations and experiments give tighter estimates. Many of these results have since been confirmed or tightened by other neutrino experiments such as more careful analysis of solar neutrinos and atmospheric neutrinos as well as experiments with artificial neutrino sources.
]
Neutron star
The bright ring around the central region of the exploded star is composed of ejected material.
SN 1987A appears to be a core-collapse supernova, which should result in a neutron star
A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. white ...
given the size of the original star.[ The neutrino data indicate that a compact object did form at the star's core. Since the supernova first became visible, astronomers have been searching for the collapsed core. The ]Hubble Space Telescope
The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...
has taken images of the supernova regularly since August 1990 without a clear detection of a neutron star.
A number of possibilities for the "missing" neutron star are being considered.[
] The first is that the neutron star is enshrouded in dense dust clouds so that it cannot be seen.[
] Another is that a pulsar
A pulsar (from ''pulsating radio source'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward Ea ...
was formed, but with either an unusually large or small magnetic field. It is also possible that large amounts of material fell back on the neutron star, so that it further collapsed into a black hole
A black hole is a region of spacetime where gravitation, gravity is so strong that nothing, including light or other Electromagnetic radiation, electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts t ...
. Neutron stars and black holes often give off light as material falls onto them. If there is a compact object in the supernova remnant, but no material to fall onto it, it would be very dim and could therefore avoid detection. Other scenarios have also been considered, such as whether the collapsed core became a quark star
A quark star is a hypothetical type of compact, exotic star, where extremely high core temperature and pressure has forced nuclear particles to form quark matter, a continuous state of matter consisting of free quarks.
Background
Some massive ...
. In 2019, evidence was presented that a neutron star was inside one of the brightest dust clumps close to the expected position of the supernova remnant. In 2021, further evidence was presented that the hard X-ray emission from SN 1987A originates in the pulsar wind nebula. The latter result is supported by a three-dimensional magnetohydrodynamic model, which describes the evolution of SN 1987A from the SN event to the current age, and reconstructs the ambient environment around the neutron star at various epochs, thus allowing to derive the absorbing power of the dense stellar material around the pulsar.
Light curve
left, A Photometric_system#Photometric_letters, visual band light curve for SN 1987A. The inset plot shows the time around peak brightness. Plotted from data published by several sources.
[}]
Much of the light curve, or graph of luminosity as a function of time, after the explosion of a type II supernova
A Type II supernova (plural: ''supernovae'' or ''supernovas'') results from the rapid collapse and violent explosion of a massive star. A star must have at least 8 times, but no more than 40 to 50 times, the mass of the Sun () to undergo this ...
such as SN 1987A is produced by the energy from radioactive decay
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...
. Although the luminous emission consists of optical photons, it is the radioactive power absorbed that keeps the remnant hot enough to radiate light. Without the radioactive heat, it would quickly dim. The radioactive decay of 56Ni through its daughters 56Co to 56Fe produces gamma-ray photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always ...
s that are absorbed and dominate the heating and thus the luminosity of the ejecta at intermediate times (several weeks) to late times (several months).[
] Energy for the peak of the light curve of SN1987A was provided by the decay of 56Ni to 56Co (half life of 6 days) while energy for the later light curve in particular fit very closely with the 77.3-day half-life of 56Co decaying to 56Fe. Later measurements by space gamma-ray telescopes of the small fraction of the 56Co and 57Co gamma rays that escaped the SN1987A remnant without absorption confirmed earlier predictions that those two radioactive nuclei were the power source.
Because the 56Co in SN1987A has now completely decayed, it no longer supports the luminosity of the SN 1987A ejecta. That is currently powered by the radioactive decay of 44Ti with a half life of about 60 years. With this change, X-rays produced by the ring interactions of the ejecta began to contribute significantly to the total light curve. This was noticed by the Hubble Space Telescope as a steady increase in luminosity 10,000 days after the event in the blue and red spectral bands.[
] X-ray lines 44Ti observed by the INTEGRAL
In mathematics
Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented i ...
space X-ray telescope showed that the total mass of radioactive 44Ti synthesized during the explosion was .[
]
Observations of the radioactive power from their decays in the 1987A light curve have measured accurate total masses of the 56Ni, 57Ni, and 44Ti created in the explosion, which agree with the masses measured by gamma-ray line space telescopes and provides nucleosynthesis constraints on the computed supernova model.[
]
Interaction with circumstellar material
Sequence of HST images from 1994 to 2009, showing the collision of the expanding remnant with a ring of material ejected by the progenitor 20,000 years before the supernova[
]
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
A stellar wind is a flow of gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric.
D ...
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; the turn-on 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
A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...
. 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.
A study reported in June 2015,[
] using images from the Hubble Space Telescope and the Very Large Telescope
The Very Large Telescope (VLT) is a telescope facility operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. It consists of four individual telescopes, each with a primary mirror 8.2 m across, ...
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.
The model also shows that X-ray emission from ejecta heated up by the shock will be dominant very soon, after which the ring would fade away. As the shock wave passes the circumstellar ring it will trace the history of mass loss of the supernova's progenitor and provide useful information for discriminating among various models for the progenitor of SN 1987A.[
]
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.[
]
Condensation of warm dust in the ejecta
File:Images of the Warm Dust in the SN 1987A debris.png, left, Images of the SN 1987A debris obtained with the instruments T-ReCS at the 8-m Gemini telescope and VISIR at one of the four VLT. Dates are indicated. An HST image is inserted at the bottom right (credits Patrice Bouchet, CEA-Saclay)
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
The Cerro Tololo Inter-American Observatory (CTIO) is an astronomical observatory located on Cerro Tololo in the Coquimbo Region of northern Chile, with additional facilities located on Cerro Pachón about to the southeast. It is approximately ...
(CTIO),[
][
] and the European Southern Observatory
The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental organization, intergovernmental research organisation made up of 16 mem ...
(ESO).[
][
] In particular, the ESO team reported an infrared excess
An infrared excess is a measurement of an astronomical source, typically a star, that in their spectral energy distribution has a greater measured infrared flux than expected by assuming the star is a blackbody radiator. Infrared excesses are o ...
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
Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) is ...
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
''Bremsstrahlung'' (), from "to brake" and "radiation"; i.e., "braking radiation" or "deceleration radiation", is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typicall ...
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.
Distribution of the dust inside the SN 1987A ejecta, as from the Lucy et al.'s model built at ESO[
]
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
Magnitude may refer to:
Mathematics
*Euclidean vector, a quantity defined by both its magnitude and its direction
*Magnitude (mathematics), the relative size of an object
*Norm (mathematics), a term for the size or length of a vector
*Order of ...
10.3 around day 650. However, further optical observations, as expressed in SN light curve, showed no inflection
In linguistic morphology, inflection (or inflexion) is a process of word formation in which a word is modified to express different grammatical categories such as tense, case, voice, aspect, person, number, gender, mood, animacy, and defin ...
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
The Atacama Large Millimeter/submillimeter Array (ALMA) is an astronomical interferometer of 66 radio telescopes in the Atacama Desert of northern Chile, which observe electromagnetic radiation at millimeter and submillimeter wavelengths. The a ...
(ALMA) in 2014.[
]
ALMA observations
Following the confirmation of a large amount of cold dust in the ejecta, ALMA has continued observing SN 1987A. Synchrotron radiation due to shock interaction in the equatorial ring has been measured. Cold (20–100K) carbon monoxide (CO) and silicate molecules (SiO) were observed. The data show that CO and SiO distributions are clumpy, and that different nucleosynthesis products (C, O and Si) are located in different places of the ejecta, indicating the footprints of the stellar interior at the time of the explosion.[
][
][
]
See also
* History of supernova observation
The known history of supernova observation goes back to 185 AD, when supernova SN 185 appeared; which is the oldest appearance of a supernova recorded by mankind. Several additional supernovae within the Milky Way galaxy have been recorded since t ...
* List of supernovae
This is a list of supernovae that are of historical significance. These include supernovae that were observed prior to the availability of photography, and individual events that have been the subject of a scientific paper that contributed to supe ...
* List of supernova remnants
This is a list of observed supernova remnants (SNRs) in the Milky Way, as well as galaxies nearby enough to resolve individual nebulae, such as the Large Magellanic Cloud, Large and Small Magellanic Clouds and the Andromeda Galaxy.
Supernova remna ...
* List of supernova candidates
This is a list of supernova candidates, or stars that astronomers have suggested are supernova progenitors. Type II supernova progenitors include stars with at least 10 solar masses that are in the final stages of their evolution. Prominent example ...
References
Sources
*
Further reading
*
External links
*
AAVSO: More information on the discovery of SN 1987A
Light curves and spectra
on th
Open Supernova Catalog
Light echoes from Sn1987a, Movie with real images by the group EROS2
*
SN 1987A at ESA/Hubble
Supernova 1987A, WIKISKY.ORG
- Space.com
{{DEFAULTSORT:Sn 1987a
Supernova remnants
Supernovae
Large Magellanic Cloud
Astronomical objects discovered in 1987
Dorado (constellation)