Getting to Know the Hidden Past of a Famous Supernova

Supernova 1987A (SN 1987A) heralded the explosive and brilliant death of a massive star, whose powerful, fiery, wandering light reached March 23, 1987, on Earth. The stellar blast occurred about 168,000 light-years from our planet, and it was bright enough to be observed with the naked eye as it ferociously exploded in the outer limits of the Tarantula Nebula in the Large Magellanic Cloud (LMC). The LMC is a small, amorphous dwarf galaxy that is a satellite of our own enormous and ancient barred-spiral The Milky Way is the galaxy. SN 1987A provided the very first opportunity for modern astronomers to observe the mysterious evolution of a supernova in detail, and the resulting valuable investigations have shed new light into how core-collapse Type II supernovae occur and develop through the passage of time. In August 2016, astronomers announced that they had been able to “see” millions of years into the secret and well-hidden past of SN 1987A, and had successfully investigated the tattered stellar ruins of this famous blast from the past that had made a brilliant spectacle of itself 29 years earlier.

The research was led by a doctoral student investigating the lingering remains of the famous star-that-was, and the new findings about supernova remnant 1987A will greatly help astrophysicists understand how similar core-collapse supernovae are triggered and evolve in general. Just like archaeologists excavating the ruins of ancient civilizations on Earth, and then interpreting what these ancient remains reveal to them about those vanished civilizations, the ancient stellar ruins of SN 1987A can open a new window into the vanished massive progenitor star’s secret past.

Peering into the hidden heart of SN 1987A, the team of astronomers were able to observe its past, millions of years before its famous final blaze of glory, using a telescope in the remote outback region of Australia at a location free of FM radio interference. A team of international astronomers exploring the region at the lowest radio frequencies ever are a part of the research team, which is being led by a doctoral student at the Australian University of Sydney. The results of these studies have contributed to a greater understanding of supernovae among scientists.

The astronomers explained that SN 1987A, the first supernova to be detected in 1987, had a brightness that peaked in with an apparent magnitude of roughly 3. May 1987. Over the following few months, the apparent magnitude gradually diminished.

The new research depicts the doomed star’s life, long before its explosive stellar farewell performance, when it was still a bright, active, and youthful hydrogen-burning star on the main-sequence of the Stellar evolution Hertzsprung-Russell diagram. The new study then went on to show how this massive progenitor main-sequence star evolved to become both the brightest and closest supernova seen from Earth–collapsing in an explosive grand finale about three decades ago.

A Brilliant Stellar Grand Finale

The known strongest stellar explosions are supernovae. They can actually be seen all the way to the outer reaches of the visible universe because they are so incredibly bright and powerful. When a massive star, such as the SN 1987A progenitor, at last reaches the unfortunate end of the road, it perishes in the rage of a core-collapse Type II supernova. However, the erstwhile star usually leaves behind a relic of its former “life” in the form of a weird, extremely dense, relatively small stellar ghost termed a neutron star–or, alternatively, in the case of the most massive stars of all, an even more bizarre inhabitant of our strange Cosmos termed a black hole of stellar mass.

The myriad of magnificent, sparkling, and fiery stars that frolic around our Universe shine brightly because they churn out energy as the product of nuclear fusion. contrary to the Sun, which is our own relatively small Star. much more massive stars contain sufficient mass to fuse elements that have an atomic mass greather than hydrogen and helium–the two lightest of all atomic elements–at ever-increasing temperatures and pressures. The degeneracy pressure of electrons and the energy churned out by these fusion reactions are sufficient to wage war against the force of gravity–thus preventing the still-“living” star from collapsing. This process enables the massive main-squence star to maintain stellar equilibrium. A main-sequence star fuses increasingly heavier and heavier atomic elements out of lighter ones, starting the process with hydrogen and helium, and then continuing on to manufacture all of the atomic elements listed in the familiar Periodic Table. This process, termed stellar nucleosynthesis, continues until a core of nickel or iron forms. The nuclear fusion of nickel or iron produces no energy output. This essentially means that no more fusion is possible, rendering the stellar core’s nickel-iron material inert. Stellar equilibrium is disturbed because there is no longer any energy output that generates an external pressure. The star is doomed.

When the extremely heavy mass of the nickel-iron core is greater than what is termed the Chandrasekhar limit of about 1.4 times the mass of our Sun, electron degeneracy cannot sustain stellar equilibrium by itself in the face of gravity. The outcome is a supernova explosion that occurs in a matter of seconds, causing the massive star to die catastrophically and spectacularly. Indeed, during this final blaze of stellar fury, the outer core of the dying star reaches an inward velocity of as much as 23% of the speed of light–and the temperature of the inner core soars to as much as 100 billion Kelvin.

Typically, supernovae blasts rip the massive dying star to pieces and violently launch its brilliant and fiery rainbow of multicolored outer gaseous layers into interstellar space. The most massive stars to frolic in the Cosmos collapse and violently blow themselves into oblivion–leaving behind a mysterious, weird stellar mass black hole. Massive stars–that are not that massive–leave behind a wildly spinning, city-sized neutron star. A teaspoon full of neutron star stuff can weigh as much as a herd of dinosaurs.

There are several differing classes of core-collapse supernova explosions. The classes differ as a result of light curve–a graph of time versus luminosity–in the aftermath of the blast. Type II-L supernovae show a linear drop of their light curve in the immediate aftermath of the explosion, whereas Type II-P display a period of considerably less rapid decline (a plateau) in their light curve that is followed by a normal decay. Type Ib and Type Ic supernovae are core-collapse supernovae that involve a massive star that has previously hurled off its outer envelope of hydrogen and (for Type Ic) helium, as well. As a result, Type Ib and Type Ic blasts appear to be devoid of these two light elements.

SN 1987A was discovered by Both Dr. Ian Shelton and Dr. Oscar Duhalde at the Las Campanas Observatory in 24 February 1987 in Chile It was independently discovered by the late Dr. Albert Jones in New Zealand From March 4-12, 1987, the supernova was observed from space by Astron, which was the largest ultraviolet space telescope at the time.

SN 1987A‘s progenitor star was a blue supergiant located about 168,000 light-years away. Blue supergiants are extremely massive and gigantic stars that are both brilliantly bright and searing-hot, with surface temperatures of between 2,000-50,000 degrees Celsius. The brightest star in the constellation of Orion, dubbed Rigel, is the most famous blue supergiant.

As well as being the closest supernova to be observed in hundreds of years, SN 1987A was also a very important event for astronomers because it was the first time that neutrinos were detected shooting out from an astronomical source other than our own Sun. Neutrinos are subatomic particles that are produced as a result of the decay of radioactive elements and have no electric charge. These almost massless subatomic particles are theoretically predicted to be born in great numbers during core-collapse supernovae explosions. Therefore, their discovery during the SN 1987A blast, strengthed some of the most basic and widely held theories about the mysterious mechanisms going on within supernovae.

About two to three hours before the visible light emanating from SN 1987A reached Earth, a flood of neutrinos was detected at three separate neutrino observatories. The reason for this observation is generally thought to be that neutrino emission occurs simultaneously with the stellar core collapse–and this occurs before there is the emission of visible light. After the shock wave has made contact with the surface of the dying star, a slower process called the transmission of visible light can start.

Even though the actual neutrino count was only 24, it was considered to be important because it was a significant rise from the previously observed background level. This was the very first time that neutrinos, shot out from a supernova, had been directly observed–and this heralded the beginning of neutrino astronomy. The observations proved to be consistent with theoretical supernova scenarios proposing that 99% of the energy produced as the result of the stellar core collapse is radiated away in the form of neutrinos. The observations are also consistent with the scenarios’ prediction of a total neutrino count of 10 to the 58th power with a total energy of 10 to the 46th power joules.

Revealing SN 1987’s Secret Past

Astronomers knew a great deal about the immediate past of SN 1987A from studying the cosmic wreckage of the dying star’s collapse in the LMC back in 1987. The most recent understandings, however, came from low-frequency radio astronomy’s discovery of the tiniest of hisses.

Only 0.1% or 20,000 years of the dead star’s multi-million-year lifespan had previously been observed. The most recent research, published in August 2016, made it possible for astronomers to look millions of years further back into the supernova’s mysterious past life than was previously possible. The study was led by Joseph Callingham, a doctoral student at the University of Sydney in Australia and the Center of Excellence for All-Sky Astrophysics at the ARC. Former Young Australian of the Year Dr. oversaw the work that was done. Currently studying at the University of Toronto in Canada is Bryan Gaensler.

Operating the Murchison Widefield Array located in the West Australian desert, the team of radio astronomers managed to “see” all the way back in time to when the dying star was still in its long-lasting red supergiant phase. Red supergiants are the largest stars in the Universe. Callingham explained, in an August 2, 2016 University of Sydney Press Release, that earlier studies had focused on the material that was hurled out into space when the star was in its final blue supergiant phase.

“Just like excavating and studying ancient ruins that teach us about the life of a past civilization, my colleagues and I have used low-frequency radio observations as a window into the star’s life,” Callingham explained in the August 2, 2016 Release from the University of Sydney.

The team of astronomers discovered that the red supergiant lost its matter at a slower rate and produced slower winds than had been assumed earlier. Pushing into its surrounding environment took some time because of the slow winds.

“Our new data improves our knowledge of the composition of space in the region of supernova 1987A; we can now go back to our simulations and tweak them, to better reconstruct the physics of supernova explosions,” Callingham went on to elaborate.

Dr. Gaensler added in the same August 2, 2016 University of Sydney Press Release that the key to obtaining these new insights was due to the quiet environment in which the radio telescope they used is situated.

“Nobody was aware of what was going on at low radio frequencies because the weak signals coming from space were drowned out by the signals from our own FM radios on Earth. Now, by studying the strength of the radio signal, astronomers for the first time can calculate how dense the surrounding gas is, and thus understand the environment of the star before it died,” Dr. Gaensler added.