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Stars and stellar evolution
Key events in the history of Supernova 1987A

On Feb. 23, 1987, telescope operator Oscar Duhalde stood outside the observatory at Las Campanas, located on a mountaintop in Chile, and looked up at the clear night sky. There, in a hazy-looking patch of brightness — a neighboring galaxy called the Large Magellanic Cloud (LMC) — is a bright star he hadn’t noticed before.

That same night at Las Campanas, Canadian astronomer Ian Shelton is also observing stars in the Large Magellanic Cloud. For Shelton, it is just routine work — until he develops the photographic plate. Telescopes at that time captured images of celestial objects on special glass plates coated with a light-sensitive substance. On that plate, he notices an extremely bright star, an intruder that he had not seen in previous observations of the same area. He races outside and looks up at the sky. There it is: a star of about fifth magnitude, glowing in the heavens. Duhalde announces that he saw the object too. Shelton realizes that this "new star" is actually an aging massive star that has blown itself apart in a supernova explosion. (The star actually blew up about 161,000 BC, but its light arrived here in 1987.)

There was no internet in 1987, so Shelton scrambled down the mountain to the nearest town to send a message announcing his discovery to the International Astronomical Union’s Bureau for Astronomical Telegrams, a clearing house for announcing astronomical discoveries.

Astronomers are excited about this discovery because it is the nearest supernova observed since 1604 — the year Johannes Kepler observed one in our Milky Way galaxy. Data taken by a small telescope aboard the International Ultraviolet Explorer (IUE) satellite help astronomers identify the exploding star's location as Sanduleak -69° 202, the former site of a blue supergiant about 20 times the mass of the sun. Astronomers name the exploding star Supernova 1987A, or SN 1987A.

Astronomers believe the star swelled up to become a red supergiant, puffed away some mass, then contracted and reheated to become a blue supergiant. Then, in less than a second, the star's core collapsed, and a wave of neutrinos — ghostly particles from the star's core — heated the inner core to 10 billion degrees Fahrenheit. This process triggered a shock wave that ripped the star apart, propelling a burst of neutrinos into space. The neutrinos were picked up by deep underground detectors: the IMB detector in Ohio and Kamiokande II in Japan. These invisible particles were the first signal of the supernova explosion, arriving even before the bright light from the dying star.

Since those initial observations of Supernova 1987A, ground-based and space-based telescopes have continued to monitor the exploded star, revealing interesting details about its death and the last stages of its life.

Supernova 1987A

This striking NASA Hubble Space Telescope image from 1994 shows three rings of glowing gas encircling the site of Supernova 1987A. Though all of the rings appear inclined to our view (so that they appear to intersect) they are probably in three different planes. The rings were a surprise because astronomers expected to see an hourglass shaped bubble of gas being blown into space by the supernova's progenitor star (based on previous HST observations, and images at lower resolution taken at ground-based observatories).

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May 1987: By studying the ultraviolet spectrum of SN 1987A, IUE discovered chemical elements in the supernova debris, which indicated that the progenitor star had already passed through the red giant phase.

July 1987: The Japanese satellite GINGA and a West German X-ray telescope called HEXE, attached to the Soviet Mir space station, detected X-rays coming from the SN 1987A debris.

August to November 1987: Several research missions, including the Solar Maximum Satellite, detected high-energy gamma rays. The gamma rays were released in the decay of radioactive elements that were formed in nuclear reactions at the core of the dying star. The data showed that the explosion created from simple building blocks a multitude of chemical elements. Among them was radioactive nickel, which decays into cobalt and rapidly transforms into stable iron. The discovery confirmed a widely-held theory that supernovas produce the heavy chemical elements that make up most things on Earth.

December 1989: Optical observations by the European Southern Observatory's New Technology Telescope in La Silla, Chile, showed a bright doughnut- or ring-like feature around the supernova.

August 1990: The Faint Object Camera, an instrument aboard the newly deployed NASA Hubble Space Telescope, clearly revealed a narrow inner ring around the stellar blast. The distance between the ring and the supernova is about three-quarters of a light-year. Some astronomers believed this ring was formed before the supernova explosion, ejected by the blue supergiant star about 20,000 years before its death.

1990: Rapidly brightening radio emissions were detected by the Australia Telescope National Facility. (Radio waves were detected for two weeks after SN 1987A was first spotted.) Astronomers determined that the radio waves were coming from an area located between the inner ring and the glowing debris from the stellar blast at the center of the ring. In that region, the most rapidly moving supernova debris was crashing into gas. Optical telescopes could not detect the gas because its density was too low and its temperature was too high.

1992: The NASA-Germany ROSAT satellite detected rapidly brightening X-rays from the exploded star. The X-rays were coming from the same collision area as the radio waves.

May 1994: Hubble’s Wide Field Planetary Camera 2 (WFPC2) discovered that two faint outer loops of glowing gas, first identified several years earlier in ground-based images, were surprisingly thin. Puzzled by Hubble's unexpected new details, astronomers were challenged to explain the processes that formed such unusual structures.

Supernova 1987A - A Ring's Light Show

These images, taken between 1994 and 2016 by NASA's Hubble Space Telescope, chronicle the brightening of a ring of gas around Supernova 1987A.

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January 1997: WFPC2 showed the supernova’s entire dumbbell-shaped structure, consisting of a bright inner ring and two faint outer rings. Hubble’s resolution was so sharp that it resolved the debris in the inner ring into two blobs of material. The blobs were racing away from each other at nearly 6 million miles per hour.

May 1997: Hubble’s Space Telescope Imaging Spectrograph (STIS) produced a detailed ultraviolet image of the inner ring, identifying specific elements such as oxygen, nitrogen, hydrogen, and sulfur. By measuring the ring's composition, astronomers hoped to figure out how it was created.

June 1997: Astronomers measured the fast-moving gas ejected by SN 1987A as it crashed into gas expelled by the progenitor star perhaps 20,000 years before the explosion. This gas was invisible until observed in ultraviolet light by STIS. The spectrograph detected the presence of glowing hydrogen expanding at a speed of 33 million miles per hour.

1998: Hubble images revealed that the gaseous inner ring was beginning to glow as the supernova blast wave slammed into the structure, heating it to millions of degrees Fahrenheit.

1999-2013: Data from NASA’s Chandra X-ray Observatory showed an expanding ring of X-ray emission that had been steadily getting brighter. The X-ray glow was caused by the blast wave from the original explosion bursting through and heating the inner ring of gas surrounding SN 1987A.

2000-2017: Hubble continued to monitor the exploded star, revealing that more of the blast wave was heating up the inner ring and making it light up.

2004: Hubble’s Advanced Camera for Surveys showed many bright spots along an inner ring of gas, which looked like pearls on a necklace. These cosmic “pearls” were produced when a supersonic shock wave unleashed during the explosion slammed into the inner ring at more than 1 million miles per hour. The collision was heating the ring, causing its innermost regions to glow. One of the bright spots on the ring [at 4 o'clock] was a star that happened to reside along Hubble’s line of sight.

2006: NASA’s Spitzer Space Telescope and the 8-meter Gemini South infrared telescope in Chile worked in tandem to probe dust contained in the SN 1987A material. The Gemini telescope revealed that the inner ring of material surrounding the supernova was shed by the star about 600,000 years before it exploded. The dust in the ring was formed in the stellar wind —a stream of charged particles — unleashed by the star before its detonation. The Spitzer telescope helped astronomers determine that the dust contained silicate particles.

2012-2017: The Atacama Large Millimeter/submillimeter Array (ALMA) observatory in Chile observed the glowing remains of the supernova. ALMA studied how the remnant was actually forging vast amounts of new dust from the new chemical elements created in the progenitor star. A portion of this dust will make its way into interstellar space and may become the building blocks of future stars and planets in another system.

2015: NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) uncovered evidence that the supernova’s massive progenitor star exploded in a lopsided fashion, sending ejected material flying in one direction and the core of the star in the other. The findings are the best proof yet that stellar explosions of this type, called Type II or core-collapse supernovae, are asymmetrical.

2017: The latest data from Hubble, Chandra, and ALMA indicated that SN 1987A had passed an important threshold. The supernova shock wave is moving beyond the dense inner ring of gas produced late in the life of the progenitor star. What lies beyond the ring is poorly known at present, and depends on the details of the evolution of the star when it was a red giant.

Multiwavelength View of Supernova 1987A

Astronomers combined observations from three different observatories to produce this colorful, multiwavelength image of the intricate remains of Supernova 1987A. The red color shows newly formed dust in the center of the supernova remnant, taken at submillimeter wavelengths by the Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile. The green and blue hues reveal where the expanding shock wave from the exploded star is colliding with a ring of material 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.

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"Tales of … Key events in the history of Supernova 1987A" presents a timeline of the discovery and subsequent observations of the nearest supernova in 400 years. This selection originally appeared as background information for a press release on the supernova.

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9-12, but the material can be adapted for use in other grades at the teacher's discretion
How to use in the classroom

Teachers can use this resource as:

A content reading selection. Teachers should discuss the meaning of unfamiliar vocabulary prior to having students read this selection.

An engagement activity. Have students read the selection. Ask them to explain how each telescope and/or detector has contributed to our study of the supernova.

An inquiry tool. Propose a question, such as, "What would you do if you found a new star?" Have students read the selection and write down as many questions as they can about the information in the text.

A source of information. Students can use this as a tool to begin studying the evolution of massive stars, which end their lives as supernovae.

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