New Life in Dead Star: Supernova 'Changing Right Before Our Eyes'

 

Ker Than for Space.com

July 24, 2006

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This image of SN 1987A combines data from NASA's orbiting Chandra X-ray Observatory and the 8-meter Gemini South infrared telescope in Chile. The X-ray light detected by Chandra is colored blue. The infrared light detected by Gemini South is shown as green and red. The ring is produced by hot gas (largely the X-ray light) and cold dust (largely the infrared light) from the exploded star interacting with the interstellar region. Credit: Gemini/NASA

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Newly detected dust found around the burst remains of a dead star could help reveal how planets and stars formed and how life began.

 

About 160,000 years ago, a star 20 times more massive than our sun erupted in a fiery explosion called a supernova. The star was located in the Large Magellanic Cloud, a nearby dwarf galaxy. In 1987, the first light from that catastrophic event reached Earth and for several months, the supernova, dubbed SN 1987A, blazed as brightly as 100 million suns before fading again.

 

Now, nearly two decades later, astronomers have detected dust particles around the supernova that they think formed before the star exploded. The new finding is the first evidence that star dust can survive a supernova explosion. It is also providing a rare glimpse into a process called "sputtering," in which dust is eroded by interactions with superheated gas.

 

"Supernova 1987A is changing right before our eyes," said Eli Dwek, a cosmic dust expert at NASA Goddard Space Flight Center in Maryland who was involved in the finding. "What we are seeing is a milestone in the evolution of a supernova."

 

Cosmic building blocks

 

Finer than grains of beach sand, stellar dust is a constant source of frustration for astronomers because it can obscure observations from distant stars. Yet the troublesome dust is also a prime ingredient in the construction of planets and of all living things. The dust is made in the fiery furnaces of stars as they burn and is scattered across space either by stellar winds or by supernova explosions.

 

Despite its importance, scientists still know very little about star dust. How much dust does a star produce throughout its lifetime? How much survives a star's death? And how do rings of dust coalesce to form stars and planets?

 

1987A's newly detected stardust, found using an infrared telescope at the Gemini South Observatory in Chile, could help astronomers answer these questions. The dust particles are intermixed with superheated, X-ray emitting gas and found within an equatorial ring around SN 1987A. About a light-year across, the ring of gas and dust is expanding very slowly.

 

This suggests that the ring was created about 600,000 years before the star exploded, the researchers say. It is therefore unlikely that the ring was created by a supernova blast during the star's death, but rather by stellar winds when the star was still alive.

 

Made visible

 

The ring of dust and gas remained invisible for nearly twenty years until shockwaves from the supernova blast caught up with it. As the shockwaves expanded, they passed through the ring, heating up its gas and normally cool dust until they glowed in the infrared.

 

"This much was expected," said study team member Patrice Bouchet of the Observatoire de Paris. "The collision between the ejecta of supernova 1987A and the equatorial ring was predicted to occur sometime in the interval of 1995 to 2007, and it is now underway."

 

What was surprising, however, was the composition of the dust, which followup observations with NASA's Spitzer Space Telescope revealed to be almost pure silicate. Also, far less dust than expected was detected. A star as massive as the one that created SN 1987A was thought to produce much more dust.

 

The dearth of dust could mean that shockwaves from the supernova blast destroyed more dust than originally thought. This could have broad implications for determining dust origins throughout the universe if confirmed, the researchers say.

 

A spate of new infrared, optical and X-ray observations of SN 1987A are now planned to follow up on the new findings.

 

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Core of Supernova Goes Missing

 

Michael Schirber for Space.com

June 6, 2005

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The remnant of supernova 1987A shows no sign of the neutron star scientists believe is lurking at its heart. The Hubble Space Telescope took this image in December 2004. Credit: P. Challis & R. Kirshner, Harvard-Smithsonian Center for Astrophysics

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A search for the remains of a nearby stellar explosion has come up empty. Astronomers observed the blast site of the supernova, SN 1987A, with the Hubble Space Telescope, but could not find any sign of the dense stellar core.

 

"We think a neutron star was formed. The question is: Why don't we see it?" astronomer Genevieve Graves of UC Santa Cruz said today.

 

A neutron star is an extremely dense ball of subatomic particles, which theory says can form as the core of a massive star collapses after exploding. This is what is believed to have happened in 1987, when a star with 20 times the mass of our Sun blew up, 165,000 light-years away in the Large Magellanic Cloud.

 

"Therein lies the mystery -- where is that missing neutron star?" said Robert Kirshner of the Harvard-Smithsonian Center for Astrophysics (CfA).

 

Neutron stars are often detected as pulsars when they emit intense beams of radio waves, like a lighthouse. It may be too soon to see radio flashes from the remnant of SN 1987A, since theory predicts that pulsars take between 100 to 100,000 years to develop after a supernova.

 

A young neutron star could, however, be seen if it is swallowing up nearby gas and debris from the explosion. This accreted material would heat up and emit light. But when the team of astronomers scoured the area of SN 1987A, they found no signature of this accretion.

 

"A neutron star could just be sitting there inside SN 1987A, not accreting matter and not emitting enough light for us to see," said Peter Challis from the CfA.

 

Future observations may uncover this quiet remnant by studying the infrared emission from dust clouds in the vicinity, which may be reprocessing the weak ultraviolet and visible light coming from the neutron star.

 

A supernova from a more massive star can form a black hole, instead of a neutron star. The progenitor of SN 1987A is right near the dividing line, so it may have created a black hole. Still, a black hole would be indirectly detectable by the same accretion mechanism that was not seen in these latest results.

 

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Hubble Reveals Dramatic New Phase of a Supernova Explosion

 

Robert Roy Britt for Space.com

19 February 2004

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A sequence of Hubble images of supernova 1987A taken from 1994 through late 2003 shows the central star has faded while bright spots in the outer ring are enhanced.

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The most dramatic stellar explosion witnessed in centuries just got more interesting. New images from the Hubble Space Telescope show a dying star's "ring of fire" entering a new phase of brightness.

 

The remarkable event is the only one of its kind ever recorded by telescopes.

 

Astronomers first saw the star explode -- an event called a supernova -- in 1987. It shone as bright as 100 million suns for several months.

 

Robert Kirshner of Harvard University and the Harvard-Smithsonian Center for Astrophysics led the latest observations. He explained what's going on around the star named 1987A. When the star first exploded, ultraviolet light raced outward and lit up a previously unknown ring of gaseous debris that the star had presumably spat out about 20,000 years prior.

 

"Then there's a blast wave going out from the supernova to the ring," Kirshner said in a telephone interview. "We all knew it was going to hit in a decade or so."

 

Shock wave hits

 

In 1996, that shock wave began to plow into the debris ring, which is about a light-year in diameter. It heated the ring material -- gas and dust -- in spots, created an increasing number of bright areas that Hubble has been documenting over the years.

 

In the latest image, the spots nearly cover the ring like pearls on a necklace. The star, meanwhile, is a million times dimmer than when it first exploded.

 

The fact that the ring did not light up all at once suggests it is not perfectly round but instead is unstable, with parts of the inner ring closer to the central star than other parts, Kirshner said. He described it as a corrugated structure, or a wall with stalactites sticking inward.

 

Inside the ring, an amorphous purplish blob surrounds the central, dying star. That blob glows because it's made of radioactive elements forged in the supernova explosion. It is probably radioactive titanium, Kirshner explained, "shredded bits of the star going out at about 3,000 kilometers per second," or 6.7 million mph.

 

"Looking at the expansion of that [blob] we get a clue to what was happening in first couple of minutes of the explosion of the star," he said.

 

Scientists have seen no other supernova evolve over time with anything approaching this sort of detail.

 

Show continues

 

The ring around 1987A should continue to brighten for a couple of decades, Kirshner said. The bright spots will merge as the debris is engulfed by the shock wave until it creates a "ring of fire," he said. Watching the evolution should help theorists understand how and why stars explode.

 

"There's going to be plenty to see," Kirshner said.

 

But its uncertain whether 1987A will be monitored continuously.

 

Like many astronomers, Kirshner said he's disappointed that under NASA's current plans, Hubble won't be around to record 1987A's progress in the latter years of this decade. The activity can be studied by X-ray and radio observatories, but valuable visible-light data would go uncollected.

 

"The value of the data keeps getting bigger as we get a longer series," Kirshner said. He added that it could be a long time before a similar event is available to astronomers and Hubble "is one of our chief instruments for doing this."

 

The last supernova to shine so brightly in Earth's skies was spotted by Johannes Kepler 400 years ago.

 

1987A was generated by a star 20 times more massive than the Sun. It resides in a nearby galaxy called the Large Magellanic Cloud. Because of the time it takes light from the event to reach Hubble, the explosion actually occurred 160,000 years ago, in the time frame of its origin.

 

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This is a wide field image from the Hubble taken of the remnant of SN 1987A. The background is the Large Magellanic Cloud-- a nearby galaxy observable from the southern hemisphere.

 

 

This image of SN 1987A was voted #6 of the Hubble's top 10 most valuable science images.