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Sanduleak -69 202
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Title: On the Progenitor of Supernova 1987A
Authors: M. Parthasarathy, David Branch, E. Baron, David J. Jeffery

A previously unpublished ultralow-dispersion spectrum of Sanduleak -69 202, the stellar progenitor of SN 1987A, is presented and the uncertain presupernova evolution of Sanduleak -69 202 is discussed.

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RE: (SN) 1987A
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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
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.

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In 1987 a massive star exploded in the Large Magellanic Cloud, a neighbouring dwarf galaxy., an event called a supernova. It was the closest supernova to Earth since the invention of the telescope centuries ago. Now, a team using the Spitzer Space Telescope and the 8-meter Gemini South infrared telescope in Chile have probed the supernova remnant and found the building blocks of rocky planets and all living creatures.

Using infrared telescopes, said Dr. Eli Dwek, a cosmic dust expert at NASA Goddard Space Flight Centre and his colleagues have been following this supernova for a year, and have detected silicate dust created by the star from before it exploded. This dust survived the intense radiation from the explosion. Nearly 20 years onward, the supernova shock wave blasting through the debris that was shed by the star prior to its fiery death is now sweeping up this dust, making the material "visible" to infrared detectors.

Dust -- chemical particles and crystals finer than beach sand -- is both a frustration and a fascination for astronomers. Dust can obscure observations of distant stars. Yet dust is the stuff from which all solid bodies are formed. This is why dust research, as bland as it sounds, is one of the most important topics in astronomy and astrobiology.

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RE: Supernova 1987A
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Recent Chandra observations have revealed new details about the fiery ring surrounding the stellar explosion that produced Supernova 1987A. The data give insight into the behaviour of the doomed star in the years before it exploded, and indicate that the predicted spectacular brightening of the circumstellar ring has begun.

The supernova occurred in the Large Magellanic Cloud, a galaxy only 160,000 light years from Earth. The outburst was visible to the naked eye, and is the brightest known supernova in almost 400 years. The site of the explosion was traced to the location of a blue supergiant star called Sanduleak -69° 202 (SK -69 for short) that had a mass estimated at approximately 20 Suns.

Subsequent optical, ultraviolet and X-ray observations have enabled astronomers to piece together the following scenario for SK -69: about ten million years ago the star formed out of a dark, dense, cloud of dust and gas; roughly a million years ago, the star lost most of its outer layers in a slowly moving stellar wind that formed a vast cloud of gas around it; before the star exploded, a high-speed wind blowing off its hot surface carved out a cavity in the cool gas cloud.

The intense flash of ultraviolet light from the supernova illuminated the edge of this cavity to produce the bright ring seen by the Hubble Space Telescope. In the meantime the supernova explosion sent a shock wave rumbling through the cavity.

In 1999, Chandra imaged this shock wave, and astronomers have waited expectantly for the shock wave to hit the edge of the cavity, where it would encounter the much denser gas deposited by the red supergiant wind, and produce a dramatic increase in X-radiation. The latest data from Chandra and the Hubble Space Telescope indicate that this much-anticipated event has begun.


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Position(2000): RA 05h 35m 28.30s Dec -69 ° 16' 11.10

Optical hot-spots now encircle the ring like a necklace of incandescent diamonds (image on right). The Chandra image (left) reveals multimillion-degree gas at the location of the optical hot-spots.

X-ray spectra obtained with Chandra provide evidence that the optical hot-spots and the X-ray producing gas are due to a collision of the outward-moving supernova shock wave with dense fingers of cool gas protruding inward from the circumstellar ring (see illustration). These fingers were produced long ago by the interaction of the high-speed wind with the dense circumstellar cloud.

The dense fingers and the visible circumstellar ring represent only the inner edge of a much greater, unknown amount of matter ejected long ago by SK -69. As the shock wave moves into the dense cloud, ultraviolet and X-radiation from the shock wave will heat much more of the circumstellar gas.

Then, as remarked by Richard McCray, one of the scientists involved in the Chandra research, "Supernova 1987A will be illuminating its own past."

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Date:
(SN) 1987A
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On February 23, 1987, observers saw a star explode in the Large Magellanic Cloud, (a nearby dwarf galaxy).
At about 169000 light years away, it was the closest seen in the past 300 years; and astronomers have continued to examine the supernova remains. Although they saw its shockwave light up surrounding clouds of gas and dust, the supernova itself appears to have left no core behind.
Astronomers now report that even the sharp eyes of the Hubble Space Telescope have failed to locate the black hole or ultra compact neutron star they believe should have been created.
"We think a neutron star was formed. The question is: Why don't we see it?" - Genevieve Graves, astronomer of UC Santa Cruz, and author of a new paper announcing recent observations.

The progenitor star (Sanduleak -69202) of supernova (SN) 1987A weighed 20 times as much as the sun, placing it right on the dividing line and leaving astronomers uncertain about what type of compact object it produced. All observations to date have failed to detect a light source in the centre of the supernova remnant, leaving the question of the outcome unanswered.


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Position(2000): RA 05 : 35 : 27 ,Dec -69 : 16.2
Visual brightness +2.9 (maximum magnitude)

Limits from the Hubble Space Telescope on a Point Source in SN 1987A
We observed supernova 1987A (SN 1987A) with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) in 1999 September, and again with the Advanced Camera for Surveys (ACS) on the HST in 2003 November. No point source is observed in the remnant. We obtain a limiting flux of F_opt < 1.6 x 10^{-14} ergs/s/cm^2 in the wavelength range 2900-9650 Angstroms for any continuum emitter at the centre of the supernova remnant (SNR). It is likely that the SNR contains opaque dust that absorbs UV and optical emission, resulting in an attenuation of ~35% due to dust absorption in the SNR. Taking into account dust absorption in the remnant, we find a limit of L_opt < 8 x 10^{33} ergs/s. We compare this upper bound with empirical evidence from point sources in other supernova remnants, and with theoretical models for possible compact sources. Bright young pulsars such as Kes 75 or the Crab pulsar are excluded by optical and X-ray limits on SN 1987A. Of the young pulsars known to be associated with SNRs, those with ages < 5000 years are all too bright in X-rays to be compatible with the limits on SN 1987A. Examining theoretical models for accretion onto a compact object, we find that spherical accretion onto a neutron star is firmly ruled out, and that spherical accretion onto a black hole is possible only if there is a larger amount of dust absorption in the remnant than predicted. In the case of thin-disk accretion, our flux limit requires a small disk, no larger than 10^{10} cm, with an accretion rate no more than 0.3 times the Eddington accretion rate. Possible ways to hide a surviving compact object include the removal of all surrounding material at early times by a photon-driven wind, a small accretion disk, or very high levels of dust absorption in the remnant.

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Photo of the Large Magellanic Cloud and supernova



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