Progentiors of GRBs: Massive Stars

Largest Explosions in the Universe May Come from the Death of Massive Stars


Figure: Artist's conception of a GRB from a massive star


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Caption:

Artist's conception of a gamma-ray burst from a massive star. In a manner of a few seconds, the iron core of a massive star implodes and a black hole is formed. Matter falls in to the black hole through an accretion disk. Energetic jets are formed which plow through the star, causing it to explode. A burst of gamma-rays is produced by the jets moving at relativistic speeds (that is, nearly the speed of light). At the same time, the exploding star becomes a supernova with a shock moving at sub-relavistic speeds. If one of the jets is pointing toward Earth (Earth is pictured here much closer to the explosion than possible), then we detect a burst of gamma-rays and a supernova explosion. If the jets are pointed away, then only a supernova is seen. In this way, the two brightest explosions in the Universe, may have a common origin: the death of a massive star. Credit: Caltech/Jonathan Willams

Figure: Now you see it! Now you Don't!


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Caption:

Now you see it! Now you Don't! Three optical (negative) pictures of the same part of the sky at three different times. Darker colors correspond to brighter objects. The so-called transient afterglow of GRB 980326 (at the center of each image) clearly faded in the first month after the burst. The object at the center image was originally interpreted as the host galaxy. But a very long exposure in December (notice how much clearer star "f" gets) revealed that the "galaxy" disappeared. Not likely! Instead, the object at the middle picture is now argued by Bloom et al. in Nature to be the underlying supernova accompanying the gamma-ray burst. The size of these images on the sky is about the size of a postage stamp as seen across a football field.

Figure: Schematic picture of supernova and gamma-ray burst optical signatures


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Caption:

Schematic picture of supernova and gamma-ray burst optical signatures. If the picture is correct, that some gamma-ray bursts are produced in the death of massive stars, then there should be two physical origins of visble-light. One component is that of the "afterglow" of the gamma-ray burst: this should be blue in color and fade away rapidly. The other component is from the supernova and should appear red if the massive star is greater than a few billion light-years from Earth. The supernova component should take a few weeks to "turn-on" and then quickly fades away. The Caltech astronomers suggest that they have seen the superposition of the supernova and gamma-ray burst afterglow: a blue, rapidly fading component early on, then a red bump about three weeks later. With an image taken with the W. M. Keck Telescope nine months later, the optical brightness had falling below the sensitivity limit (shown with a green dashed line).

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This page and in-house links were created and maintained by Joshua Bloom (jsb@astro.caltech.edu).