Hubble captured the best sequence of images of the reverberation of light through space caused by the outburst of a star. In January 2002, an unexplained flash of light from a red supergiant star left what looked like an expanding bubble of debris. In fact, the light was simply illuminating clouds that were already in place around the star. Since light travels at a finite speed, the flash took years to reach the most distant clouds and expose them. This phenomenon, called a “light echo,” is reminiscent of sound waves echoing down a canyon and “revealing” its walls.
![Hubble view of an expanding halo of light around star v838 monocerotis](https://science.nasa.gov/wp-content/uploads/2023/04/hubble-v838mon-heic0405a-jpg.webp?w=4096&format=png)
The red star at the center is an unusual, erupting supergiant called V838 Monocerotis, located about 20,000 light-years away. During its outburst, the star's intrinsic brightness flared to roughly 600,000 times that of our Sun. The star may have swallowed a companion star or planet, triggering the burst. The dark gaps around the red star are voids in the dust – like empty pockets within Swiss cheese. Light echoes common around supernovas, but V838 Mon did not detonate itself; the flash seems to be a unique and little-understood transient phenomenon.
RS Puppis
Hubble captured another light echo around the Cepheid variable star called RS Puppis in 2013. Each time the star pulsates, it sends another wave of light into the cloud of gas and dust that surrounds it. These rippling light flashes are similar to the ripples produced in a pond when a series of stones is thrown into the water. To our eye, they create a ripple pattern that appears to be expanding outward from the star. Hubble's Advanced Camera for Surveys took these images in visible light over seven days in March and April of 2010. Each individual image had an exposure time of 23 minutes.
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Explore Other Hubble Science Highlights
Learn about some of Hubble's most exciting scientific discoveries.
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Hubble is instrumental in uncovering the various stages of galactic evolution.
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Hubble’s near-infrared instruments see through the gas and dust clouds surrounding newborn stars.
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The Death Throes of Stars
From colliding neutron stars to exploding supernovae, Hubble reveals details of some of the mysteries surrounding the deaths of stars.
![depiction of gravitational lensing](https://science.nasa.gov/wp-content/uploads/2023/04/macs_j1149-2223-jpg.webp?w=4096&format=png)
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Hubble’s observations help astronomers uncover the underlying structure of the universe.
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Uncovering Icy Objects in the Kuiper Belt
Hubble’s discoveries helped NASA plan the New Horizon spacecraft’s flyby of Pluto and beyond.
![Comma shaped curved cloud of gases in bright white edged with bright-pink star forming regions, and threaded with rusty-brown tendrils of dust at center and throughout the comma shaped merger. All set against the black of deep space.](https://science.nasa.gov/wp-content/uploads/2021/12/hubble-antennaegalaxies-potw1345a-jpg.webp?w=4096&format=png)
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Hubble’s unique capabilities allow it to explore planetary systems around other stars.
![animation of a binary asteroid with a shifting tail](https://science.nasa.gov/wp-content/uploads/2023/04/comet3.gif?w=4096&format=png)
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