Seeing Light Echoes

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

"Starry Night", Vincent van Gogh's famous painting, is renowned for its bold whorls of light sweeping across a raging night sky. Although this image of the heavens came only from the artist's restless imagination, a new picture from the NASA/ESA Hubble Space Telescope bears remarkable similarities to the van Gogh work, complete with never-before-seen spirals of dust swirling across trillions of kilometres of interstellar space. This image, obtained with the Advanced Camera for Surveys on February 8, 2004, is Hubble's latest view of an expanding halo of light around a distant star, named V838 Monocerotis (V838 Mon). The illumination of interstellar dust comes from the red supergiant star at the middle of the image, which gave off a flashbulb-like pulse of light two years ago. V838 Mon is located about 20,000 light-years away from Earth in the direction of the constellation Monoceros, placing the star at the outer edge of our Milky Way galaxy.

NASA, the Hubble Heritage Team (AURA/STScI) and ESA

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.

In January 2002, a red supergiant star named V838 Monocerotis expanded very quickly, heating the surrounding interstellar dust to extreme, glowing temperatures. This movie, created using eight images from the Hubble Space Telescope, reveals the dramatic changes observed between 2002 and 2006. A morphing sequence was applied to create smooth, seamless transitions between images. For reasons unknown, the star’s outer surface suddenly and greatly expanded resulting in it becoming the brightest star in the entire Milky Way Galaxy. Although the star’s flash appears to expel material into space (like a supernova), what we are actually seeing is an outwardly moving light echo of the bright flash. In a light echo, rings of interstellar dust that already surround the star reflect light from the flash. The light echo spans about six light years in diameter. The star, which lies about 20,000 light-years away from Earth, presumably ejected the illuminated dust shells in previous outbursts. The star has some similarities to highly unstable aging stars called eruptive variables, which suddenly and unpredictably increase in brightness. Credit: ESA/Hubble, NASA's Goddard Space Flight Center, ESA

NASA astronomer, Dr. Padi Boyd, takes us inside the Hubble image of V838 Monocerotis. Credit: NASA's Goddard Space Flight Center; Producer and Director: James Leigh

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.

This movie shows the reflection nebula around the Cepheid variable RS Puppis at seven equally spaced intervals during its 41.4-day pulsation period. Each time RS Puppis reaches maximum brightness, it sends another wave of illumination into the surrounding dust. Thus a pattern of apparently expanding bull's-eyes surrounds the variable star, similar to the ripples in a pond produced when a series of stones is thrown into the water. These images were taken with Hubble's Advanced Camera for Surveys in a visual filter over the following dates in 2010: March 25 and 31, April 6, 11, 18, 24, and 29. Each individual image in this sequence had an exposure time of 23 minutes. Credit: NASA, ESA, G. Bacon (STScI), the Hubble Heritage Team (STScI/AURA)-Hubble/Europe Collaboration, and H. Bond (STScI and Pennsylvania State University)

Learn More

Flash From Star V838 Mon Echoes Through Space
Hubble images of the star V838 Monocerotis (V838 Mon) reveal dramatic changes in the illumination of surrounding dusty cloud structures.
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