Seeing Light Echoes

Like ripples on a pond, pulses of light reverberate through cosmic clouds forming echoes of light.

Hubble view of an expanding halo of light around star v838 monocerotis

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)

Explore Other Hubble Science Highlights

Learn about some of Hubble's most exciting scientific discoveries.

Cepheid star in Andromeda galaxy (Hubble observations)

Discovering the Runaway Universe

Our cosmos is growing, and that expansion rate is accelerating.

Hubble Ultra Deep Field image

Tracing the Growth of Galaxies

Hubble is instrumental in uncovering the various stages of galactic evolution.

Hubble image left to right: Jupiter, Uranus, Saturn, Neptune

Studying the Outer Planets and Moons

Hubble’s systematic observations chart the ever-changing environments of our solar system's giant planets and their moons. 

Hubble observations of galaxies' centers

Monster Black Holes are Everywhere

Supermassive black holes lie at the heart of nearly every galaxy.

Hubble observations of Carina Nebula section

Exploring the Birth of Stars

Hubble’s near-infrared instruments see through the gas and dust clouds surrounding newborn stars.

An oval of colorful tendrils of gas and dust stretching from lower-left to upper right. Ova's outer ring is rusty-red tendrils, followed by a yellow/lime-green ring of tendrils. Oval's center is bright turquoise with white tendrils bisecting it. All set on a black background.

The Death Throws 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

Shining a Light on Dark Matter

Hubble’s observations help astronomers uncover the underlying structure of the universe.

Thirty proplyds in a 6 by 5 grid. Each one is unique. Some look like tadpoles, others like bright points in a cloudy disk.

Finding Planetary Construction Zones

Hubble’s sensitivity can reveal great disks of gas and dust around stars.

Three views of Pluto. Three mottled circles in colors of yellow, grey, rusty-orange, and black.

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.

Galaxy Details and Mergers

Hubble’s observations reveal a menagerie of galaxies.

Blue background. Center of image is a disk blocking the light of a star. Below and just to the left of the disk, at about seven o'clock, is a bright white point. This is PDS 70b.

Recognizing Worlds Beyond Our Sun

Hubble’s unique capabilities allow it to explore planetary systems around other stars. 

animation of a binary asteroid with a shifting tail

Tracking Evolution in the Asteroid Belt

These conglomerates of rock and ice may hold clues to the early solar system.