Most massive binary star identified

  
NASA, ESA, D. Lennon en E. Sabbi (ESA/STScI)

By NOVA, Leiden

Published: April 19, 2013

Astronomers have observed a binary star that potentially weighed 300 to 400 solar masses at birth. The present day total mass of the two stars is between 200 and 300 times that of the Sun, depending on its evolutionary stage, which possibly makes it the most massive binary star known to date.

The massive binary star R144 is located in an outer area of the star-forming region 30 Doradus in the Large Magellanic Cloud. A number of particularly bright stars can be found in the center of that region with a characteristic pattern of spectral lines. The masses of these so-called Wolf-Rayet stars are up to 250 times the mass of the Sun. R144 is the visually brightest light source of this type in the star-forming region 30 Doradus and radiates strongly in X-rays. This was an indication that R144 is a binary star. Scientists have now confirmed this presumption thanks to the discovery of periodic (orbital) changes in the spectrum.

Astronomers obtained spectra of R144 with the X-shooter spectrograph on the European Southern Observatory’s Very Large Telescope. X-shooter is one of the most sensitive spectrographs on Earth and can observe light from the near-ultraviolet to the near-infrared in one shot. “The identification of this candidate would have been a great challenge without X-shooter. This spectrograph makes observations a lot easier and much more efficient, especially because less observation time is required to cover a large spectral range,” said Hugues Sana from the University of Amsterdam.

The spectrum forms the fingerprint of a star. From the changing shape and position of the spectral lines, it becomes clear that R144 is a binary star. The spectral lines also suggest that the binary system is formed by two hydrogen-rich Wolf-Rayet stars with similar masses, and a current total mass of 200 to 300 solar masses. NGC 3603-A1 was formerly known as the most massive binary star, with a total mass that is equal to 212 times the mass of the Sun.

“It is a mystery how extremely massive stars form,” said Frank Tramper from the University of Amsterdam. “According to the most widely accepted theories, stars of hundreds of solar masses can only form in massive star clusters. The fact that R144 lies far out from the central star cluster in 30 Doradus is possibly an indication that these systems can form in isolation.”

“There is an alternative scenario for the formation of R144,” said Alex de Koter, also from the University of Amsterdam, “namely that R144 was formed in the central star cluster, but that it was ejected by dynamical interactions with other massive stars.” The team is already working on follow-up observations to determine whether R144 is indeed a “runaway” star to definitively establish its mass and its other physical properties in order to decide whether R144 really is the most massive double star discovered so far.

Giant Eruption from Eta Carinae

These images reveal light from a massive stellar outburst in the Carina Nebula reflecting off dust clouds surrounding a behemoth double-star system. The color image at left shows the Carina Nebula, a star-forming region located 7,500 light-years from Earth. The massive double-star system Eta Carinae resides near the top of the image. The star system, about 120 times more massive than the Sun, produced a spectacular outburst that was seen on Earth from 1837 to 1858. The three black-and-white images at right show light from the eruption illuminating dust clouds near the doomed star system as it moves through them. The effect is like shining a flashlight on different regions of a vast cavern. The images were taken over an eight-year span by the U.S. National Optical Astronomy Observatory's Blanco 4-meter telescope at the CTIO.

By Carnegie Institution for Science, Washington, D.C.

Date: February 15, 2012

Eta Carinae, one of the most massive stars in our Milky Way Galaxy, unexpectedly increased in brightness in the 19th century. For 10 years in the mid-1800s, it was the second-brightest star in the sky — now it is not even in the top 100. The increase in luminosity was so great that it earned the rare title of Great Eruption. New research from a team, including Carnegie’s Jose Prieto, now at Princeton University in New Jersey, has used a “light echo” technique to demonstrate that this eruption was much different than previously thought.

Eta Carinae is a Luminous Blue Variable (LBV), meaning it has periods of dimness followed by periods of brightness. The variations in brightness of an LBV are caused by increased instability and loss of mass. The Great Eruption was an extreme and unique event in which the star, which is more than 100 times the mass of the Sun, lost several times the mass of our star. Scientists have believed that this rare type of eruption was caused by a stellar wind.

The team of scientists, led by Armin Rest of the Space Telescope Science Institute in Baltimore, Maryland, used images of Eta Carinae over eight years to study light echoes of the Great Eruption. For the first time, they observed light from the eruption that bounced, or echoed, off interstellar dust tens of light-years from the star. Those extra light-years mean that the light is reaching Earth now rather than in the 1800s when people on Earth observed the light that traveled here directly.

They then used the Magellan and du Pont telescopes at Las Campanas Observatories in Chile to obtain spectra of the echoes of light. The spectra allow them to precisely separate the light into its constituents, much like a drop of rain naturally acts as a prism and separates sunlight into the colors of the rainbow. These observations give important information about the chemical composition, temperature, and velocity of the material ejected during the 19th century Great Eruption.

Most surprisingly, their observations show that the Great Eruption is different from “supernova impostors,” events in nearby galaxies that are thought to be eruptions from LBVs. For example, the Great Eruption was significantly cooler than allowed by simple stellar-wind models used to explain supernova impostors.

“This star’s Giant Eruption has been considered a prototype for all supernova imposters in external galaxies,” Prieto said. “But this research indicates that it is actually a rather unique event.”

Scientists still don’t know what phenomenon caused Eta Carinae to erupt and lose such a quantity of mass without being destroyed. Further research is necessary to determine whether other proposed models could have triggered this activity instead.

Star heavier than 250 solar systems!!!!!!!

Fig: The Young Cluster R136a and Star R136a1

July 21, 2010

Using a combination of instruments on the European Southern Observatory's (ESO) Very Large Telescope (VLT), a team of astronomers has discovered the most massive stars to date. One star at birth had more than 300 times the mass of the Sun, twice as much as the currently accepted limit. The existence of these monsters — millions of times more luminous than the Sun, losing mass through very powerful winds — may provide an answer to the question, "How massive can stars be?"

A team of astronomers led by Paul Crowther from University of Sheffield, United Kingdom, used ESO's VLT, as well as archival data from the NASA/European Space Agency's (ESA) Hubble Space Telescope, to study two young clusters of stars, NGC 3603 and RMC 136a. NGC 3603 is a cosmic factory where stars form frantically from the nebula's extended clouds of gas and dust, located 22,000 light-years from the Sun. RMC 136a (nicknamed R136) is another cluster of young, massive, and hot stars, located inside the Tarantula Nebula, in one of our neighboring galaxies, the Large Magellanic Cloud, 165,000 light-years away.

The team found several stars with surface temperatures more than 7 times hotter than our Sun, tens of times larger, and several million times brighter. Comparisons with models imply that several of these stars were born with masses in excess of 150 solar masses. The star R136a1, found in the R136 cluster, is the most massive star ever found with a current mass of about 265 solar masses and a birth mass of as much as 320 times that of the Sun.

In NGC 3603, the astronomers could also directly measure the masses of two stars that belong to a double star system. The stars A1, B, and C in this cluster have estimated masses at birth above or close to 150 solar masses. The star A1 is a double star with an orbital period of 3.77 days. The two stars in the system have, respectively, 120 and 92 times the mass of the Sun, which means that they formed as stars of 148 and 106 solar masses, respectively.

Massive stars have such high luminosities with respect to their mass that they produce powerful outflows. "Unlike humans, these stars are born heavy and lose weight as they age," said Crowther. "Being a little over a million years old, the most extreme star, R136a1, is already 'middle-aged' and has undergone an intense weight-loss program, shedding a fifth of its initial mass over that time, or more than 50 solar masses."

If R136a1 replaced the Sun in our solar system, it would outshine the Sun by as much as the Sun currently outshines the Full Moon. "Its high mass would reduce the length of Earth's year to 3 weeks, and it would bathe the Earth in incredibly intense ultraviolet radiation, rendering life on our planet impossible," said Raphael Hirschi from Keele University, Staffordshire, United Kingdom.

These heavyweight stars are extremely rare, forming solely within the densest star clusters. To distinguish the individual stars for the first time required the exquisite resolving power of the VLT.

The team also estimated the maximum possible mass for the stars within these clusters and the relative number of the most massive ones. "The smallest stars are limited to more than about 80 times more than Jupiter, below which they are 'failed stars' or brown dwarfs," said team member Olivier Schnurr from the Astrophysikalisches Institut Potsdam, Germany. "Our new finding supports the previous view that there is also an upper limit to how big stars can get, but it raises the limit by a factor of two to about 300 solar masses."

Within R136, only four stars weighed more than 150 solar masses at birth, yet they account for nearly half of the wind and radiation power of the entire cluster, comprising approximately 100,000 stars in total. R136a1 alone energizes its surroundings by more than a factor of 50 compared to the Orion Nebula cluster.

An observer on a (hypothetical) planet in the R136 cluster would have a dramatic view. The density of stars in the cluster is about 100,000 times higher than around our Sun. Many of these stars are incredibly bright, so the planet's sky would never get dark.

Understanding how high-mass stars form is puzzling enough due to their short lives and powerful winds, so the identification of such extreme cases as R136a1 raises the challenge to theorists still further. "Either they were born so big or smaller stars merged together to produce them," said Crowther.

Stars between about 8 and 150 solar masses explode at the end of their short lives as supernovae, leaving behind exotic remnants of either a neutron star or a black hole. Having established the existence of stars between 150 and 300 solar masses, the astronomers' findings raise the prospect of the existence of exceptionally bright, "pair instability supernovae" that completely blow themselves apart, failing to leave behind any remnant and dispersing up to 10 solar masses of iron into their surroundings. A few candidates for such explosions have already been proposed in recent years.

Not only is R136a1 the most massive star ever found, but also it has the highest luminosity too, close to 10 million times greater than the Sun. "Owing to the rarity of these monsters, I think it is unlikely that this new record will be broken any time soon," said Crowther.

Massive Star Pair Raises Dust While Doing the Tango

2002 February 25

A Canadian-led research team using the Gemini Observatory has released tantalizing evidence that tiny dust particles ejected by hot, massive stars, may survive long enough to reach the interstellar medium. This kind of process might have provided some of the materials necessary for the early formation of planetary systems in the young Universe.The research team used the advanced mid-infrared imaging capabilities of the Gemini North Telescope, on Mauna Kea in Hawaii, to study the dynamic interaction between a massive binary star pair engaged in a dusty orbital tango. The star system, named "WR 112", pits stellar winds from one star against the other to produce a bow shock where the stronger wind pushes back the weaker. The extreme compression at the bow shock forms dust that subsequently flows out from the system, tracing a giant spiral that hints at the star pair's ongoing orbital dance."These massive, most unsuspecting dust-producing Wolf-Rayet stars have been observed as they orbit in binary pairs before, but this is the first time that we have imaged one at multiple, mid-infrared wavelengths at this resolution," says Dr. Sergey Marchenko, formerly of the Université de Montréal (now at the Western Kentucky University) and lead-author of the paper published in the January 20, 2002 Astrophysical Journal Letters. "Looking at this system with Gemini we have revealed that the carbon dust particles, while tiny, are about 100 times larger than state-of-the-art theory predicts. In addition, a significant portion of the dust appears to be escaping into interstellar space before it can be destroyed by the lethal radiation field emanating from the hot, massive stars of the binary system."

Theory predicts that very early in the history of the Universe, the majority of stars may have been very massive, like those that become Wolf-Rayet (WR) stars. Because of their high mass, these stars burn rapidly and intensely, living lives about 1000 times shorter than stars like our Sun. It is therefore likely that this process could have injected a large amount of heavy-element (mainly carbon from the nuclear fusion of helium) dust into the interstellar medium while the Universe was still relatively young. "As a result, we might need to consider a relatively early epoch in the history of the Universe when the necessary ingredients first became available in the interstellar medium to seed and form planetary systems," said Marchenko.

The images produced by Gemini of this system clearly show the spiraling dust cloud formed by the dance of these two giant stars. Anthony Moffat also of the Université de Montréal, and co-PI with Marchenko, describes the result of this interaction in more earthly terms, "If you look downstream, beyond the central region where the winds from the two stars collide, we see a trail of dust that spirals out due to the combined orbital motions of the two stars. This outflowing is much like the path that water takes as a playful gardener swings around a high pressure garden hose!"

One mystery that remains is how the amorphous carbon dust particles form and survive in the harsh environment surrounding these stars. It is also unknown what processes lead to the formation of dust grains that are almost two orders of magnitude larger than theory predicts. Even at this size, each dust particle is still only about the size of cigarette smoke particles, or about 1 micron across.

What is understood is that the stellar wind from the carbon-rich Wolf-Rayet star in the WR112 pair is much stronger than that of the companion. As the wind from the Wolf-Rayet star encounters the weaker wind from its companion, a "shock-zone" is formed that bends back around the companion. The increased pressure in the shock-zone is believed to spark the formation of these larger grains of amorphous carbon dust. The dust then is obliged by the stronger WR stellar wind to flow away from and out of the system in the distinctive spiral pattern that was revealed by the Gemini mid-infrared images.WR112 is thought to lie at about 14,000 light-years from the Earth and consist of one fairly massive Wolf-Rayet star that is gravitationally bound to another more normal yet very massive "O" type star. The two stars orbit each other with an orbital period that is estimated to be about 25 years, based on the known wind speed of the WR star, the form of the spiral and the estimated distance from Earth. The detectable dust spiral extends at least to a radius of about 12000 AU or over 100 times the radius of our solar system assuming the estimated distance to the system is accurate.

Members of the team which conducted this research led by Marchenko and Moffat included W.D Vacca – Max-Planck-Institut fuer extraterrestrische, Astrophysik Germany/Garching, S. Côté – Herzberg Inst. of Astrophysics, National Research Council Canada/Victoria, R. Doyon – Université de Montréal. The instrument used to make these observations on Gemini was the "Observatory Spectrometer and Camera for the Infrared" (OSCIR) that was built by the University of Florida, funded by the United States' National Science Foundation (NSF) and NASA and operated by the OSCIR Team led by Dr. Charles Telesco. The research was based upon images that were obtained at wavelengths of 7.9, 12.5 and 18.2 microns in the mid-infrared region of the electromagnetic spectrum. Additional near-infrared images of WR112 were obtained in 1999 and 2000 at the Canada-France-Hawaii Telescope and NASA Infrared Telescope Facility. Those shorter wavelength images helped to constrain characteristics of the hotter dust particles closer to the stars.

Previous observations of massive binary pairs have been made by other research groups, most notably the observations of WR98a and WR104 by P. Tuthill, J. Monnier and W. Danchi using the W.M. Keck Observatory, exposing beautiful, ever-changing dust spirals emanating from the binaries. These two systems also contain relatively cool carbon-rich WR stars, but in smaller orbits with periods of about a year. These observations have been crucial to our understanding of the dynamics around these systems by providing data at shorter infrared wavelengths that revealed details on the hotter dust in the vicinity of the binary star, but did not place any firm restrictions on the size of the particles or the full extent of the dust shell.

Gemini Spies Strong Stellar Gusts in Nearby Massive Star

photo: This dramatic infrared image sheds new light on the early stages of the formation of giant stars in our galaxy. This image reveals remarkable details in a nebula of gas and dust expelled from AFGL 2591. This expulsion is a common feature in the formation of stars similar in size to the Sun, but it is far less common in their massive counterparts. The resolution of this image is 0.4 arcseconds.

2001 July 23

A dramatic infrared image released today by the Gemini Observatory sheds new light on the early stages of the formation of giant stars in our galaxy. The image, taken by the Gemini North telescope on Hawaii's Mauna Kea, reveals remarkable details in a nebula of gas and dust expelled from a young star named AFGL 2591. This expulsion is a common feature in the formation of stars similar in size to the Sun, but it is far less common in their massive counterparts."Almost everything in this set of infrared images would be invisible with an optical telescope, since it is occurring within a dense molecular cloud of gas and dust," says Gemini scientist Colin Aspin, who made the observation. "Gemini's unparalleled sensitivity and resolution in the infrared allows us to move beyond simply detecting such structures in general to being able to study them in great detail."

AFGL 2591 is located within the Milky Way more than 3,000 light-years from Earth, in the constellation of Cygnus. Over the course of the last few thousand years, it has created a vast expanding nebula larger than 500 times the diameter of our solar system. The star is at least 10 times the size of the Sun, and over 20,000 times as bright, but perhaps only one million years old.

The wispy white and blue structure in the expanding nebula to the right of the young star is a huge outflow of gas and dust driven by the infall of material onto the star's surface. Gemini scientists believe that the outflow is likely occurring symmetrically around the star - a second giant-sized expanding nebula to the left of the star is hidden from view by a dense and extensive disk (or torus) of material encircling AFGL 2591.

"We strongly suspect the outflow occurs on both sides of the star in a bipolar structure, because we detect faint traces of gas at that location which indicate interactions between the outflowing gas and the material forming the parent molecular cloud," says Aspin, a scientific staff member at the Gemini Observatory International Headquarters in Hilo, HI.

"A unique feature of this object is a series of four distinct rings of nebulosity. These rings suggest that the expulsion of the material is not constant with time, but rather has occurred several times over the lifetime of the object," he adds. "Studying the structure and velocity of these rings, and their relation to the infalling material, will allow us to better understand why such features are created and what functions they serve."

This striking image is part of a series of early images taken with the Gemini Near Infrared Imager (NIRI) instrument during its commissioning on the Gemini North telescope. Once fully operational later this year, NIRI will be the prime near-infrared instrument on Gemini North.

The color image and others that show hints of the left-hand outflow and more details in the right-hand structure are available on the Internet in various file sizes (different files will go here).

The Gemini Observatory is an international collaboration that has built two identical 8-meter telescopes. The telescopes are located at Mauna Kea, Hawaii, (Gemini North) and Cerro Pachón in central Chile (Gemini South), and hence provide full coverage of both hemispheres of the sky. Both telescopes incorporate new technologies that allow large, relatively thin mirrors under active control to collect and focus both optical and infrared radiation from space. Gemini North recently began science operations and Gemini South is scheduled to begin scientific operations in August 2001.

The Gemini Observatory provides the astronomical communities in each partner country with state-of-the-art astronomical facilities that allocates observing time in proportion to each country's contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the UK Particle Physics and Astronomy Research Council (PPARC), the Canadian National Research Council (NRC), the Chilean Comisión Nacional de Investigación Cientifica y Tecnológica (CONICYT), the Australian Research Council (ARC), the Argentinean Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and the Brazilian Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). The Observatory is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership.

The largest star in our galaxy has gone Crazy

January 8, 2007

Using NASA's Hubble Space Telescope and the W.M. Keck Observatory, Kameula, Hawaii, astronomers have learned that the gaseous outflow from one of the brightest super-sized stars in the sky is more complex than originally thought.

The outbursts are from VY Canis Majoris, a red supergiant star that is also classified as a hypergiant because of its very high luminosity. The eruptions have formed loops, arcs, and knots of material moving at various speeds and in many different directions. The star has had many outbursts over the past 1,000 years as it nears the end of its life.

A team of astronomers led by Roberta Humphreys of the University of Minnesota used NASA's Hubble Space Telescope and the W.M. Keck Observatory to measure the motions of the ejected material and to map the distribution of the highly polarized dust, which reflects light at a specific orientation. The polarized light shows how the dust is distributed. Astronomers combined the Hubble and Keck information to produce a three-dimensional image of the matter emitted from VY Canis Majoris.

"We thought mass loss in red supergiants was a simple, spherical, and uniform outflow, but in this star it is very complex," Humphreys said. "VY Canis Majoris is ejecting large amounts of gas at a prodigious rate and is consequently one of our most important stars for understanding the high-mass loss episodes near the end of massive star evolution. During the outbursts, the star loses about 10 times more mass than its normal rate.

"With these observations, we have a complete picture of the motions and directions of the outflows, and their spatial distribution, which confirms their origin from eruptions at different times from separate regions on the star."

Humphreys and her collaborators presented their findings today (Jan. 8) at the American Astronomical Society meeting in Seattle, Wash.

Astronomers have studied VY Canis Majoris for more than a century. The star is located 5,000 light-years away. It is 500,000 times brighter and about 30 to 40 times more massive than the Sun. If the Sun were replaced with the bloated VY Canis Majoris, its surface could extend to the orbit of Saturn.It's radius is 2000 times more than our parent sun.

Images with Hubble's Wide Field and Planetary Camera 2 revealed for the first time the complexity of the star's ejecta. The first images provided evidence that the brightest arcs and knots were created during several outbursts. The random orientations of the arcs also suggested that they were produced by localized eruptions from active regions on the star's surface.

With spectroscopy obtained using the Keck Telescope, Humphreys and her team learned more about the shape, motion, and origin of the star's outflow. Line of sight velocities, measured from the spectra, showed that the arcs and knots were expanding relative to the star. With recently obtained Hubble images, the group measured the ejecta's motions across the line of sight.

The team found that the numerous arcs, loops, and knots were moving at different speeds and in various directions, confirming they were produced from separate events and from different locations on the star.

The astronomers also used the measurements to determine when the outbursts happened. The outermost material was ejected about 1,000 years ago, while a knot near the star may have been ejected as recently as 50 years ago.

The arcs and knots represent massive outflows of gas probably ejected from large star spots or convective cells on the star's surface, analogous to the Sun's activity with sunspots and prominences associated with magnetic fields, but on a vastly larger scale. Magnetic fields have been measured in VY Canis Majoris's ejecta that correspond to field strengths on its surface comparable to the magnetic fields on the Sun. These measurements show that the supergiant star's magnetic fields would supply sufficient energy for these massive outflows.

The astronomers used the measurements to map the velocity and direction of the outflows with respect to the embedded star. When combined with the dust distribution map, they also determined the location of the arcs and knots, yielding the three-dimensional shape of VY Canis Majoris and its ejecta.

"With these observations, we may have captured a short-lived phase in the life of a massive star," Humphreys said. "The most luminous red supergiants may all eventually experience high-mass loss episodes like VY Canis Majoris before ending their lives."

The typical red supergiant phase lasts about 500,000 years. A massive star becomes a red supergiant near the end of its life, when it exhausts the hydrogen fuel at its core. As the core contracts under gravity, the outer layers expand, the star gets 100 times larger, and it begins to lose mass at a higher rate. VY Canis Majoris has probably already shed about half of its mass, and it will eventually explode as a supernova.

The Hibernating Stellar Magnet

photo: The Hibernating Stellar Magnet

Date: sep 2008

First Optically Active Magnetar-Candidate Discovered

Astronomers have discovered a most bizarre celestial object that emitted 40 visible-light flashes before disappearing again. It is most likely to be a missing link in the family of neutron stars, the first case of an object with an amazingly powerful magnetic field that showed some brief, strong visible-light activity.

This weird object initially misled its discoverers as it showed up as a gamma-ray burst, suggesting the death of a star in the distant Universe. But soon afterwards, it exhibited some unique behaviour that indicates its origin is much closer to us. After the initial gamma-ray pulse, there was a three-day period of activity during which 40 visible-light flares were observed, followed by a brief near-infrared flaring episode 11 days later, which was recorded by ESO's Very Large Telescope. Then the source became dormant again.

"We are dealing with an object that has been hibernating for decades before entering a brief period of activity", explains Alberto J. Castro-Tirado, lead author of a paper in this week's issue of Nature.

The most likely candidate for this mystery object is a 'magnetar' located in our own Milky Way galaxy, about 15 000 light-years away towards the constellation of Vulpecula, the Fox. Magnetars are young neutron stars with an ultra-strong magnetic field a billion billion times stronger than that of the Earth. “A magnetar would wipe the information from all credit cards on Earth from a distance halfway to the Moon,” says co-author Antonio de Ugarte Postigo. "Magnetars remain quiescent for decades. It is likely that there is a considerable population in the Milky Way, although only about a dozen have been identified."

Some scientists have noted that magnetars should be evolving towards a pleasant retirement as their magnetic fields decay, but no suitable source had been identified up to now as evidence for this evolutionary scheme. The newly discovered object, known as SWIFT J195509+261406 and showing up initially as a gamma-ray burst (GRB 070610), is the first candidate. The magnetar hypothesis for this object is reinforced by another analysis, based on another set of data, appearing in the same issue of Nature.

Light Echo from Star V838 Monocerotis

These are the most recent NASA Hubble Space Telescope views of an unusual phenomenon in space called a light echo. Light from a star that erupted nearly five years ago continues propagating outward through a cloud of dust surrounding the star. The light reflects or "echoes" off the dust and then travels to Earth.

Because of the extra distance the scattered light travels, it reaches the Earth long after the light from the stellar outburst itself. Therefore, a light echo is an analog of a sound echo produced, for example, when sound from an Alpine yodeler echoes off of the surrounding mountainsides.

The echo comes from the unusual variable star V838 Monocerotis (V838 Mon), located 20,000 light-years away on the periphery of our Galaxy. In early 2002, V838 Mon increased in brightness temporarily to become 600,000 times brighter than our Sun. The reason for the eruption is still unclear.

Hubble has been observing the V838 Mon light echo since 2002. Each new observation of the light echo reveals a new and unique "thin-section" through the interstellar dust around the star. The new images of the light echo were taken with Hubble's Advanced Camera for Surveys in November 2005 (left) and September 2006 (right). Particularly noticeable in the images are numerous whorls and eddies in the interstellar dust, which are possibly produced by effects of magnetic fields.