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Saturday, July 7, 2012

Everything you ever wanted to know about V1647 Ori and McNeil's Nebula

 
An artist's impression of what might be happening behind the thick dust disc surrounding the young Sun-like star V1647 Ori. X-ray observations by ESA's XMM-Newton, NASA's Chandra and Japan's Suzaku space observatories have probed the interior of the dust disc to find a rapidly-rotating star spinning with a period of one day. At 80 per cent the mass of our Sun and with a diameter approximately four times larger, spinning at this rate nears break-up speed for a star of this size. The data also suggest that matter is accreting onto the stellar surface in two pancake-shaped hotspots located on opposite sides of the star, in which the matter heats up and the high temperature plasma is confined. Copyright: ESA/C. Carreau

X-raying the beating heart of a newborn star – ESA (July 3, 2012)

An international team of scientists has used the world's most powerful X-ray observatories - including ESA's XMM-Newton orbiter - to probe the dusty surroundings of a newborn star and discover some of its innermost secrets. These findings shed new light on one of the most fundamental processes in the Universe, the creation of stars.

Our Galaxy contains numerous clouds of gas and dust - stellar nurseries where stars are born as the result of gravitational collapse and gradually grow in size until hydrogen fusion begins, enabling them to blaze forth in all their glory. Although the basic outline of the story is fairly well understood, there are still many questions that need to be answered.

It is generally believed that infant stars – known as 'protostars' – grow as the result of mass accretion. Large amounts of matter fall onto them from the innermost part of a surrounding disc, which is created by the gravitational collapse of a molecular cloud.

Fast-moving jets of material have been observed flowing outward from many protostars, suggesting the influence of powerful magnetic fields and highly energetic processes in the innermost regions of protostellar discs. However, the presence of the cocoon of gas and dust makes it extremely difficult to discover what is happening to the fledgling star in the centre.

In order to learn more about the growth of protostars, the team decided to use data from three orbiting X-ray observatories - XMM-Newton, Chandra and Suzaku - to study a young, low-mass star, known as V1647 Ori, which is located at the apex of McNeil's Nebula.

Writing in The Astrophysical Journal, an international team of scientists has now re-examined X-ray data obtained during two optical outbursts that are associated with mass accretion on V1647 Ori – one that occurred during the period 2003-2006 and another that has been under way since 2008.

Previous studies had shown that the protostar's X-ray output increased 100 times when the optical outbursts occurred, whilst the temperature of the plasma soared to about 50 million Kelvin. However, the cause of these soaring temperatures was unclear. Acceleration of this material due to the influence of gravity alone is insufficient to raise the temperature of the plasma above a few million degrees.

"In some ways it's like a huge waterfall, cascading down under gravity," said Kenji Hamaguchi from NASA's Goddard Space Flight Center, lead author of the paper. "We found that the 50 million degree plasma produced by mass accretion activity is located at the bottom of the accretion flow.

"In order to explain the sizzling temperature, the plasma stream must be hitting the star's surface at a speed of around 2000 km/s. The most likely explanation is that magnetic reconnection – a sudden reconfiguration of the magnetic field lines close to the young star - is accelerating the material."

The team also identified a regular, short period, variation in the protostar's powerful X-ray emissions.

"During the two outbursts, we identified strong similarities in 11 separate X-ray light curve observations of V1647 Ori, obtained with three different space observatories," said Hamaguchi.

The light curve with the longest duration, obtained with XMM-Newton in 2005, shows that the X-ray flux stays constant for about 5½ hours, rises by a factor of 5 over the next four hours, remains at an elevated level for more than 8 hours and then falls gradually to the original flux level.

"Subsequent observations with Suzaku enabled us to identify a similar light curve, indicating a periodic variation in the X-ray emission that lasts about one day," said Nicolas Grosso, a CNRS researcher at Strasbourg Astronomical Observatory in France, and a co-author of the paper.

"Since V1647 Ori has an estimated mass of 0.8 solar masses and a radius about five times larger than the Sun, this periodicity indicates that the star is rotating so quickly that it is close to breaking apart."

What is causing the periodic changes in X-ray output? According to the team, the most likely interpretation is that localised 'hot spot' regions of X-ray plasma are moving in and out of our line of sight as the star rotates. Rises and falls in the light curves would then correspond to appearances and disappearances of X-ray bright spots.

"The phases of low and high flux in the light curve cannot be reproduced by a single spot," said Hamaguchi. "We, therefore, assume two spots with identical shapes, located on opposite sides of the star."

Modelling of the X-ray light curve indicates that the extremely hot plasma resides in large, pancake-shaped magnetic footprints, where the material from the disc is colliding with the surface of the newborn star.

The sustained X-ray periodicity of V1647 Ori demonstrates that such protostellar accretion can be stable over timescales of years. The duration of the rises and falls in the flux suggests that the spots cover a large area of the protostar's surface.

"The footprint of the infall is comparable to the size of the Sun's disc" said Hamaguchi. "Our calculations suggest that the bright spot is about five times more luminous than the faint spot. The brighter spot is located at a stellar latitude of about 49 degrees, whereas the star's inclination - the tilt of its polar axis toward our line of sight - is about 68 degrees. This alignment enables us to detect the accretion footprint."

"How stars are created is one of the fundamental questions in modern astrophysics, so studies such as this, which reveal the physical processes at work, are extremely important," said Norbert Schartel, ESA's Project Scientist for XMM-Newton.

X-ray lightcurve of V1647 Ori. Observations of the young, low-mass star, V1647 Ori, with the XMM-Newton, Chandra and Suzaku observatories, have revealed periodic variations in the X-ray emission from this protostar. The authors propose that these periodic changes arise from localised 'hot spot' regions of X-ray plasma that are moving in and out of our line of sight as the star rotates. Rises and falls in the light curves would then correspond to appearances and disappearances of X-ray bright spots. This lightcurve shows the best-fit result of their model to data from XMM-Newton and Suzaku. The green line indicates the contribution from the bright spot, the blue line the contribution from the blue spot, and the red line is the modelled total emission. The sequence above the lightcurve depicts the locations of hot spots at the corresponding phases. Credit: K. Hamaguchi et al.
During outbursts, the infant star in McNeil's Nebula may brighten by 100 times at X-ray energies. In this animation, based on findings by NASA's Chandra Observatory, the Japan/U.S. Suzaku spacecraft, and Europe's XMM-Newton satellite, magnetic fields drive powerful flows onto the star, creating two hot spots that produce the high-energy emission. Credit: NASA's Goddard Space Flight Center
Periodic X-ray emission (yellow line) from V1647 Ori is best explained as the combined X-ray output of a pair of hot spots (green and red lines) located on opposite sides of the star. Both of the spots are about the size of the sun, but the southern spot is producing more X-rays. Illustrations across the top show how the changing orientation of the spots correlates to the star's X-ray emission. Crosses indicate the actual X-ray data points. Credit: NASA/Goddard Space Flight Center
Variation in x-ray flux from V1647 Ori observed by the Japanese satellite Suzaku in 2008. Credit: JAXA

In McNeil's Nebula, a Young Star Flaunts its X-ray Spots – NASA (July 3, 2012)

Using combined data from a trio of orbiting X-ray telescopes, including NASA's Chandra X-ray Observatory and the Japan-led Suzaku satellite, astronomers have obtained a rare glimpse of the powerful phenomena that accompany a still-forming star. A new study based on these observations indicates that intense magnetic fields drive torrents of gas into the stellar surface, where they heat large areas to millions of degrees. X-rays emitted by these hot spots betray the newborn star's rapid rotation.

Astronomers first took notice of the young star, known as V1647 Orionis, in January 2004, near the peak of an outburst. The eruption had brightened the star so much that it illuminated a conical patch of dust now known as McNeil's Nebula. Both the star and the nebula are located about 1,300 light-years away in the constellation Orion.

Astronomers quickly determined that V1647 Ori was a protostar, a stellar infant still partly swaddled in its birth cloud. "Based on infrared studies, we suspect that this protostar is no more than a million years old, and probably much younger," said Kenji Hamaguchi, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md., and lead author of the study.

Protostars have not yet developed the energy-generating capabilities of a normal star such as the sun, which fuses hydrogen into helium in its core. For V1647 Ori, that stage lies millions of years in the future. Until then, the protostar shines from the heat energy released by the gas that continues to fall onto it, much of which originates in a rotating circumstellar disk.

The mass of V1647 Ori is likely only about 80 percent of the sun's, but its low density bloats it to nearly five times the sun's size. Infrared measurements show that most of the star's surface has a temperature around 6,400 degrees Fahrenheit (3,500 C), or about a third cooler than the sun's.

Yet during the 2003 outburst, the protostar's X-ray brightness increased by 100 times and the temperature of its X-ray-emitting regions reached about 90 million F (50 million C). A new eruption began in 2008 and continues today.

During the outbursts, the brightness variations at optical and infrared wavelengths could be accounted for by changes in the protostar's main energy source, the inflow of matter onto the star. Because changes in X-ray brightness closely followed those in the optical and infrared, the higher-energy emission must also be linked to accretion.

"V1647 Ori gave us the first direct evidence that a protostar surges in X-ray activity as its rate of mass accretion rises," said co-author Nicolas Grosso, an astrophysicist of the French National Center for Scientific Research (CNRS) at the Strasbourg Astronomical Observatory. This connection since has been underscored by a few other young stars whose outbursts included elevated X-rays.

To explore the emission process in detail and identify where on the star or disk the X-rays arise, the scientists re-analyzed all observations of V1647 Ori from three premier X-ray satellites – Chandra, Suzaku and the European Space Agency's XMM-Newton. Their goal was to find patterns that might provide clues to the sites of and mechanisms for producing the high-energy emission.

Writing in the July 20 issue of The Astrophysical Journal, the team reports that strong similarities among 11 separate X-ray light curves allowed them to identify cyclic X-ray variations. Remarkably, these periodic signals establish that the star is spinning once each day. V1647 Ori is among the youngest stars whose spin rates have been determined using an X-ray-based technique.

"Considering that V1647 Ori is about five times the size of the sun, the rapid spin confirms that we're watching a young stellar object that is in the process of pulling itself together," said co-author Joel Kastner, a professor of imaging science and astronomical sciences and technology at the Rochester Institute of Technology in New York.

The cyclic X-ray changes represent the appearance and disappearance of hot regions on the star that rotate in and out of view. The model that best agrees with the observations, say the researchers, involves two hot spots of unequal brightness located on opposite sides of the star. Both spots are thought to be pancake-shaped areas about the size of the sun, but the more southerly spot is about five times brighter.

The hot spots represent the footprints of magnetically driven accretion flows from the disk to the surface of the young star. To reach the high temperatures associated with X-ray emission, matter must be hitting the protostar at a speed of about 4.5 million mph (2,000 km/s). As a result, the hot spots reach temperatures some 13,000 times hotter than anywhere else on the star.

"One attractive possibility for driving such high-speed matter involves magnetic fields that are undergoing a continual cycle of shearing and reconnection in mass accretion," said David Weintraub, a professor of astronomy at Vanderbilt University in Nashville, Tenn., and a member of the study team.

Both the star and its circumstellar disk possess magnetic fields. Because the star rotates faster than the disk, these fields become twisted and sheared, storing up energy much like a wound-up rubber band. When the tangled field eventually rearranges into a more stable state, it suddenly unleashes its stored energy in a powerful blast. This process, called magnetic reconnection, also powers X-ray flares on the sun.

But while the physical processes may be similar, their time scales are vastly different. The peak X-ray output of a solar flare lasts less only minutes. The outbursts of V1647 Ori persist for years.

For comparison, consider the most powerful solar flare on record, the X28 eruption of Nov. 4, 2003. Hamaguchi calculates that the steady X-ray brightness of V1647 Ori's current outburst is a few thousand times stronger than the peak luminosity of the solar flare. What actually causes the star's outbursts? Astronomers don't really know. They suspect that gas from the outer portion of the disk makes its way inward, gradually building up the inner disk closer to the star. The strong magnetic activity may only turn on after some threshold is reached, but once it does the gas rapidly flows onto the hotspots and produces X-rays.

Thanks to Chandra, Suzaku and XMM-Newton, the outbursts of V1647 Ori are giving astronomers a glimpse of the extreme childhood of a sun-like star.

Artist's impression of V1647 Ori's side view. Credit: NASA/Goddard Space Flight Center
Artist's interpretation of upper spot. Credit: NASA/Goddard Space Flight Center
Artist's interpretation of lower spot. Credit: NASA/Goddard Space Flight Center
Animation showing the rotation of V1647 Ori with its two bright hotspots. Credit: NASA's Goddard Space Flight Center

Oh, Baby! A Young Star Flaunts its X-ray Spots in McNeil’s Nebula – Rochester Institute of Technology (July 3, 2012)

X-ray observations have revealed something curious about the young star that illuminates McNeil’s Nebula, a glowing jewel of cosmic dust in the Orion constellation: The object is a protostar rotating once a day, or 30 times faster than the sun. The stellar baby also has distinct birthmarks—two X-ray-emitting spots, where gas flows from a surrounding disk, fueling the infant star.

The young star, V1647 Orionis, first made news in early 2004, when it erupted and lit up McNeil’s Nebula, located 1,300 light years away in a region of active star formation within the constellation of Orion. The initial outburst died down in early 2006, but then V1647 Ori erupted again in 2008, and has since remained bright.

More recently, astronomers combined 11 observations of V1647 Ori from NASA’s Chandra X-ray Observatory, the Japan-led Suzaku satellite, and the European Space Agency’s XMM-Newton to determine the source of the high-energy emission. The team began monitoring the star shortly after its eruption in 2004 and continued to keep watch through 2010, a period covering both eruptions.

Strong similarities among X-ray light curves captured over this six-year period allowed the lead author on the study, Kenji Hamaguchi, astrophysicist at NASA’s Goddard Space Flight Center, to identify cyclic X-ray variations. Hamaguchi and the rest of the team determined the star is rotating once per day, making V1647 among the youngest stars whose spin has been determined using an X-ray-based technique. Results from the study will appear in the paper “X-raying the Beating Heart of a Newborn Star: Rotational Modulation of High-energy Radiation from V1647 Ori,” in the July 20 issue of The Astrophysical Journal.

“The observations give us a look inside the cradle at a very young star,” says co-author Joel Kastner, a professor of imaging science and astronomical sciences and technology at Rochester Institute of Technology. “It’s as though we’re able to see its beating heart. We’re actually able to watch it rotate. We caught the star at a point where it is rotating so fast as it gains material that it’s barely able to hold itself together. It’s rotating at near break-up speed.”

The team identified V1647 Ori as a protostar in formation. “Based on infrared studies, we suspect that this protostar is no more than a million years old, and probably much younger,” Hamaguchi says.

V1647 Ori presently feeds on gas channeled from a surrounding disk and will likely continue to do so—though not nearly so rapidly—for millions of years. At that point it will finally be able to generate its own energy by fusing hydrogen into helium in its core like the sun and other mature stars.

Hamaguchi’s analysis focused on repetitive behavior found in the data from all three of the X-ray observatories. By combining data, he pieced together a picture showing the daily rotation of two X-ray-emitting spots on V1647 Ori that are thousands of times hotter than the rest of the star.

The hot spots are located at opposite sides of the star, with the southerly one five times brighter than its companion. Each spot is about the diameter of the sun. In comparison, the low density of V1647 Ori bloats the star itself to nearly five times the size of the sun.

“We think these spots are showing us X-ray-emitting regions that are very tightly constrained to a couple positions on the star by magnetic fields,” says Kastner, director of the Laboratory for Multiwavelength Astrophysics in RIT’s Chester F. Carlson Center for Imaging Science. “For six years, through two different eruptions, we’ve seen it rotate like this. That means the magnetic field configuration—the overall geometry between the disk and the star—is very stable. At the same time, the local disruption of magnetic fields probably generates the X-rays.”

“One attractive possibility for driving such high-speed matter involves magnetic fields that are undergoing a continual cycle of shearing and reconnection in mass accretion,” says co-author David Weintraub, professor of astronomy at Vanderbilt University.

In this picture, X-ray outbursts result from interplay of the magnetic fields belonging to the star and the disk. The star spins faster than the disk and winds up the magnetic fields until they snap like rubber bands. The pent up energy creates a powerful blast when the tangled magnetic fields fall back into place. The process, called magnetic reconnection, also powers X-ray flares on the sun.

During the outbursts, the star’s luminosity varied at optical and infrared wavelengths. The astronomers associated this to changes in the protostar’s main energy source, the inflow of matter onto the star. Because changes in the X-ray brightness of V1647 Ori closely followed those in the optical and infrared, the team established that its higher-energy emission is also closely linked to accretion.

“V1647 Ori gave us the first direct evidence that a protostar surges in X-ray activity as its rate of mass accretion rises,” says co-author Nicolas Grosso, an astrophysicist of the French National Center for Scientific Research at the Strasbourg Astronomical Observatory.

The finding that an accretion burst could be accompanied a surge of high-energy X-rays during the formation of a young star was originally announced by essentially the same study team, led by Kastner, in a paper published in Nature in 2004. In that paper, the team first argued that X-rays emitted by V1647 Ori were coming from material falling onto the star from a surrounding disk.

Up until then, the more widely accepted mechanism for producing X-rays from protostars was thought to be via coronae that are far more powerful than the sun’s, Kastner explains. Signatures in X-ray observations of a handful of stars in formative stages had led to the hunch that accretion might also contribute to or even dominate protostellar X-ray emission. The eruptions of V1647 Ori and a few other young stars that were accompanied by elevated X-ray emission levels have since underscored this connection, Kastner notes.

“The exciting and unexpected thing about our fresh look at the whole set of X-ray data for V1647 Ori is that this is the first time we’ve seen a star in such an early stage of formation with a regular rotation that you can measure in X-rays,” Kastner says.

Kastner and team hope to confirm the X-ray study’s findings at infrared wavelengths using NASA’s Spitzer Space Telescope.

KPNO Optical Image of McNeil's Nebula. McNeil's Nebula was discovered with a 3-inch telescope by amateur astronomer Jay McNeil in January 2004. A young star buried deep in a cloud had brightened suddenly, illuminating the nebula. This optical image of McNeil's Nebula and the surrounding area was taken by the Kitt Peak National Observatory (KPNO). Credit: NSF/NOAO/KPNO/A.Block et al.
The bottom right inset shows the four x-ray sources observed by Chandra. Number 3 is V1647 Ori. Credit: X-ray: NASA/CXC/RIT/J.Kastner et al.; Optical: NSF/NOAO/KPNO/A.Block et al.
Chandra X-ray Image with Optical Contours of McNeil's Nebula. The Chandra data is overlaid with contours from a short-exposure (10 sec) image of the nebula obtained with the European Southern Observatory's Very Large Telescope (VLT). The VLT and Chandra images were obtained on February 18 and March 7, 2004, respectively. The Chandra image is color-coded for energy (red = 0.5-1.5 keV; green = 1.5-2.4 keV; blue = 2.4-8.0 keV). Note the predominance of high-energy X-rays (blue) from source 3 (named CXO J054613.1-000604), which lies at the apex of McNeil's Nebula. Credit: X-ray: NASA/CXC/RIT/J.Kastner et al.; Optical: ESO/VLT/
This sequence leads the viewer from a ground-based optical view around McNeil's Nebula through to Chandra's up-close X-ray image. It begins with the picture of the region that amateur astronomer Jay McNeil took with his 3-inch telescope, which led to the discovery of the nebula (and hence the name). The images then proceed to increasingly smaller optical views of the nebula and its immediate environment. The sequence ends by showing Chandra's observation of the source at the apex of McNeil's Nebula, which was seen to flare in X-rays. The X-ray data suggest the outburst was caused by an infall of material onto the star's surface from an orbiting disk of gas. Credit: Optical, wide-fields: Jay McNeil / Optical, close-up: NSF/NOAO/KPNO/A.Block et al. / X-ray: NASA/CXC/RIT/J.Kastner et al.

McNeil's Nebula: X-ray Outburst from a Young Star - Chandra X-Ray (July 22, 2004)

The X-ray/optical comparison of the region surrounding McNeil's Nebula shows that the position of a source detected by Chandra is coincident with that of a bright infrared and optical source at the apex of the nebula. Source 3, thought to be a very young star, is illuminating the fan-shaped cloud of gas, or nebula. The others sources in the field, labeled 1, 2, and 4, are other young, X-ray emitting stars in the region.

The small nebula, which lies in the constellation Orion about 1300 light years from Earth, was discovered with a 3-inch telescope by amateur astronomer Jay McNeil in January 2004. A young star buried deep in a cloud had brightened suddenly, illuminating the nebula. The coincident X-ray source was also observed to brighten fifty-fold as measured in Chandra observations obtained before and just after the optical outburst. The X-ray data are strong evidence that the probable cause of the outburst is the sudden infall of matter onto the surface of the star from an orbiting disk of gas.

The coupling of the magnetic field of the star and the magnetic field of its circumstellar disk regulates the inflow of gas from the disk onto the star. This slow, steady inflow suddenly can become much more rapid if a large amount of gas accumulates in the disk, and the disk and the star are rotating at different rates.

The differing rotation rates can twist and shear the magnetic field, storing up energy. This energy is eventually released in an energetic, X-ray producing outburst as the magnetic field violently rearranges back to a more stable state. During this period, a large amount of gas can fall onto the star, producing the observed optical and infrared outburst.

A new buildup of gas in the disk could lead to a new outburst in the future. Such a scenario may explain why the brightness of McNeil's Nebula appears to vary with time. It appears in optical images taken of this region of Orion in the 1960s, but is absent from images taken in the 1950s and 1990s.

The reflection nebula M78 glows because dust grains in the cloud reflect and scatter the light of nearby stars. Dark dusty lanes, the birthing ground of protostars, thread throughout the region. This image was taken in 2006, between V1647 Ori’s 2003–2005 outburst and before the protostar’s next eruption in 2008, which is why McNeil’s Nebula is barely visible. Located some 1,600 light-years away, M78 is part of the vast Orion Complex, a large region of star-forming gas and dust. Credit: T. A. Rector/Univ. of Alaska Anchorage, H. Schweiker/WIYN and NOAO/AURA/NSF
The protostar V1647 Orionis resides at the tip of a conical glow called McNeil's Nebula, which was discovered in January 2004 near the peak of an outburst. This image, from the Frederick C. Gillett Gemini Telescope in Hawaii, shows the nebula as it appeared on Feb. 14, 2004. Credit: Gemini Observatory

Celestial Beacon Sheds New Light on Stellar Nursery - Gemini Observatory (June 2004)

A timely discovery by American amateur astronomer Jay McNeil, followed immediately by observations at the Gemini Observatory, has provided a rare glimpse into the slow, yet violent birth of a star about 1,500 light-years away. The resulting findings reveal some of the strongest stellar winds ever detected around an embryonic Sun-like star.

McNeil's find was completely serendipitous. He was surveying the sky in January from his backyard in rural Kentucky and taking electronic images through his 3-inch (8-centimeter) telescope. When he examined his work, he noticed a small glowing smudge of light in the constellation of Orion that wasn't there before. "I knew this part of the sky very well and I couldn't believe what I was seeing," said McNeil. Astronomers were alerted almost immediately, via the Internet, and quickly realized that he had come across something special.

"It is extremely rare that we have an opportunity to study an important event like this, where a newly born star erupts and sheds light on its otherwise dark stellar nursery," said Gemini astronomer Dr. Colin Aspin. Dr. Aspin and Dr. Bo Reipurth, (of the University of Hawaii's Institute for Astronomy), published the first paper on this object, now known as McNeil's Nebula. Their work, based on observations using the Frederick C. Gillett Gemini North Telescope on Mauna Kea, is in press for Astrophysical Journal Letters.

"McNeil's Nebula is allowing us to add another important piece to the puzzle of the long, protracted birth of a star," said Reipurth. "It has been more than thirty years since anything similar has been seen, so for the first time, we have an opportunity to study such an event with modern instrumentation like that available at Gemini."

Detailed images and spectra of the stellar newborn, taken using the Gemini Near-Infrared Imager and Multi-Object Spectrograph, demonstrate that the star has brightened considerably. It is blasting gas away from itself at speeds of more than 600 kilometers per second (over 2000 times faster than a typical commercial airplane). The observations indicate the eruption was triggered by complex interactions in a rotating disk of gas and dust around the star. For reasons that are still not fully understood, the inner part of the disk begins to heat up, causing the gases to glow. At the same time, some gas funnels along magnetic field lines onto the surface of the star, creating very bright hot spots and causing the star to grow. The eruption also cleared out some of the dust and gas surrounding the young star, allowing light to escape and illuminate a cone-shaped cavity carved out by previous eruptions into the gas.

The birth of a star takes several tens of thousands of years and these observations are but a brief snapshot of the process. Although this is a very rapid schedule on astronomical time scales, Reipurth explained that it's impossibly slow compared to a human lifetime. "We astronomers therefore have no choice but to compare various objects where each one is in a different state of development," he said. "This is very similar to the imaginary situation of an alien landing on Earth with only half an hour to understand the full life cycle of humans. By looking at people of various ages and using some logic, this alien could piece together our growth from infant to old age. This is how we are beginning to understand the birth and youth of stars. Rare events like the one McNeil discovered help to fill in the blanks in our understanding of stellar origins."

This outburst may not be the first time the star has flared during its long tumultuous birth. Following McNeil's discovery, an inspection of archival plates revealed that a similar event took place in 1966, when the star flared and faded again into its enshrouding gas. "We know so little about these kinds of eruptions that we cannot even say whether the star will continue to flare or will rapidly fade from view again," said Aspin. "We were extremely fortunate that Mr. McNeil discovered this when he did. In an event like this, the earlier we can observe it, the better our chances are of understanding what is going on."

Fortunately for Aspin and Reipurth, McNeil discovered this in the early winter while the Orion region is still high in the night-time sky. It was also fortunate that McNeil was so familiar with this part of the sky that he noticed right away that something had changed. This combination of circumstances enabled the astronomers to prepare an observation run on Gemini very quickly. "Our window for observing this object is closing rapidly but it will become visible again later this year," said Aspin. "By then this eruption could be over."

A striking color image from Gemini reveals fine details in McNeil's Nebula. The star and its bright disk shine like a lighthouse through the cavity of gas and dust.

The young star V1647 Ori at a quiescent stage early in the birth process. It is surrounded by a circumstellar disk and a shroud of gas and dust. Very little of the star's optical light can escape, so it shines primarily in the infrared part of the spectrum. Credit: Jon Lomberg / Gemini Observatory Illustrations
The beginning of the 2004 eruption. Gas rotating through inner regions of the disk begins to heat up and glow. At the same time, some gas is caught on magnetic field lines and is lifted out of the disk. Then it falls onto the star where it creates one or more hot spots. Credit: Jon Lomberg / Gemini Observatory Illustrations
Zoom on the central region of the previous image. Credit: Jon Lomberg / Gemini Observatory Illustrations
The eruption at a later stage when the luminous inner disk and the blinding white hot spots produce more light than the star. Gemini spectroscopic observations reveal that gas escapes from the erupting star-disk system with velocities of more than 600 km/second. This is one of the fastest winds ever recorded around a young star. The outflow clears away some of the surrounding gas and dust that shrouds the embryonic star, allowing the visible light from the star to shine through. Credit: Jon Lomberg / Gemini Observatory Illustrations
A more distant view of the system. It depicts how light from the brightened star and disk illuminate the surrounding outflow cavity. This is what we see as McNeil's Nebula. Credit: Jon Lomberg / Gemini Observatory Illustrations
The approximate location of McNeil's Nebula near the well-known reflection nebula called M78. Located above the three stars that form the belt of Orion, McNeil's Nebula can be viewed in a small telescope from nearly any location on Earth until this part of the sky is obscured by the glare of the Sun for several months between late April and late August. Credit: Jon Lomberg / Gemini Observatory Illustrations

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