Category: Astronomy

Eta Carinae. Image credit: Hubble. Click to enlarge.
Scientists using NASA’s Far Ultraviolet Spectroscopic Explorer satellite made the first direct detection of a companion star of Eta Carinae. Eta Carinae is one of the most massive and unusual stars in the Milky Way galaxy. The detection was made possible by the high temperature of the companion star and the unique sensitivity of the satellite at the shortest ultraviolet wavelengths.

Eta Carinae is an unstable star thought to be rapidly approaching the final stage of its life. It is clearly visible from the southern hemisphere and has been the subject of intense studies for decades. This mysterious star is located about 7,500 light-years from Earth in the constellation Carina. Scientists thought a companion star in orbit around Eta Carinae might explain some of its strange properties, but researchers lacked direct evidence a companion star existed.

“Until now, Eta Carinae’s partner has evaded direct detection,” said Dr. Rosina Iping, a research scientist at Catholic University of America in Washington. “This discovery significantly advances our understanding of the enigmatic star.”

Evidence that Eta Carinae might be a double star system was inferred from a repeating pattern of changes in visual, X-ray, radio and infrared light over approximately 5.5 years. Astronomers thought a second star in a 5.5 year orbit around Eta Carinae might cause the repeated changes in its light. The strongest indirect evidence supporting the double star theory is that once every 5.5 years, the X-rays coming from the system disappear for about three months. Eta Carinae is too cool to generate X-rays, but it continuously blasts a flow of gas into space as a stellar wind at about 300 miles per second.

If its companion has a similar wind, their stellar winds would collide with enough force to generate the X-rays. This collision region must lie somewhere between the two stars.

As Eta Carinae moves in its orbit, it passes in front of the region where the winds collide, as viewed from Earth. When this occurs, Eta Carinae eclipses the X-rays once every 5.5 years, causing them to disappear. The last X-ray eclipse began on June 29, 2003. The 5.5 year orbit places the companion star only about 10 times farther from Eta Carinae than Earth is from the sun. Eta Carinae is too far away for telescopes to distinguish two stars in such a close orbit.

Another way to find evidence of a double-star system would be to detect the light of the second star, which in this case is much fainter than Eta Carinae. Several scientists searched for light from Eta Carinae’s companion using ground-based telescopes, but none succeeded. Because the companion is thought to be much hotter than Eta Carinae, astronomers reasoned it should be brighter at shorter wavelengths like ultraviolet light. However, it still escaped detection when it was searched for using the ultraviolet capabilities of the Hubble Space Telescope.

Iping and her collaborators used the satellite to detect the companion, because it can see even shorter ultraviolet wavelengths than Hubble. The team observed the far-ultraviolet light from Eta Carinae with the satellite on June 10, 17 and 27, 2003, right before the expected X-ray eclipse. While the far ultraviolet light from Eta Carinae was seen in the observations from June 10 and 17, it vanished on the 27, two days before the X-ray eclipse.

The disappearance of far ultraviolet light so close to the X-ray eclipse implies when Eta Carinae eclipsed the X-rays, it also eclipsed the companion star. The far-ultraviolet light observed prior to the eclipse was from the hotter companion, because Eta Carinae is too cool to emit much far-ultraviolet light.

“This far ultraviolet light comes directly from Eta Carinae’s companion star, the first direct evidence that it exists,” said Dr. George Sonneborn. He is Far Ultraviolet Spectroscopic Explorer Project Scientist at NASA’s Goddard Space Flight Center, Greenbelt, Md. “The companion star is much hotter than Eta Carinae, settling a long-standing mystery about this important star.”

This discovery will be published today in the Astrophysical Journal Letters. Authors include Iping, Sonneborn and Ted Gull of Goddard; Derck Massa of SGT Inc., Greenbelt, Md.; and John Hiller of the University of Pittsburgh. The project is a NASA Explorer mission developed in cooperation with the French and Canadian space agencies by Johns Hopkins University, Baltimore, University of Colorado, Boulder, and University of California, Berkeley. Goddard manages the program for NASA’s Science Mission Directorate. For images and information about the project on the Web, visit:

Original Source: NASA News Release

Black widow nebula. Image credit: NASA/Spitzer. Click to enlarge.
Unsuspecting prey be warned! Hiding in the darkest corner of the constellation Circinus is a gigantic black widow spider waiting for its next meal. For decades, this galactic creepy crawler has remained largely invisible, cunningly escaping visible-light detection. At last, it has finally been caught by NASA’s Spitzer Space Telescope’s dust-piercing, infrared eyes.

The spider is actually a star-forming cloud of gas and dust. In this Halloween interactive image comparison, an hourglass-shaped insignia, typically found on the underbelly of a black widow spider, can be seen faintly in the visible-light image from Digital Sky Survey (DSS). As Spitzer’s infrared image fades in, the veil of galactic dust shrouding the rest of the spider is lifted to reveal a poisonous widow.

In the Spitzer image, the two opposing bubbles that make up the black widow’s body are being formed in opposite directions by the powerful outflows from massive groups of forming stars. The baby stars can be seen inside the widow’s “stomach” where the two bubbles meet.

When individual stars form from molecular clouds of gas and dust they produce intense radiation and very strong particle winds. Both the radiation and the stellar winds blow the dust outward from the star creating a cavity or, bubble.

In the case of the Black Widow Nebula, astronomers suspect that a large cloud of gas and dust condensed to create multiple clusters of massive star formation. The combined winds from these large stars probably blew out bubbles into the direction of least resistance, forming a double-bubble.

Original Source: Spitzer News Release

Image credit: Derek Breit. Click to enlarge.
Findings of this nature are one of the many reasons why International Occultation Timing Association (IOTA) members pursue their craft. One of the notable and historic discoveries on a standard star by occultation means happened in 1819 when Antares’ companion star was observed. However, the name of the astronomy game is confirmation – and also filming and timing the northern limit event at differing locations were Walt Morgan and Ed Morana.

Contacting IOTA’s Dr. David Dunham, Breit forwarded his findings, contacted team members and started seeking an answer for two unusual seconds of video. According to Dunham’s response, “Almost 2 seconds with a distance of much more than a km; it’s unlikely that the Moon would be that smooth, it would have to be within about 5m or less for the brightness to remain faint and constant at that level so long. Especially since this apparently occurred at nearly every event, a faint, close companion, only 0.01″ to 0.02″ north of the primary, seems likely.”

And Morgan clarifies, “The disappearances and reappearances by upsilon Geminorum as it passed lunar peaks were usually slow transitions, that is, the star appeared to fade (or brighten) over a matter of several video frames. That was not considered unusual because of the fairly large angular diameter of the star. However, in some instances the magnitude 4.1 star did not seem to completely disappear on Breit’s record: a very faint point of light remained visible right at the lunar limb.”

But confirmation of such importance to the scientific community doesn’t stop there. Breit’s findings went out to all IOTA observers and the critical timing information provided them with the clues they needed. Also recording the event was Dr. Richard Nolthenius, whose answer was, “Derek’s right! I’ve just reduced my upsilon Gem graze video recording from last Friday. I used a PC164c on an 8″ f/10 operating at f/6.3, recorded on my Canon ZR45mc. And the conclusion is…. Derek’s camcorder is not going crazy! I fully confirm his observations and conclusions – this star is a very close double star.”

As they continue to work through the geometry and astrometric angles, Dr. Nolthenius offers the following information from his own recordings: “The second and 3rd D’s look especially like there is an 11th magnitude companion, and the final D most dramatic of all, with the initial fade happening in just 3 frames, followed by a definite but very faint 11th magnitude star left over for fully 1 second before finally disappearing.”

Although it might seem that in a sky filled with innumerable double stars that a revelation of this type would be of little significance, IOTA member – Dr. Michael Richmond – knew better: “I did a little searching to see if there was any other indication that upsilon Geminorum might be double. The Hipparcos observations indicate that it is slightly variable, with an amplitude of about 0.08 mag, but there is no indication of a period. The Astrophysics Data Service has a number of references which mention upsilon Geminorum. This star has been chosen to be a calibrator for optical interferometers; that is, people have decided that it’s a good star to use as a reference when doing high angular resolution measurements. There are two recent papers which list measurements of its angular size: Borde et al. (A&A 393, 183, 2002), which finds an angular diameter of 5.00 +/- 0.051 mas, and Richichi and Percheron (A&A 386, 492, 2002), which lists angular diameter of 5.23 +/- 0.31 mas. Given the Hipparcos parallax of 13.57 mas, this means that the star’s diameter is roughly 0.37 AU. The main star has spectral type listed as late K or early M giant, with V-band mag 4.08 and K-band mag 0.24. If this is a double star, with a companion of roughly mag 11, then it would be important to let other astronomers know: it would no longer be a really good calibration star.”

But, Dr. Richmond did not let his findings rest there and he continued to look for more precise information. Says Richmond, “I found that both of the catalogue entries were NOT based on direct measurements of angular size; instead, they were simply estimates, based on the observed brightness and the shape of the spectrum. In other words, they were basically fits to a blackbody with a given temperature. I was surprised to find such indirect evidence appearing in catalogues of angular size, for use as a calibrator for interferometers.”

Recognizing the importance of such a finding as opposed to known data definitely changes the way we perceive information. Astronomy is a continually upgrading science as Dr. Nolthenius notes: “For some 9th magnitude star, finding yet another double is one thing, but for such a bright star, being a standard for certain measurements should be checked, as you did. The star is apparently in that fall-through-the-cracks area of parameter space: a wide enough double to not make for noticeable periodicity in the radial velocity on a time scale of a few years – the period is likely in the 100+ year range, (although this is something I will calculate later) and yet impossibly difficult as a visual binary without using interferometry or lunar occultations.”

Of course, there is far more to this picture than just the discovery of undisclosed double star. By recording, timing, and observing both grazing and occultation events, IOTA is able to help determine proper movement, orbit and lunar limb features as well. As Dr. Nolthenius explains, “The absolute UT’s of the events will help in assessing the slope of the moon at the event points. However, the most convincing case for duplicity will be identifying significant periods of time of constant brightness at the very faint levels.” The diffraction of large stars aids astronomers in making more accurate calculations, “Perhaps there is a secondary that is of order 1 radius or less above the surface of upsilon Geminorum.” hypothesizes Nolthenius, “If such extended periods of very faint levels might be consistent with limb darkening which is very extended. As a K giant, I would not expect the limb darkening to be so extreme – normally limb darkening is more extreme the cooler the star, and late K is not all that cool.”

More confirmation was needed and the findings were sent to Dr. Mitsuru Soma of the National Astronomical Observatory of Japan. Says Soma, “From the comparison of your faint flash mentioned above and the short duration (0.7s) from R to D of the primary of Walter Morgan the companion’s separation from the primary is estimated to be about 0.04 arcsec, and this is consistent with the duration of your gradual R’s at 4:39:07 and at 4:40:21 (UT). The spectral type of ups Gem is K5III which is the same as Aldebaran according to the Hipparcos catalogue, so I assume that the actual radius of ups Gem is almost the same as Aldebaran. The angular radius of Aldebaran was estimated to be about 0.010 arcsec from lunar occultations.”

But confirmation means being very sure that there is no chance of this being a diffraction effect. As Dr. Soma explains, “The distance to ups Gem is 3.6 times the distance to Aldebaran (ups Gem’s parallax is 0.014 arcsec and Aldebaran’s parallax is 0.050 arcsec) so the angular radius of ups Gem should be about 0.003 arcsec, which is small so that I think the error arisen from the assumption that the star is a point source is almost negligible when we estimate the diffraction effects. Referring to this fact I think 0.04 arcsec I mentioned above is too large to be attributed to the diffraction effects.”

Confirmation continues on a deeper level when Dr. Michael Richmond plots the photometry of all three tapes of the Upsilon Geminorum event: “The thing I find very interesting and encouraging is that I see an asymmetry in these light curves.” says Richmond, “If this is true, then I think we can make a good case that there may be a faint companion to the primary star. The companion must be “ahead” of the primary, so that the moving limb of the moon first blocks (or reveals) the companion, before it blocks (or reveals) the primary.”

Dr. Mitusuru Soma also continued with his analysis and presented the papers at the Journees 2005 meeting in Warsaw on 2005 September 19-21. Based on available information says, “My conclusion about the position of the secondary of upsilon Geminorum relative to the primary is 0″.04 +/- 0″.01 in separation and 70deg +/- 20deg in PA.” Although these findings are preliminary, Soma will continue to review the data and clarify the results of all accumulative information.

Seeing double? The answer is quite probable. In the mean time IOTA members will continue to review of the data and further research the duplicity of upsilon Geminorum. There’s a whole big wide sky out there, and each time an observation of this type is made it adds more to our understanding. While speckle interferometry is cutting edge of double star detection – the occultation method can reveal far more. Contributions from dedicated members are what makes the International Occultation and Timing Association play an important role in today’s astronomy.

Says Breit, “It was a pretty darn good feeling when Dr Nolthenius wrote “Derek’s RIGHT!” When four PhD’s say I have found something special doing a hobby I taught myself from the age of six, that’s pretty good. Something to tell the grandkids… But my real thought was that I finally have a great video to show others and hopefully get them interested in observing these very dynamic and temporal events!” So what are the chances of IOTA members Derek Breit, Walt Morgan, Ed Morana and Michael Richmond making a contribution to the scientific community?

I’d say double.

Written by Tammy Plotner.

Our planet. Image credit: NASA/JPL. Click to enlarge.
New research allows geologists to estimate the time at which the Earth’s core separated from its rocky outer shell.

A paper in this week’s Nature [26 October 2005] shows how the problem can be resolved by considering the effect of a giant impact with the Earth.

Previous research, using two different types of radioactive ‘clocks’ (hafnium-tungsten and uranium-lead), appeared to give conflicting core formation times of about 35 and 80 million years, respectively, after the origin of the solar system.

The collision of a Mars-sized object with the Earth is thought to have contributed to the last ten percent of the Earth’s mass, as well as forming the Moon.
“The explanation may be that the hafnium-tungsten clock represents the initial phase of core formation, whereas the uranium-lead clock, that gives a younger age, has been reset by the upheaval introduced by the giant impact.”
Professor Bernie Wood

Professor Bernard Wood, who completed this research while at Bristol University, and Professor Alex Halliday from Oxford University, propose that the impact would have also changed the conditions of core formation.

They put forward a model that explains the discrepancy between the two isotope clocks if the effects of the oxidation state of the mantle are taken into account.

Professor Wood said: “The explanation may be that the hafnium-tungsten clock represents the initial phase of core formation, sometime before 35 million years after the origin of the solar system, whereas the uranium-lead clock, that gives a younger age of about 80 million years after the origin of the solar system, has been reset by the upheaval introduced by the giant impact.”

The impact could have produced an oxidation state under which a sulphur-rich metal formed – of which the core is now composed. This oxidation state would have readily allowed lead to dissolve, effectively resetting the uranium-lead clock and resulting in the younger age.

Original Source: University of Bristol News Release

Artist illustration of microscopic crystals surrounding a dusty disk. Image credit: NASA/JPL. Click to enlarge.
NASA’s Spitzer Space Telescope has spotted the very beginnings of what might become planets around the puniest of celestial orbs – brown dwarfs, or “failed stars.”

The telescope’s infrared eyes have for the first time detected clumps of microscopic dust grains and tiny crystals orbiting five brown dwarfs. These clumps and crystals are thought to collide and further lump together to eventually make planets. Similar materials are seen in planet-forming regions around stars and in comets, the remnants of our own solar system’s construction.

The findings provide evidence that brown dwarfs, despite being colder and dimmer than stars, undergo the same initial steps of the planet-building process.

“We are learning that the first stages of planet formation are more robust than previously believed,” said Dr. Daniel Apai, an astronomer at the University of Arizona, Tucson, and member of the NASA Astrobiology Institute’s Life and Planets Astrobiology Center. “Spitzer has given us the possibility to study how planets are built in widely different environments.”

The observations also imply that brown dwarfs might be good targets for future planet-hunting missions. Astronomers do not know if life could exist on planets around brown dwarfs.

Brown dwarfs differ from stars largely due to their mass. They lack the mass to ignite internally and shine brightly. However, they are believed to arise like stars, out of thick clouds of gas and dust that collapse under their own weight. And like stars, brown dwarfs develop disks of gas and dust that circle around them. Spitzer has observed many of these disks, which glow at infrared wavelengths.

Apai and his team used Spitzer to collect detailed information on the minerals that make up the dust disks of six young brown dwarfs located 520 light-years away, in the Chamaeleon constellation. The six objects range in mass from about 40 to 70 times that of Jupiter, and they are roughly 1 to 3 million years old.

The astronomers discovered that five of the six disks contain dust particles that have crystallized and are sticking together in what may be the early phases of planet assembling. They found relatively large grains and many small crystals of a mineral called olivine.

“We are seeing processed particles that are linking up and growing in size,” said Dr. Ilaria Pascucci, a co-author also of the University of Arizona. “This is exciting because we weren’t sure if the disks of such cool objects would behave the same way that stellar disks do.”

The team also noticed a flattening of the brown dwarfs’ disks, which is another sign that dust is gathering up into planets.

A paper on these findings appears online today in Science. Authors of the paper also include Drs. Jeroen Bouwman, Thomas Henning and Cornelis P. Dullemond of the Max Planck Institute for Astronomy, Germany; and Dr. Antonella Natta of the Osservatorio Astrofisico di Arcetri, Italy.

NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer mission for NASA’s Science Mission Directorate. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spitzer’s infrared spectrograph, which made the observations, was built by Cornell University, Ithaca, N.Y. Its development was led by Dr. Jim Houck of Cornell. The NASA Astrobiology Institute, founded in 1997, is a partnership between NASA, 16 major U.S. teams and six international consortia.

For artist concepts, graphics and more information about Spitzer, visit http://www.spitzer.caltech.edu/spitzer/ . For more information about the NASA Astrobiology Institute, visit http://nai.arc.nasa.gov/ . For more information about NASA and agency programs on the Web, visit http://www.nasa.gov/home/ .

Original Source: NASA/JPL News Release

Spiral Galaxy NGC 2403. Image credit: Subaru. Click to enlarge.
Subaru Telescope, using Suprime-Cam, took the clearest most complete image to date of the spiral galaxy NGC 2403. At a distance of 10 million light years, NGC 2403 is an Sc type galaxy, which has open spiral arms and a small nucleus. It is approximately half the mass of our own galaxy, the Milky Way, and has an abundance of neutral hydrogen gas. In the spiral arms we see active star formation regions in red, clusters of young blue stars called OB associations, and darker regions called dust lanes where light is blocked by gas and dust within the galaxy.

This is not the first time NGC 2403 has been studied. Edwin Hubble used NGC 2403 as evidence that more distant galaxies move more quickly away from us, now called Hubble’s Law. It was also used to develop the Tully-Fisher relation, which states that there is a relation between a galaxy’s rotational speed and its brightness. NGC 2403 has become an important standard galaxy when deciding the distances to other galaxies, as we recognize the vast expanse of space.

Larger galaxies are thought to have developed from the collision and merger of smaller galaxies. Mergers can leave enduring marks on a galaxy’s halo, the most extended and generally spherical component of a galaxy. There is evidence that relatively young stars exist in the halo of NGC 2403, hinting at a recent merger with another galaxy. Astronomers are now studying this image to see if the color and brightness of the stars in the halo of NGC 2403 will reveal conclusive evidence of past mergers.

Original Source: Subaru News Release

Giant mosaic of Andromeda made up of 11,000 images. Image credit: NASA/JPL. Click to enlarge.
NASA’s Spitzer Space Telescope has captured a stunning infrared view of Messier 31, the famous spiral galaxy also known as Andromeda.

Andromeda is the most-studied galaxy outside our own Milky Way, yet Spitzer’s sensitive infrared eyes have detected captivating new features, including bright, aging stars and a spiral arc in the center of the galaxy. The infrared image also reveals an off-centered ring of star formation and a hole in the galaxy’s spiral disk of arms. These asymmetrical features may have been caused by interactions with the several satellite galaxies that surround Andromeda.

“Occasionally small satellite galaxies run straight through bigger galaxies,” said Dr. Karl Gordon of the Steward Observatory, University of Arizona, Tucson, lead investigator of the new observation. “It appears a little galaxy punched a hole through Andromeda’s disk, much like a pebble breaks the surface of a pond.”

The new false-color Andromeda image is available at http://www.spitzer.caltech.edu/spitzer/ .

Approximately 2.5 million light-years away, Andromeda is the closest spiral galaxy and is the only one visible to the naked eye. Unlike our Milky Way galaxy, which we view from the inside, Andromeda is studied from the outside. Astronomers believe that Andromeda and the Milky Way will eventually merge together.

Spitzer detects dust heated by stars in the galaxy. Its multiband imaging photometer’s 24-micron detector recorded approximately 11,000 separate infrared snapshots over 18 hours to create the new comprehensive mosaic. This instrument’s resolution and sensitivity is a vast improvement over previous infrared technologies, enabling scientists to trace the spiral structures within Andromeda to an unprecedented level of detail.

“In contrast to the smooth appearance of Andromeda at optical wavelengths, the Spitzer image reveals a well-defined nuclear bulge and a system of spiral arms,” said Dr. Susan Stolovy, a co-investigator from the Spitzer Science Center at the California Institute of Technology, Pasadena.

The galaxy’s central bulge glows in the light emitted by warm dust from old, giant stars. Just outside the bulge, a system of inner spiral arms can be seen, and outside this, a well-known prominent ring of star formation.

NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology. The Jet Propulsion Laboratory is a division of Caltech.

Original Source: NASA/JPL News Release

Chandra image of Sgr A*. Image credit: Chandra. Click to enlarge.
NASA’s Chandra X-ray Observatory revealed a new generation of stars spawned by a super-massive black hole at the center of the Milky Way galaxy. This novel mode of star formation may solve several mysteries about these super-massive black holes that reside at the centers of nearly all galaxies.

“Massive black holes are usually known for violence and destruction,” said Sergei Nayakshin of the University of Leicester, United Kingdom. “So it’s remarkable this black hole helped create new stars, not just destroy them.”

Black holes have earned their fearsome reputation because any material, including stars, that falls within their “event horizon” is never seen again. These new results indicate immense disks of gas, orbiting many black holes at a safe distance from the event horizon, can help nurture the formation of new stars. This conclusion comes from new clues that could only be revealed in X-rays. Until the latest Chandra results, researchers have disagreed about the origin of a mysterious group of massive stars discovered by infrared astronomers.

The stars orbit less than a light year from the Milky Way’s central black hole, which is known as Sagittarius A* (Sgr A*). At such close distances to Sgr A*, the standard model for star forming gas clouds predicts they should have been ripped apart by tidal forces from the black hole. Two models, based on previous research, to explain this puzzle have been proposed. In the disk model, the gravity of a dense disk of gas around Sgr A* offsets the tidal forces and allows stars to form.

In the migration model, the stars formed in a cluster far away from the black hole and then migrated in to form the ring of massive stars. The migration scenario predicts about a million low mass, sun-like stars in and around the ring. In the disk model, the number of low mass stars could be much less.

Researchers used Chandra observations to compare the X-ray glow from the region around Sgr A* to the X-ray emission from thousands of young stars in the Orion Nebula star cluster. They found the Sgr A* star cluster contains only about 10,000 low mass stars, thereby ruling out the migration model. Because the galactic center is shrouded in dust and gas, it has not been possible to look for the low-mass stars in optical observations. X-ray data have allowed astronomers to penetrate the veil of gas and dust and look for these low mass stars.

This research, coauthored by Nayakshin and Rashid Sunyaev of the Max Plank Institute for Physics in Garching, Germany, will appear in an upcoming issue of the Monthly Notices of the Royal Astronomical Society.

“In one of the most inhospitable places in our galaxy, stars have prevailed,” Nayakshin said. “It appears star formation is much more tenacious than we previously believed.” “We can say the stars around Sgr A* were not deposited there by some passing star cluster, rather they were born there,” Sunyaev said. “There have been theories that this was possible, but this is the first real evidence. Many scientists are going to be very surprised by these results.”

The research suggests the rules of star formation change when stars form in the disk surrounding a giant black hole. Because this environment is very different from typical star formation regions, there is a change in the proportion of stars that form. For example, there is a much higher percentage of massive stars in the disks around black holes.

NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the Science Mission Directorate. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass. For more information about this research on the Web, visit:

Additional information and images are available at:

http://chandra.harvard.edu and http://chandra.nasa.gov

Original Source: Chandra News Release

Artist illustraton of a black hole consuming a neutron star. Image credit: Dana Berry/NASA. Click to enlarge.
Scientists have solved a 35-year-old mystery of the origin of powerful, split-second flashes of light called short gamma-ray bursts. These flashes, brighter than a billion suns yet lasting only a few milliseconds, have been simply too fast to catch… until now.

If you guessed that a black hole is involved, you are at least half right. Short gamma-ray bursts arise from collisions between a black hole and a neutron star or between two neutron stars. In the first scenario, the black hole gulps down the neutron star and grows bigger. In the second scenario, the two neutron stars create a black hole.

Gamma-ray bursts, the most powerful explosions known, were first detected in the late 1960s. They are random, fleeting, and can occur from any region of the sky. Try finding the location of a camera flash somewhere in a vast sports stadium and you’ll have a sense of the challenge facing gamma-ray burst hunters. Solving this mystery took unprecedented coordination among scientists using a multitude of ground-based telescopes and NASA satellites.

Two years ago scientists discovered that longer bursts, lasting over two seconds, arise from the explosion of very massive stars. About 30 percent of bursts, however, are short and under two seconds.

Four short gamma-ray bursts have been detected since May. Two of these are featured in four papers in the October 6 issue of Nature. One burst from July provides the “smoking gun” evidence to support the collision theory. Another burst goes a step further by providing tantalizing, first-time evidence of a black hole eating a neutron star—first stretching the neutron star into a crescent, swallowing it, and then gulping up crumbs of the broken star in the minutes and hours that followed.

These discoveries might also aid in the direct detection of gravitational waves, never before seen. Such mergers create gravitational waves, or ripples in spacetime. Short gamma-ray bursts could tell scientists when and where to look for the ripples.

“Gamma-ray bursts in general are notoriously difficult to study, but the shortest ones have been next to impossible to pin down,” said Dr. Neil Gehrels of NASA Goddard Space Flight Center in Greenbelt, Md., principal investigator of NASA’s Swift satellite and lead author on one of the Nature reports. “All that has changed. We now have the tools in place to study these events.”

The Swift satellite detected a short burst on May 9, and NASA’s High-Energy Transient Explorer (HETE) detected another on July 9. These are the two bursts featured in Nature. Swift and HETE quickly and autonomously relayed the burst coordinates to scientists and observatories via cell phone, beepers and e-mail.

The May 9 event marked the first time scientists identified an afterglow for a short gamma-ray burst, something commonly seen after long bursts. That discovery was the subject of a May 11 NASA press release. The new results published in Nature represent thorough analyses of these two burst afterglows, which clinch the case for the origin of short bursts.

“We had a hunch that short gamma-ray bursts came from a neutron star crashing into a black hole or another neutron star, but these new detections leave no doubt,” said Dr. Derek Fox of Penn State, lead author on one Nature report detailing a multi-wavelength observation.

Fox’s team discovered the X-ray afterglow of the July 9 burst with NASA’s Chandra X-ray Observatory. A team led by Prof. Jens Hjorth of the University of Copenhagen then identified the optical afterglow using the Danish 1.5-meter telescope at the La Silla Observatory in Chile. Fox’s team then continued its studies of the afterglow with NASA’s Hubble Space Telescope; the du Pont and Swope telescopes at Las Campanas, Chile, funded by the Carnegie Institution; the Subaru telescope on Mauna Kea, Hawaii, operated by the National Astronomical Observatory of Japan; and the Very Large Array, a stretch of 27 radio telescopes near Socorro, N.M., operated by the National Radio Astronomy Observatory.

The multi-wavelength observation of the July 9 burst, called GRB 050709, provided all the pieces of the puzzle to solve the short burst mystery.

“Powerful telescopes detected no supernova as the gamma-ray burst faded, arguing against the explosion of a massive star,” said Dr. George Ricker of MIT, HETE Principal Investigator and co-author of another Nature article. “The July 9 burst was like the dog that didn’t bark.”

Ricker added that the July 9 burst and probably the May 9 burst are located in the outskirts of their host galaxies, where old merging binaries are expected to be. Short gamma-ray bursts are not expected in young, star-forming galaxies. It takes billions of years for two massive stars, coupled in a binary system, to first evolve to the black hole or neutron star phase and then to merge. The transition of a star to a black hole or neutron star involves an explosion (supernova) that can kick the binary system far from its origin and out towards the edge of its host galaxy.

This July 9 burst and a later one on July 24 showed unique signals that point to not just any old merger but, more specifically, a black hole – neutron star merger. Scientists saw spikes of X-ray light after the initial gamma-ray burst. The quick gamma-ray portion is likely a signal of the black hole swallowing most of the neutron star. The X-ray signals, in the minutes to hours that followed, could be crumbs of neutron star material falling into the black hole, a bit like dessert.

And there’s more. Mergers create gravitational waves, ripples in spacetime predicted by Einstein but never detected directly. The July 9 burst was about two billion light years away. A big merger closer to the Earth could be detected by the National Science Foundation’s Laser Interferometer Gravitational-Wave Observatory (LIGO). If Swift detects a nearby short burst, LIGO scientists could go back and check the data with a precise time and location in mind.

“This is good news for LIGO,” said Dr. Albert Lazzarini, of LIGO Laboratory at Caltech. “The connection between short bursts and mergers firms up projected rates for LIGO, and they appear to be at the high end of previous estimates. Also, observations provide tantalizing hints of black hole – neutron star mergers, which have not been detected before. During LIGO’s upcoming yearlong observation we may detect gravitational waves from such an event.”

A black hole – neutron star merger would generate stronger gravitational waves than two merging neutron stars. The question now is how common and how close these mergers are. Swift, launched in November 2004, can provide that answer.

Original Source: NASA News Release

Mysterious dust cloud in various wavelengths. Image credit: CfA. Click to enlarge.
In an exercise that demonstrates the power of a multiwavelength investigation using diverse facilities, astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) have deciphered the true nature of a mysterious object hiding inside a dark cosmic cloud. They found that the cloud, once thought to be featureless, contains a baby star, or possibly a failed star known as a “brown dwarf,” that is still forming within its dusty cocoon.

Observations indicate that the mystery object has a mass about 25 times that of Jupiter, which would place it squarely in the realm of brown dwarfs. However, its mass may eventually grow large enough to qualify it as a small star. The object also is cool and faint, shining with less than 1/20 the sun’s luminosity.

“This object is the runt of the star formation family,” said CfA astronomer Tyler Bourke.

Establishing the true nature of the object required the unique capabilities of the Submillimeter Array (SMA) in Hawaii. “The SMA spotted what no single-dish telescope could see,” said Bourke.

Using the SMA, scientists detected a weak outflow of material predicted by star formation theories. That outflow – 10 times smaller in mass than any seen before – confirmed both the low-mass nature of the object and its association with the surrounding dark cloud. “The sensitivity and resolution of the Submillimeter Array with its multiple antennas were crucial in detecting the outflow,” said Bourke.

The puzzling object was discovered using a Smithsonian-developed infrared camera on board NASA’s Spitzer Space Telescope. Spitzer studied the dusty cosmic cloud named L1014 as part of the Cores to Disks Legacy program. A core is the densest region of a cloud, massive enough to make a star like the sun.

L1014, located about 600 light-years away in the constellation Cygnus the Swan, initially was classified as a “starless core” because it showed no evidence for star formation. Astronomers were surprised when Spitzer images revealed a faint infrared light source that appeared to be within the core.

Additional data were needed to confirm that the faint object was directly associated with the dark core, rather than being a chance superposition of a more distant, more mundane background object.

Near-infrared observations by the MMT Observatory in Arizona revealed a scattered light nebula surrounding the faint central object in L1014. “Light from the object is bouncing off surrounding dust and toward us,” said CfA astronomer Tracy Huard, who took the MMT images. “Reflection nebulosity like that is a fingerprint of an embedded object.”

The apparent size of the nebulosity indicated that the light source likely was located within L1014 and not in a more distant cloud. MMT data also gave investigators the orientation in space, or tilt, of the object within L1014. Astronomers then turned to the SMA for final confirmation.

“The Spitzer observations gave us hints to the nature of the object inside L1014. The MMT strengthened the association between the infrared source and the starless core. The Submillimeter Array clinched the case and revealed this object’s true identity,” said Bourke.

By studying faint, young objects like the one still forming within L1014, astronomers hope to learn more about the early stages of star formation.

“The most elusive part of star formation is the moment of birth,” said CfA astronomer Phil Myers. “In order to answer how it happens, you need examples of very young systems. This system is only about 10,000 to 100,000 years old – a baby as far as stars or brown dwarfs go.”

The combined capabilities of Spitzer, the SMA and the MMT were essential for finding and examining this object. Those facilities undoubtedly will prove useful in studying similar very dim, very young objects – objects so young that they are still growing. “They’re so young and faint that we can’t tell how much mass they will accumulate,” Myers added. “There’s no prenatal test for these objects. We’re not sure exactly what we’ll get in the end!”

A paper by Tyler L. Bourke et al. covering the SMA observations will be published in an upcoming issue of The Astrophysical Journal Letters and is available online at http://arxiv.org/abs/astro-ph/0509865.

A second paper by Tracy L. Huard et al. covering the MMT observations will be published in The Astrophysical Journal and is available online at http://arxiv.org/abs/astro-ph/0509302.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: CfA News Release