New Chandra Deep X-ray Image of the Galactic Center

•A deep new image of the center of the Milky Way by the Chandra X-ray Observatory. NASA/CXC/UMass/D. Wang et al.

Chandra has done it again in creating some of the most visually stunning images of our Universe. This time, Chandra’s X-ray eyes show a dramatic new vista of the center of the Milky Way galaxy. This mosaic from 88 different images exposes new levels of the complexity and intrigue in the Galactic center, providing a look at stellar evolution, from bright young stars to black holes, in a crowded, hostile environment dominated by a central, supermassive black hole.

Permeating the region is a diffuse haze of X-ray light from gas that has been heated to millions of degrees by winds from massive young stars – which appear to form more frequently here than elsewhere in the Galaxy – explosions of dying stars, and outflows powered by the supermassive black hole – known as Sagittarius A* (Sgr A*). Data from Chandra and other X-ray telescopes suggest that giant X-ray flares from this black hole occurred about 50 and about 300 years earlier.

See this link for an animation that provides greater detail of the galactic center.

The area around Sgr A* also contains several mysterious X-ray filaments. Some of these likely represent huge magnetic structures interacting with streams of very energetic electrons produced by rapidly spinning neutron stars or perhaps by a gigantic analog of a solar flare.

Scattered throughout the region are thousands of point-like X-ray sources. These are produced by normal stars feeding material onto the compact, dense remains of stars that have reached the end of their evolutionary trail – white dwarfs, neutron stars and black holes.

Because X-rays penetrate the gas and dust that blocks optical light coming from the center of the galaxy, Chandra is a powerful tool for studying the Galactic Center. This image combines low energy X-rays (colored red), intermediate energy X-rays (green) and high energy X-rays (blue).

The image is being released at the beginning of the “Chandra’s First Decade of Discovery” symposium being held in Boston, Mass. This four-day conference will celebrate the great science Chandra has uncovered in its first ten years of operations. To help commemorate this event, several of the astronauts who were onboard the Space Shuttle Columbia – including Commander Eileen Collins – that launched Chandra on July 23, 1999, will be in attendance.

Source: Chandra

New View Toward Carina Reveals Star Fest, Exploding “Engine”

A remarkable new view of the Milky Way toward the constellation Carina is alive with a flurry of stars — and the pièce de résistance is a binary star that’s all dressed up in a nebula of its own making.

The European Southern Observatory (ESO) released the new images this week.

The unusual star, HD 87643, has been extensively studied with several ESO telescopes, including the Very Large Telescope Interferometer (VLTI). Surrounded by a complex, extended nebula that is the result of previous violent ejections, the star has been shown to have a companion. Interactions in this double system, surrounded by a dusty disc, may be the engine fueling the star’s remarkable nebula.

Credit: European Southern Observatory (ESO)

HD 87643 is at the center of the extended nebula of dust and gas on the first image, obtained with the Wide Field Imager on the ESO/MPG 2.2-meter (7.2-foot) telescope at La Silla Observatory in Chile. The central panel is a zoom on the star obtained with NACO on ESO’s VLT on Paranal. The last panel zooms further , showing an image obtained with the AMBER instrument making use of three telescopes of the VLTI. The field of view of this last panel is less than one pixel of the first image.

HD 87643 is a member of the exotic class of B[e] stars — luminous, powerful blue stars with strong spectral evidence of hydrogen. The new image is part of a set of observations that provide astronomers with the best ever picture of a B[e] star.

The central star’s wind appears to have shaped the surrounding nebula, leaving bright, ragged tendrils of gas and dust. A careful investigation of these features seems to indicate that there are regular ejections of matter from the star every 15 to 50 years.

A team of astronomers, led by Florentin Millour of the Max-Planck Institute for Radio Astronomy in Bonn, Germany, has studied the star HD 87643 in great detail.

The sheer range of the observations, from the panoramic WFI image to the fine detail of the VLTI observations, corresponds to a zoom-in factor of 60,000 between the two extremes. The astronomers found that HD 87643 has a companion located at about 50 times the Earth–Sun distance and is embedded in a compact dust shell. The two stars probably orbit each other in a period between 20 and 50 years. A dusty disc may also be surrounding the two stars.

The presence of the companion could be an explanation for the regular ejection of matter from the star and the formation of the nebula: as the companion moves on a highly elliptical orbit, it would regularly come very close to HD 87643, triggering an ejection.

Source: European Southern Observatory (ESO). Check the site for more images and a video. A paper about the results is here.

Past Climate Change Cannot Be Tied to Earth Passing Through Galactic Plane

The latest map of the Milky Way shows only two arms. Credit: NASA/ Spitzer Space Telescope


Earth’s climate has changed over time, but the cause for the changes has been hotly debated. One idea (Shaviv and Veizer,2003), suggested that perhaps two-thirds to three-fourths of the variance in Earth’s temperature over the past 500 million years may be attributable to when our solar system passes through the spiral arms of the Milky Way galaxy. The evidence seemed to fit: there appears to be a 140 million year cycle of global climate change, and that correlates when our solar system seems to move between spiral arms, too. Or at least it used to. Since 2003 we have revised our map of the galaxy, which changes the estimation of when Earth transits through the spiral arms.

“Although previous work found a correlation between the 140 Myr climate cycle on Earth and the intersection with spiral arms,” write researchers Adrian Melott, Andrew Overholt, and Martin Pohl, “with new data on the structure of the galaxy, this correlation disappears.”

On Earth, the 140 million year cycle is estimated from the timing of ice ages and abundances of fossils.

The basic idea of the earlier research was that when the solar system journeys through the Milky Way’s spiral arms the event rate of cosmic rays in the Earth’s atmosphere greatly increases, since the number of supernovae in spiral arms is clearly much larger than in between the arms. This could affect cloud formation on Earth and therefore strength of greenhouse effect.

But that assumed the Milky Way had four arms, and was less massive than new calculations show. In 2008, new information from the Spitzer Space Telescope helped astronomers conclude that the Milky Way consisted of two spiral arms and a large central bar. Additionally, in 2009 Spitzer data helped scientists conclude that our galaxy is much more massive than originally thought, and is moving faster than originally estimated.

Red vertical lines represent the midpoints of the last seven ice ages, which don't correlate with the passage of the solar system through the galactic plane. Credit Melott, Overholt and Pohl.
Red vertical lines represent the midpoints of the last seven ice ages, which don't correlate with the passage of the solar system through the galactic plane. Credit Melott, Overholt and Pohl.

So just when has Earth passed through the galactic arms? With changing estimations of mass and smaller number of arms, no one can be absolutely sure. But Melott and his team have compared the times of transit between regions of the new galactic map with changes in Earth’s climate and found that the 140 million year correlations no longer apply.

The team also says the 140 million year cycle cannot be made to match up with any cyclical movement of the solar system through the galaxy.

“The only periodic trend that can be found with the new data is the relative orbital period of our solar system,” the team writes in their paper, “relative to the previously assumed pattern speed around the galactic plane, which is slightly larger than 500 Myr. Though one could create varying periodic trends by changing this pattern speed, the orbital period relative to the galactic pattern could never reach the 140 Myr time as this is less than the orbital period itself, meaning the pattern and the Sun would be required to move in opposite directions.”

So, the researchers conclude, the solar system passing through the plane of the galactic arms could have no direct tie with past climate change on Earth.

The team’s paper can be read here.

Graphic caption: Red vertical lines represent the midpoints of the last seven ice ages, which don’t correlate with the passage of the solar system through the galactic plane. Credit Melott, Overholt and Pohl.

Source: arXiv, Technology Review Blog

Astronomers Announce First Newborn Stars at Milky Way’s Core

The Galactic Center. Credit: Suzan Stolovy (SSC/Caltech), JPL-Caltech, NASA


Astronomers have found the first evidence of newborn stars at the center of the Milky Way, a region once thought to be inhospitable to the formation of new stars.

Solange Ramirez, the principal investigator of the research program at NASA’s Exoplanet Science Institute at Caltech, announced three objects during a press conference today as part of the 214th meeting of the American Astronomical Society meeting in Pasadena.

“These baby stars … are stars that have just ignited their core, and are just starting to produce light,” she said. “It is a very early phase.”

The discovery was made using the infrared vision of NASA’s Spitzer Space Telescope.

The heart of our spiral galaxy is cluttered with stars, dust, and gas, and at its very center, a supermassive black hole. Conditions there are harsh, with fierce stellar winds, powerful shock waves, and other factors that make it difficult for stars to form. Astronomers have known that stars can form in this chaotic place, but they’re baffled as to how this occurs. Confounding the problem is all the dust standing between us and center of our galaxy. Until now, nobody had
been able to definitively locate any baby stars.

“These stars are like needles in a haystack,” Ramirez said. “There’s no way to find them using optical light, because dust gets in the way. We needed Spitzer’s infrared instruments to cut through the dust and narrow in on the objects.”

Ramirez and her colleagues plan to look for additional baby stars in the future, and ultimately to piece together what types of conditions allow stars to form in such an inhospitable environment as our galaxy’s core.

“By studying individual stars in the galactic center, we can better understand how stars are formed in different interstellar environments,” said Deokkeun An, also of Caltech, who is lead author of a paper submitted for publication in the Astrophysical Journal.

“The Milky Way galaxy is just one of more than hundreds of billions of galaxies in the visible universe. However, our galaxy is so special because we can take a closer look at its individual stellar components.”

The core of the Milky Way is a mysterious place about 600 light-years across. While this is just a fraction of the size of entire the Milky Way, which is about 100,000 light-years across, the core is stuffed with 10 percent of all the gas in the galaxy — and loads of stars.

Before now, there were only a few clues that stars can form in the galaxy’s core. Astronomers had found clusters of massive adolescent stars, in addition to clouds of charged gas — a sign that new stars are beginning to ignite and ionize surrounding gas. Past attempts had been unsuccessful in finding newborn stars, or as astronomers call them, young stellar objects.

The astronomers looked at their candidate stars with Spitzer’s spectrograph — an instrument that breaks light apart to reveal its rainbow-like array of infrared colors. Molecules around stars leave imprints in their light, which the spectrograph can detect.

The results revealed three stars with clear signs of youth, for example certain warm, dense gases. These youthful features are found in other places in the galaxy where stars are being formed.

“It is amazing to me that we have found these stars,” said Ramirez. “The galactic center is a very interesting place. It has young stars, old stars, black holes, everything. We started mining a catalog of about one million sources and managed to find three young stars — stars that will help reveal the secrets at the core of the Milky Way.”

The young stellar objects are all less than about one million years old. They are embedded in cocoons of gas and dust, which will eventually flatten to disks that, according to theory, later lump together to form planets.

Source: AAS teleconference and press release (meeting teleconferences available via UStream)

Nearsighted No More: Astronomers Resolve Milky Way’s Mysterious X-Ray Glow


The map above details the Galactic ridge X-ray emission, first detected 25 years ago and observed recently by NASA’s Rossi X-ray Timing Explorer (RXTE) observatory. The inset shows the zoomed Chandra image of the region, close to the center of the galaxy. 

The mysterious — and formerly blurry — X-ray source puzzled astronomers for a quarter century, but a new paper release today by the journal Nature has helped to clear the air.

Region close to the Galactic Center obtained by Spitzer infrared telescope in three spectral band. The field of view of CHANDRA is shown by the white square. Credit: M. Revnivtsev


Lead author Mikhail Revnivtsev, of Munich Technical University in Garching, Germany, and his colleagues report that the formerly unresolved X-ray glow has a spectrum characteristic of a hot (100 million degrees Kelvin) optically thin plasma, with a prominent iron emission line.

But the gravitational well of the Galactic disk is far too shallow to confine such a hot interstellar medium; it would flow away at a velocity of a few thousand kilometers per second, exceeding the speed of sound in the gas.

Replenishing such energy losses would require a source that exceeds all plausible energy sources in the Milky Way — including supernovae — by orders of magnitude, they write.

Based on their observations, the team is proposing that the hot plasma is instead bound to many faint sources: plain old stars.

“Here we report that at energies of 6–7 keV, more than 80 percent of the seemingly diffuse X-ray emission is resolved into discrete sources, probably accreting white dwarfs and coronally active stars,” they write.

“Such stellar X-ray sources are of the common ‘garden variety’ in the Sun’s neighbourhood,” writes Michael Shull, an astrophysicist at the University of Colorado at Boulder, in an accompanying editorial. “However, at the distance of the Galactic ridge from Earth, their combined light becomes a diffuse blur, the X-ray equivalent of the many stars that make up the Milky Way, as Galileo first saw with his telescope in visible light.”

Shull notes that the results are a testament to the increased power of telescopes like Chandra, which de-mystified the source of the X-ray glow — and he cautions astronomers about describing faint backgrounds at all wavelengths, before getting a good look.

“As Revnivtsev and colleagues’ work demonstrates, sometimes the exotic explanation can be set aside by more accurate imaging and spectroscopy,” he writes.

LOWER IMAGE CAPTION: Region close to the Galactic Center obtained by Spitzer infrared telescope in three spectral band. The field of view of CHANDRA is shown by the white square. Credit: M. Revnivtsev

Source: Nature

Stars at Milky Way Core ‘Exhale’ Carbon, Oxygen

Carbon exists only in a fine-tuned universe( 'Cat's Eye' Planetary Nebula)
Cat's Eye Nebula. Researchers have found carbon and oxygen in dusty planetary nebulae surrounding stars at the center of the Milky Way. Credit: NASA/JPL-Caltech/J. Hora (Harvard-Smithsonian CfA


Carbon and oxygen have been spotted in the dust around stars in the center of the Milky Way galaxy, suggesting that the stars have undergone recent disruptions of some kind — and hinting how stars can send heavy elements — like oxygen, carbon, and iron — out across the universe, paving the way for life.

Scientists have long expected to find carbon-rich stars in our galaxy because we know that significant quantities of carbon must be created in many such stars. But carbon had not previously shown up in the clouds of gas around these stars, said Matthew Bobrowsky, an astrophysicist at the University of Maryland and a co-author of a new study reporting the discovery.

“Based on our findings, this is because medium-sized stars rich in carbon sometimes keep that carbon hidden until very near the end of their stellar lives, releasing it only with their final ‘exhalations’,” explained Bobrowsky.

The new results appear in the February issue of the journal Astronomy and Astrophysics.

Bobrowsky and his team, led by J. V. Perea-Calderón at the European Space Astronomy Centre in Madrid, Spain, used the Spitzer Space Telescope to view each star and its surrounding clouds of dust and particles, called a planetary nebulae. The researchers measured the light emitted by the stars and the surrounding dust and were able to identify carbon compounds based on the wavelengths of light emitted by the stars. Looking in an area at the center of the Milky Way called the “Galactic Bulge,” the team observed 26 stars and their planetary nebulae and found 21 with carbon “signatures.”

But the scientists did not just find carbon around these stars; they also found oxygen in these 21 dust clouds, revealing a surprising mixture of ingredients for space dust. They report in their paper that this is likely due to a thermal pulse where a wave of high-pressure gas mixes layers of elements like carbon and oxygen and spews them out into the surrounding cloud.

The finding of carbon and oxygen in the dust clouds surrounding stars suggests a recent change of chemistry in this population of stars, according to the authors.

“Stars in the center of the Milky Way are old and ‘metal-rich’ with a high abundance of heavy elements,” Bobrowsky said. “They are different in chemical composition than those found in the disc, farther out from the center.”

Studying the chemistry of the stars helps scientists learn how the matter that makes up our earth and other planets in our galaxy left its stellar birthplaces long ago. 

As a star burns hotter and hotter, the hydrogen gas that originally made up almost all of its mass is converted, through nuclear fusion, first to helium, and then to progressively heavier elements. The hottest region in the core fuses together the heaviest elements. And these can reach the surface of the star only when its life is almost over.

“The Big Bang produced only hydrogen and helium,” Bobrowsky said. “Heavier elements like carbon and oxygen only come from getting ‘cooked up’ in stars. Nuclear reactions in stars created the heavier elements found in ‘life as we know it’.”

In the last 50,000 years of their 10 billion-year lives, sun-sized stars expel carbon atoms along with hydrogen and helium to form a surrounding cloud of gas that soon disperses into space, perhaps to eventually become the stuff of new stars, solar systems, or perhaps even life on some earth-like planet. Much larger stars expel their heavier matter in massive explosions called supernovae.

“All the heavy elements [which astronomers call ‘metals,’ and include all elements heavier than hydrogen and helium] on Earth were created by nuclear fusion reactions in previous generations of stars,” said Bobrowsky. “Those earlier stars expelled those elements into space and then our solar system formed out of that gas containing all the heavy elements that we now find in Earth and in life on Earth.”

LEAD IMAGE CAPTION: Cat’s Eye Nebula. Researchers have found carbon and oxygen in dusty planetary nebulae surrounding stars at the center of the Milky Way. Credit: NASA/JPL-Caltech/J. Hora (Harvard-Smithsonian CfA)

Source: Astronomy & Astrophysics and Spitzer, via AAS

Triple Whammy: Milky Way More Massive, Spinning Faster and More Likely to Collide

Artist's Conception of our Milky Way Galaxy: Blue, green dots indicate distance measurements. CREDIT: Robert Hurt, IPAC; Mark Reid, CfA, NRAO/AUI/NSF


For many of us, looking closely in the mirror and stepping on the bathroom scale just after the holidays can reveal a substantial surprise. Likewise, astronomers looking closely at the Milky Way have found our galaxy is more massive than previously thought. High-precision measurements of the Milky Way disclose our galaxy is rotating about 100,000 miles per hour faster than previously understood. That increase in speed, said Mark Reid of the Harvard-Smithsonian Center for Astrophysics, increases the Milky Way’s mass by 50 percent. The larger mass, in turn, means a greater gravitational pull that increases the likelihood of collisions with the Andromeda galaxy or smaller nearby galaxies. So even though we’re faster, we’re also heavier and more likely to be annihilated. Bummer!

The scientists are using the National Science Foundation’s Very Long Baseline Array (VLBA) radio telescope to remake the map of the Milky Way. Taking advantage of the VLBA’s unparalleled ability to make extremely detailed images, the team is conducting a long-term program to measure distances and motions in our Galaxy. At the American Astronomical Society’s meeting in Long Beach, California, Reid said they are using trigonometric parallax to make the measurements. “This is exactly what surveyors use on Earth to measure distances,” he said. “And this is gold standard of measurement in astronomy.”

Trigonometric parallax was first used in 1838 to measure the first stellar distance. However, with better technology, the accuracy is now about 10,000 times greater.

Our solar system is about 28,000 light-years from the Milky Way’s center. At that distance, the new observations indicate, we’re moving at about 600,000 miles per hour in our Galactic orbit, up from the previous estimate of 500,000 miles per hour.

The scientists observed 19 regions of prolific star formation across the Galaxy. In areas within these regions, gas molecules are strengthening naturally-occurring radio emission in the same way that lasers strengthen light beams. These areas, called cosmic masers, serve as bright landmarks for the sharp radio vision of the VLBA. By observing these regions repeatedly at times when the Earth is at opposite sides of its orbit around the Sun, the astronomers can measure the slight apparent shift of the object’s position against the background of more distant objects.

The astronomers found that their direct distance measurements differed from earlier, indirect measurements, sometimes by as much as a factor of two. The star-forming regions harboring the cosmic masers “define the spiral arms of the Galaxy,” Reid explained. Measuring the distances to these regions thus provides a yardstick for mapping the Galaxy’s spiral structure.

The star forming regions are shown in the green and blue dots on the image above. Our sun (and us!) are where the red circle is located.

The VLBA can fix positions in the sky so accurately that the actual motion of the objects can be detected as they orbit the Milky Way’s center. Adding in measurements of motion along the line of sight, determined from shifts in the frequency of the masers’ radio emission, the astronomers are able to determine the full 3-dimensional motions of the star-forming regions. Using this information, Reid reported that “most star-forming regions do not follow a circular path as they orbit the Galaxy; instead we find them moving more slowly than other regions and on elliptical, not circular, orbits.”

The researchers attribute this to what they call spiral density-wave shocks, which can take gas in a circular orbit, compress it to form stars, and cause it to go into a new, elliptical orbit. This, they explained, helps to reinforce the spiral structure.

Reid and his colleagues found other surprises, too. Measuring the distances to multiple regions in a single spiral arm allowed them to calculate the angle of the arm. “These measurements,” Reid said, “indicate that our Galaxy probably has four, not two, spiral arms of gas and dust that are forming stars.” Recent surveys by NASA’s Spitzer Space Telescope suggest that older stars reside mostly in two spiral arms, raising a question of why the older stars don’t appear in all the arms. Answering that question, the astronomers say, will require more measurements and a deeper understanding of how the Galaxy works.

So, now that we know we’re more massive, how do we compare with other galaxies in our neighborhood? “In our local group of galaxies, Andromeda was thought to be the dominant big sister,” said Reid at the conference, “but we’re basically equal in size and mass. We’re not identical twins, but more like fraternal twins. And its likely the two galaxies will collide sooner than we thought, but it depends on a measurement of the sideways motion, which hasn’t been done yet.”

The VLBA is a system of 10 radio-telescope antennas stretching from Hawaii to New England and the Caribbean. It has the best resolving power, of any astronomical tool in the world. The VLBA can routinely produce images hundreds of times more detailed than those produced by the Hubble Space Telescope. The VLBA’s tremendous resolving power, equal to being able to read a newspaper in Los Angeles from the distance of New York, is what permits the astronomers to make precise distance determinations.

Source: AAS, Harvard-Smithsonian Center for Astrophysics