milky way Archives

January 4, 2010December 24, 2015 by Nicholos Wethington

Intergalactic Connection is Older, Longer than Thought

Our galaxy has a streamer, though it’s not like the ones you had on your bike as a kid: this streamer is a flow of largely hydrogen gas that originates in the Large and Small Magellanic Clouds, two of our closest galactic neighbors. New observations of the stream have helped to revise its age and extent, and show it to be longer and much older than previous estimates.

The Magellanic Stream, which was discovered over 30 years ago, flows from the two galaxies closest to the Milky Way, the Large and Small Magellanic Clouds. These clouds, which are actually two irregular dwarf galaxies, are 150,000 to 200,000 light-years away, and are visible in the southern hemisphere.

The stream connects up with the Milky Way about 70,000 light years from the Solar System, in the constellation of the Southern Cross.

Using the Green Bank Telescope (GBT), a team of astronomers took over 100 hours of observations of the streamer. These observations were combined with those from other radio telescopes, including the Aricebo telescope in Puerto Rico, to further constrain both its extent and age.

Their observations were presented at the American Astronomical Society’s meeting in Washington D.C., and a paper has been submitted to the Astrophysical Journal. The team included David Nidever and Steven Majewski of the Department of Astronomy at the University of Virginia, Butler Burton of the Leiden Observatory and the National Radio Astronomy Observatory and Lou Nigra of the University of Wisconsin.

Previous observations of the stream showed it to have gaps between the Magellanic Clouds and where it enters the Milky Way, but these revised observations show it to be one continuous stream between the three galaxies. The stream is also at least forty percent longer that previously estimated.

The Magellanic Stream was also determined by the astronomers to be much older than had been estimated before: up from 1.75 billion years old to 2.5 billion years old. Just how does this long-lived intergalactic trail of hydrogen crumbs start off in the Magellanic Clouds?

“The new age of the stream puts its beginning at about the time when the two Magellanic Clouds may have passed close to each other, triggering massive bursts of star formation. The strong stellar winds and supernova explosions from that burst of star formation could have blown out the gas and started it flowing toward the Milky Way,” said David Nidever in a NRAO press release.

By getting a better picture of how the gas flows from the Magellanic Clouds into the Milky Way, astronomers have been able to determine with better accuracy just how far away the two galaxies are, as well as their interactions with the tidal forces of the Milky Way.

This team has collaborated before on the exploration of the Magellanic Stream and its origins. You can read about their previous findings on Arxiv right here, which were also published in the Astrophysical Journal.

Source: NRAO press release

December 3, 2009April 26, 2016 by Nicholos Wethington

Stellar Escapees Await Detection

Stars wandering outside the galactic plane of the Milky Way could number in the billions. Image Credit: APOD

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The structure of the Universe and the formation of stars from concentrated dust leads them to be clumped into galaxies of all sorts. But adrift between the galaxies may be billions of undiscovered lonely stars. These escaped stars, thrown out of their homes by gravitational interactions, may number in the billions for the Milky Way galaxy alone, and would provide details of historic galactic formations and mergers.

The theory that escaped and wandering stars exist isn’t new, and ejected stars from other galaxies have already been observed (see Hyperfast Star Ejected from the Large Magellanic Cloud). Our Milky Way formed as the result of many mergers with smaller dwarf galaxies, and as a result of these gravitational train wrecks, billions of stars could have been thrown out of the system, breaking free of their gravitational bonds to wander between the galaxies forever.

Wandering stars – those that have loosely bound orbits around a galaxy – and escaped stars that have left the galaxy altogether could be discovered in the near future by the Large Synoptic Survey Telescope, planned for development in Chile, and Pan-STARRS. In the December 10 issue of Astrophysical Journal Letters, a team of astronomers led by Michael Shara of the American Museum of Natural History explores the provenance of these drifters, and estimates the lower limit of their numbers to be 0.05% of the Milky Way galaxy’s stellar population. That places their numbers well in the billions.

Red giant stars and classical novae have been detected outside the Milky Way, but only in clusters. Finding the individual escaped stars would be a challenge because of how dim they would appear. Because of the mechanism that ejects them from the Milky Way, many would be older and redder, having formed when the galaxy was much younger. But the phenomenon of novae and supernovae would allow upcoming large scale sky surveys to pick up the few that exploded.

Building up a database of these intergalactic novae and supernovae would give astronomers better information on their orbital characteristics, which in turn would allow for improved modeling of how the Milky Way formed: knowing where the stars are now and what their velocity is gives information as to where they were in the past. Research into older, high-velocity stars that travel back into the Milky Way is ongoing, and would supplement the figure for how many of these galactic jailbreakers exist.

Source: Arxiv, nod to Scientific American

December 2, 2009December 24, 2015 by Nancy Atkinson

Get the Big Picture of the Milky Way at the Adler Planetarium

Spitzer infrared image on display at the Adler Planetarium. Credit: Adler

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Astronomy is all about getting the big picture of our place in the cosmos, but some pictures are bigger than others. This one is really big. The world’s largest image of our Milky Way galaxy went on display today at the Adler Planetarium in Chicago. The image spans an area of 37 meters (120 feet) long by 1 meter (3 feet) wide at its sides, bulging to 2 meters (6 feet) to show the center of our humongous galaxy. The panorama represents 800,000 separate images taken by the Spitzer Space Telescope over a five-year period.

“This is the highest-resolution, largest, most sensitive infrared picture ever taken of our Milky Way,” said Sean Carey of NASA’s Spitzer Science Center, speaking when the image was unveiled in 2008 at the American Astronomical Society meeting in St. Louis (see our article and image of the unveiling). “Where previous surveys saw a single source of light, we now see a cluster of stars. With this data, we can learn how massive stars form, map galactic spiral arms and make a better estimate of our galaxy’s star-formation rate.”

Spitzer Survey image compiled. Credit: NASA/JPL

Data from Spitzer’s Infrared Array Camera (IRAC) and the Multiband Imaging Photometer were used to create the image.

If you want to download a very large version of this image (2400 x 3000) click here — warning: very big file.

From our vantage point on Earth, we see the Milky Way as a blurry, narrow band of light that stretches across the sky. In the visible, we only see about 5% of what’s actually out there. But with Spitzer’s dust-piercing infrared eyes, astronomers have peered 60,000 light-years away into this fuzzy band, called the galactic plane, and saw all the way to the other side of the galaxy.

The panorama reveals star formation as never seen before on both the large and small scale. Most of the star forming regions had not been seen before this project was undertaken.

I had the good fortune of seeing the image in St. Louis, and I highly recommend taking the opportunity to go see it at the Adler Planetarium if you are in Chicago. Here’s a video that explains how astronomers took the images and put them all together to form this gigantic panorama.

*Serendipitously, I am currently at the dotAstronomy conference where Eli Bressert from the Chandra X-Ray Center talked about the GLIMPSE Viewer. Here’s the link to see the Spitzer image with GLIMPSE (Galactic Legacy Infrared Midplane Extraordinaire).

Adler Planetarium is located at 1300 South Lake Shore Drive, Chicago, Ill., 60605. Phone: 312-922-7827. Adler Planetarium website. .

November 25, 2009December 24, 2015 by Nancy Atkinson

Astronomers Dig Up Relic of the Milky Way’s Central Bulge

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Like archaeologists who dig through the layers of dirt to unearth crucial pieces of the history of mankind, astronomers have been gazing through the thick layers of interstellar dust obscuring the central bulge of the Milky Way and have unveiled an extraordinary cosmic relic. Within the bulge is an unusual mix of stars in the stellar grouping known as Terzan 5, and such a mix has never been observed anywhere in the bulge before. This peculiar conglomeration of stars suggests that Terzan 5 is one of the bulge’s primordial building blocks, most likely the relic of a dwarf galaxy that merged with the Milky Way during its very early days.

The new observations of Terzan 5 show that this object, unlike all but a few exceptional globular clusters, does not harbor stars which are all born at the same time — what astronomers call a “single population” of stars. Instead, the multitude of glowing stars in Terzan 5 formed in at least two different epochs, the earliest probably some 12 billion years ago and then again 6 billion years ago.

“Only one globular cluster with such a complex history of star formation has been observed in the halo of the Milky Way: Omega Centauri,” says team member Emanuele Dalessandro. “This is the first time we see this in the bulge.”

Using ESO’s Very Large Telescope, equipped with the Multi-conjugate Adaptive Optics Demonstrator (MAD), the astronomers were able to “disperse the fog” of the dust clouds in the central bulge to reveal the myriad of stars.

Through the sharp eye of the VLT, the astronomers also found that Terzan 5 is more massive than previously thought: along with the complex composition and troubled star formation history of the system, this suggests that it might be the surviving remnant of a disrupted dwarf galaxy, which merged with the Milky Way during its very early stages and thus contributed to form the galactic bulge.

The team hopes this is only the first in a series of discoveries on the origin of bulges in galaxies.

“The history of the Milky Way is encoded in its oldest fragments, globular clusters and other systems of stars that have witnessed the entire evolution of our galaxy,” says Francesco Ferraro, lead author of a paper appearing in this week’s issue of the journal Nature. “Our new study opens a new window on yet another piece of our galactic past.”

Source: ESO

November 10, 2009December 24, 2015 by Nancy Atkinson

Great Observatories Combine for Stunning Look at Milky Way

All we can say is, “Wow!” In celebration of the International Year of Astronomy 2009, NASA’s Great Observatories — the Hubble Space Telescope, the Spitzer Space Telescope, and the Chandra X-ray Observatory — have collaborated to produce an unprecedented image of the central region of our Milky Way galaxy. This is a never-before-seen view of the turbulent heart of our home galaxy. The image is being unveiled by NASA to commemorate the anniversary of when Galileo first turned his telescope to the heavens in 1609. NASA provided this image and the individual images taken by each of the Great Observatories to more than 150 planetariums, museums, nature centers, libraries, and schools across the country.

In this spectacular image, observations using infrared light and X-ray light see through the obscuring dust and reveal the intense activity near the galactic core. Note that the center of the galaxy is located within the bright white region to the right of and just below the middle of the image. The entire image width covers about one-half a degree, about the same angular width as the full moon.

For more about the image or to download larger versions, go to this page on the HubbleSite.

October 30, 2009December 24, 2015 by Nancy Atkinson

1 Milky Way; 3,000 Images

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What a gorgeous and immense image! And it’s full of stars! An astronomer from Central Michigan University has put together a new high-resolution panoramic image of the full night sky , with the Milky Way galaxy as its centerpiece. Axel Mellinger stitched together over 3,000 images to create this beautiful image, which also comes in an interactive version, showing stars 1,000 times fainter than the human eye can see, as well as hundreds of galaxies, star clusters and nebulae.

View an interactive version at Mellinger’s website.

Mellinger spent 22 months and traveled over 26,000 miles to take digital photographs at dark sky locations in South Africa, Texas and Michigan. After the photographs were taken, “the real work started,” Mellinger said.

Simply cutting and pasting the images together into one big picture would not work. Each photograph is a two-dimensional projection of the celestial sphere. As such, each one contains distortions, in much the same way that flat maps of the round Earth are distorted. In order for the images to fit together seamlessly, those distortions had to be accounted for. To do that, Mellinger used a mathematical model—and hundreds of hours in front of a computer.

Another problem Mellinger had to deal with was the differing background light in each photograph.

“Due to artificial light pollution, natural air glow, as well as sunlight scattered by dust in our solar system, it is virtually impossible to take a wide-field astronomical photograph that has a perfectly uniform background,” Mellinger said.

To fix this, Mellinger used data from the Pioneer 10 and 11 space probes. The data allowed him to distinguish star light from unwanted background light. He could then edit out the varying background light in each photograph. That way they would fit together without looking patchy.

The result is an image of our home galaxy that no star-gazer could ever see from a single spot on earth. Mellinger plans to make the giant 648 megapixel image available to planetariums around the world.

Source: EurekAlert

October 2, 2009December 24, 2015 by Nancy Atkinson

Herschel Sees Hidden Stars in the Southern Cross

Herschel sees a reservoir of cold gas in the constellation of the Southern Cross. Credit: ESA

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Science observations have begun in earnest for the Herschel Space Telescope, and this spectacular image is the first produced by combining data from two cameras aboard Herschel, the Spectral and Photometric Imaging REceiver (SPIRE), and the Photoconductor Array Camera and Spectrometer (PACS). It shows a tumultuous region in the Southern Cross, visible only because the instruments are tuned to “see” in five different infrared wavelengths. Stunning vistas of cold gas clouds lying near the plane of the Milky Way reveal intense, unexpected activity. The dark, cool region is dotted with stellar factories, like pearls on a cosmic string.

Herschel, one of the largest telescopes in space, was launched in May. For this image, the two instruments were aimed at an area in the plane of the Milky Way about 60° from its center. It covers around 16 times the area of the Full Moon as seen in the sky.

The images were taken on September 3, 2009 during the first trial run with the two instruments working together. Herschel will go on to survey large areas of our galaxy.

Herschel SPIRE (left) and PACS images. Credit: ESA

The five original infrared wavelengths have been color-coded to allow scientists to differentiate extremely cold material (red) from the surrounding, slightly warmer stuff (blue).

The images reveal structure in cold material in our Galaxy, as we have never seen it before, and even before a detailed analysis, scientists have gleaned information on the quantity of the material, its mass, temperature, composition and whether it is collapsing to form new stars.

Beautiful evidence that our galaxy keeps giving birth to new generations of stars!

Source: ESA

September 22, 2009December 24, 2015 by Nancy Atkinson

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.

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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

August 5, 2009December 24, 2015 by Anne Minard

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.

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.

June 26, 2009December 24, 2015 by Nancy Atkinson

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

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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.

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