milky way Archives

September 10, 2010December 24, 2015 by Jon Voisey

The Thick Disk: Galactic Construction Project or Galactic Rejects?

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The disk of spiral galaxies is comprised of two main components: The thin disk holds the majority of stars and gas and is the majority of what we see and picture when we think of spiral galaxies. However, hovering around that, is a thicker disk of stars that is much less populated. This thick disk is distinct from the thin disk in several regards: The stars there tend to be older, metal deficient, and orbit the center of the galaxy more slowly.

But where this population of the stars came from has been a long standing mystery since its identification in the mid 1970’s. One hypothesis is that it is the remainder of cannibalized dwarf galaxies that have never settled into a more standard orbit. Others suggest that these stars have been flung from the thin disk through gravitational slingshots or supernovae. A recent paper puts these hypothesis to the observational test.

At a first glance, both propositions seem to have a firm observational footing. The Milky Way galaxy is known to be in the process of merging with several smaller galaxies. As our galaxy pulls them in, the tidal effects shred these minor galaxies, scattering the stars. Numerous tidal streams of this sort have been discovered already. The ejection from the thin disk gains support from the many known “runaway” and “hypervelocity” stars which have sufficient velocity to escape the thin disk, and in some cases, the galaxy itself.

The new study, led by Marion Dierickx of Harvard, follows up on a 2009 study by Sales et al., which used simulations to examine the features stars would take in the thick disk should they be created via these methods. Through these simulations, Sales showed that the distribution of eccentricities of the orbits should be different and allow a method by which to discriminate between formation scenarios.

By using data from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), Dierickx’s team compared the distribution of the stars in our own galaxy to the predictions made by the various models. Ultimately, their survey included some 34,000 stars. By comparing the histogram of eccentricities to that of Sales’ predictions, the team hoped to find a suitable match that would reveal the primary mode of creation.

The comparison revealed that, should ejection from the thin disk be the norm there were too many stars in nearly circular orbits as well as highly eccentric ones. In general, the distribution was too wide. However, the match for the scenario of mergers fit well lending strong credence to this hypothesis.

While the ejection hypothesis or others can’t be ruled out completely, it suggests that, at least in our own galaxy, they play a rather minor role. In the future, additional tests will likely be employed, analyzing other aspects of this population.

June 29, 2010December 24, 2015 by Nancy Atkinson

Finding the Origin of Milky Way’s Ancient Stars

Simulation showing a Milky Way-like galaxy around five billion years ago, when most satellite galaxy collisions were happening. Credit: Andrew Cooper, John Helly (Durham University)

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From the Royal Astronomical Society

Many of the Milky Way’s ancient stars are remnants of other smaller galaxies torn apart by violent galactic collisions around five billion years ago, according to researchers at Durham University, who publish their results in a new paper in the journal Monthly Notices of the Royal Astronomical Society.

Scientists at Durham’s Institute for Computational Cosmology and their collaborators at the Max Planck Institute for Astrophysics, in Germany, and Groningen University, in Holland, ran huge computer simulations to recreate the beginnings of our Galaxy.

The simulations revealed that the ancient stars, found in a stellar halo of debris surrounding the Milky Way, had been ripped from smaller galaxies by the gravitational forces generated by colliding galaxies.

Cosmologists predict that the early Universe was full of small galaxies which led short and violent lives. These galaxies collided with each other leaving behind debris which eventually settled into more familiar looking galaxies like the Milky Way.

The researchers say their finding supports the theory that many of the Milky Way’s ancient stars had once belonged to other galaxies instead of being the earliest stars born inside the Galaxy when it began to form about 10 billion years ago.

Simulation showing the stellar halo of a Milky Way-like galaxy in the present day. Credit: Andrew Cooper (Durham University)

Lead author Andrew Cooper, from Durham University’s Institute for Computational Cosmology, said: “Effectively we became galactic archaeologists, hunting out the likely sites where ancient stars could be scattered around the galaxy.

“Our simulations show how different relics in the Galaxy today, like these ancient stars, are related to events in the distant past.

“Like ancient rock strata that reveal the history of Earth, the stellar halo preserves a record of a dramatic primeval period in the life of the Milky Way which ended long before the Sun was born.”

The computer simulations started from shortly after the Big Bang, around 13 billion years ago, and used the universal laws of physics to simulate the evolution of dark matter and the stars.

These simulations are the most realistic to date, capable of zooming into the very fine detail of the stellar halo structure, including star “streams” – which are stars being pulled from the smaller galaxies by the gravity of the dark matter.

One in one hundred stars in the Milky Way belong to the stellar halo, which is much larger than the Galaxy’s familiar spiral disk. These stars are almost as old as the Universe.

Professor Carlos Frenk, Director of Durham University’s Institute for Computational Cosmology, said: “The simulations are a blueprint for galaxy formation.

“They show that vital clues to the early, violent history of the Milky Way lie on our galactic doorstep.

“Our data will help observers decode the trials and tribulations of our Galaxy in a similar way to how archaeologists work out how ancient Romans lived from the artefacts they left behind.”

The research is part of the Aquarius Project, which uses the largest supercomputer simulations to study the formation of galaxies like the Milky Way and was partly funded by the UK’s Science and Technology Facilities Council (STFC).

Aquarius was carried out by the Virgo Consortium, involving scientists from the Max Planck Institute for Astrophysics in Germany, the Institute for Computational Cosmology at Durham University, UK, the University of Victoria in Canada, the University of Groningen in the Netherlands, Caltech in the USA and Trieste in Italy.

Durham’s cosmologists will present their work to the public as part of the Royal Society’s 350th anniversary ‘See Further’ exhibition, held at London’s Southbank Centre until July 4th.

May 28, 2010May 4, 2017 by Fraser Cain

What Galaxy is the Earth In?

What galaxy is Earth in? We're in the Milky Way

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Were you wondering what galaxy is the Earth in? You’ll probably recognize the answer: it’s the Milky Way Galaxy.

If you go to a dark spot, away from the bright city lights, and look up, you should be able to see the Milky Way as a cloudy band stretching across the sky. It really does look like spilt milk spread across the sky. But if you take a telescope and examine it more closely, you’ll see that the clouds are actually the collective light from thousands of stars.

Since we’re embedded inside the Milky Way, we’re seeing our home galaxy edge-on, from the inside. To get a better idea, grab a dinner plate and take a look at it edge on, so you can’t see the circular shape of the galaxy. You can only see the edge of the plate.

The Milky Way is an example of a barred spiral galaxy. It measures approximately 100,000 light years across and it’s only 1,000 light years thick; although, it’s more thick at the core where the galaxy bulges out. If you could fly out of the Milky Way in a rocket and then look back, you’d see a huge spiral shaped galaxy with a bar at the center. At the ends of this bar, there are two spiral arms which twist out forming the structure of the Milky Way.

The Earth is located in the Solar System, and the Solar System is located about 25,000 light-years away from the core of the galaxy. This also means that we’re about 25,000 light-years away from the outer edge of the Milky Way. We’re located in the Orion Spur, which is a minor arm located in between the two major galactic arms.

If you’d like more information on the Milky Way, check out NASA’s Starchild info on the Milky Way, and here’s more info from the WMAP mission.

We’ve written many articles about the Milky Way for Universe Today. Here’s an article with facts about the Milky Way, and here is a map of the Milky Way.

We’ve also recorded several episodes of Astronomy Cast about the Milky Way. Listen here, Episode 99: The Milky Way.

May 26, 2010December 24, 2015 by Nicholos Wethington

Newly-Discovered Stellar Nurseries in the Milky Way

The Orion Nebula, one of the most brilliant star-forming regions in our galaxy. Other, newly-discovered regions like the Orion Nebula could help astronomers determing the chemical composition of our galaxy. Image Credit: APOD/Hubble Space Telescope

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Our Milky Way churns out about seven new stars per year on average. More massive stars are formed in what’s called H II regions, so-named because the gas present in these stellar nurseries is ionized by the radiation of the young, massive stars forming there. Recently-discovered regions in the Milky Way that are nurseries for massive stars may hold important clues as to the chemical composition and structural makeup of our galaxy.

Thomas Bania, of Boston University, said in an NRAO press release, “We can clearly relate the locations of these star-forming sites to the overall structure of the Galaxy. Further studies will allow us to better understand the process of star formation and to compare the chemical composition of such sites at widely different distances from the Galaxy’s center.”

The announcement of these newly discovered regions was made in a presentation today at the American Astronomical Society meeting in Miami, Florida. The team of astronomers that collaborated on the search includes Thomas Bania of Boston University, Loren Anderson of the Astrophysical Laboratory of Marseille in France, Dana Balser of the National Radio Astronomy Observatory (NRAO), and Robert Rood of the University of Virginia.

H II regions that you may be familiar with include the Orion Nebula (M42), visible just South of Orion’s Belt with the naked eye, and the Horsehead Nebula, so famously imaged by the Hubble Space Telescope. For more information on other known regions (and lots of pictures), visit the 2Micron All-Sky Survey at IPAC.

By studying such regions in other galaxies, and our own, the chemical composition and distribution of a galaxy can be determined. H II regions form out of giant molecular clouds of hydrogen, and remain stable until a collision happens between two clouds, creating a shockwave, or the resulting shockwave from a nearby supernova collapses some of the gas to form stars. As these stars form and start to shine, their radiation strips the molecular hydrogen of its electrons.

The astronomers used both infrared and radio telescopes to see through the thick dust and gas that pervades the Milky Way. By combing surveys taken by the Spitzer Space Telescope’s infrared camera, and the Very Large Array (VLA) radio telescope, they identified “hot spots” that would be good candidates for H II regions. To further verify their findings, they used the Robert C. Byrd Green Bank Telescope (GBT), a sensitive radio telescope that allowed them to detect radio frequencies emitted by electrons as they rejoined protons to form hydrogen. This process of recombination to form hydrogen is a telltale sign of regions that contain ionized hydrogen, or H II.

The location of the regions is concentrated near the ends of the central bar of the Milky Way, and in its spiral arms. Over 25 of the regions discovered were further from the center of the galaxy than our own Sun – a more detailed study of these outlying regions could give astronomers a better understanding of the evolution and composition of our Milky Way.

“There is evidence that the abundance of heavy elements changes with increasing distance from the Galactic center,” Bania said. “We now have many more objects to study and improve our understanding of this effect.”

Source: NRAO Press Release

March 3, 2010December 24, 2015 by Nancy Atkinson

Second-Generation Star Supports Cannibal Theory of Milky Way

The newly discovered red giant star S1020549 supports the theory that our galaxy underwent a "cannibal" phase, growing to its current size by swallowing dwarf galaxies and other galactic building blocks. Credit: David A. Aguilar (CfA)

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A newly discovered red giant star is a relic from the early universe — a star that may have been among the second generation of stars to form after the Big Bang. Located in the dwarf galaxy Sculptor some 290,000 light-years away, the star has a remarkably similar chemical make-up to the Milky Way’s oldest stars. Its presence supports the theory that our galaxy underwent a “cannibal” phase, growing to its current size by swallowing dwarf galaxies and other galactic building blocks.

“This star likely is almost as old as the universe itself,” said astronomer Anna Frebel of the Harvard-Smithsonian Center for Astrophysics, lead author of the Nature paper reporting the finding.

Dwarf galaxies are small galaxies with just a few billion stars, compared to hundreds of billions in the Milky Way. In the “bottom-up model” of galaxy formation, large galaxies attained their size over
billions of years by absorbing their smaller neighbors.

“If you watched a time-lapse movie of our galaxy, you would see a swarm of dwarf galaxies buzzing around it like bees around a beehive,” explained Frebel. “Over time, those galaxies smashed together and mingled their stars to make one large galaxy — the Milky Way.”

If dwarf galaxies are indeed the building blocks of larger galaxies, then the same kinds of stars should be found in both kinds of galaxies, especially in the case of old, “metal-poor” stars. To astronomers, “metals” are chemical elements heavier than hydrogen or helium. Because they are products of stellar evolution, metals were rare in the early Universe, and so old stars tend to be metal-poor.

Old stars in the Milky Way’s halo can be extremely metal-poor, with metal abundances 100,000 times poorer than in the Sun, which is a typical younger, metal-rich star. Surveys over the past decade have
failed to turn up any such extremely metal-poor stars in dwarf galaxies, however.

“The Milky Way seemed to have stars that were much more primitive than any of the stars in any of the dwarf galaxies,” says co-author Josh Simon of the Observatories of the Carnegie Institution. “If dwarf
galaxies were the original components of the Milky Way, then it’s hard to understand why they wouldn’t have similar stars.”

The team suspected that the methods used to find metal-poor stars in dwarf galaxies were biased in a way that caused the surveys to miss the most metal-poor stars. Team member Evan Kirby, a Caltech
astronomer, developed a method to estimate the metal abundances of large numbers of stars at a time, making it possible to efficiently search for the most metal-poor stars in dwarf galaxies.

“This was harder than finding a needle in a haystack. We needed to find a needle in a stack of needles,” said Kirby. “We sorted through hundreds of candidates to find our target.”

Among stars he found in the Sculptor dwarf galaxy was one faint, 18th-magnitude speck designated S1020549. Spectroscopic measurements of the star’s light with Carnegie’s Magellan-Clay telescope in Las Campanas, Chile, determined it to have a metal abundance 6,000 times lower than that of the Sun; this is five times lower than any other star found so far in a dwarf galaxy.

The researchers measured S1020549’s total metal abundance from elements such as magnesium, calcium, titanium, and iron. The overall abundance pattern resembles those of old Milky Way stars, lending the first observational support to the idea that these galactic stars originally formed in dwarf galaxies.

The researchers expect that further searches will discover additional metal-poor stars in dwarf galaxies, although the distance and faintness of the stars pose a challenge for current optical telescopes. The next generation of extremely large optical telescopes, such as the proposed 24.5-meter Giant Magellan Telescope, equipped with high-resolution spectrographs, will open up a new window for studying the growth of galaxies through the chemistries of their stars.

In the meantime, says Simon, the extremely low metal abundance in S1020549 study marks a significant step towards understanding how our galaxy was assembled. “The original idea that the halo of the Milky
Way was formed by destroying a lot of dwarf galaxies does indeed appear to be correct.”

Source: Harvard-Smithsonian Center for Astrophysics

February 21, 2010December 24, 2015 by Jean Tate

All-Sky Radio Image in 60 Seconds, No Moving Parts

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This image is a software-calibrated image with high signal-to-noise ratio at a frequency of 120 MHz, of the radio sky above Effelsberg, Germany, on November10, 2009. It has North at the top and East at the left, just as a person would have seen the entire sky when lying on their back on a flat field near Effelsberg late in the afternoon on November 10, if their eyes were sensitive to radio waves.

The two bright (yellow) spots are Cygnus A – a giant radio galaxy powered by a supermassive black hole – near the center of the image, and Cassiopeia A – a bright radio source created by a supernova explosion about 300 years ago – at the upper-left in the image. The plane of our Milky Way galaxy can also be seen passing by both Cassiopeia A and Cygnus A, and extending down to the bottom of the image. The North Polar Spur, a large cloud of radio emission within our own galaxy, can also be seen extending from the direction of the Galactic center in the South, toward the western horizon in this image. “We made this image with a single 60 second “exposure” at 120 MHz using our high-band LOFAR field in Effelsberg”, says James Anderson, project manager of the Effelsberg LOFAR station.

“The ability to make all-sky images in just seconds is a tremendous advancement compared to existing radio telescopes which often require weeks or months to scan the entire sky,” Anderson went on. This opens up exciting possibilities to detect and study rapid transient phenomena in the universe.

LOFAR, the LOw Frequency ARray, was designed and developed by ASTRON (Netherlands Institute for Radio Astronomy) with 36 stations centered on Exloo in the northeast of The Netherlands. It is now an international project with stations being built in Germany, France, the UK and Sweden connected to the central data processing facilities in Groningen (NL) and the ASTRON operations center in Dwingeloo (NL). The first international LOFAR station (IS-DE1) was completed on the area of the Effelsberg radio observatory next to the 100-m radio telescope of the Max-Planck-Institut für Radioastronomie (MPIfR).

Operating at relatively low radio frequencies from 10 to 240 MHz, LOFAR has essentially no moving parts to track objects in the sky; instead digital electronics are used to combine signals from many small antennas to electronically steer observations on the sky. In certain electronic modes, the signals from all of the individual antennas can be combined to make images of the entire radio sky visible above the horizon.

IS-DE1: Some of the 96 low-band dipole antennas, Effelsberg LOFAR station (foreground); high-band array (background) (Credit: James Anderson, MPIfR)

LOFAR uses two different antenna designs, to observe in two different radio bands, the so-called low-band from 10 to 80 MHz, and the high-band from 110 to 240 MHz. All-sky images using the low-band antennas at Effelsberg were made in 2007.

Following the observation for the first high-band, all-sky image, scientists at MPIfR made a series of all-sky images covering a wide frequency range using both the low-band and high-band antennas at Effelsberg.

Effelsberg sky through LOFAR eyes (Credit: James Anderson, MPIfR)

The movie of these all-sky images has been compiled and is shown above. The movie starts at a frequency of 35 MHz, and each subsequent frame is about 4 MHz higher in frequency, through 190 MHz. The resolution of the Effelsberg LOFAR telescope changes with frequency. At 35 MHz the resolution is about 10 degrees, at 110 MHz it is about 3.4 degrees, and at 190 MHz it is about 1.9 degrees. This change in resolution can be seen by the apparent size of the two bright sources Cygnus A and Cassiopeia A as the frequency changes.

Scientists at MPIfR and other institutions around Europe will use measurements such as these to study the large-sky structure of the interstellar matter of our Milky Way galaxy. The low frequencies observed by LOFAR are ideal for studying the low energy cosmic ray electrons in the Milky Way, which trace out magnetic field structures through synchrotron emission. Other large-scale features such as supernova remnants, star-formation regions, and even some other nearby galaxies will need similar measurements from individual LOFAR telescopes to provide accurate information on the large-scale emission in these objects. “We plan to search for radio transients using the all-sky imaging capabilities of the LOFAR telescopes”, says Michael Kramer, director at MPIfR, in Bonn. “The detection of rapidly variable sources using LOFAR could lead to exciting discoveries of new types of astronomical objects, similar to the discoveries of pulsars and gamma-ray bursts in the past decades.”

“The low-frequency sky is now truly open in Effelsberg and we have the capability at the observatory to observe in a wide frequency range from 10 MHz to 100 GHz”, says Anton Zensus, also director at MPIfR. “Thus we can cover four orders of magnitude in the electromagnetic spectrum.”

Source: Max-Planck-Institut für Radioastronomie

January 6, 2010April 26, 2016 by Ryan Anderson

Milky Way Has a “Squashed Beachball”-Shaped Dark Matter Halo

This illustration shows the visible Milky Way galaxy surrounded by a “squashed beachball”-shaped dark matter halo. Source: UCLA

Our galaxy is shaped like a flat spiral right? Not if you’re talking about dark matter. Astronomers announced today that the Milky Way’s dark matter halo, which represents about 70% of the galaxy’s mass, is actually shaped like a squashed beachball.

Dark matter is completely invisible, but it still obeys the law of gravity, so the existence of dark matter haloes, and their shape, can be inferred by monitoring the orbits of dwarf galaxies orbiting the much larger Milky Way.

Unfortunately, to determine the orbit of an object, you have to measure its position at several points in that orbit, and dwarf galaxies take about a billion years to go around the Milky Way. Astronomers just haven’t been around long enough to watch even a fraction of a complete orbit. Luckily, they don’t have to.

Dwarf galaxies, just like their full-sized counterparts, and made of billions of stars. When the tidal forces from a big galaxy like the Milky Way act on a dwarf galaxy, the result is a streamer of stars that trace out the dwarf galaxy’s orbit. By using data from huge all-sky surveys, a group of astronomers led by David Law at UCLA were able to reconstruct the orbit of the Sagittarius Dwarf Galaxy. There was just one problem: different parts of the dwarf galaxy had different orbits, which led to wildly different dark matter halo shapes.

Law and his colleagues Steven Majewski (University of Virginia) and Kathryn Johnston (Columbia University) solved this problem by allowing models of the dark matter halo to be “triaxial” – in other words, have different lengths in all three dimensions. The best model solution results in a halo shaped like a beach ball that has been squashed sideways.

“We expected some amount of flattening based on the predictions of the best dark-matter theories,” said Law, “but the extent, and particularly the orientation, of the flattening was quite unexpected. We’re pretty excited about this, because it begs the question of how our galaxy formed in its present orientation.”

Sagittarius is not the only dwarf galaxy orbiting the Milky Way, and Law and his colleagues plan to study the orbits of other dwarf galaxies to refine their model. “It will be important to see if these results hold up as precise orbits are measured for more of these galaxies. In the meantime, such a squashed dark-matter halo is one of the best explanations for the observed data.”

This illustration shows the visible Milky Way galaxy (blue spiral) and the streams of stars represent the tidally shredded Sagittarius dwarf galaxy. Source: UCLA

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

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