Posted on by Jason Rhian

Voyager 1 Spacecraft Enters New Region of Solar System

The Voyager 1 spacecraft has started to transverse what JPL has dubbed as a "cosmic purgatory" between our solar system - and interstellar space. Image Credit: NASA/JPL

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Voyager 1 is in uncharted territory. The long-lived spacecraft has entered a new region of space that lies between where our solar system ends and where interstellar space begins. This area is not a place of sightseeing however, as a NASA press release referred to it as a kind of “cosmic purgatory.”

Here, the solar winds ebb somewhat, the magnetic field increases and charged particles from within our solar system – is leaking out into interstellar space. This data has been compiled from information received from Voyager 1 over the course of the last year.

The Voyager spacecraft's compliment of scientific instruments have provided scientists back on Earth with information about what the space environment at the fringes of our sun's influence is truly like. Image Credit: NASA/JPL - Caltech

“Voyager tells us now that we’re in a stagnation region in the outermost layer of the bubble around our solar system,” said Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena. “Voyager is showing that what is outside is pushing back. We shouldn’t have long to wait to find out what the space between stars is really like.”

Despite the fact that Voyager 1 is approximately 11 billion miles (18 billion kilometers) distant from the sun – it still has not encounter interstellar space. The information that scientists have gleaned from the Voyager 1 spacecraft indicates that the spacecraft is still located within the heliosphere. The heliosphere is a “bubble” of charged particles that the sun blows around itself and its retinue of planets.

Voyager 1 has traveled far past the realm of the gas or even ice giants and is now in uncharted territory where scientists are learning more and more about the dynamic environment at the far-flung edges of our solar system. Image Credit: NASA/JPL - Caltech

The latest findings were made using Voyager’s Low Energy Charged Particle instrument, Cosmic Ray Subsystem and Magnetometer.

Experts are not certain how long it will take the Voyager 1 spacecraft to finally breach this bubble and head out into interstellar space. Best estimates place the length of time when this could happen anywhere from the next few months – to years. These findings counter findings announced in April of 2010 that showed that Voyager 1 had essentially crossed the heliosphere boundary. The discoveries made during the past year hint that this region of space is far more dynamic than previously thought.

Voyager 1 has entered into a region of space between the sun's influence and the beginning of interstellar space that NASA has dubbed the "stagnation region." Image Credit: NASA/JPL - Caltech

The magnetometer aboard Voyager 1 has picked up an increase in the intensity of the magnetic field located within this “stagnation field.” Essentially the inward pressure from interstellar space is compressing the magnetic field to twice its original density. The spacecraft has also detected a 100-fold increase in the intensity of high-energy electrons diffusing into our solar system from outside – this is yet another indicator that Voyager 1 is approaching the heliosphere.

The interplanetary probe was launched from Cape Canaveral Air Force Station’s Space Launch Complex 41 (SLC-41) on Sept. 5, 1977, Voyager 1’s sister ship, Voyager 2 is also in good health and is about 9 billion miles (15 billion kilometers) from the sun (it too was launched in 1977). The spacecraft itself was built by NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

“Voyager is a mission of discovery and it’s at the edge of the solar system still making discoveries,” said Stone said. “The stagnation is the latest in the whole journey of discovery. We are all excited because we believe it means we’re getting very close to boundary of heliosphere and the entry into interstellar space.”

Both of the Voyager spacecraft were thrust to orbit by the powerful Titan boosters - and both in the same year - 1977. Photo Credit: NASA
Posted on by Nancy Atkinson

The Space Program Is Over? Nobody Told Us!

With the space shuttle program ending, erroneous reports of NASA’s space program being “over” have surfaced on various websites and news outlets. But astronauts on the International Space Station want to assure everyone that NASA is alive and well. A new video series called “Inside the Space Station” premiers with this pilot episode, and has astronaut host Mike Massimino talking with Ron Garan and Mike Fossum, when they were on board the ISS (Garan returned home in September and Fossum in November). The video confirms humans are still doing many things in space (there’s been a continuous human presence on the ISS since Nov. of 2000); and also includes great images and footage from the space station.

Posted on by Ray Sanders

SETI to Resume Search for Extraterrestrial Intelligence; Will Target Kepler Data

The Allen Telescope Array. Image Credit: SETI Institute

After being shut down for over six months due to financial problems, The Allen Telescope Array (ATA) is once again searching other planetary systems for radio signals, looking for evidence of extraterrestrial intelligence.

Some of the first targets in SETI’s renewed search will be a selection of recently discovered exoplanet candidates by NASA’s Kepler mission.

“This is a superb opportunity for SETI observations,” said Dr. Jill Tarter, the Director of the Center for SETI Research at the SETI Institute. “For the first time, we can point our telescopes at stars, and know that those stars actually host planetary systems – including at least one that begins to approximate an Earth analog in the habitable zone around its host star. That’s the type of world that might be home to a civilization capable of building radio transmitters.”

What other studies will SETI be performing with the array, and how were they able to restart the Allen Telescope Array?

This past April, SETI was forced to place the ATA into hibernation mode, due to budget cuts of SETI’s former partner, U.C Berkeley. Since Berkeley operated Hat Creek Observatory where the ATA is located, their withdrawal from the program left SETI without a way to operate the ATA.

SETI has since acquired new funding to operate the ATA and can now resume observations where they left off – examining planetary candidates detected by the Kepler mission. The planetary candidates SETI will examine first will be those that are thought to be in their star’s habitable zone (the range of orbital distance from a planet’s host star which may allow for surface water). Many astrobiologists theorize that liquid water is essential for life to exist on a planet.

“In SETI, as with all research, preconceived notions such as habitable zones could be barriers to discovery.” Tarter added. “So, with sufficient future funding from our donors, it’s our intention to examine all of the planetary systems found by Kepler.”

SETI will spend the next two years observing the planetary systems detected by Kepler in the naturally-quiet 1 to 10 GHz terrestrial microwave window. Part of what makes this comprehensive study possible is that the ATA can provide ready access to tens of millions of channels at any one time.

Resuming ATA operations was made possible due to tremendous public support via SETI’s www.SETIStars.org web site. In addition to the funds raised by the public, the United States Air Force has also provided funding to SETI in order to assess the ATA’s capabilities for space situational awareness.

Tarter notes, “Kepler’s success has created an amazing opportunity to focus SETI research. While discovery of new exoplanets via Kepler is backed with government monies, the search for evidence that some of these worlds might be home to intelligence falls to SETI alone. And our SETI exploration depends entirely on private donations, for which we are deeply grateful to our donors.”

“The year-in and year-out fundraising challenge we tackle in order to conduct SETI research is an absolute human and organizational struggle,” said Tom Pierson, CEO of the SETI Institute, “yet it is well worth the hard work to help Jill’s team address what is one of humanity’s most profound research questions.”

Dr. Tarter will be presenting during the first Kepler Science Conference (at NASA Ames Research Center) from December 5 to 9, 2011. You can view the agenda for the meeting, along with the abstract for her talk on Earth analogs at: http://kepler.nasa.gov/Science/ForScientists/keplerconference/sessions/.

If you’d like to learn more about SETI, or would like to make a donation to help fund their efforts, visit: https://setistars.org/donations/new

Read more about SETI’s partnership with the United States Air Force at: http://www.seti.org/afspc

Source: SETI Institute press release

Posted on by Tammy Plotner

Incredible Spinning Star Rotates At A Million Miles Per Hour!

This is an artist's concept of the fastest rotating star found to date. The massive, bright young star, called VFTS 102, rotates at a million miles per hour, or 100 times faster than our Sun does. Centrifugal forces from this dizzying spin rate have flattened the star into an oblate shape and spun off a disk of hot plasma, seen edge on in this view from a hypothetical planet. The star may have "spun up" by accreting material from a binary companion star. The rapidly evolving companion later exploded as a supernova. The whirling star lies 160,000 light-years away in the Large Magellanic Cloud, a satellite galaxy of our Milky Way. Credit: NASA, ESA, and G. Bacon (STScI)

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Located in the Large Magellanic Cloud, a star named VFTS 102 is spinning its heart out… Literally. Rotating at a mind-numbing speed of a million miles per hour (1.6 million kph), this hot blue giant has reached the edge where centrifugal forces could tear it apart. It’s the fastest ever recorded – 300 times faster than our Sun – and may have been split off from a double star system during a violent explosion.

Thanks to ESO’s Very Large Telescope at the Paranal Observatory in Chile, an international team of astronomers studying the heaviest and brightest stars in the Tarantula Nebula made quite a discovery – a huge blue star 25 times the mass of the Sun and about one hundred thousand times brighter was cruising through space at a speed which drew their attention.

“The remarkable rotation speed and the unusual motion compared to the surrounding stars led us to wonder if this star had an unusual early life. We were suspicious.” explains Philip Dufton (Queen’s University Belfast, Northern Ireland, UK), lead author of the paper presenting the results.

ESO's Very Large Telescope has picked up the fastest rotating star found so far. This massive bright young star lies in our neighbouring galaxy, the Large Magellanic Cloud, about 160 000 light-years from Earth. Astronomers think that it may have had a violent past and has been ejected from a double star system by its exploding companion. Credit: ESO

What they’ve discovered could possibly be a “runaway star” – one that began life as a binary, but may have been ejected during a supernova event. Further evidence which supports their theory also exists: the presence of a pulsar and a supernova remnant nearby. But what made this crazy star spin so fast? It’s possible that if the two stars were very close that streaming gases could have started the incredible rotation. Then the more massive of the pair blew its stack – expelling the star into space. So what would be left? It’s elementary, Watson… A supernova remnant, a pulsar and a runaway!

Even though this is a rather tidy conclusion, there’s always room for doubt. As Dufton concludes, “This is a compelling story because it explains each of the unusual features that we’ve seen. This star is certainly showing us unexpected sides of the short but dramatic lives of the heaviest stars.”

Original Story Source: HubbleSite News Release and ESO News Release. For Further Reading: he VLT-FLAMES Tarantula Survey I. Introduction and observational overview.

Posted on by Jason Rhian

Commander of Final Shuttle Mission to Leave NASA

Chris Ferguson, the commander of the final mission of the shuttle program, STS-135 has announced that he will leave the space agency. Photo Credit: NASA.gov

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On Dec. 9, 2011, NASA will witness the departure of the astronaut who served as commander for the final space shuttle mission STS-135. Chris Ferguson has announced his plans to retire from the space agency so that he can enter the private sector. With Ferguson’s departure, all of the commanders who flew the final three shuttle missions have left or will be departing NASA.

With no defined human space flight mission objectives in place and with the only ride to space currently being Russia’s Soyuz Spacecraft many astronauts are leaving the agency for other prospects. The space agency is losing an astronaut at the rate of one astronaut every two months. As of Dec. 9 NASA will have 58 astronauts in its active roster.

Ferguson has flown into space, twice on space shuttle Atlantis, logging over 40 days in space. Photo Credit: NASA.gov

Ferguson is a retired U.S. Navy captain – his command of Atlantis’ final flight marked his third trip into space. The 13-day mission was a resupply flight to the International Space Station and saw some 10,000 pounds of supplies and spare parts delivered to the orbiting outpost. With the final landing, conducted on July 21, 2011, Ferguson and his crew wrapped up the shuttle program’s 30 year history.

“Chris has been a great friend, a tremendous professional and an invaluable asset to the NASA team and the astronaut office,” said Peggy Whitson, chief of the Astronaut Office. “His exceptional leadership helped ensure a perfect final flight of the space shuttle,
a fitting tribute to the thousands who made the program possible.”

Ferguson (third from left) has opted to leave NASA to pursue a job in the private sector. His departure comes at a time when NASA is losing many of its experienced space flyers. Image Credit: NASA.gov

Ferguson’s very first mission, STS-115, was also on Atlantis. He served as the pilot on this mission which took place in 2006 and delivered the P3 and P4 truss segments to the space station. His next shuttle flight was STS-126 on shuttle Endeavour, this mission saw water reclamation and habitation systems transported to the ISS (as well as conducting a crew swap out). Ferguson has over 40 days of space flight experience.

Ferguson joined NASA’s astronaut corps in 1998. Upon his completion of initial astronaut training, he performed technical duties related to the shuttle’s main engines (SSMEs), the orbiter’s large, orange external tank, solid rocket boosters (SRBs) as well as software utilized on the shuttles. Before he was given the nod to be the commander of STS-135, Ferguson was the deputy chief of the Astronaut Office at NASA’s Johnson Space Center located in Houston, Texas.

“Chris has been a true leader at NASA,” said NASA Administrator Charles Bolden, “not just as a commander of the space shuttle, but also as an exemplary civil servant, a distinguished Navy officer and a good friend. I am confident he will succeed in his next career as he brings his skill and talents to new endeavors.”

Chris Ferguson has served NASA in a variety of roles since being accepted as an astronaut in 1998. Photo Credit: NASA.gov
Posted on by Amy Shira Teitel

Are Gas-Formed Gullies the Norm on Mars?

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In June 2000, Martian imaging scientists made a striking discovery — data from NASA’s Mars Global Surveyor spacecraft found gullies on the red planet. Gullies on Earth form when water runs down steep slopes and carves soil out of its way, so the discovery of this geologic feature on Mars was enticing evidence that liquid water existed on or near the surface of Mars.

But gullies have also been spotted in the Mars’ polar regions where the temperature is too cold for water to exist in its liquid form. Adding to the puzzle is the suggestion that the apparent gullies are actually formed by wind or underground gases causing sand and dust to roll down a steep hill and create what looks like a gully formed by Water. So what’s behind the gullies at Mars’ poles?

A gully that looks like it was made by water eroding hard rock. Image credit: NASA/JPL/Malin Space Science Systems

Frozen carbon dioxide — more commonly known as dry ice — isn’t an uncommon feature on Mars. It can freeze out of the carbon dioxide rich atmosphere on Mars and, after a dust storm, be covered by a thin layer of dust or sand. Recently, researchers are looking to this subsurface dry ice as a possible explanation for Martian gullies, particularly at the frozen poles.

The key here is sublimation — the phenomenon of a solid passing directly into its gaseous state. You’ve seen this happen if you’ve ever poured water on dry ice. The water warms the solid dry ice and turn it into a gas. On Mars, it’s possible that changes in temperatures with seasons could be enough to sublimate the frozen carbon dioxide. The expulsion of the gas through the soil on the surface could cause it to roll down a hill like a fluid. The same thing would happen with water coming up from under ground.

Whether or not dry ice sublimation is behind polar gullies became a focus of Yolanda Cedillo-Flores and three colleagues at the Lunar and Planetary Institute in Houston, Texas.

A previous study testing whether sublimating dry ice could form gullies, led by Cedillo-Flores, was brilliant in its simplicity. They piled sand into Mars-like slopes then blew air underneath the sand. The sand flowed down the slope, much like a liquid would, and formed was looked very much like a gully.

Recently, the team at the Lunar and Planetary Institute have been testing the possibility of this phenomenon happening on Mars. They used the average daytime and seasonal temperatures of the Martian year to calculate the sublimation rate of dry ice on Mars. Then, they ran models of this event on Martian areas without any sediment as well as those with layers of sand and dust of varying thickness over the average seasonal deposit of dry ice. When simulated spring came, enough heat reached the dry ice that it sublimated and acted like a fluid. Turns out, Mars is just right for seasonal sublimation of frozen carbon dioxide.

They finally came to the conclusion that carbon dioxide sublimation is the likeliest cause behind the gullies forming in Mars’ polar regions.

Sources: Martian gullies: Produced by fluidization of dry material, CO2 gas fluidization in the initiation and formation of Martian polar gullies.

Between 1999 and 2005, a new gully popped up. Image credit: NASA/JPL/Malin Space Science Systems
Posted on by Paul Scott Anderson

Kepler Confirms First Planet in Habitable Zone of Sun-Like Star

This artist's illustration of Kepler 22-b, an Earth-like planet in the habitable zone of a Sun-like star about 640 light years (166 parsecs) away. Credit: NASA/Ames/JPL-Caltech

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Scientists from the Kepler mission announced this morning the first confirmed exoplanet orbiting in the habitable zone of a Sun-like star, the region where liquid water could exist on the surface of a rocky planet like Earth. Evidence for others has already been found by Kepler, but this is the first confirmation. The planet, Kepler-22b, is also only about 2.4 times the radius of Earth — the smallest planet found in a habitable zone so far — and orbits its star, Kepler-22, in 290 days. It is about 600 light-years away from Earth, and Kepler-22 is only slightly smaller and cooler than our own Sun. Not only is the planet in the habitable zone, but astronomers have determined its surface temperature averages a comfortable 22 degrees C (72 degrees F). Since the planet’s mass is not yet known, astronomers haven’t determined if it is a rocky or gaseous planet. But this discovery is a major step toward finding Earth-like worlds around other stars. A very exciting discovery, but there’s more…

It was also announced that Kepler has found 1,094 more planetary candidates, increasing the number now to 2,326! That’s an increase of 89% since the last update this past February. Of these, 207 are near Earth size, 680 are super-Earth size, 1,181 are Neptune size, 203 are Jupiter size and 55 are larger than Jupiter. These findings continue the observational trend seen before, where smaller planets are apparently more numerous than larger gas giant planets. The number of Earth size candidates has increased by more than 200 percent and the number of super-Earth size candidates has increased by 140 percent.

According to Natalie Batalha, Kepler deputy science team lead at San Jose State University in San Jose, California, “The tremendous growth in the number of Earth-size candidates tells us that we’re honing in on the planets Kepler was designed to detect: those that are not only Earth-size, but also are potentially habitable. The more data we collect, the keener our eye for finding the smallest planets out at longer orbital periods.”

Regarding Kepler-22b, William Borucki, Kepler principal investigator at NASA Ames Research Center at Moffett Field, California stated: “Fortune smiled upon us with the detection of this planet. The first transit was captured just three days after we declared the spacecraft operationally ready. We witnessed the defining third transit over the 2010 holiday season.”

Comparison of the Kepler-22 system with our own inner solar system. Credit: NASA/Ames/JPL-Caltech

Previously there were 54 planetary candidates in habitable zones, but this was changed to 48, after the Kepler team redefined the definition of what constitutes a habitable zone in order to account for the warming effects of atmospheres which could shift the zone farther out from a star.

The announcements were made at the inaugural Kepler science conference which runs from December 5-9 at Ames Research Center.

See also the press release from the Carnegie Institution for Science here.

Posted on by Tammy Plotner

Earth’s Magnetic Pole Reversal – Don’t “Flip Out”!

Schematic illustration of Earth's magnetic field. Credit/Copyright: Peter Reid

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Have you heard or read stories about how Earth will some day reverse its magnetic poles? If you have, then chances are very good you’ve also heard this perfectly normal function of our planet could spell disaster. Before you buy into another “end of the world as we know it” scenario, let’s take a look at the facts.

For the record, we know that Earth’s magnetic field has changed its polarity more than once in its lifetime. For example, if you could step back in time some 800,000 years ago with a compass in your hand, you’d see the needle pointed to south – instead of north. Why? Because a compass works on magnetic fields, its needle directs you to the magnetic pole, measured as either positive or negative. The markings on the modern compass dial would be incorrect if the polarity of Earth’s magnetic fields were reversed! Like a witch hunt, many would-be prophets say natural occurrences like this might signal doom… But could their theories be correct? Unfortunately for hyperbole, the geologic and fossil records from past reversals show the answer is “No.” We’ll still be around.

Just like the Sun reversing its magnetic poles, Earthly switches are just a part of our planet’s schedule. During about the last 20 million years of our formation, Earth has settled into a pattern of switching magnetic poles about every 200,000 to 300,000 years… with a period of twice that long since our last reversal. And, it’s not a thing that happens rapidly. Magnetic pole reversal takes up to several hundred thousands of years to complete. The fields blend together and magnetic poles pop up at odd latitudes as it happens. It’s not that scary! Scientists say that Earth has reversed its magnetic field hundreds of times over the last three billion years and have sped up slightly with time.

How do we know about the impacts of magnetic pole reversal? We take a look at the deep evidence – sediment cores taken from the ocean floor. These samples are perfect fossil records which show us what direction the magnetic field was pointed in as the underwater lava emerged. These ancient flows were magnetized in the field’s direction at the time of their creation and exist on either side of the Mid-Atlantic Rift where the North American and European continental plates are moving away from each other.

“The last time that Earth’s poles flipped in a major reversal was about 780,000 years ago, in what scientists call the Brunhes-Matuyama reversal. The fossil record shows no drastic changes in plant or animal life.” says NASA’s Patrick Lynch. ” Deep ocean sediment cores from this period also indicate no changes in glacial activity, based on the amount of oxygen isotopes in the cores. This is also proof that a polarity reversal would not affect the rotation axis of Earth, as the planet’s rotation axis tilt has a significant effect on climate and glaciation and any change would be evident in the glacial record.”

A schematic diagram of Earth's interior and the movement of magnetic north from 1900 to 1996. The outer core is the source of the geomagnetic field. Graphic Credit: Dixon Rohr
Unlike a hard-wired magnet, Earth’s polarity isn’t constant – it moves around a bit. The reason we have a magnetic field is our solid iron core surrounding by hot, fluid metal. According to computer modeling, this flow creates electric currents which spawn the magnetic fields. While it’s not possible at this point in time to measure the outer core of our planet directly, we can guess at its movement by the changes in the magnetic field. One such change has occurred for almost 200 years now… Our northern pole has been shifting even more northward. Since it was first located, the pole has shifted its place by more than 600 miles (1,100 km)! What’s more, it’s speeding up. It would seem that it’s moving almost 40 miles per year now, instead of the 10 miles per year as recorded in the early 20th century.

Don’t be fooled by those saying a magnetic pole reversal would leave us temporarily without a magnetic field, either. This is simply isn’t going to happen and we’re not going to be exposed to harmful solar activity. While our magnetic field goes through weaker and stronger phases, there is simply no evidence to be found anywhere that it has ever disappeared completely. Even if it were weakened, our atmosphere would protect us against incoming particles and we’d have more auroral displays at lower latitudes!

So, go ahead… Sleep at night. Earthly magnetic pole reversal is a normal function of our planet and when it does happen its effects will be spread out over hundreds of thousands of years – not flipped like a pancake.

Original Story Source: NASA Earth News. For Further Reading: Earth’s Inconstant Magnetic Field..

Posted on by Jason Rhian

X-37B – The Gift That Keeps On Giving

The Orbital Test Vehicle or OTV has been launched twice by the United States Air Force. There is one currently on orbit that has had its mission extended - past the officially stated endurance time that the USAF had previously announced. Photo Credit: USAF


Video provided courtesy of United Launch Alliance

The United States Air Force’s second flight of the X-37B – is headed into extra innings. Known as the Orbital Test Vehicle 2 (OTV-2) this robotic mini space shuttle launched from Cape Canaveral Air Force Station’s Space Launch Complex 41 (SLC-41) on Mar. 5, 2011. Although the U.S. Air Force has kept mum regarding details about the space plane’s mission – it has announced that the OTV-2 has exceeded its endurance limit of 270 days on orbit as of the end of November.

The OTV is launched atop a United Launch Alliance (ULA) Atlas V 501 rocket. The space plane is protected within a fairing until it reaches orbit. After separation, the diminutive shuttle begins its mission.

OTV mission USA-226, as it is officially known, is by all accounts going smoothly and the spacecraft is reported to be in good health. The U.S. Air Force has not announced when OTV-2 will be directed to land.

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The fact that the space plane will continue to orbit beyond what its stated limits are highlights that the OTV has greater capabilities than what was officially announced. The first OTV flight launched in April of 2011 and landed 224 days later at Vandenberg Air Force Base in California. The U.S. Air Force is undoubtedly being more judicious with fuel stores on board the robotic spacecraft, allowing for a longer duration flight.

Much like NASA’s retired fleet of space shuttle orbiters, the OTV has a payload bay that allows for payloads and experiments to be conducted on-orbit. What payloads the U.S. Air Force has had on either mission – remains a secret.

Boeing has announced that the X-37B could be modified to conduct crewed missions to and from orbit. Tentatively named the X-37C, this spacecraft would be roughly twice the size of its unmanned cousin. If this variant goes into service it would be used to transport astronauts to and from the orbiting International Space Station (ISS).

OTV USA-226 launched on Mar. 5, 2011 and has helped prove out the mini space plane's design. Photo Credit: Alan Walters/awaltersphoto.com

The X-37B has become a bit controversial of late. Members of the Chinese press have stated that the space plane raises concerns of an arms race in space. Xinhua News Agency and China Daily have expressed concern that the OTVs could be used to deliver weapons to orbit. The Pentagon has flatly denied these allegations. The clandestine nature of these flights have led to a wide variety of theories as to what the OTVs have been used to ferry to orbit.

Posted on by Ray Sanders

Sagittarius Dwarf Galaxy – A Beast With Four Tails?

A map of the sky showing the numbers of stars counted in the Sagittarius streams. The dotted red lines trace out the Sagittarius streams, and the blue ellipses in the center show the current location of the Sagittarius Dwarf Galaxy. Image credit: S. Koposov and the SDSS-III collaboration

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Galactic interactions can have big effects on the shapes of the disks of galaxies. So what happens when a small galaxy intermingles with the outer part of our own larger Milky Way Galaxy? It’s not pretty, as rivers of stars are being sheared off from a neighboring dwarf galaxy, Sagittarius, according to research by a team of astronomers led by Sergey Koposov and Vasily Belokurov (University of Cambridge).

Analyzing data from the latest Sloan Digital Sky Survey (SDSS-III), the team found two streams of stars in the Southern Galactic hemisphere that were torn off Sagittarius dwarf galaxy. This new discovery also connects newly found streams with two previously discovered streams in the Northern Galactic hemisphere.

Describing the phenomenon, Koposov said, “We have long known that when small dwarf galaxies fall into bigger galaxies, elongated streams, or tails, of stars are pulled out of the dwarf by the enormous tidal field.”

Wyn Evans, one of the other team members commented, “Sagittarius is like a beast with four tails.”

At one time, the Sagittarius dwarf galaxy was one of the brightest of our Galaxy’s satellites. Now its remains are on the other side of our Galaxy, and in the process of being broken apart by immense tidal forces. Estimates show that the Sagittarius dwarf galaxy lost half its stars and gas over the past billion years.

Before the SDSS-III data analysis, it was known that Sagittarius had two tails – one in front of and one behind the remnant. This discovery was made by using previous SDSS imaging, specifically a 2006 study which found the Sagittarius tidal tail in the Northern Galactic sky appears to be split in two.

Commenting on the previous discovery, Belokurov added, “That was an amazing discovery, but the remaining piece of the puzzle, the structure in the South, was missing until now.”

Analyzing density maps of over 13 million stars in the SDSS-III data, Koposov and his team found that the Sagittarius stream in the South is also split into two. One stream is thicker and brighter, while the other is thinner and fainter. According to the paper, the fainter stream is simpler and more metal-poor, while the brighter stream is more complex and metal-rich.

The deduction makes sense since each successive generation of stars will create and distribute (via supernovae) more metals into the next generation of star formation.

An artist's impression of the four tails of the Sagittarius Dwarf Galaxy (the orange clump on the left of the image) orbiting the Milky Way. The bright yellow circle to the right of the galaxy's center is our Sun (not to scale). Image credit: Amanda Smith (University of Cambridge)

While the exact cause of the tidal tail split is unknown, astronomers believe that the Sagittarius dwarf may have been part of a binary galactic system, much like the Large and Small Magellanic Clouds, visible in our Southern hemisphere. Despite the nature of the tidal tail split being presently unknown, astronomers have known that over time, many smaller galaxies have been torn apart or absorbed by our Milky Way Galaxy, as well as other galaxies in the Universe.

The movie (below) shows multiple streams produced by the disruption of the Sagittarius dwarf galaxy in the Milky Way halo. Our Sun is depicted by the orange sphere. The Sagittarius dwarf galaxy is in the middle of the stream. The area shown in the movie is roughly 200,000 parsecs (about 600,000 light-years.) Movie credit: S. Koposov and the SDSS-III collaboration.

If you’d like to learn more, you can read the full scientific paper at: arxiv.org

Source: SDSS press release, arXiv paper #1111.7042