Found: Two ‘Exact Matches’ to the Milky Way Galaxy

This image shows one of the two ‘exact matches’ to the Milky Way system found in a new survey. The larger galaxy, denoted GAMA202627, which is similar to the Milky Way clearly has two large companions off to the bottom left of the image. InImage Credit: Dr Aaron Robotham, ICRAR/St Andrews using GAMA data.

Here’s something astronomers haven’t seen before: galaxies that look just like our own Milky Way. It’s not that our spiral-armed galaxy is rare but instead the whole neighborhood in which we reside seems to be unusual. Until now, a galaxy paired with close companions like the Magellanic Clouds has not been found elsewhere. But using data from a new radio astronomy survey, astronomers found two Milky Way look-alikes and several others that were similar.

“We’ve never found another galaxy system like the Milky Way before, which is not surprising considering how hard they are to spot!” said Dr. Aaron Robotham with the International Centre for Radio Astronomy Research (ICRAR). “It’s only recently become possible to do the type of analysis that lets us find similar groups.”

“Everything had to come together at once,” Robotham added. “We needed telescopes good enough to detect not just galaxies but their faint companions, we needed to look at large sections of the sky, and most of all we needed to make sure no galaxies were missed in the survey.”

Robotham presented his new findings at the International Astronomical Union General Assembly in Beijing this week.

Using what astronomer consider the most detailed map of the local Universe yet — the Galaxy and Mass Assembly survey (GAMA) — Robotham and his colleagues found that although companions like the Magellanic Clouds are rare, when they are found they’re usually near a galaxy very like the Milky Way, meaning we’re in just the right place at the right time to have such a great view in our night sky.

“The galaxy we live in is perfectly typical, but the nearby Magellenic Clouds are a rare, and possibly short-lived, occurrence. We should enjoy them whilst we can, they’ll only be around for a few billion more years,” said Robotham.

Astronomers have used computer simulations of how galaxies form and they don’t produce many examples similar to the Milky Way and its surroundings, so they have predicted them to be quite a rare occurrence. Astronomers they really haven’t been able to tell just how rare they are, until now, using the new survey which looks at hundreds of thousands of galaxies.
“We found about 3% of galaxies similar to the Milky Way have companion galaxies like the Magellanic Clouds, which is very rare indeed,” Robotham said. “In total we found 14 galaxy systems that are similar to ours, with two of those being an almost exact match.”

The Milky Way is locked in a complex cosmic dance with its close companions the Large and Small Magellanic Clouds, which are clearly visible in the southern hemisphere night sky. Many galaxies have smaller galaxies in orbit around them, but few have two that are as large as the Magellanic Clouds.

Robotham and his team will continue searching for more Milky Way twin systems.

The paper “Galaxy and Mass Assembly (GAMA): In search of Milky-Way Magellanic Cloud Analogues” can be read here or (free version) at arXiv

Source: ICRAR

Stunning Astrophoto: Road to the Stars by Jack Fusco

Last week we posted an astrophoto by Jack Fusco, and when I looked at more of his images, this one just absolutely blew me away! Jack took a trip to Acadia National Park in Maine, USA, and his night sky images from that location are just gorgeous. “It’s amazing to me that every single person in Acadia isn’t awake the entire night out stargazing,” Jack said on Google+ . “The amount of stars is just absolutely incredible here and I could not have asked for any better conditions.”

Of this image, Jack said, “It’s important to not just worry about the destination, but to notice all of the things that we go through on our path there,” and then quoted musician Frank Turner: “We’re going nowhere slowly, but we’re seeing all the sights.”

See more of Jack’s work on Flickr, Google+ and his website, www.jackfusco.com

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Astrophoto: Milky Way Over the Bungle Bungles by Mike Salway

Photographer Mike Salway recently took a trip to the western Australia Kimberly Region of the Outback, and has posted some amazing night sky images of his adventures. This picture — and the name of the geologic features — especially caught my eye. The Bungle Bungles of Purnululu National Park are an incredible sight in themselves, huge beehive-shaped sandstone formations. But Mike was able to take a panoramic view of the Milky Way arching over the formations, a symmetrical halo of light in the full sky.

“You know the skies are dark when you can see the Milky Way overhead, even when there’s a more than half-moon shining brightly high in the west sky,” Mike wrote on his website. “And that’s what it was like at the Bungle Bungles.”

This image is an 8 frame panorama, taken on the Piccaninny Creek bed with his Canon 5D Mk II and Samyang 14mm f/2.8 lens.

See more images from Mike’s trip, and all his other work, too, plus check out his IceInSpace website, a collection of amateur astronomer images of the Solar System.

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Astrophoto: On the Lookout for the Milky Way

Caption: ‘The Lookout’ – Bass Harbor Lighthouse – Acadia National Park, Maine. Credit: Jack Fusco.

This gorgeous shot of the Bass Harbor Lighthouse — seemingly on the lookout for the Milky Way — almost got away from astrophotographer Jack Fusco, but luckily he had a backup plan!

Jack’s description of the photo:

This was the shot that almost got away. I had this in mind and planned out well before I had arived in Acadia. Before the Milky Way was in place on my first visit, the sky was covered by almost the only clouds I saw all trip. A change in forecast for the night before my drive back to New Jersey gave me one last chance to capture it. I set up to take some star trails while waiting for everything to be in position only to have my battery die moments before I took this. Luckily, I had a fully charged backup battery in my bag. I ran to grab it, set back up and started to shoot again. Sitting out under the stars and listening to the water crash against the rocks was an experience that words can not do justice.

Checkout more of Jack’s work at his Flickr page.

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Weekly SkyWatcher’s Forecast: July 16-22, 2012

Messier 19 - Credit: Doug Williams, REU Program/NOAO/AURA/NSF

Greetings, fellow SkyWatchers! My satellite dish and internet connection has now returned from the land of Oz. While it was great to have a span of days where no electric meant no annoying lights, it also meant creative cooking excursions on the gas grill in 100 degree weather. Ah, well… the things we do for dark skies! This is New Moon week, so get out there and enjoy the Milky Way! Whenever you’re ready, meet me in the back yard…

Monday, July 16 – Today in 1850 at Harvard University, the first photograph of a star (other than the Sun) was made. The honors went to Vega! In 1994, an impact event was about to happen as nearly two dozen fragments of Comet Shoemaker-Levy 9 were speeding their way to the surface of Jupiter. The result was spectacular, and the visible features left behind on the planet’s atmosphere were the finest ever recorded.

Now let’s return again to the oblate and beautiful M19 and drop two fingerwidths south for another misshapen globular – M62 (Right Ascension: 17 : 01.2 – Declination: -30 : 07).

At magnitude 6, this 22,500 light-year distant Class IV cluster can be spotted in binoculars, but comes to wonderful life in the telescope. First discovered by Messier in 1771, Herschel was the first to resolve it and report on its deformation. Because it is so near to the galactic center, tidal forces have “crushed” it – much like M19. You will note when studying in the telescope that its core is very off center. Unlike M19, M62 has at least 89 known variable stars – 85 more than its neighbor – and the dense core may have undergone collapse. A large number of X-ray binaries have also been discovered within its structure, perhaps caused by the close proximity of stellar members. Enjoy it tonight!

Tuesday, July 17 – If you’re up to another challenge tonight, let’s go hunting Herschel I.44, also known as NGC 6401. You’ll find this 9.5 magnitude globular cluster around two fingerwidths northeast of Theta Ophiuchi and a little more than a degree due east of star 51 (Right Ascension: 17 : 38.6 – Declination: -23 : 55).

Discovered by William Herschel in 1784 and often classed as “uncertain,” today’s powerful telescopes have placed this halo object as a Class VIII and given it a rough distance from the galactic center of 8,800 light-years. Although neither William nor John could resolve this globular, and they listed it originally as a bright nebula, studies in 1977 revealed a nearby suspected planetary nebula named Peterson 1. Thirteen years later, further study revealed this to be a symbiotic star.

Symbiotic stars are a true rarity – not a singular star at all, but a binary system. A red giant dumps mass towards a white dwarf in the form of an accretion disc. When this reaches critical mass, it then causes a thermonuclear explosion resulting in a planetary nebula. While no evidence exists that this phenomenon is physically located within metal-rich NGC 6401, just being able to see it in the same field makes this journey both unique and exciting!

Wednesday, July 18 – On this day 27 years ago, India launched its first satellite (Rohini 1), and 31 years ago in the United States Gemini 10 launched carrying John Young and Michael Collins to space.

Now, let’s carry ourselves into space as we take a very unusual and beautiful journey to a bright and very colorful pair of stars known as Omicron 1 Cygni. Easily located about halfway between Alpha (Deneb) and Delta on the western side, this is a pure delight in binoculars or any size telescope. The striking gold color of 3.7 magnitude 31 Cygni (Omicron 1) is easily highlighted against the blue of same field companion, 5th magnitude 30 Cygni. Although this wide pairing is only an optical one, the K-type giant is a double star – an eclipsing variable around 150 times larger than or own Sun – and is surrounded by a gaseous corona more than double the size as the star itself. If you are using a scope, you can easy spot the blue tinted, 7th magnitude B star about one third the distance as between the two giants. Although our true pair are some 1.2 billion miles apart, they are oriented nearly edge-on from our point of view – allowing the smaller star to be totally eclipsed during each revolution. This total eclipse lasts for 63 days and happens about every 10.4 years, but don’t stay up too late… We’ve still got 7 years to wait!

Thursday, July 19 – Today in 1846, Edward Pickering was born. Although his name is not well known, he became a pioneer in the field of spectroscopy. Pickering was the Harvard College Observatory Director from 1876 to 1919, and it was during his time there that photography and astronomy began to merge. Known as the Harvard Plate Collection, these archived beginnings still remain a valuable source of data.

It’s New Moon, so why not have a look at something that would make Edward Pickering proud? He enthusiastically encouraged amateur astronomers, and founded the American Association of Variable Star Observers – so set your sights on RR Scorpius about two fingerwidths northeast of Eta and less than a fingerwidth southwest M62 (RA 16 56 37.84 Dec -30 34 48.2). This very red Mira type can reach as high as magnitude 5 and drop as low as 12 in about 280 days!

Tonight let’s just enjoy a little stargazing and revel in the beauty of our own galaxy’s spiral arm – the Milky Way. For those living in the city, you owe it to yourself to get away to a dark location to enjoy this veritable “river of stars” which spans out of the galactic center south and runs overhead. Almost directly behind you from the galactic anti-center stretches the Perseus arm, and the sight is a beautiful one. If skies are fine, you can easily see the dark dust rift where the arm separates and the billows of light of unresolved stars. It’s the most glorious sight of summer! While we have many days yet before the Aquarid meteor shower officially reaches its peak, you will be pleasantly surprised at this year’s high activity. They’ve been flying out of the night sky for almost two weeks now, and it would not surprise me if you saw ten or more per hour of these quick, bright visitors.

Friday, July 20 – Today was a busy day in astronomy history! In 1969, the world held its breath as the Apollo 11 lander touched down and Neil Armstrong and Edwin Aldrin became the first humans to touch the lunar surface. We celebrate our very humanity because even Armstrong was so moved that he messed up his lines! The famous words were meant to be “A small step for a man. A giant leap for mankind.” That’s nothing more than one small error for a man, and mankind’s success continued on July 20, 1976 when Viking 1 landed on Mars – sending back the first images ever taken from that planet’s surface.

If you’re out at sunset, be sure to look for the slimmest crescent Moon you can imagine… It will point your way to nearby Mercury! For lucky viewers “down under” this is an occultation event and will only be observable after sunset from southernmost regions of central Australia. Be sure to check the resources for websites like IOTA for specific times and locations.

The first assignment of the evening is a pair of interacting galaxies. 40 degrees northwest of Beta Canum Venaticorum is NGC 4490 (Right Ascension: 12 : 30.6 – Declination: +41 : 38) and smaller, fainter companion NGC 4485 (Right Ascension: 12 : 30.5 – Declination: +41 : 42). This pair, also known as Arp 269, are quite unusual in appearance to the larger scope. NGC 4490 is around magnitude 10 and shows a bright, irregular core region and a rather strange profile. Known as the “Cocoon” galaxy, it appears to almost reach toward its companion 3 degrees to the north. Progressively larger scopes under ideal conditions will be able to make out some faint mottling in the NGC 4490’s structure.

Now let’s honor southern skies by exploring the fantastic, NGC 3372 (Right Ascension: 10 : 43.8 – Declination: -59 : 52) – the Eta Carinae Nebula. As a giant, diffuse nebula with a visual brightness of magnitude 1, (wow!) it contains the most massive and luminous star in our Milky Way galaxy, Eta Carinae. It’s also home to a small cluster, Collinder 228, which is only one of 8 cataloged open clusters within the area of this huge star-forming region; the others are Bochum (Bo) 10, Trumpler (Tr) 14 (also cataloged as Cr 230), Tr 15 (= Cr 231), Cr 232, Tr 16 (= Cr 233), Cr 234, and Bo 11. Star Eta Carinae is involved in open cluster Trumpler 16. This fantastic nebula contains details which northerners can only dream about, such as the dark “Keyhole” and the “Homunkulus” around the giant star itself. A fantastic region for exploration with both telescopes and binoculars!

Saturday, July 21 – Today in 1961, Mercury 4 was launched, sending Gus Grissom into suborbital space on the second manned flight, and he returned safely in Liberty Bell 7.

Since the moonlight will now begin to interfere with our early evening globular cluster studies, let’s waive them for a while as we take a look at some of the region’s most beautiful stars. Tonight your goal is to locate Omicron Ophiuchi, about a fingerwidth northeast of Theta. At a distance of 360 light-years, this system is easily split by even small telescopes. The primary star is slightly dimmer than magnitude 5 and appears yellow to the eye. The secondary is near 7th magnitude and tends to be more orange in color. This wonderful star is part of many double star observing lists, so be sure to note it!

Tonight would be an ideal time to look at a brilliant open cluster about a fist width east of Epsilon Scorpii – M6 (Right Ascension: 17 : 40.1 – Declination: -32 : 13). On a moonless night, the 50 or so members of this 2000 light year distant, 100 million year old cluster can usually be seen unaided as a small fuzzy patch just above the Scorpion’s tail. Tonight we visit because the brighter skies will aid you in seeing the primary stars distinctive asterism. Using binoculars or telescope at lowest power, the outline of stars does truly resemble its namesake – the “Butterfly Cluster”. The M6 is much more than “just a pretty face” and we’ll be back to study under darker skies.

Sunday, July 22 – Tonight instead of lunar exploration, we will note the work of Friedrich Bessel, who was born on this day in 1784. Bessel was a German astronomer and mathematician whose functions, used in many areas of mathematical physics, still carry his name. But, you may put away your calculator, because Bessel was also the very first person to measure a star’s parallax. In 1837, he chose 61 Cygni and the result was no more than a third of an arc second. His work ended a debate that had stretched back two millennia to Aristotle’s time and the Greek’s theories about the distances to the stars.

Although you’ll need to use your finderscope with tonight’s brighter skies, you’ll easily locate 61 between Deneb (Alpha) and Zeta on the eastern side. Look for a small trio of stars and choose the westernmost. Not only is it famous because of Bessel’s work, but it is one of the most noteworthy of double stars for a small telescope. 61 Cygni is the fourth nearest star to Earth, with only Alpha Centauri, Sirius, and Epsilon Eridani closer. Just how close is it? Try right around 11 light-years.

Visually, the two components have a slightly orange tint, are less than a magnitude apart in brightness and have a nice separation of around 30 degrees to the south-southeast. Back in 1792, Piazzi first noticed 61’s abnormally large proper motion and dubbed it “The Flying Star.” At that time, it was only separated by around 10 degrees and the B star was to the northeast. It takes nearly 7 centuries for the pair to orbit each other, but there is another curiosity here. Orbiting the A star around every 4.8 years is an unseen body that is believed to be about 8 times larger than Jupiter. A star – or a planet? With a mass considerably smaller than any known star, chances are good that when you view 61 Cygni, you’re looking toward a distant world!

Until next week, dreams really do come true when you keep on reaching for the stars!

Astrophoto: Galactic Relaxation

Ah, the good life! “Probably one of my favorite things to do is sit outside underneath the stars,” said astrophotographer Harley Grady from Texas, who took this self- and galactic-portrait on June 19, 2012. Grady said this is a single 30 second exposure, with a red LED light to illuminate himself and 6″ Dob telescope.

How many of our other readers could take a similar picture of themselves?

Shot with a Nikon D700,Tokina 16-28mm f2.8 Lens, ISO 3200, WB 4000K.

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Image caption: Galactic Relaxing. Credit and copyright: Harley Grady 2012

Galactic Gong – Milky Way Struck and Still Ringing After 100 Million Years

Small Magellanic Cloud
Small Magellanic Cloud

When galaxies collide, stars are thrown from orbits, spiral arms are stretched and twisted, and now scientists say galaxies ring like a bell long after the cosmic crash.

A team of astronomers from the United States and Canada say they have heard echoes of that ringing, possible evidence of a galactic encounter 100 million years ago when a small satellite galaxy or dark matter object passed through the Milky Way Galaxy; close to our position in the galaxy, as if a rock were thrown into a still pond causing the stars to bounce up and down on the waves. Their results were published in the Astrophysical Journal Letters.

“We have found evidence that our Milky Way had an encounter with a small galaxy or massive dark matter structure perhaps as recently as 100 million years ago,” said Larry Widrow, professor at Queen’s University in Canada. “We clearly observe unexpected differences in the Milky Way’s stellar distribution above and below the Galaxy’s midplane that have the appearance of a vertical wave — something that nobody has seen before.”

Astronomers took observations from about 300,000 nearby stars in the Sloan Digital Sky Survey. Stars move up and down at 20-30 kilometers per second while see-sawing around the galaxy at 220 kilometers per second. By comparison, the International Space Station putters around Earth at 7.71 kilometers per second; Voyager 1, the fastest man-made object, currently is leaving the solar system at about 17.46 kilometers per second. Widrow and colleagues at the University of Kentucky, The University of Chicago and Fermi National Accelerator Laboratory found that the positions of nearby stars is not quite as regular as previously thought. The team noticed a small but statistically significant difference in the distribution of stars above and below the midplane of the Milky Way.

“Our part of the Milky Way is ringing like a bell,” said Brian Yanny, of the Department of Energy’s Fermilab. “But we have not been able to identify the celestial object that passed through the Milky Way. It could have been one of the small satellite galaxies that move around the center of our galaxy, or an invisible structure such as a dark matter halo.”

Susan Gardner, professor of physics at the University of Kentucky added, “The perturbation need not have been a single isolated event in the past, and it may even be ongoing. Additional observations may well clarify its origin.”

Other possibilities considered for the variations were the effect of interstellar dust or simply the way the stars were selected in the survey. But as those events failed to explain fully the observations, the astronomers began to explore possible recent events in the history of the galaxy.

More than 20 visible satellite galaxies circle the Milky Way. Invisible satellites made up of dark matter, hypothetical matter that cannot be seen but is thought to make up a majority of the mass of the Universe, might also orbit our galaxy. Scientists believe that most of the mass orbiting the galaxy is in the form of dark matter. Using computer simulations to explore the effects of a small galaxy or dark matter structure passing through the disk of the Milky Way, the scientists developed a clearer picture of the see-saw effects they were seeing.

In terms of the nine-billion lifetime of the Milky Way Galaxy, the effects are short-lived. This part of the galaxy has been “ringing” for 100 million years and will continue for 100 million years more as the up-and-down motion dissipates, say the astronomers – unless we are hit again.

Image caption: The Small Magellanic Cloud is one of 20 visible satellite galaxies that orbit the Milky Way Galaxy. Astronomers report that a smaller counterpart or dark matter object passed through the Milky Way near our position about 100 million years ago.

Milky Way to Concordia Base… Come In, Concordia Base…

This stunning photo of the Milky Way was captured from what may be the coldest and most isolated research facility on Earth: the French-Italian Concordia Base station, located at 3,200 meters (nearly 10,500 feet) altitude on the Antarctic plateau, 1,670 km (1,037 miles) from the geographic south pole.

Taken by Dr. Alexander Kumar, a doctor, researcher and photographer who’s been living at the Base since January, the image shows the full beauty of the sky above the southern continent — a sky that doesn’t see the Sun from May to August.

During the winter months no transportation can be made to or from Concordia Base — no deliveries or evacuations, not for any reason. The team there is truly alone, very much like future space explorers will one day be. This isolation is one reason that Concordia is used by ESA for research for missions to Mars.

Of course, taking photos outside is no easy task. Temperatures outside the Base in winter can drop down to -70ºC (-100ºF)!

 Still, despite the isolation, darkness and cold, Dr. Kumar finds inspiration in his surroundings.

“The dark may cause fear, but if you take the time to adapt and look within it, you never know what you may find – at the bottom of the ocean, in the night sky, or under your bed in the middle of the night,” writes Kumar on the Concordia blog. “If you don’t overcome your fear of the ‘unknown’ and ‘monsters’, you will never see marvellous secrets hidden in the dark.

“I hope this photo inspires you too for the days, weeks and months ahead. In terms of the space exploration we are only beginning. We have to continue pushing out into the great beyond.”

Read more of the “Chronicles from Concordia” here.

 Image credits: ESA/IPEV/PNRA – A. Kumar

It’s Inevitable: Milky Way, Andromeda Galaxy Heading for Collision

This illustration shows a stage in the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy, as it will unfold over the next several billion years. In this image, representing Earth's night sky in 3.75 billion years, Andromeda (left) fills the field of view and begins to distort the Milky Way with tidal pull. (Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger)

Astronomers have known for years that our Milky Way and its closest neighbor, the Andromeda galaxy, (a.k.a M31) are being pulled together in a gravitational dance, but no one was sure whether the galaxies would collide head-on or glide past one another. Precise measurements from the Hubble Space Telescope have now confirmed that the two galaxies are indeed on a collision course, headed straight for a colossal cosmic collision.

No need to panic for the moment, as this is not going to happen for another four billion years. And while astronomers say it is likely the Sun will be flung into a different region of our galaxy, Earth and the solar system will probably just go along for the ride and are in no danger of being destroyed.

“In the ‘worst-case-scenario’ simulation, M31 slams into the Milky Way head-on and the stars are all scattered into different orbits,” said team member Gurtina Besla of Columbia University in New York, N.Y. “The stellar populations of both galaxies are jostled, and the Milky Way loses its flattened pancake shape with most of the stars on nearly circular orbits. The galaxies’ cores merge, and the stars settle into randomized orbits to create an elliptical-shaped galaxy.”

The simulations Besla was talking about came from precise measurements by Hubble, painstakingly determining the motion of Andromeda, looking particularly at the sideways motion of M31, which until now has not been able to be done.

“This was accomplished by repeatedly observing select regions of the galaxy over a five- to seven-year period,” said Jay Anderson of STScI.

Right now, M31 is 2.5 million light-years away, but it is inexorably falling toward the Milky Way under the mutual pull of gravity between the two galaxies and the invisible dark matter that surrounds them both.

Of course, the collision is not like a head-on between two cars that takes place in an instant. Hubble data show that it will take an additional two billion years after the encounter for the interacting galaxies to completely merge under the tug of gravity and reshape into a single elliptical galaxy similar to the kind commonly seen in the local universe.

Astronomers said the stars inside each galaxy are so far apart that they will not collide with other stars during the encounter. However, the stars will be thrown into different orbits around the new galactic center. Simulations show that our solar system will probably be tossed much farther from the galactic core than it is today.

There’s also the complication of M31’s small companion, the Triangulum galaxy, M33. This galaxy will join in the collision and perhaps later merge with the M31/Milky Way pair. There is a small chance that M33 will hit the Milky Way first.

The astronomers working on this project said that they were able to make the precise measurements because of the upgraded cameras on Hubble, installed during the final servicing mission. This gave astronomers a long enough time baseline to make the critical measurements needed to nail down M31’s motion.

The Hubble observations and the consequences of the merger are reported in three papers that will appear in an upcoming issue of the Astrophysical Journal.

This series of photo illustrations shows the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy. Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas, and A. Mellinger

First Row, Left: Present day.
First Row, Right: In 2 billion years the disk of the approaching Andromeda galaxy is noticeably larger.
Second Row, Left: In 3.75 billion years Andromeda fills the field of view.
Second Row, Right: In 3.85 billion years the sky is ablaze with new star formation.
Third Row, Left: In 3.9 billion years, star formation continues.
Third Row, Right: In 4 billion years Andromeda is tidally stretched and the Milky Way becomes warped.
Fourth Row, Left: In 5.1 billion years the cores of the Milky Way and Andromeda appear as a pair of bright lobes.
Fourth Row, Right: In 7 billion years the merged galaxies form a huge elliptical galaxy, its bright core dominating the nighttime sky.

Source: HubbleSite See more images and videos here and here.

Ghostly Jets Haunt the Milky Way’s Black Hole

This artist's conception shows an edge-on view of the Milky Way galaxy and newly discovered gamma-ray jets extending from the central black hole. Credit: David A. Aguilar (CfA)

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A ghost is haunting the Milky Way’s central black hole, revealing the galactic nucleus was likely much more active in the past than it is now. Scientists using the Fermi space telescope have found faint apparitions of what must have been powerful gamma-ray jets emanating from our galaxy’s center.

“These faint jets are a ghost or after-image of what existed a million years ago,” said Meng Su, an astronomer at the Harvard-Smithsonian Center for Astrophysics (CfA), and lead author of a new paper in the Astrophysical Journal. “They strengthen the case for an active galactic nucleus in the Milky Way’s relatively recent past.”

This is the first time this type of jet has been detected from the Milky Way’s black hole. Scientists know that other active galaxies have cores that glow brightly, powered by supermassive black holes swallowing material, and often spit twin jets in opposite directions.

The two beams, or jets found by Fermi observations extend from the galactic center to a distance of 27,000 light-years above and below the galactic plane.
The newfound jets may be related to mysterious gamma-ray bubbles that Fermi detected in 2010. Those bubbles also stretch 27,000 light-years from the center of the Milky Way. However, where the bubbles are perpendicular to the galactic plane, the gamma-ray jets are tilted at an angle of 15 degrees. This may reflect a tilt of the accretion disk surrounding the supermassive black hole.

“The central accretion disk can warp as it spirals in toward the black hole, under the influence of the black hole’s spin,” explained co-author Douglas Finkbeiner of the CfA. “The magnetic field embedded in the disk therefore accelerates the jet material along the spin axis of the black hole, which may not be aligned with the Milky Way.”

The two structures also formed differently. The jets were produced when plasma squirted out from the galactic center, following a corkscrew-like magnetic field that kept it tightly focused. The gamma-ray bubbles likely were created by a “wind” of hot matter blowing outward from the black hole’s accretion disk. As a result, they are much broader than the narrow jets.

Both the jets and bubbles are powered by inverse Compton scattering. In that process, electrons moving near the speed of light collide with low-energy light, such as radio or infrared photons. The collision increases the energy of the photons into the gamma-ray part of the electromagnetic spectrum.

The discovery leaves open the question of when the Milky Way was last active. A minimum age can be calculated by dividing the jet’s 27,000-light-year length by its approximate speed. However, it may have persisted for much longer.

“These jets probably flickered on and off as the supermassive black hole alternately gulped and sipped material,” said Finkbeiner.

It would take a tremendous influx of matter for the galactic core to fire up again. Finkbeiner estimates that a molecular cloud weighing about 10,000 times as much as the Sun would be required.

“Shoving 10,000 suns into the black hole at once would do the trick. Black holes are messy eaters, so some of that material would spew out and power the jets,” he said.

Source: CfA