Posted on by Fraser Cain

Most Milky Way Stars Are Single

An artist’s illustration of a rocky planet orbiting around a red dwarf star. Image credit: ESO Click to enlarge
Common wisdom among astronomers holds that most star systems in the Milky Way are multiple, consisting of two or more stars in orbit around each other. Common wisdom is wrong. A new study by Charles Lada of the Harvard-Smithsonian Center for Astrophysics (CfA) demonstrates that most star systems are made up of single stars. Since planets probably are easier to form around single stars, planets also may be more common than previously suspected.

Astronomers have long known that massive, bright stars, including stars like the sun, are most often found to be in multiple star systems. This fact led to the notion that most stars in the universe are multiples. However, more recent studies targeted at low-mass stars have found that these fainter objects rarely occur in multiple systems. Astronomers have known for some time that such low-mass stars, also known as red dwarfs or M stars, are considerably more abundant in space than high-mass stars.

By combining these two facts, Lada came to the realization that most star systems in the Galaxy are composed of solitary red dwarfs.

“By assembling these pieces of the puzzle, the picture that emerged was the complete opposite of what most astronomers have believed,” said Lada.

Among very massive stars, known as O- and B-type stars, 80 percent of the systems are thought to be multiple, but these very bright stars are exceedingly rare. Slightly more than half of all the fainter, sun-like stars are multiples. However, only about 25 percent of red dwarf stars have companions. Combined with the fact that about 85 percent of all stars that exist in the Milky Way are red dwarfs, the inescapable conclusion is that upwards of two-thirds of all star systems in the Galaxy consist of single, red dwarf stars.

The high frequency of lone stars suggests that most stars are single from the moment of their birth. If supported by further investigation, this finding may increase the overall applicability of theories that explain the formation of single, sun-like stars. Correspondingly, other star-formation theories that call for most or all stars to begin their lives in multiple-star systems may be less relevant than previously thought.

“It’s certainly possible for binary star systems to ‘dissolve’ into two single stars through stellar encounters,” said astronomer Frank Shu of National Tsing Hua University in Taiwan, who was not involved with this discovery. “However, suggesting that mechanism as the dominant method of single-star formation is unlikely to explain Lada’s results.”

Lada’s finding implies that planets also may be more abundant than astronomers realized. Planet formation is difficult in binary star systems where gravitational forces disrupt protoplanetary disks. Although a few planets have been found in binaries, they must orbit far from a close binary pair, or hug one member of a wide binary system, in order to survive. Disks around single stars avoid gravitational disruption and therefore are more likely to form planets.

Interestingly, astronomers recently announced the discovery of a rocky planet only five times more massive than Earth. This is the closest to an Earth-size world yet found, and it is in orbit around a single red dwarf star.

“This new planet may just be the tip of the iceberg,” said Lada. “Red dwarfs may be a fertile new hunting ground for finding planets, including ones similar in mass to the earth.”

“There could be many planets around red dwarf stars,” stated astronomer Dimitar Sasselov of CfA. “It’s all in the numbers, and single red dwarfs clearly exist in great numbers.”

“This discovery is particularly exciting because the habitable zone for these stars – the region where a planet would be the right temperature for liquid water – is close to the star. Planets that are close to their stars are easier to find. The first truly Earth-like planet we discover might be a world orbiting a red dwarf,” added Sasselov.

This research has been submitted to The Astrophysical Journal Letters for publication and is available online at http://arxiv.org/abs/astro-ph/0601375

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: CfA News Release

Posted on by Fraser Cain

Neutron Star Swapping Leads to Gamma-Ray Bursts

M15 has a double neutron star system that will eventually merge violently. Image credit: NOAO Click to enlarge
Gamma-ray bursts are the most powerful explosions in the universe, emitting huge amounts of high-energy radiation. For decades their origin was a mystery. Scientists now believe they understand the processes that produce gamma-ray bursts. However, a new study by Jonathan Grindlay of the Harvard-Smithsonian Center for Astrophysics (CfA) and his colleagues, Simon Portegies Zwart (Astronomical Institute, The Netherlands) and Stephen McMillan (Drexel University), suggests a previously overlooked source for some gamma-ray bursts: stellar encounters within globular clusters.

“As many as one-third of all short gamma-ray bursts that we observe may come from merging neutron stars in globular clusters,” said Grindlay.

Gamma-ray bursts (GRBs) come in two distinct “flavors.” Some last up to a minute, or even longer. Astronomers believe those long GRBs are generated when a massive star explodes in a hypernova. Other bursts last for only a fraction of a second. Astronomers theorize that short GRBs originate from the collision of two neutrons stars, or a neutron star and a black hole.

Most double neutron star systems result from the evolution of two massive stars already orbiting each other. The natural aging process will cause both to become neutron stars (if they start with a given mass), which then spiral together over millions or billions of years until they merge and release a gamma-ray burst.

Grindlay’s research points to another potential source of short GRBs – globular clusters. Globular clusters contain some of the oldest stars in the universe crammed into a tight space only a few light-years across. Such tight quarters provoke many close stellar encounters, some of which lead to star swaps. If a neutron star with a stellar companion (such as a white dwarf or main-sequence star) exchanges its partner with another neutron star, the resulting pair of neutron stars will eventually spiral together and collide explosively, creating a gamma-ray burst.

“We see these precursor systems, containing one neutron star in the form of a millisecond pulsar, all over the place in globular clusters,” stated Grindlay. “Plus, globular clusters are so closely packed that you have a lot of interactions. It’s a natural way to make double neutron-star systems.”

The astronomers performed about 3 million computer simulations to calculate the frequency with which double neutron-star systems can form in globular clusters. Knowing how many have formed over the galaxy’s history, and approximately how long it takes for a system to merge, they then determined the frequency of short gamma-ray bursts expected from globular cluster binaries. They estimate that between 10 and 30 percent of all short gamma-ray bursts that we observe may result from such systems.

This estimate takes into account a curious trend uncovered by recent GRB observations. Mergers and thus bursts from so-called “disk” neutron-star binaries – systems created from two massive stars that formed together and died together – are estimated to occur 100 times more frequently than bursts from globular cluster binaries. Yet the handful of short GRBs that have been precisely located tend to come from galactic halos and very old stars, as expected for globular clusters.

“There’s a big bookkeeping problem here,” said Grindlay.

To explain the discrepancy, Grindlay suggests that bursts from disk binaries are likely to be harder to spot because they tend to emit radiation in narrower blasts visible from fewer directions. Narrower “beaming” might result from colliding stars whose spins are aligned with their orbit, as expected for binaries that have been together from the moment of their birth. Newly joined stars, with their random orientations, might emit wider bursts when they merge.

“More short GRBs probably come from disk systems – we just don’t see them all,” explained Grindlay.

Only about a half dozen short GRBs have been precisely located by gamma-ray satellites recently, making thorough studies difficult. As more examples are gathered, the sources of short GRBs should become much better understood.

The paper announcing this finding was published in the January 29 online issue of Nature Physics. It is available online at http://www.nature.com/nphys/index.html and in preprint form at http://arxiv.org/abs/astro-ph/0512654.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: CfA News Release

Posted on by Fraser Cain

Dione’s Tectonic Faults

False colour view of Dione. Image credit: NASA/JPL/SSI Click to enlarge
This view highlights tectonic faults and craters on Dione, an icy world that has undoubtedly experienced geologic activity since its formation.

To create the enhanced-color view, ultraviolet, green and infrared images were combined into a single black and white picture that isolates and maps regional color differences. This “color map” was then superposed over a clear-filter image. The origin of the color differences is not yet understood, but may be caused by subtle differences in the surface composition or the sizes of grains making up the icy soil.

This view looks toward the leading hemisphere on Dione (1,126 kilometers, or 700 miles across). North is up and rotated 20 degrees to the right.

See Dione Has Her Faults (Monochrome) for a similar monochrome view.

All images were acquired with the Cassini spacecraft narrow-angle camera on Dec. 24, 2005 at a distance of approximately 151,000 kilometers (94,000 miles) from Dione and at a Sun-Dione-spacecraft, or phase, angle of 99 degrees. Image scale is 896 meters (2,940 feet) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Stardust Placed Into Hibernation

An artist’s conception of Stardust spacecraft. Image credit: NASA/JPL Click to enlarge
NASA’s Stardust spacecraft was placed into hibernation mode yesterday. Stardust successfully returned to Earth samples of a comet via its sample return capsule on Jan. 15. The spacecraft has logged almost seven years of flight.

“We sang our spacecraft to sleep today with a melody of digital ones and zeros,” said Tom Duxbury, Stardust project manager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Stardust has performed flawlessly these last seven years and 2.88 billion miles and deserves a rest for a while, like the rest of the team.”

The “song” was actually a series of commands that was sent up to the spacecraft yesterday, Jan. 29 at 4 p.m. Pacific time (7 p.m. Eastern time). The commands deactivated all but a few essential systems, such as Stardust’s solar arrays and receive antenna – which will remain powered on. This long-term hibernation state could allow for almost indefinite (tens of years) out-of-contact operations while maintaining the spacecraft health.

“Placing Stardust in hibernation gives us options to possibly reuse it in the future,” said Dr. Tom Morgan, Stardust Program Executive at NASA Headquarters, Washington. “The mission has already been a great success, but if at all possible we may want to add even more scientific dividends to this remarkable mission’s record of achievement.”

The Stardust spacecraft is currently in an orbit that travels from a little closer to the Sun than that of the Earth to well beyond the orbit of Mars. It will next fly past Earth on January 14, 2009, at a distance of about 1 million kilometers (621,300 miles).

NASA’s Stardust sample return mission successfully concluded its prime mission on Jan. 15, 1006, when its sample return capsule carrying cometary and interstellar particles successfully touched down at 2:10 a.m. Pacific time (3:10 a.m. Mountain time) in the desert salt flats of the Utah Test and Training Range.

Stardust scientists at NASA’s Johnson Space Center in Houston are currently analyzing what could be considered a treasure-trove of cometary and interstellar dust samples that exceeded their grandest expectations. Scientists believe these precious samples will help provide answers to fundamental questions about comets and the origins of the solar system.

NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the Stardust mission for NASA’s Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, developed and operated the spacecraft.

For information about the Stardust mission on the Web, visit www.nasa.gov/stardust. For information about NASA and agency programs on the Web, visit http://www.nasa.gov/home .

Original Source: NASA News Release

Posted on by Fraser Cain

The Smell of Moondust

Apollo 17 astronaut Jack Schmitt, with his spacesuit grayed by moondust. Image credit: NASA Click to enlarge
Moondust. “I wish I could send you some,” says Apollo 17 astronaut Gene Cernan. Just a thimbleful scooped fresh off the lunar surface. “It’s amazing stuff.”

Feel it?it’s soft like snow, yet strangely abrasive.

Taste it?”not half bad,” according to Apollo 16 astronaut John Young.

Sniff it?”it smells like spent gunpowder,” says Cernan.

How do you sniff moondust?

Every Apollo astronaut did it. They couldn’t touch their noses to the lunar surface. But, after every moonwalk (or “EVA”), they would tramp the stuff back inside the lander. Moondust was incredibly clingy, sticking to boots, gloves and other exposed surfaces. No matter how hard they tried to brush their suits before re-entering the cabin, some dust (and sometimes a lot of dust) made its way inside.

Once their helmets and gloves were off, the astronauts could feel, smell and even taste the moon.

The experience gave Apollo 17 astronaut Jack Schmitt history’s first recorded case of extraterrestrial hay fever. “It’s come on pretty fast,” he radioed Houston with a congested voice. Years later he recalls, “When I took my helmet off after the first EVA, I had a significant reaction to the dust. My turbinates (cartilage plates in the walls of the nasal chambers) became swollen.”

Hours later, the sensation faded. “It was there again after the second and third EVAs, but at much lower levels. I think I was developing some immunity to it.”

Other astronauts didn’t get the hay fever. Or, at least, “they didn’t admit it,” laughs Schmitt. “Pilots think if they confess their symptoms, they’ll be grounded.” Unlike the other astronauts, Schmitt didn’t have a test pilot background. He was a geologist and readily admitted to sniffles.

Schmitt says he has sensitive turbinates: “The petrochemicals in Houston used to drive me crazy, and I have to watch out for cigarette smoke.” That’s why, he believes, other astronauts reacted much less than he did.

But they did react: “It is really a strong smell,” radioed Apollo 16 pilot Charlie Duke. “It has that taste — to me, [of] gunpowder — and the smell of gunpowder, too.” On the next mission, Apollo 17, Gene Cernan remarked, “smells like someone just fired a carbine in here.”

Schmitt says, “All of the Apollo astronauts were used to handling guns.” So when they said ‘moondust smells like burnt gunpowder,’ they knew what they were talking about.

To be clear, moondust and gunpowder are not the same thing. Modern smokeless gunpowder is a mixture of nitrocellulose (C6H8(NO2)2O5) and nitroglycerin (C3H5N3O9). These are flammable organic molecules “not found in lunar soil,” says Gary Lofgren of the Lunar Sample Laboratory at NASA’s Johnson Space Center. Hold a match to moondust–nothing happens, at least, nothing explosive.

What is moondust made of? Almost half is silicon dioxide glass created by meteoroids hitting the moon. These impacts, which have been going on for billions of years, fuse topsoil into glass and shatter the same into tiny pieces. Moondust is also rich in iron, calcium and magnesium bound up in minerals such as olivine and pyroxene. It’s nothing like gunpowder.

So why the smell? No one knows.

ISS astronaut Don Pettit, who has never been to the moon but has an interest in space smells, offers one possibility:

“Picture yourself in a desert on Earth,” he says. “What do you smell? Nothing, until it rains. The air is suddenly filled with sweet, peaty odors.” Water evaporating from the ground carries molecules to your nose that have been trapped in dry soil for months.

Maybe something similar happens on the moon.

“The moon is like a 4-billion-year-old desert,” he says. “It’s incredibly dry. When moondust comes in contact with moist air in a lunar module, you get the ‘desert rain’ effect–and some lovely odors.” (For the record, he counts gunpowder as a lovely odor.)

Gary Lofgren has a related idea: “The gases ‘evaporating’ from the moondust might come from the solar wind.” Unlike Earth, he explains, the moon is exposed to the hot wind of hydrogen, helium and other ions blowing away from the sun. These ions hit the moon’s surface and get caught in the dust.

It’s a fragile situation. “The ions are easily dislodged by footsteps or dustbrushes, and they would be evaporated by contact with warm air inside the lunar module. Solar wind ions mingling with the cabin’s atmosphere would produce who-knows-what odors.”

Want to smell the solar wind? Go to the moon.

Schmitt offers yet another idea: The smell, and his reaction to it, could be a sign that moondust is chemically active.

“Consider how moondust is formed,” he says. “Meteoroids hit the moon, reducing rocks to jagged dust. It’s a process of hammering and smashing.” Broken molecules in the dust have “dangling bonds”–unsatisfied electrical connections that need atomic partners.

Inhale some moondust and what happens? The dangling bonds seek partners in the membranes of your nose. You get congested. You report strange odors. Later, when the all the bonds are partnered-up, these sensations fade.

Another possibility is that moondust “burns” in the lunar lander’s oxygen atmosphere. “Oxygen is very reactive,” notes Lofgren, “and would readily combine with the dangling chemical bonds of the moondust.” The process, called oxidation, is akin to burning. Although it happens too slowly for smoke or flames, the oxidation of moondust might produce an aroma like burnt gunpowder. (Note: Burnt and unburnt gunpowder do not smell the same. Apollo astronauts were specific. Moondust smells like burnt gunpowder.)

Curiously, back on Earth, moondust has no smell. There are hundreds of pounds of moondust at the Lunar Sample Lab in Houston. There, Lofgren has held dusty moon rocks with his own hands. He’s sniffed the rocks, sniffed the air, sniffed his hands. “It does not smell like gunpowder,” he says.

Were the Apollo crews imagining things? No. Lofgren and others have a better explanation:

Moondust on Earth has been “pacified.” All of the samples brought back by Apollo astronauts have been in contact with moist, oxygen-rich air. Any smelly chemical reactions (or evaporations) ended long ago.

This wasn’t supposed to happen. Astronauts took special “thermos” containers to the moon to hold the samples in vacuum. But the jagged edges of the dust unexpectedly cut the seals of the containers, allowing oxygen and water vapor to sneak in during the 3-day trip back to Earth. No one can say how much the dust was altered by that exposure.

Schmitt believes “we need to study the dust in situ–on the moon.” Only there can we fully discover its properties: Why does it smell? How does it react with landers, rovers and habitats? What surprises await?

NASA plans to send people back to the moon in 2018, and they’ll stay much longer than Apollo astronauts did. The next generation will have more time and better tools to tackle the mystery.

We’ve only just begun to smell the moondust.

Original Source: NASA News Release

Posted on by Fraser Cain

What’s Up This Week – January 30 – February 5, 2006

What's Up 2006

Download our free “What’s Up 2006” ebook, with entries like this for every day of the year.

M43: “The Fishmouth”. Image credit: N.A. Sharp/NOAO/AURA/NSF. Click to enlarge.
Monday, January 30 – The Moon is now a thin crescent at sunset but no problem for dark sky observing. Tonight let’s have a look at the “Great Nebula” in Orion and its shy neighbor – M43.

M43 has its own special beauty. First discovered by Jean-Jacques D’Ortous de Mairan in the early eighteenth century, M43 is actually a continuation of M42 blocked by a dark slash of nebulosity called the “Fishmouth.” The star illuminating M43 is variable NU Orionus – which ranges about one magnitude in brilliance. Like its overpowering neighbor, M43 is a stellar nursery with the beginnings of its own cluster held close to its heart.

Tuesday, January 31 – Tonight in 1862, Alvan Graham Clark, Jr. made an unusual discovery. While watching Sirius, Clark uncovered the intense star’s faint companion while testing an 18″ refractor for Dearborn Observatory. The scope itself was built by Clark, his father and his brother. Imagine his excitement when it turned up the white dwarf – Sirius B! Based on the strange way Sirius A wobbles in the sky, Friedrich Bessel proposed its B’s existence back in 1844, but this is the first time it was confirmed visually.

Sirius B is nicknamed “the Pup,” and tonight we’ll have a serious look at Sirius, and see what it takes to uncover its little companion. Sirius is the brightest star that normally graces the night sky. At magnitude -1.6, it produces so much light that the atmosphere won’t stand still for it – sometimes even flashing in vibrant colors! This means that poor “Pup” hardly stands a chance of being seen. At magnitude 8.5 it could easily be caught in binoculars if it were on its own. So how do you find it? First, you’ll need a mid-to-large telescope with a high power eyepiece. Second, add a stable evening – not night – sky around the time Sirius is as high up as possible. Third, you’ll have to train your eye to perceive something that will cause you to say “I could hardly believe my eyes!” – because it’s that faint. Seeing the Pup is a Sirius matter, but practice will help you walk “the Pup” out of the evening sky!

If you had problems finding it, don’t worry… Others have problems, too. On this night in 1948, the first test photos using the Hale 5-meter (200-inch) telescope at Mt. Palomar were underway. Believe it or not, problems with the configuration and mounting of the mirror meant that it was almost 2 years later before the first observing run was made by a scheduled astronomer!

Wednesday, February 1 – The Moon has returned. Could you spot its slender crescent last night? If not, then try again tonight as we aim binoculars and telescopes toward the lunar surface.

Look almost centrally on the terminator for the very conspicuous crater Langrenus. Depending on your viewing location and time, it may be divided by the terminator, but will be quite recognizable. Spanning 85 miles in diameter, the steep, rugged walls rise almost 16,200 feet above the crater’s floor and you’ll see their bright outline on the western edge. Can you spot its central peak? It’s small for a crater this size and will present a challenge for binoculars.

While we’re out, let’s revisit the Crab Nebula in Taurus – there’s so much to learn and see about this very special nebula. The label “planetary” is a definite misnomer. Unlike most with this designation, M1 hardly looks like a globe and varies in other significant ways. Most planetaries have central stars that spew out atmospheric gases on a regular basis – but not this one. M1 did it all at once and we know exactly when it happened.

As one of only about 20 supernovae seen before the invention of the telescope, 11th century Chinese astronomers thought it four times brighter than Venus. Seen in broad daylight, the supernova remained visible for more than three weeks and continued to be seen in the night sky for almost two years. The position recorded for that July 4th, 1054 AD discovery now corresponds with that of the Crab Nebula.

Thursday, February 2 – There’s no missing the Moon tonight, so let’s go explore. Notice how crater Langrenus has changed in just 24 hours! Our study will be a trio of craters that look very much like a?? paw print on the surface. Just northeast of Langrenus’ border, look for the collection of Naonobu (north), Atwood (south) and Bilharz (west). Power up and try an even more challenging crater almost on the edge of Langrenus’ northern rim. This small pock-mark is known as Acosta.

When the Moon has begun to set, let’s have a look at a pair of neighboring open clusters in Gemini – M35 and NGC 2158. While both can be seen in the same low-power field, only M35 is visible in binoculars – as a round nebulosity as large as the Moon’s disc and peppered with faint stars. This is precisely how NGC 2158 looks in a mid-sized telescope. Like many of the brighter Messier studies, M35 was observed by others before Charles began looking for comets and kept running into deep sky objects. Keep in mind as you view these two galactic clusters that faint NGC 2158 is 16,000 light years away. That’s five times more distant than M35!

Tomorrow morning, observers in far western North America and Hawaii, will have the opportunity to see the Moon occult 4.5 magnitude Epsilon Piscium. Check the IOTA webpage to determine times and locales for Epsilon’s disappearance on the Moon’s shadowed side and reappearance on its bright limb. Keep the site bookmarked and use it as a reference throughout the observing year for other similar events.

Friday, February 3 – On this day in 1966, the first soft landing on the Moon occurred as Soviet probe Luna 9 touched down and sent back the very first pictures from the surface. Although Luna 9’s landing area in the Oceanus Procellarum is not visible tonight, we’ll discover two giants – Atlas and Hercules.

Located in the northeastern quarter of the lunar surface, this pair of craters is very prominent tonight in either binoculars or telescopes. The smaller, western crater is Hercules and the larger one is Atlas. When Hercules is near the terminator its western bright wall is in strong contrast to an interior so deep that it remains in shadow. Spanning 45 miles in diameter and plunging down 12,500 feet, Crater Hercules also contains an interior crater revealed as the Sun rises over it in the next 24 hours. Far more detail tonight is shown in much older crater Atlas. Spanning 54 miles in diameter and more shallow at 10,000 feet, Atlas contains a small interior peak. Power up and see if you can spot a Y-shaped crack along Atlas’ floor known as the Rimae Atlas.

If you’re in the mood to stay out a bit later, let the Moon set and have a look at the Eskimo Nebula (NGC 2392) in Gemini. Discovered by William Herschel in 1787, the 5000 light year distant NGC 2392 gives the appearance of a parka hooded face in large telescopes. In the center is a single 10th magnitude star – the source of both the planetary’s nebulosity and its light. Smaller scopes easily show both the central star and bright mantle of gas with a hint of “fuzzy” around the edge. Although the Eskimo is looking at us – it’s moving away at 75 km per second.

To find the “Eskimo,” start at Delta Geminorum and look about a finger width east/southeast for dim star 63. NGC 2392 is a little more than half a degree southeast, very near the ecliptic. Power up to get the best possible view of this 10th magnitude beauty. For those with a nebula filter, try it. This particular nebula will look much like a glowing green telrad.

Saturday, February 4 – Today is the birthday of Clyde Tombaugh. Born in 1906, Tombaugh discovered Pluto 24 years and two weeks after his birth. It will be a few months before we have an opportunity to see Pluto, but it’s grand to think that hard work and perseverance can accomplish some extraordinary things.

Let’s have a look at the lunar surface tonight and return to crater Posidonius. Located on the northeast shore of Mare Serenitatis and near the terminator, this large, ancient walled plain is an example of a Class V crater. Posidonius appears to be very flat – and with good reason. While its dimensions are roughly 52 by 61 miles, the crater itself is only 8,500 feet deep. The bright ring of the structure remains conspicuous to binoculars throughout all lunar phases, but a telescope is needed to appreciate the many fine features found on Posidonius’ floor. Power up to observed the stepped, stadium-like wall structure and numerous resolvable mountain peaks joining its small, central interior crater.

Before the Moon dominates the evening skies, let’s turn our attention towards the faintest of the three Messier open clusters in Auriga – M38. You’ll find it located almost precisely between Iota and Theta Aurigae. This 6.4 magnitude galactic cluster resolves into more than two dozen stars in small scopes, with its brighter members giving the appearance of an “X” in space. Like M35, M38 shares the field with a much fainter and denser companion. Look another half degree see to find the 8th magnitude cluster NGC 1907.

Sunday, February 5 – On this day in 1963, Maarten Schmidt measured the first redshift of a distant quasar and revealed just how luminous these stellar appearing objects are. And in 1974 the first close-up photograph of Venus was made by Mariner10.

The most outstanding feature tonight on the Moon will be a southern crater near the terminator – Maurolycus. Depending on your viewing time, the terminator may be running through it. These shadows will multiply its contrast many times over and display its vivid formations. As an Astronomy League challenge, Maurolycus will definitely catch your eye with its black interior and western crest stretched over the terminator’s darkness. Too many southern craters to be sure? Don’t worry. Maurolycus dominates them all tonight. Look for its double southern wall and multiple crater strikes along its edges.

Now let’s journey towards Auriga and drop a fist’s width south of Alpha (Capella). Congratulations on finding M38 under the moonlight! We’ll look again at this superb open cluster under darker skies.

May all your journeys be at light speed… ~Tammy Plotner. Additional writing by Jeff Barbour @ astro.geekjoy.com

Posted on by Fraser Cain

Podcast: Galactic Exiles

Artist illustration of a galactic exile. Image credit: CfA. Click to enlarge.
Listen to the interview: Galactic Exiles (6.2 MB)

Or subscribe to the Podcast: universetoday.com/audio.xml

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Fraser Cain: Can you tell me about the stars you observed and how they’ve come to be kicked out of our galaxy?

Dr. Warren Brown: What we discovered are two stars in the far out regions of the Milky Way that are traveling at speeds that no one has ever really seen stars in our galaxy, at least stars outside of the galactic centre. Except that these stars are hundreds of thousands of light years away from the galactic centre. And yet, the only plausible explanation for their velocity is that they were ejected by the supermassive black hole at the centre of the galaxy.

Fraser: So they strayed too close to the supermassive black hole and were kind of kicked out?

Brown: Yeah, so here’s the picture. This scenario requires three bodies, and astronomers say that the most likely way that it happened is if you have a pair of stars. As you may be aware, something like half the stars in the sky are actually systems containing a pair, or sometimes more stars. And so if you have a tightly bound pair of stars that, for some reason, travel too close to the supermassive black hole, at some point the black hole’s gravity will exceed the binding energy between the pair of stars and rip one of those stars away. It’ll capture the one star, but the other star then leaves the system with the orbital energy of the pair. And that’s how you get this extra boost of velocity. It’s that the supermassive black hole is basically able to unbind one star, capture it, and leave the other one with the entire amount of energy that the pair used to have. And that star then gets ejected right out of the galaxy.

Fraser: Then if a regular, single star came too close, it wouldn’t have the energy to be ejected. I think I’ve seen some simulations where the star gets too close to the black hole and kind of changes the direction of its orbit, but it’s still continuing to orbit around.

Brown: Sure, you could imagine it’s like a spacecraft that gets slingshot around Jupiter or something. You can imagine that you might be changing the trajectory, and gaining some speed. But there’s no mechanism in the galaxy to gain this much speed for something that’s the mass of a 3-4 solar mass star. That requires a three body interaction to create the velocity we see. And what we observe is their motion with respect to us. They’re moving away from us at a velocity of about 1-1.5 million miles an hour.

Fraser: How fast would the stars have been going when they came in to meet their breakup?

Brown: I don’t know for sure. Probably something 10 times that, right before that moment when they’re swinging past the black hole. Of course, as you leave that gravitational potential well of the black hole, they slow down pretty suddenly. Their final escape velocity is what we observe now; it’s on the order of a million miles an hour. And that’s well over twice the velocity that you need to escape our galaxy altogether. These stars really are exiles. They’re being outcast from the galaxy and they’ll never return.

Fraser: And one star is kicked out. What happens to the other star?

Brown: That’s an interesting question. In fact there’s a theory paper that some theorists have written that suggested that these stars in very long elliptical orbits around the central massive black hole might be the former companions to these so-called hypervelocity stars that we’ve discovered. And that’s the sort of orbit you’d expect. Unless the star is so unlucky as to fall straight into the black hole, if it misses just a little bit, it’s going to just swing around and then be on a very long elliptical orbit around the central massive black hole.

Fraser: And where did the pair originate? Is this a fate that might affect some nearby binary stars?

Brown: Well, that actually gets to the bigger picture. The galactic centre is an interesting place. It has lots of young stars. Three of the youngest massive star clusters discovered in the galaxy come from right near the galactic centre. And they contain some of the most massive stars in the galaxy. So there’s lots of young stars orbiting around down there. The question is, how do you get a star to tweak its orbit so that it shoots straight towards the supermassive black hole, instead of just orbiting around it, like the Earth orbiting the Sun. And that’s an open question. And one thing that these hypervelocity stars we’ve discovered are starting to give us hints about maybe how that mechanism works. Because, for example, one idea is that with these star clusters we’ve observed. Perhaps by dynamical friction, as they encounter other stars, they can sink slowly down towards the galactic centre where there’s the black hole. And it that were to happen, you could imagine that suddenly there were a whole bunch of stars right by that massive black hole. You could get a burst of these hypervelocity stars. There’s all sorts of stars to eject. And yet the stars that we observe all have different travel times from the galactic centre. This is only suggestive, but already we’re starting to be able to say something about the history of stars interacting with the supermassive black hole. And what appears so far, is that there’s no evidence for star clusters falling into the galactic centre.

Fraser: There could be some kind of conveyor belt that stars are born and then they slowly sink down and then they’re kicked out as they get too close.

Brown: Yeah, that’s sort of one idea. For that conveyor belt to work, you need some kind of massive place like a star cluster for that conveyor to work. To be able to sink something down towards the massive black hole. As a massive object encounters lots of massive objects, it turns out the less massive objects will tend to give off a little more energy. As the massive object, in this case a star cluster, loses energy, its orbit decays and it gets close to the galactic centre.

Fraser: With the few number of stars that you’ve found, and the large number of stars in the galaxy, it must have been a pretty difficult job to track these guys down. What was the method that you used?

Brown: Yeah, that’s actually one of the exciting results of this time. The first discovery, a year ago, after the first hypervelocity star, it was something of a serendipitous discovery. And this time we were actively looking for them. And the trick was that these things ought to be very rare. Theorists estimate that there’s perhaps a thousand of these stars in the entire galaxy. And the galaxy contains over a 100 billion stars. So we had to look in a way that gave us a pretty good chance of finding more of them. And our strategy was twofold. One is that the outskirts of the Milky Way contain mostly old, dwarf stars. Stars like the Sun, or less stars that are red. There’s no young, blue massive stars, and that’s the kind of star that we decided to look for; stars that are young, and luminous so that we can see them far away, but where there shouldn’t be these stars like that in the outskirts of the galaxy. And the other part of the strategy was to look for faint stars. The further out you go, the less background galaxy stars you have to contend with. And the more likely you’ll come across these hypervelocity stars, as opposed to another star that’s just orbiting the galaxy.

Fraser: And what’s the method you use to actually tell how fast that the star is moving?

Brown: For that we had to take a spectrum of the star. Using the 6.5 MMT telescope in Arizona, we pointed the star at one of our candidate stars and we take the light from that star and we put it into a rainbow spectrum and take a picture of that spectrum. And the elements in the stellar atmosphere serve as a fingerprint. You can see absorption lines due to hydrogen and helium and other elements. And it was using the motions, the Doppler shifts – in this case the red shifts – of those wavelengths told us how fast the stars were moving away from us. And most of the stars in our sample were normal galaxy stars; they were moving fairly slow velocities, and then two of these happened to be traveling quite fast, and that’s the two that we announced just now.

Fraser: And what do you think this tells us about the formation of stars, or the centre of the galaxy, or…

Brown: Well, that’s actually an interesting part of the story this time around. Now that we actually have a sample of these, these are really a new class of objects, these hypervelocity stars, we can start to say something about where they come from, which is the galactic centre. These stars are uniquely suited for telling us the story about what’s been happening at the galactic centre. Their travels times tell us something about the history, what’s been happening, but also the kinds of stars we’re seeing. In this case, these young, blue stars – these 3-4 solar mass stars – which astronomers call them B-type stars. The fact that we’ve seen two in our survey region, which we’ve carried out for about 5% of the sky, is consistent with the average distribution of stars you’d see in the galaxy. But inconsistent with what a lot of these stars clusters you see in the galactic centre. So just the fact of the type of stars you’re seeing is starting to tell us about the population of what’s been shot out of the galaxy. In this case it doesn’t look like it’s these supermassive clusters of stars, but rather your average star that’s wandering through the galaxy.

Fraser: And if you had some kind of super Hubble telescope at your disposal, what would you want to look for?

Brown: Oh, we’d want to look for the motion of these stars in the sky. So all we know if their minimum velocity. The only thing that we can measure is their velocity in the line of sight with respect to us. What we don’t know is there velocity in the plane of the sky, the so called proper motion. It’s possible to do that with Hubble, if you have 3-5 year baselines with which to see these stars move. It should be a very small motion. If you had a super Hubble, maybe you could see it in a year. So that would be very interesting to know. Not only would that tell you for sure that these really are coming from the galactic centre, and not from some place else, but also their trajectories. If you knew exactly how they’re moving out, any deviation off a straight line from the galactic centre tells you about how the gravity of the galaxy has been affecting their trajectory over time. And that’s also very interesting to know.

Fraser: Right, so that would help with plotting out the distribution of dark matter.

Brown: Exactly, exactly. So astronomers infer the presence of dark matter. We see stars orbiting the galaxy faster than they should be just because there appears to be mass that we can’t account for holding them in their orbits. And this dark matter, it’s hard to get a handle on how it’s distributed around the galaxy. But these stars are already at the outskirts of the galaxy, and as they pass through it, this perturbation, this gravitational pull of dark matter as these things travel through the galaxy slowly adds up as they go. So they’re actually measuring the distribution of this dark matter, just on their orbits. So if you could measure their motion, of a sample of stars, it actually starts giving you a handle on how the dark matter is distributed around the galaxy.

Posted on by Fraser Cain

Dione’s Colour Map

Saturn’s moon Dione in a false colour view. Image credit: NASA/JPL/SSI Click to enlarge
The leading hemisphere of Dione displays subtle variations in color across its surface in this false color view.

To create this view, ultraviolet, green and infrared images were combined into a single black and white picture that isolates and maps regional color differences.

This “color map” was then superposed over a clear-filter image. The origin of the color differences is not yet understood, but may be caused by subtle differences in the surface composition or the sizes of grains making up the icy soil.

Terrain visible here is on the moon’s leading hemisphere. North on Dione (1,126 kilometers, or 700 miles across) is up and rotated 17 degrees to the right.

See Detail on Dione (Monochrome) for a similar monochrome view.

All images were acquired with the Cassini spacecraft narrow-angle camera on Dec. 24, 2005 at a distance of approximately 597,000 kilometers (371,000 miles) from Dione and at a Sun-Dione-spacecraft, or phase, angle of 21 degrees. Image scale is 4 kilometers (2 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Posted on by R. Jay Gabany

Astrophoto: The Orion Nebula by Rob Gendler

Image credit: M-42 by Rob Gendler
One of our galaxy’s nearest, and certainly most productive ranches is located only 1,500 light years from our planet, south in the sky-farmlands we call Orion the hunter.

Although invisible to unaided eyes, hold a camera’s shutter open for a while and it will reveal that the area is a vast fertile field of dust and molecular gasses where a bumper crop of new stars have been harvested and many times more are still ripening. One tract of this farm continues to produce blue ribbon winners each year for best of show – in fact, its yield is stellar! Situated below the three stars of Orion’s belt, it’s known as the Great Nebula or M-42.

Behold the flowering of nature’s bounty on an unimaginable scale – here spanning about forty five light years in width! This scene is seeded with open stellar clusters, nurseries hiding suns yet to be, fast moving jets and disks surrounding new stars, called proplyds. Much of the delicate filaments that appear to be blowing like willow branches on a breezy day result when fast moving material meets slower moving gas and dust to form massive waves. The sense of motion evident in this spectacular image is as real as it is mesmerizing.

This picture was produced by combining hundreds of separate images to form a single exposure totaling over ninety hours! It was taken by Rob Gendler (known for his green photographic thumb) from his remote controlled observatory in New Mexico’s south central mountains near the end of 2005.

Do you have photos you’d like to share? Post them to the Universe Today astrophotography forum or email them, and we might feature one in Universe Today.

Written by R. Jay GaBany

Posted on by Fraser Cain

Podcast: Galactic Exiles

Young hot blue star – the supermassive black hole has spoken, it’s time for you leave the galaxy. When binary stars stray too close to the centre of the Milky Way, they’re violently split apart. One star is put into an elliptical orbit around the supermassive black hole, and the other is kicked right out of the galaxy. Dr. Warren Brown from the Harvard-Smithsonian Center for Astrophysics was one of the astronomers who recently turned up two exiled stars.
Continue reading “Podcast: Galactic Exiles”