Pulsar Has Almost Completely Devoured a Star

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Astronomers using NASA’s Swift and Rossi X-ray Timing Explorer satellites have discovered a very bizarre object. It only has about 7 times the mass of Jupiter, but instead of orbiting a star, it’s orbiting a pulsar. Oh, and it’s not a planet. It’s all that’s left from a star after the pulsar siphoned away most of its material.

The ghastly duo was discovered on June 7 when Swift picked up a burst of X-rays and gamma rays coming from the direction of the galactic centre. Rossi turned to gaze at the source as well, and confirmed that it’s pulsing out X-rays 182.07 times a second. These are the classic characteristics of a pulsar – the rapidly spinning remains of a massive star.

Normally a pulsar like this is slowing down over time, releasing energy that decreases its rotational velocity. However, in the case of SWIFT J1756.9-2508, it’s actually speeding up. This means that some source is supplying the pulsar with additional material to increase its spin rate.

The researchers were able to detect that a low mass object is orbiting the pulsar, tugging it back and forth, towards and away from the Earth. Astronomers were then able to calculate that this binary companion has somewhere between 7 and 30 times the mass of Jupiter.

The system probably formed billions of years ago as a very massive star and a smaller companion with 1 to 3 solar masses. The massive star evolved quickly and then detonated as a supernova. The smaller star eventually died as well, becoming a red giant, and encompassing the pulsar. This slowed down their orbits enough to begin them spiraling inward.

Today they’re so close that the pulsar produces a tidal bulge on the surface of the dead star, siphoning material away. Sometimes there’s so much mass accumulated that it piles up and explodes as the outburst that led astronomers to the discovery in the first place.

Don’t think of the companion as a planet. “Despite its extremely low mass, the companion isn’t considered a planet because of its formation,” says researcher Christopher Deloye of Northwestern University. “It’s essentially a white dwarf that has been whittled down to a planetary mass.”

Original Source: NASA News Release

Mars Has Had Many, Many Ice Ages

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The polar ice caps on Mars have been there for a long time; although, they haven’t always stayed the same size, or shape. They cover the surface between the poles and approximately 60° latitude today, but Norbert Schorghofer of the Institute for Astronomy and NASA Astrobiology Institute in Hawaii has shown that Mars has had at least forty major ice ages during the past five million years.

The Martian ice caps are divided into three layers: a massive bottom sheet, a porous middle layer and a thin, dry, dusty top layer. The makeup and extent of the ice coverage has varied over its long history due to both precipitation of water vapor from the atmosphere, and the diffusion and condensation of water from pores in the ice.

“Although neither of the two mechanisms by itself could simultaneously account for the mass fraction and latitudinal boundary of the observed ice, their combination provides just enough ice at the right places,” Schorghofer said.

Unlike the Earth, Mars doesn’t have a Moon to keep its tilt in check. Instead, the planet is able to tilt as much as 10-degrees from its current angle. This can create tremendous variation in the size of its ice sheets.

Earlier studies of the ice showed that the shifting of the ice was due largely to Mars’ varying tilt (obliquity), and thus changes in global and local temperatures affecting the humidity levels of the entire planet. Schorghofer used computer modeling that takes into account thermal and atmospheric conditions, as well as the growth and retreat of the ice sheets. His research shows that the transfer of water vapor from the ice into the atmosphere, and the condensation of this water back into the ice profoundly altered the way in which the ice caps melted and re-froze.

Closer to the poles, the amount of ice changes very little over time. But near the edges of the sheets, the volume of ice has varied by as much as 100,000 cubic km during each ice age. Mars’ icy love handles have each also shrunk an overall depth of 60cm over the past 2.5 million years.

Understanding the cause for ice ages on Mars may help us learn more about the climate history of other planets, including Earth.

“The dynamic nature of the ice sheets makes Mars an ideal system in which to test and expand our knowledge of astronomical climate forcing. A great deal could be learned about terrestrial ice ages from the study of Martian ice stratigraphy – a longer, cleaner and simpler record than Earth’s,” Schorghofer said.

When the Phoenix Mars Lander arrives at the Red Planet in 2008, it might just see the different kinds of ice layers that Schorghofer is predicting.

Original Source: IfA

Opportunity is Entering Victoria Crater

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With the powerful Martian dust storms dissipating, the Mars Exploration Rovers are ready to resume their duties, apparently no worse for wear. When we last met our heroes, Opportunity was about to climb down into Victoria Crater to look for evidence of ancient water. Now it took its first tentative steps into the crater, putting all six wheels onto the slope. And then it crawled back out again. Easy does it…

Victoria Crater measures 800 metres (half a mile) across, and it’s the largest impact crater either of the rovers have encountered during their travels on Mars. Since the crater cuts down through Martian rock, it gives scientists an unprecedented opportunity to peer back in time, when layers of rock were put down – ideally when there was liquid water present.

The rover team commanded Opportunity to drive just far enough on September 11, 2007 that all six of its wheels got onto the inner slope. The rover was then asked to come back out again, so the team could measure the amount that its wheels slipped on the slope. Right at the end, as Opportunity was just crawling out, its wheels slipped further than the rover team wanted, so they had it stop, with its front wheels still on the slope.

Now that they’ve gathered data on Opportunity’s traction on this angle, the rover team will analyze it to understand if entering or exiting the crater is going to pose a hazard.

Original Source: Rover status report

Hubble Looks at Four Dead Stars

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Planetary nebulae are some of the most beautiful objects in the Universe. Don’t let the name confuse you, though, they have nothing to do with planets. They’re all that’s left behind when stars at the end of their lives cast off their outer layers into space. Here’s a nice image released from the Hubble Space Telescope, containing 4 different planetary nebulae.

As a star like our Sun reaches the end of its long life, its ejects its outer layers in a series of dramatic events. The ultraviolet light from the star illuminates the material, causing it to glow like we see in this Hubble photograph. This same ultraviolet light also disperses the cloud of material, pushing it outward so that it eventually fades away into the vacuum of space.

Although the star might have lived for 10 billion years, its planetary nebula lasts for just a moment – only 10,000 years.

In this Hubble image there are 4 planetary nebula.

At the top left is He 2-47, nicknamed the “starfish” because of its shape. It has six different lobes, which indicates that the original star shed material three different times in three different directions. With each ejection event, the star blasted out twin jets of material.

At the top right is NGC 5315, which seems to have an x-shaped structure. As with the previous nebula, it suffered two different ejection events, casting away its outer layers and firing out jets in opposite directions.

IC 4593 is on the bottom left, and it’s in the northern constellation Hercules. My good friend Phil Plait actually did a cool write up about this object, so I link you to his site for the scoop.

And finally, NGC 5307 is down at the bottom right, and has a beautiful spiral pattern. The dying star might have had a serious wobble as it was expelling gas, creating the complex shapes in the picture.

Original Source: Hubble News Release

Meteoroids Carve Tunnels as They Burrow Through the Atmosphere

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Every day, material is raining down on the Earth. Fortunately, we’ve got an atmosphere to protect us. As the tiny particles impact the atmosphere, air piles up in front of them, heating up, and blazing a trail in the sky. That’s a meteor. According to a team of Japanese researchers, as the micrometeoroids rain down, they carve out tiny tunnels just a few millimetres across.

Astronomers used to believe that meteors opened up gaps in the atmosphere less than a metre across, but they weren’t exactly sure how wide they really were. But new observations from the powerful Subaru telescope located atop Mauna Kea, Hawaii have narrowed the size down to just a few millimetres.

Observing meteors with the Subaru telescope is actually very difficult. It was designed to observe deep space astronomical objects, nothing as close as the Earth’s atmosphere. This means that the meteor trails look blurry. Even observations of satellites look blurry. Despite the blur, the researchers were able to get their data.

Over the course of a 19-hour observation, 13 meteor tracks were observed. Scientists then carefully analyzed the images, to see how many photons were released as the meteor passed through the atmosphere. Based on the number of photons they detected, the researchers were able to calculate that the trails are just a few millimetres across.

Original Source: Subaru News Release

The Triangle that Skimmed Past the Earth: Asteroid 2002 NY40

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In August 2002, a bizarre looking asteroid made its closest approach to the Earth, skimming only 540,000 km above the Earth’s surface. That’s only 1.5 times the distance between the Earth and Moon. This gave astronomers an unprecedented opportunity to study the asteroid as it zipped past. Perhaps its most unusual feature? It’s shaped like a triangle.

Asteroid 2002 NY40 was first discovered as part of the automated LINEAR system in New Mexico on July 14, 2002. And then, just a month later it made this closest approach, coming within 540,000 km of the Earth. As it approached, it gained in brightness, reaching as high as 8th magnitude – not visible with the unaided eye, but easy to spot with binoculars or a backyard telescope (if you knew where to look).

2002 NY40’s close approach was a rare event. Near Earth asteroids only get this close once every 50 years or so. The last asteroid to get this near was NEA 2001 CU11 which passed just outside the Moon’s orbit on August 31, 1925. And it wasn’t discovered for 77 years after it made the flyby – astronomers had to go back and calculate when it passed us by.

On the evening of August 17/18, 2002 NY40 was scheduled to make its closest approach. During this night, astronomers around the world, including a team of researchers from Boeing and the US Air Force focused in on it. The Boeing/Air Force team brought the 3.6 metre AEOS Adaptive Optics telescope in Hawaii to bear and studied the asteroid in unprecedented detail, revealing a tremendous amount of surface features. With all this data, they were able to better understand the physical makeup of the asteroid, and get an idea of its structure. Their results will be published in an upcoming issue of the journal Icarus.

Oh yeah, and it looks like a triangle.

The first observations were made with the Raven telescope located at the Remote Maui Experiment site at the base of Haleakala in Kihei, Hawaii. The telescope was configured so that it could track a fast moving object, like 2002 NY40 as it moved quickly through the telescope’s field of view. The researchers modified their exposure times dynamically – ranging from 15 seconds to 60 seconds – as the asteroid came and went. This allowed them to get the same amount of light for every image; it let them compare apples to apples.

Getting these high resolution images of the asteroid was actually pretty difficult. At its very brightest, closest point, when Asteroid 2002 NY40 could be seen at the greatest resolution, it was moving very quickly across the sky – it covered the diameter of the Moon every 6 minutes, zipping across the sky at 65,000 km/hour. The background stars changed with every image. Instead of calibrating against a single set of background stars, the researchers had to calibrate each image against whatever images happened to be in the field of view at the time.

Asteroid 2002 NY40 is tumbling. Its main rotation takes about 20 hours, and its secondary rotation takes about 18.5 hours. Living on this asteroid would be disorienting, to say the least.

According to the best images, 2002 NY40 is about 800 metres across. Once again, this was challenging to discern because the asteroid was casting shadows on itself for part of the flyby. Only at the moment of its closest approach, were astronomers able to get a good image showing its size. This team’s estimates are actually much larger than previous estimates, which calculated it being 250-450 metres.

It turns out, astronomers were quite lucky with the flyby. 2002 NY40 was perfectly positioned during its closest approach to present its largest face to the Earth. With this much data, the researchers were able to classify it as a Q-type asteroid; an uncommon class of inner-belt asteroids that have some metal in them.

And of course, one of the most amazing observations is its strange triangular shape. Getting these images out of the raw data was the hardest part. Lewis Roberts, one of the researches that did the work remarked that, “the imaging was the most challenging. It was a difficult object to acquire good data on and the raw data did not look great. The image processing was top notch and pulled out some good images.”

Original Source: Arxiv Paper

Iapetus Revealed

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As I mentioned a few days ago, I’m incredibly excited about Cassini’s recently flyby of Saturn’s moon Iapetus. Passing only 1,200 km (800 miles) above the surface of the bizarre moon, the spacecraft has captured dozens of new images. Perhaps now planetary geologists can figure out what’s caused that amazing ridge, the walnut shape, and the bizarre light and dark hemispheres.

The moment the new Cassini images came in, Emily Lakdawalla from the Planetary Society jumped on them, and started analyzing. She was able to stitch together several images into a large mosaic that just looks amazing. Especially that ridge. What is up with that ridge?

There are some original raw images available from the flyby from NASA, but I highly recommend you check out Emily’s analysis while we wait for NASA’s official results.

Podcast: Astronomy in Science Fiction

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This is a very different episode of Astronomy Cast. As we mentioned last week, Pamela recently attended the Dragon*Con science fiction convention in Atlanta, Georgia. While she was there, she participated in a special live edition of Astronomy Cast with special guest Dr. Kevin Frazier. Kevin is a NASA scientist, and the science consultant for the TV shows Battlestar Galactica and Eureka. He and Pamela work through physics and astronomy in popular science fiction. What they get right, and what they get wrong… oh so very wrong.

Click here to download the episode

Astronomy in Science Fiction – Show notes and transcript

Or subscribe to: astronomycast.com/podcast.xml with your podcatching software.

What’s Up this Week: September 10 – 16, 2007

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Monday, September 10 – Today is the birthday of James E. Keeler. Born in 1857, the American Keeler was a pioneer in the field of spectroscopy and astrophysics. In 1895, Keeler proved that different areas in Saturn’s rings rotate at different velocities. This clearly showed that Saturn’s rings were not solid, but were instead a collection of smaller particles in independent orbits.

While we are studying some of the summer’s finest objects, we’d be very remiss if we didn’t look at another cosmic curiosity – “The Blinking Planetary.” Located a couple of degrees east of visible star Theta Cygni, and in the same lower power field as 16 Cygni, it is formally known as NGC 6826.

Viewable in even small telescopes at mid to high power, you’ll learn very quickly how its name came about. When you look directly at it, you can only see the central 9th magnitude star. Now, look away. Focus your attention on visual double 16 Cygni. See that? When you avert, the nebula itself is visible. This is actually a trick of the eye. The central portion of our vision is more sensitive to detail and will only see the central star. At the edge of our vision, we are more likely to see dim light, and the planetary nebula appears. Located around 2,000 light-years from our solar system, it doesn’t matter if the “Blinking Planetary” is a trick of the eye or not… Because it’s cool!

Also known as Herschel IV.73 and Caldwell object 16, this tiny planetary shows an abundance of carbon and dust pockets in its structure. It skyrocketed to fame when viewed by the Hubble Space Telescope which revealed the mysterious red “FLIERS,” whose bow shocks point towards this planetary nebula – instead of away from it.

Tuesday, September 11 – For viewers in South America, you’re in for a partial solar eclipse on this Universal date. Be sure to check local information for precise times and viewing locations. Wishing you clear skies!

Today celebrates the birthday of Sir James Jeans. Born in 1877, English-born Jeans was an astronomical theoretician. During the beginning of the 20th century, Jeans worked out the fundamentals of the process of gravitational collapse. This was an important contribution to the understanding of the formation of solar systems, stars, and galaxies.

Tonight is New Moon and a great opportunity to have another look at all the things we’ve studied this week. However, I would encourage those of you with larger binoculars and telescopes to head for a dark sky location, because tonight we are going on a quest…the quest for the holy “Veil.”

By no means is the Veil Nebula Complex an easy one. The brightest portion, NGC 6992, can be spotted in large binoculars and you can find it just slightly south of a central point between Epsilon and Zeta Cygni. NGC 6992 is much better in a 6″ scope however, and low power is essential to see the long ghostly filaments which span more than a degree of sky. About two and a half degrees west-southwest, and incorporating star 52, is another long narrow ribbon of what may be classified as a supernova remnant. When aperture reaches the 12″ range, so does the true breadth of this fascinating complex. It is possible to trace these long filaments across several fields of view. They sometimes dim and at other times widen, but like a surreal solar flare, you will not be able to tear your eyes away from this area. Another undesignated area lies between the two NGCs, and the whole 1,500 light-year distant area spans over two and a half degrees. Sometimes known as the Cygnus Loop, it’s definitely one of late summer’s finest objects.

Wednesday, September 12 – Today in 1959, the USSR’s Luna 2 scored a mark as it became the first manmade object to hit the moon. The successful mission landed in the Paulus Putredinus area. Today also celebrates the 1966 Gemini 11 launch.

Tonight let’s take the time to hunt down an often overlooked globular cluster – M56.

Located roughly midway between Beta Cygni and Gamma Lyrae (RA 19 15 35.50 Dec +30 11 04.2), this class X globular was discovered by Charles Messier in 1779 on the same night he discovered a comet, and was later resolved by Herschel. At magnitude 8 and small in size, it’s a tough call for a beginner with binoculars, but is a very fine telescopic object. With a general distance of 33,000 light-years, this globular resolves well with larger scopes, but doesn’t show as much more than a faint, round area with small aperture. However, the beauty of the chains of stars in the field makes it quite worth the visit!

While you’re there, look carefully: M56 is one of the very few objects for which the photometry of its variable stars was studied strictly with amateur telescopes. While one bright variable had been known previously, up to a dozen more have recently been discovered. Of those, six had their variability periods determined using CCD photography and telescopes just like yours!

Thursday, September 13 – Today in 1922, the highest air temperature ever recorded at the surface of the Earth occurred. The measurement was taken in Libya and burned in at a blistering 136°F (58°C), but did you know that the temperatures in the sunlight on the Moon double that? Your first challenge for tonight will be to see if you can spot the slender crescent Moon right after sunset. If so, keep your binoculars on hand and look for Mercury about 2 degrees to the north. If you thought the surface of the Moon was a bit too warm for comfort, then know surface temperatures on the closest planet to the Sun can reach up to 800°F (427°C) at the equator during the day! As odd as it may sound, even that close to the Sun – Mercury could very well have ice deposits hidden below the surface at its poles.

Tonight we’ll move on to Aquila and look at the hot central star of an interesting planetary nebula – NGC 6804. You’ll find it almost 4 degrees due west of Altair (RA 19 31 35.17 Dec +09 13 32.0). Discovered by Herschel and classed as open cluster H VI.38, it wasn’t until Pease took a closer look that its planetary nature was discovered. Interacting with clouds of interstellar dust and gases, NGC 6804 is a planetary in decline, with its outer shell around magnitude 12 and the central star at about magnitude 13. While only larger telescopes will get a glimpse of the central, it’s one of the hottest objects in space – with temperatures around 30,000°K!

Friday, September 14 – Tonight as the Moon rises, look for the splendid appearance of Spica about 1.7 degrees to the north. Before it overpowers the sky, let’s use this opportunity to have a look at one of the prettiest clusters in the night – M11.

Discovered in 1681 by German astronomer Gottfried Kirch at the Berlin Observatory, M11 was later cataloged by Charles Messier in 1764 and first dubbed the “Wild Duck” by Admiral Smyth. To our modern telescopes and binoculars, there is little doubt as to how this rich galactic cluster earned its name – for it has a distinctive wedge-shaped pattern that closely resembles a flight of ducks. This fantastic open cluster of several thousand stars (about 500 of them are magnitude 14 or brighter) is approximately 250 million years old.

M11 is easily located by identifying Altair, the brightest star in Aquila. By counting two stars down the “body” of Aquila and stopping on Lambda, you will find your starhop guide. Near Lambda you will see three stars, the centermost is Eta Scuti. Now just aim! Even small binoculars will have no problem finding M11, but a telescope is required to start resolving individual stars. The larger the telescope’s aperture the more stars will be revealed in this most concentrated of all open clusters!

Saturday, September 15 – In 1991 the Upper Atmosphere Research Satellite (UARS) was launched from Space Shuttle Discovery. The successful mission lasted well beyond its life expectancy – sending back critical information about our ever-changing environment. After 14 years and 78,000 orbits, UARS remains a scientific triumph.

Tonight your lunar mission is to journey to the edge of the east limb and slightly south of central to identify crater Humboldt. Seen on the curve, this roughly 200 km wide crater holds a wealth of geographical details. Its flat, cracked floor has central peaks and a small mountain range, as well as radial rille structure. If libration and steadiness of skies are in your favor, power up and look for dark pyroclastic areas and a concentric inner crater.
Now, let’s have a look at Beta and Gamma Lyrae, the lower two stars in the “Harp.” Beta is actually a quick changing variable which drops to less than half the brightness of Gamma in around 12 days. For a few days the pair will seem of almost equal brightness and then you will notice the star closest to Vega fades away. Beta is one of the most unusual spectroscopic stars in the sky, and it is possible that its eclipsing binary companion may be the prototype of the “collapsar” (yep, a black hole!), rather than a true luminous body.

Sunday, September 16 – If you were unable to identify Humboldt last night, try again tonight with Petavius as your guide. Although we have studied Petavius before, now is your chance once again to mark your studies of the Petavius Wall. Look for unusual features, such as 57 kilometer diameter Wrottesley on Petavius’ northwest wall, or 83 kilometer wide Hase to the south, with its deep interior impact… Or how about long, shallow Legendre and Phillips on Humboldt’s west wall? If libration is good you might even spot the edge of Barnard on Humboldt’s southeast edge!

While the Moon will dominate tonight’s sky, we can still 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 its 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 of the star itself. If you are using a scope, you can easily spot the blue tinted, 7th magnitude B star about one-third the distance between the two giants. Although our true pair are some two billion kilometers 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 five years to wait!

Astrosphere for September 7th, 2007

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Today’s astrophoto is brought to you by Bokmakierie. It’s an image of the Alpine Valley on the Moon. You’ll want to click the image to enlarge it and read the text. Bokmakierie compares this image with one taken by ESA’s SMART-1 at only 6,000 km altitude above the surface.

I think this is a really fascinating article at the Christian Science Monitor. Scientists have figured out a way to search for hurricanes in the past – looking for ash from ancient wildfires. When a hurricane strikes, it knocks down lots of trees, and this creates a greater risk for wildfires.

When she’s not writing for Universe Today, Nancy Atkinson has been busy with other freelance activities. Check out this new magazine called Space Lifestyle, where Nancy profiles our good friend Phil Plait. With extra quotiness from me.

I love it when people come together to organize and create cool content. Here’s a website called The Moon Wiki. Volunteers are cataloging every single crater and feature on the Moon, and linking it to photographs. They still need help, so check it out.