Closely-Orbiting Stellar Companions Surrounded by “Mystery Dust”

Artist’s concept showing a dust disk around a binary system containing a white dwarf and a less-massive M (red) dwarf companion. (P. Marenfeld and NOAO/AURA/NSF)

Even though NASA’s Wide-field Infrared Survey Explorer spacecraft — aka WISE — ran out of coolant in October 2010, bringing its infrared survey mission to an end, the data that it gathered will be used by astronomers for decades to come as it holds clues to some of the most intriguing and hard-to-find objects in the Universe.

Recently astronomers using WISE data have found evidence of a particularly curious disk of dust and gas surrounding a pair of stars — one a dim red dwarf and the other the remains of a dead Sun-sized star — a white dwarf. The origin of the gas is a mystery, since based on standard models of stellar evolution it shouldn’t be there… yet there it is.

The binary system (which has the easy-to-remember name SDSS J0303+0054) consists of a white dwarf and a red dwarf separated by a distance only slightly larger than the radius of the Sun — about 700,000 km — which is incredibly close for two whole stars. The stars orbit each other quickly too: once every 3 hours.

The stars are so close that the system is referred to as a “post-common envelope” binary, because at one point the outer material of one star expanded out far enough to briefly engulf the other completely in what’s called a “common envelope.” This envelope of material brought the stars even closer together, transferring stellar material between them and ultimately speeding up the death of the white dwarf.

The system was first spotted during the Sloan Digital Sky Survey (hence the SDSS prefix) and was observed with WISE’s infrared abilities during a search for dust disks or brown dwarfs orbiting white dwarf stars. To find both a red (M) dwarf star 40-50 times the mass of Jupiter and a disk of dust orbiting the white dwarf in this system was unexpected — in fact, it’s the only known example of a system like it.

The entire mass of the dust (termed an infrared excess) is estimated to be “equivalent to the mass of an asteroid a few tens of kilometers in radius” and extends out to about the same distance as Venus’ orbit — just over 108 million kilometers, or 0.8 AU.

Why is the dust so unusual? Because, basically, it shouldn’t even be there. At that distance from the white dwarf, positioned just out of reach (but not terribly far away at all) anything that was within that zone when the original Sun-sized star swelled into its red giant phase should have spiraled inwards, getting swallowed up by the expanding stellar atmosphere.

Such is the fate that likely awaits the inner planets of our own Solar System — including Earth — when the Sun reaches the final phases of its stellar life.

So this requires that there are other sources of the dust. According to the WISE science update, “One possibility is that it is caused by multiple asteroids that orbit further away and somehow are perturbed close to the binary and collide with each other. [Another] is that the red dwarf companion releases a large amount of gas in a stellar wind that is trapped by the gravitational pull of its more massive white dwarf companion. The gas then condenses and forms the dust disk that is observed.

“Either way, this new discovery provides an interesting laboratory for the study of binary star evolution.”

See the team’s paper here, and read more on Berkeley’s WISE mission site here.

WISE launched into space on Dec. 14, 2009 on a mission to map the entire sky in infrared light with greatly improved sensitivity and resolution over its predecessors. From its polar orbit 525 kilometers (326 miles) in altitude it scanned the skies, collecting images taken at four infrared wavelengths of light. WISE took more than 2.7 million images over the course of its mission, capturing objects ranging from faraway galaxies to asteroids relatively close to Earth before exhausting the supply of coolant necessary to mask its own heat from its ultra-sensitive sensors.

Inset:  Infrared images of SDSS J0303+0054.  (NASA/JPL and  John H. Debes et. al.)

How Many Asteroids Are Out There?

Answer: a LOT. And there’s new ones being discovered all the time, as this fascinating animation by Scott Manley shows.


Created using data from the IAU’s Minor Planet Center and Lowell Observatory, Scott’s animation shows the progression of new asteroid discoveries since 1980. The years are noted in the lower left corner.

As the inner planets circle the Sun, asteroids light up as they’re identified like clusters of fireflies on a late summer evening. The clusters are mainly positioned along the outer edge of Earth’s orbit, as this is the field of view of most of our telescopes.

Once NASA’s WISE spacecraft begins its search around 2010 the field of view expands dramatically, as well as does the rate of new discoveries. This is because WISE’s infrared capabilities allowed it to spot asteroids that are composed of very dark material and thus reflect little sunlight, yet still emit a telltale heat signature.

While Scott’s animation gives an impressive — and somewhat disquieting — illustration of how many asteroids there are knocking about the inner Solar System, he does remind us that the scale here has been very much compacted; a single pixel at the highest resolution corresponds to over 500,000 square kilometers! So yes, over half a million asteroids is a lot, but there’s also a lot of space out there (and this is just a 2D top-down view too… it doesn’t portray any vertical depth.)

While most asteroids are aligned with the horizontal plane of the Solar System, there are a good amount whose orbits take them at higher inclinations. And on a few occasions they even cross Earth’s orbit.

(Actually, on more than just a few.)

Read: 4700 Asteroids Want to Kill You

An edge-on view of the Solar System shows the positions of asteroids identified by the NEOWISE survey. About 4700 potentially-hazardous asteroids (PHAs) have been estimated larger than 100 meters in size. (NASA/JPL-Caltech)

As far as how many asteroids there are… well, if you only consider those larger than 100 meters orbiting within the inner Solar System, there’s over 150 million. Count smaller ones and you get even more.

I don’t know about you but even with the distances involved it’s starting to feel a little… crowded.

You can see more of Scott Manley’s videos on YouTube here (including some interesting concepts on FTL travel) and learn more about asteroids and various missions to study them here.

Inset image: the 56-km (35-mile) wide asteroid Ida and its satellite, seen by the Galileo spacecraft in 1993. (NASA)

WISE Spies a Hunter’s Flame

A vast star-forming cloud of gas and dust in the constellation Orion shines brightly in this image from NASA’s WISE space telescope, where infrared light is represented in visible wavelengths. It’s part of a recent data release from WISE, a trove of infrared images acquired during the telescope’s second sky scan from August to September of 2010 — just as it began to run out of its essential cryogenic coolant.

Shining brightly in infrared radiation, the Flame nebula (NGC 2024) is at the heart of the cloud.  Just below it is the reflection nebula NGC 2023, and the small, bright loop protruding from the edge of the gas and dust cloud just to its lower right is the Horsehead nebula  — whose famous equine profile appears quite different in infrared light than it does in visible.

The two bright blue stars at the upper right portion of the image are both stars in Orion’s belt. Alnitak, the brighter one closer to the Flame nebula, is a multiple star system located 736 light-years away whose stellar wind is responsible for ionizing the Flame nebula and causing it to shine in infrared. Alnilam, the dimmer star at the uppermost corner, is a blue supergiant 24 times the radius of our Sun and 275,000 times as bright, but 1,980 light-years distant.

The red arc at lower right is the bow shock of Sigma Orionis, a multiple-star system that’s hurtling through space at a speed of 5,260,000 mph (2,400 kilometers per second). As its stellar wind impacts the interstellar medium and piles up before it, an arc of infrared-bright radiation is emitted.

Sigma Orionis is also the star responsible for the glow of the Horsehead nebula.

This rich astronomical scene is an expanded view from WISE’s previously-released image of the region (at right) which used data from only three of its four infrared detectors. In contrast, all four detectors were used in the image above, making more of the nebulae’s intricate structures visible as well as providing comparative information for researchers.

“If you’re an astronomer, then you’ll probably be in hog heaven when it comes to infrared data,” said Edward (Ned) Wright of UCLA, the principal investigator of the WISE mission. “Data from the second sky scan are useful for studying stars that vary or move over time, and for improving and checking data from the first scan.”

Read more on the NASA news release here.

Top and right images: NASA/JPL-Caltech/WISE team. Horsehead nebula visible light image was taken with the 0.9-meter telescope at Kitt Peak National Observatory. Photo credit & copyright: Nigel Sharp (NOAO), KPNO, AURA, NSF. Comparison by J. Major/Universe Today.

The Heavens are Ablaze With Blazars

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From a JPL press release:

Astronomers are actively hunting a class of supermassive black holes throughout the universe called blazars thanks to data collected by NASA’s Wide-field Infrared Survey Explorer (WISE). The mission has revealed more than 200 blazars and has the potential to find thousands more.

Blazars are among the most energetic objects in the universe. They consist of supermassive black holes actively “feeding,” or pulling matter onto them, at the cores of giant galaxies. As the matter is dragged toward the supermassive hole, some of the energy is released in the form of jets traveling at nearly the speed of light. Blazars are unique because their jets are pointed directly at us.

“Blazars are extremely rare because it’s not too often that a supermassive black hole’s jet happens to point towards Earth,” said Francesco Massaro of the Kavli Institute for Particle Astrophysics and Cosmology near Palo Alto, Calif., and principal investigator of the research, published in a series of papers in the Astrophysical Journal. “We came up with a crazy idea to use WISE’s infrared observations, which are typically associated with lower-energy phenomena, to spot high-energy blazars, and it worked better than we hoped.”

The findings ultimately will help researchers understand the extreme physics behind super-fast jets and the evolution of supermassive black holes in the early universe.

WISE surveyed the entire celestial sky in infrared light in 2010, creating a catalog of hundreds of millions of objects of all types. Its first batch of data was released to the larger astronomy community in April 2011 and the full-sky data were released last month.

This artist's concept shows a "feeding," or active, supermassive black hole with a jet streaming outward at nearly the speed of light. Such active black holes are often found at the hearts of elliptical galaxies. Not all black holes have jets, but when they do, the jets can be pointed in any direction. If a jet happens to shine at Earth, the object is called a blazar. Image credit: NASA/JPL-Caltech

Massaro and his team used the first batch of data, covering more than one-half the sky, to test their idea that WISE could identify blazars. Astronomers often use infrared data to look for the weak heat signatures of cooler objects. Blazars are not cool; they are scorching hot and glow with the highest-energy type of light, called gamma rays. However, they also give off a specific infrared signature when particles in their jets are accelerated to almost the speed of light.

One of the reasons the team wants to find new blazars is to help identify mysterious spots in the sky sizzling with high-energy gamma rays, many of which are suspected to be blazars. NASA’s Fermi mission has identified hundreds of these spots, but other telescopes are needed to narrow in on the source of the gamma rays.

Sifting through the early WISE catalog, the astronomers looked for the infrared signatures of blazars at the locations of more than 300 gamma-ray sources that remain mysterious. The researchers were able to show that a little more than half of the sources are most likely blazars.

“This is a significant step toward unveiling the mystery of the many bright gamma-ray sources that are still of unknown origin,” said Raffaele D’Abrusco, a co-author of the papers from Harvard Smithsonian Center for Astrophysics in Cambridge, Mass. “WISE’s infrared vision is actually helping us understand what’s happening in the gamma-ray sky.”

The team also used WISE images to identify more than 50 additional blazar candidates and observed more than 1,000 previously discovered blazars. According to Massaro, the new technique, when applied directly to WISE’s full-sky catalog, has the potential to uncover thousands more.

“We had no idea when we were building WISE that it would turn out to yield a blazar gold mine,” said Peter Eisenhardt, WISE project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., who is not associated with the new studies. “That’s the beauty of an all-sky survey. You can explore the nature of just about any phenomenon in the universe.”

PacMan Nebula Takes A “Bite” Out Of Space

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If you have a large telescope and an appetite for nebulae, then you’ve probably seen the Pac Man Nebula. Located 9,200 light years away in the constellation Cassiopeia, NGC 281 (RA 00 52 59.3 – Dec +56 37 19) is a seasonal favorite… and in this new image it’s showing a real “Halloween” face!

Discovered in August 1883 by E. E. Barnard, this diffuse HII region is home to open cluster IC 1590, the multiple star HD 5005, and several Bok globules. To the eye of the amateur telescope, it’s a soft, round region with a distinctive notch that makes it resemble the PacMan of video game fame. However, when seen in infrared light by NASA’s Wide-field Infrared Survey Explorer, or WISE, the PacMan appears to have “teeth”!

Of course, astronomers know these fanciful fangs are actually pillars where new stars are forming. They are created when stellar winds and radiation from the accompanying cluster blow away the gas and dust, revealing the dense star dough. If you see small red sprinkles in this cosmic cookie, then you’re looking at what could be very young stars in the process of springing to life.

According to JPL News, this image was made from observations by all four infrared detectors aboard WISE. Blue and cyan (blue-green) represent infrared light at wavelengths of 3.4 and 4.6 microns, respectively, which is primarily from stars, the hottest objects pictured. Green and red represent light at 12 and 22 microns, respectively, which is primarily from warm dust (with the green dust being warmer than the red dust).

It’s a great trick… or “treat”!

Original Story Source: JPL News.

Space Telescopes Provide New Look at 2,000 Year Old Supernova

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What caused a huge explosion nearly 2,000 years ago, seen by early Chinese astronomers? Scientists have long known that a “guest star” that had mysteriously appeared in the sky and stayed for about 8 months in the year 185 was the first documented supernova. But now the combined efforts of four space observatories have provided insight into this stellar explosion and why it was so huge – and why its shattered remains — the object known as RCW 86 – is now spread out to great distances.

“This supernova remnant got really big, really fast,” said Brian Williams, an astronomer at North Carolina State University in Raleigh. “It’s two to three times bigger than we would expect for a supernova that was witnessed exploding nearly 2,000 years ago. Now, we’ve been able to finally pinpoint the cause.”

By studying new infrared observations from the Spitzer Space Telescope and data from the Wide-field Infrared Survey Explorer, and previous data from NASA’s Chandra X-ray Observatory and the European Space Agency’s XMM-Newton Observatory, astronomers were able to determine that the ancient supernova was a Type Ia supernova. And doing some “forensics” on the stellar remains, the astronomers could piece together that prior to exploding, winds from the white dwarf cleared out a huge “cavity,” a region of very low-density surrounding the system. The explosion into this cavity was able to expand much faster than it otherwise would have. The ejected material would have traveled into the cavity, unimpeded by gas and dust and spread out quickly.

This is the first time that astronomers have been able to deduce that this type of cavity was created, and scientists say the results may have significant implications for theories of white-dwarf binary systems and Type Ia supernovae.

At about 85 light-years in diameter, RCW occupies a region of the sky that is slightly larger than the full moon. It lies in the southern constellation of Circinus.

Source: JPL

Did Asteroid Baptistina Kill The Dinosaurs? Think Other WISE…

It's long been thought that a giant asteroid, which broke up long ago in the main asteroid belt between Mars and Jupiter, eventually made its way to Earth and led to the extinction of the dinosaurs. New studies say that the dinosaurs may have been facing extinction before the asteroid strike, and that mammals were already on the rise. Image credit: NASA/JPL-Caltech

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Once upon a time, about 65 million years ago, scientists hypothesize a sizable asteroid crashed into Earth and contributed to the extinction of the dinosaurs. The evidence is a 150-kilometer-wide crater located just off the Yucatan peninsula and legend has it the 10-kilometer-wide asteroid was a fragment of a larger parent – Baptistina. Now, thanks to observations by NASA’s Wide-field Infrared Survey Explorer (WISE), we just might have to re-think that theory.

While there’s almost absolutely no doubt an asteroid crash was responsible for a cataclysmic climate change, science has never been particularly sure of what asteroid caused it. A visible-light study done by terrestrial telescopes in 2007 pointed a finger at a huge asteroid known as Baptistina. The conjecture was that about 160 million years ago, it collided with another main belt asteroid and sent pieces flying. Even though it was plausible, the theory was quickly challenged and now infra-red evidence from WISE may finally lay this family of asteroids to rest.

“As a result of the WISE science team’s investigation, the demise of the dinosaurs remains in the cold case files,” said Lindley Johnson, program executive for the Near Earth Object (NEO) Observation Program at NASA Headquarters in Washington. “The original calculations with visible light estimated the size and reflectivity of the Baptistina family members, leading to estimates of their age, but we now know those estimates were off. With infrared light, WISE was able to get a more accurate estimate, which throws the timing of the Baptistina theory into question.”

For over a year, WISE took an infra-red survey of the entire sky and asteroid-hunting portion of the mission, called NEOWISE, cataloged 157,000 members – discovering an additional 33,000 new ones. By utilizing the more accurate infra-red data, the team examined 1,056 members of the Baptistina family and discovered its break-up was closer to 80 million years ago – less than half the time previously suggested. By better knowing their size and reflectivity, researchers are able to calculate how long it would take for Baptistina members to reach their current position. The results show that in order for this particular asteroid to have caused an extinction level event, that it would have had to have impacted Earth much sooner… like about 15 million years.

“This doesn’t give the remnants from the collision very much time to move into a resonance spot, and get flung down to Earth 65 million years ago,” said Amy Mainzer, a study co-author and the principal investigator of NEOWISE at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena. Calif. “This process is thought to normally take many tens of millions of years.”

Like bouncing a super ball off the walls, resonance spots can jettison asteroids out of the main belt. This means a dinosaur-killing Baptistina event isn’t likely, but other asteroid families in NEOWISE study show similar reflective properties and one day we may be able to locate a responsible party.

“We are working on creating an asteroid family tree of sorts,” said Joseph Masiero, the lead author of the study. “We are starting to refine our picture of how the asteroids in the main belt smashed together and mixed up.”

Original Story Source: JPL/NASA News.

Dust in the Wind

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The stellar wind, that is! This beautiful image, taken by NASA’s Wide-Field Infrared Explorer (WISE) shows a vast ring of interstellar dust and gas being forced outwards by the wind and radiation from a massive star.

The star, HR8281, is located in the center of the image, the topmost star in a small triangular formation of blue stars to the upper left of the tip of a bright elongated structure – the end of the “elephant trunk” that gives the nebula its name. The star may not look like much, but HR8281’s powerful stellar wind is what’s sculpting the huge cloud of dust into the beautiful shapes seen in this infrared image.

Located 2,450 light-years from Earth, the Elephant’s Trunk Nebula spans 100 light-years. The “trunk” itself is about 30 light-years long. (That’s about, oh… 180 trillion miles!)

Structures like this are common in nebulae. They are formed when the stellar wind – the outpouring of ultraviolet radiation and charged particles that are constantly streaming off stars – blows away the gas and dust near a star, leaving only the densest areas. It’s basically erosion on a massive interstellar scale.

The tip of the "trunk" and the triangle of stars, the topmost of which is HR8281.

It’s not just a destructive process, though. Within those dense areas new stars can form… in fact, in the bright tip of the trunk above a small dark spot can be seen. That’s an area that’s been cleared by the creation of a new star. When a baby star “ignites” and its nuclear fusion factory turns on, its stellar wind clears away the dust and gas in the cloud it was formed from. Nebulae aren’t just pretty clouds in space… they’re stellar nurseries!

The red-colored stars in this image are other newborn stars, still wrapped in their dusty “cocoons”.

The colors used in this image represent specific wavelengths of infrared light. Blue and cyan (blue-green) represent light emitted at wavelengths of 3.4 and 4.6 microns, which is predominantly from stars. Green and red represent light from 12 and 22 microns, respectively, which is mostly emitted by dust.

Read more about this image on the WISE site here.

Image Credit: NASA/JPL-Caltech/WISE Team

Runaway Star Creates Quite a Shock

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Faster than a speeding bullet, this supergiant star looks like it might be wearing a red cape. Alpha Camelopardalis, the bright star in the middle of this image, is a runaway star, moving at incredible speeds – astronomers believe could be zooming along at somewhere between 680 and 4,200 kilometers per second (between 1.5 and 9.4 million miles per hour). The speed of this star is so fast, a huge bow shock is being created as the star moves through space. Alpha Cam’s bow shock can’t be seen in visible light, but WISE’s infrared detectors allow us to see this arc of heated gas and dust around the star.

Runaway stars are kicked into motion either through the supernova explosion of a companion star or through gravitational interactions with other stars in a cluster. The WISE team explains the bow shock:

“Because Alpha Cam is a supergiant star, it gives off a very strong wind. The speed of the wind is boosted in the forward direction the star is moving in space. When this fast-moving wind slams into the slower-moving interstellar material, a bow shock is created, similar to the wake in front of the bow of a ship in water. The stellar wind compresses the interstellar gas and dust, causing it to heat up and glow in infrared.”

Just as astronomers aren’t quite sure about the speed Alpha Cam is traveling, its distance is also somewhat uncertain, but it is probably somewhere between 1,600 and 6,900 light-years away. It is located in the constellation Camelopardis, near Ursa Major. (Right ascension: 4h 54m 03.0113s, declination: +66° 20′ 33.641”)

The colors used in this image represent specific wavelengths of infrared light. Stars are seen primarily in blue and cyan (blue-green), because they are emitting light brightly at 3.4 and 4.6 microns. Green represents 12-micron light, primarily emitted by dust. The red of the blow shock represents light emitted at 22 microns.

Source: WISE

Gallery: WISE’s Greatest Hits

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The WISE mission is now over, with the spacecraft taking its final image on Feb. 1, 2011. WISE was a “cool” infrared mission, with the optics chilled to less than 20 degrees centigrade above absolute zero (20 Kelvins). In its low Earth orbit (523 km above the ground), the spacecraft explored the entire Universe and collected infrared light coming from everywhere in space and studied asteroids, the coolest and dimmest stars, and the most luminous galaxies. Expect to hear and see more from WISE, however in the future. More images will be released from the team in April and in the spring of 2012. Here’s a look back at some of the great images from WISE’s 13 months in space:

The red dot at the center of this image is the first near-Earth asteroid discovered by NASA's Wide-Field Infrared Survey Explorer, or WISE Image credit: NASA/JPL-Caltech/UCLA
The red smudge at the center of this picture is the first comet discovered by NASA's Wide-Field Infrared Survey Explorer, or WISE. Image credit: NASA/JPL-Caltech/UCLA
The immense Andromeda galaxy, also known as Messier 31 or simply M31, is captured in full in this February 2010 image from WISE. credit: NASA/JPL-Caltech/UCLA
NGC 3603, as seen by WISE. credit: NASA/JPL-Caltech/UCLA
NGC 1514, sometimes called the Crystal Ball nebula shows a new double ring feature in an image from WISE. Image credit: NASA/JPL-Caltech/UCLA
This image from WISE shows the Tadpole nebula. Image credit: NASA/JPL-Caltech/UCLA
The Heart and Soul nebulae are seen in this infrared mosaic from WISE. Image credit: NASA/JPL-Caltech/UCLA
An image released in August 2010 from WISE image of the Small Magellanic Cloud. Image credit: NASA/JPL-Caltech/WISE Team
This oddly colorful nebula is the supernova remnant IC 443 as seen by WISE. Image credit: NASA/JPL-Caltech/UCLA
The last image that will ever be taken by the WISE spacecraft. Credit: NASA/JPL-Caltech/WISE Team

And if you want to see how it all started, here’s a video of WISE’s launch: