Nancy Atkinson, Author at Universe Today

January 6, 2009December 24, 2015 by Nancy Atkinson

With No Smoke or Mirrors, Spacecraft Hunts for Active Galaxies with Central Black Holes

Swift's Hard X-ray Survey offers the first unbiased census of active galactic nuclei in decades. Dense clouds of dust and gas, illustrated here, can obscure less energetic radiation from an active galaxy's central black hole. High-energy X-rays, however, easily pass through. Credit: ESA/NASA/AVO/Paolo Padovani

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NASA’s Swift spacecraft is designed to hunt for gamma-ray bursts. But in the time between these almost-daily cosmic explosions, Swift’s Burst Alert Telescope (BAT) scans the sky, performing an ongoing X-ray survey. Some of the first results of that survey were shared at the American Astronomical Society meeting in Long Beach, California. The BAT is revealing differences between nearby active galaxies and those located about halfway across the universe. Understanding these differences will help clarify the relationship between a galaxy and its central black hole. But unlike most telescopes, the BAT observations are not done with mirrors, optics or direct focusing. Instead, images are made by analyzing the shadows cast by 52,000 randomly placed lead tiles on 32,000 hard X-ray detectors. And BAT is becoming a workhorse: The survey is now the largest and most sensitive census of the high-energy X-ray sky.

“There’s a lot we don’t know about the workings of supermassive black holes,” says Richard Mushotzky of NASA’s Goddard Space Flight Center in Greenbelt, Md. Astronomers think the intense emission from the centers, or nuclei, of active galaxies arises near a central black hole containing more than a million times the sun’s mass. “Some of these feeding black holes are the most luminous objects in the universe. Yet we don’t know why the massive black hole in our own galaxy and similar objects are so dim.”

“The BAT sees about half of the entire sky every day,” Mushotzky said. “Now we have cumulative exposures for most of the sky that exceed 10 weeks.”

Galaxies that are actively forming stars have a distinctly bluish color (“new and blue”), while those not doing so appear quite red (“red and dead”). Nearly a decade ago, surveys with NASA’s Chandra X-Ray Observatory and ESA’s XMM-Newton showed that active galaxies some 7 billion light-years away were mostly massive “red and dead” galaxies in normal environments.

The BAT survey looks much closer to home, within about 600 million light-years. There, the colors of active galaxies fall midway between blue and red. Most are spiral and irregular galaxies of normal mass, and more than 30 percent are colliding. “This is roughly in line with theories that mergers shake up a galaxy and ‘feed the beast’ by allowing fresh gas to fall toward the black hole,” Mushotzky says.

Until the BAT survey, astronomers could never be sure they were seeing most of the active galactic nuclei. An active galaxy’s core is often obscured by thick clouds of dust and gas that block ultraviolet, optical and low-energy (“soft”) X-ray light. Dust near the central black hole may be visible in the infrared, but so are the galaxy’s star-formation regions. And seeing the black hole’s radiation through dust it has heated gives us a view that is one step removed from the central engine. “We’re often looking through a lot of junk,” Mushotzky says.

But “hard” X-rays — those with energies between 14,000 and 195,000 electron volts — can penetrate the galactic junk and allow a clear view. Dental X-rays work in this energy range.

Astronomers think that all big galaxies have a massive central black hole, but less than 10 percent of these are active today. Active galaxies are thought to be responsible for about 20 percent of all energy radiated over the life of the universe, and are thought to have had a strong influence on the way structure evolved in the cosmos.

The Swift spacecraft was launched in 2004.

Source: NASA

January 6, 2009December 24, 2015 by Nancy Atkinson

“Lighthouse” Analogy No Longer Works for Pulsars

NASA's Fermi Gamma-ray Space Telescope has found 12 previously unknown pulsars (orange). Fermi also detected gamma-ray emissions from known radio pulsars (magenta, cyan) and from known or suspected gamma-ray pulsars identified by NASA's now-defunct Compton Gamma-Ray Observatory (green). Credit: NASA/Fermi/LAT Collaboration

NASA’s Fermi Gamma-ray Space Telescope has found 12 previously unknown gamma-ray only pulsars, as well as identifying gamma-ray emissions from 18 known or suspected radio pulsars. And what the telescope is finding is changing the way we think of these stellar cinders. The old analogy for pulsars was a lighthouse: gamma-rays were thought to pulse out in a narrow beam from the neutron star’s magnetic poles. But this new research shows that cannot be the case. A new class of gamma-ray-only pulsars shows that the gamma rays must form in a broader region than the lighthouse-like radio beam. “We used to think the gamma rays emerged near the neutron star’s surface from the polar cap, where the radio beams form,” says Alice Harding of NASA’s Goddard Space Flight Center. “The new gamma-ray-only pulsars put that idea to rest.” She and Roger Romani from Stanford University in California spoke today at the American Astronomical Society meeting.

A pulsar is a rapidly spinning and highly magnetized neutron star, the crushed core left behind when a massive sun explodes. Most were found through their pulses at radio wavelengths, and were thought to be caused by narrow, lighthouse-like beams emanating from the star’s magnetic poles.

If the magnetic poles and the star’s spin axis don’t align exactly, the spinning pulsar sweeps the beams across the sky. Radio telescopes on Earth detect a signal if one of those beams happens to swing our way. Unfortunately, any census of pulsars is automatically biased because we only see those whose beams sweep past Earth.

“That has colored our understanding of neutron stars for 40 years,” Romani says. The radio beams are easy to detect, but they represent only a few parts per million of a pulsar’s total power. Its gamma rays, on the other hand, account for 10 percent or more. “For the first time, Fermi is giving us an independent look at what heavy stars do,” he adds.

Watch an animation of the new look at these pulsars.

Pulsars are phenomenal cosmic dynamos. Through processes not fully understood, a pulsar’s intense electric and magnetic fields and rapid spin accelerate particles to speeds near that of light. Gamma rays let astronomers glimpse the particle accelerator’s heart.

Astronomers now believe the pulsed gamma rays arise far above the neutron star. Particles produce gamma rays as they accelerate along arcs of open magnetic field. For the Vela pulsar, the brightest persistent gamma-ray source in the sky, the emission region is thought to lie about 300 miles from the star, which is only 20 miles across.

Existing models place the gamma-ray emission along the boundary between open and closed magnetic field lines. One version starts at high altitudes; the other implies emission from the star’s surface all the way out. “So far, Fermi observations to date cannot distinguish which of these models is correct,” Harding says.

Because rotation powers their emissions, isolated pulsars slow as they age. The 10,000-year-old CTA 1 pulsar, which the Fermi team announced in October, slows by about a second every 87,000 years.

Fermi also picked up pulsed gamma rays from seven millisecond pulsars, so called because they spin between 100 and 1,000 times a second. Far older than pulsars like Vela and CTA 1, these seemingly paradoxical objects get to break the rules by residing in binary systems containing a normal star. Stellar matter accreted from the companion can spin up the pulsar until its surface moves at an appreciable fraction of light speed.

“We know of 1,800 pulsars, but until Fermi we saw only little wisps of energy from all but a handful of them,” said Romani. “Now, for dozens of pulsars, we’re seeing the actual power of these machines.”

Source: NASA

January 6, 2009December 24, 2015 by Nancy Atkinson

Molecules in Gamma-Ray Burst Detected

This image merges Swift optical (blue, green) and X-ray views of GRB 080607. The white spot at center is the burst’s optical afterglow. Credit: NASA/Swift/Stefan Immler

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Gamma-ray bursts are the universe’s most brilliant events, and now astronomers have been able to shed light on the composition of these spectacular phenomena, providing insight into star formation when the universe was about one-sixth its present age. Combining data from NASA’s Swift satellite, the W. M. Keck Observatory in Hawaii, and other facilities astronomers have, for the first time, identified gas molecules in the host galaxy of a gamma-ray burst. “We clearly see absorption from two molecular gases: hydrogen and carbon monoxide. Those are gases we associate with star-forming regions in our own galaxy,” said Xavier Prochaska, from the University of California Santa Cruz. He and his team believe that the burst exploded behind a thick molecular cloud similar to those that spawn stars in our galaxy today.

The explosion, designated GRB 080607, occurred in June, 2008. “This burst gave us the opportunity to ‘taste’ the star-forming gas in a young galaxy more than 11 billion light-years away,” said Prochaska.

Gamma rays from GRB 080607 triggered Swift’s Burst Alert Telescope shortly after 2:07 a.m. EDT on June 7, 2008. Swift calculated the burst’s position, beamed the location to a network of observatories, and turned to study the afterglow.

That night, University of California, Berkeley, professor Joshua Bloom and graduate students Daniel Perley and Adam Miller were using the Low Resolution Imaging Spectrometer on the 10m Keck I Telescope in Hawaii. “Because afterglows fade rapidly, we really had to scramble when we received the alert,” Perley says. “But in less than 15 minutes, we were on target and collecting data.”

The Peters Automated Infrared Imaging Telescope (PAIRITEL) in Arizona caught GRB 080607’s afterglow (circled) about three minutes after the explosion. The afterglow’s light has been greatly dimmed and reddened by interstellar dust in its host galaxy, 11.5 billion light years away. Credit: Adam Miller and Daniel Perley/UC Berkeley

A pair of robotic observatories also responded quickly. The NASA-supported Peters Automated Infrared Imaging Telescope (PAIRITEL) on Mount Hopkins, Ariz., and the Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory on Mount Hamilton, Calif., observed the burst’s afterglow within three minutes of Swift’s alert.

The spectrum from Keck established that the explosion took place 11.5 billion light-years away. GRB 080607 blew up when the universe was just 2.2 billion years old.

The molecular cloud in the burst’s host galaxy was so dense, less than 1 percent of the afterglow’s light was able to penetrate it. “Intrinsically, this afterglow is the second brightest ever seen. That’s the only reason we were able to observe it at all,” Prochaska says.

Screening from thick molecular clouds provides a natural explanation for so-called “dark bursts,” which lack associated afterglows. “We suspect that previous events like GRB 080607 were just too faint to be observed,” says team member Yaron Sheffer of the University of Toledo, Ohio.
Nearly half of the absorption lines found in the Keck spectrum are unidentified. The team expects that understanding them will provide new data on the simplest space molecules.

Prochaska and Sheffer presented the findings today at the 213th meeting of the American Astronomical Society in Long Beach, Calif. A paper describing the results will appear in a future issue of Astrophysical Journal Letters.

Most gamma-ray bursts occur when massive stars run out of nuclear fuel. As the star’s core collapses into a black hole or neutron star, gas jets punch through the star and into space. Bright afterglows occur as the jets heat gas that was previously shed by the star. Because a massive star lives only a few tens of millions of years, it never drifts far from its natal cloud.

Source: NASA

January 6, 2009December 24, 2015 by Nancy Atkinson

Could Mystery Outburst be a New Stellar Phenomenon?

Hubble's mystery object. Credit: NASA, ESA, and K. Barbary (University of California, Berkeley/Lawrence Berkeley National Lab, Supernova Cosmology Project)

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The Hubble Space Telescope serendipitously captured a mysterious burst of light on February 21, 2006. Over the next 100 days, the object, cataloged as SCP 06F6, brightened and then slowly faded. Astronomers do not know the object’s distance, so it can either be in our Milky Way galaxy or at a great astronomical distance, and the light-signature of this event does not match the behavior of a supernova or any previously observed astronomical transient phenomenon in the universe. It might represent an entirely new class of stellar phenomena that has previously gone undetected in the universe, said Kyle Barbary of the Lawrence Berkeley National Laboratory (LBNL) in Berkeley, Calif.y researchers. “No one has been able to come up with a good explanation for this object” he said at a press conference at today’s American Astronomical Society meeting in Long Beach, California. (Read on for an outlandish explanation one scientist proposed!)

Astronomers commonly observe intense flashes of light from a variety of stellar explosions and outbursts, such as novae and supernovae. But the rise and fall in brightness has a signature that simply has never been recorded for any other type of celestial event. Supernovae peak after no more than 70 days, and gravitational lensing events are much shorter. Therefore, this observation defies a simple explanation, said Barbary. “We have never seen anything like it.”

Hubble was aimed at a cluster of galaxies 8 billion light-years away in the spring constellation Bootes. But the mystery object could be anywhere in between, even in the halo of our own Milky Way galaxy.

Papers published by other researchers since the event was reported in June 2006, have suggested a bizarre zoo of possibilities: the core collapse and explosion of a carbon rich star, a collision between a white dwarf and an asteroid, or the collision of a white dwarf with a black hole. At the press conference Barbary was asked what the most bizarre explanation of the object was: “Jokingly, someone said it was another civilization turning on their Large Hadron Collider and exploding,” — which got laughs from the audience. “Don’t quote me on that!,” he added.

But Barbary does not believe that any model offered so far fully explains the observations. “I don’t think we really know what the discovery means until we can observe similar objects in the future.”

All-sky surveys for variable phenomena, such as those to be conducted with the planned Large Synoptic Survey Telescope, may ultimately find similar transient events in the universe.

Source: HubbleSite

January 6, 2009December 24, 2015 by Nancy Atkinson

Cassiopeia A Comes Alive in 3-D Movies

Cassiopeia A from Chandra. Credit: NASA/CXC/D.Berry

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Want to know what it’s like to fly through a supernova remnant? Then, THIS, you have to see. You’ll be able to experience SNR Cassiopeia A (Cas A) as never before, and see it across both time and space. Another time lapse animation shows the remnant’s expansion and changes over time, and still another provides a 3-D model of Cas A. Almost ten years ago, Chandra’s “First Light” image of Cas A revealed previously unseen structures and detail, and now, after eight years of observation, scientists have been able to construct these incredible animations which were presented at today’s American Astronomical Society meeting in Long Beach, California.

The fly-through movie is based on data from Chandra, NASA’s Spitzer Space Telescope, and ground-based optical telescopes. “We have always wanted to know how the pieces we see in two dimensions fit together with each other in real life,” said Tracey Delaney of the Massachusetts Institute of Technology. “Now we can see for ourselves with this ‘hologram’ of supernova debris.”

Delaney said there are two components to the explosion, a spherical component from the outer layers of the star and a flattened component from the inner layers of the star. Most intriguing, said Delaney is that the jets of the explosion are not all over the place but came out of the same plane in the supernova. Plumes, or jets, of silicon appear in the northeast and southwest, while plumes of iron are seen in the southeast and north. Astronomers had known about the plumes and jets before, but did not know that they all came out in a broad, disk-like structure.

Cas A expansion. Credit: NASA/CXC/SAO/D.Patnaude et al.

The time-lapse animation tracks the remnant’s expansion and changes over time, measuring the expansion velocity of features in Cas A. “With Chandra, we have watched Cas A over a relatively small amount of its life, but so far the show has been amazing,” said Daniel Patnaude of the Smithsonian Astrophysical Observatory in Cambridge, Mass. “And, we can use this to learn more about the aftermath of the star’s explosion.”

Using estimates of the properties of the supernova explosion, including its energy and dynamics, Patnaude’s group show that about 30% of the energy in this supernova has gone into accelerating cosmic rays, energetic particles that are generated, in part, by supernova remnants and constantly bombard the Earth’s atmosphere. The flickering in the movie provides valuable new information about where the acceleration of these particles occurs.

The researchers found the expansion is slower than expected based on current theoretical models. Patnaude thinks the explanation for this mysterious loss of energy is cosmic ray acceleration.

Cas A in 3-D. Credit: NASA/CXC/MIT/T.Delaney et al.

The 3-D model of Cas A was made possible through a collaboration with the Astronomical Medicine project based at Harvard. The goal of this project is to bring together the best techniques from two very different fields, astronomy and medical imaging.

“Right now, we are focusing on improving three-dimensional visualization in both astronomy and medicine,”said Harvard’s Alyssa Goodman who heads the Astronomical Medicine project. “This project with Cas A is exactly what we have hoped would come out of it.”

3-D visualization and the 3-D expansion model provide researchers with a unique ability to study this remnant. The implication of this work is that astronomers who build models of supernova explosions must now consider that the outer layers of the star come off spherically, but the inner layers come out more disk like with high-velocity jets in multiple directions.

Cassiopeia A is the remains of a star thought to have exploded about 330 years ago, and is one of the youngest remnants in the Milky Way galaxy. The study of Cas A and remnants like it help astronomers better understand how the explosions that generate them seed interstellar gas with heavy elements, heat it with the energy of their radiation, and trigger blast waves from which new stars form.

Source: Chandra site

January 6, 2009December 24, 2015 by Nancy Atkinson

New Ares Construction “Towers” Over 39B

On Launch Pad 39B at NASA's Kennedy Space Center, a crane completes construction of one of the towers in the new lightning protection system for the Constellation Program. Credit: NASA

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Things are a-changing over at the Kennedy Space Center launch complex. The first lightning tower for the Ares rockets has been completed, dwarfing all the other structures on pad 39B. The tower is for the new lightning protection system for the Constellation Program. Other towers are being constructed at left and behind the service structures on the pad. Each of the three new lightning towers will be 152 meters (500 feet) tall with an additional 30 meter (100-foot) fiberglass mast atop supporting a catenary, or overhead wire system. This compares to the height of the shuttle Fixed Service Structure at 105.7 meters (347ft) to the top of the lightning mast. The new and improved lightning protection system allows for the taller height of the Ares I rocket compared to the space shuttle. Pad 39B will be the site of the first Ares vehicle launch, including the Ares I-X test flight that is targeted for July 2009. See image below for what the completed system will look like.

This is an artist’s rendition of what the new lightning protection system being built at Launch Pad 39B will look like when fully completed. The launch pad will also be modified to support future launches of Ares and Orion spacecraft.

January 5, 2009December 24, 2015 by Nancy Atkinson

Watch More Events Live from AAS on Tuesday Jan. 6

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Once again our sister site Astronomy Cast LIVE will be providing live video coverage of press events at the 213th AAS meeting being held in Long Beach CA. The video streams can be found at Astronomy Cast’s UStream Channel. You can join the chat to suggestion questions to ask at the news conference or report any issues with the feed.

If for some reason this link does not work try searching for Astronomy Cast on at www.ustream.tv

Here is the tentative schedule for tomorrow, Tuesday January 6. We’ll try to keep you updated if there are any changes, or check back with Astronomy Cast Live for updates. All times are Pacific Standard Time so please adjust accordingly. These recordings may or may not be available for viewing later.

9:00 AM – Cassiopeia A

10:30 AM – Star News

11:30 AM – Bright Flashes in the Universe

1:00 PM – News from Fermi and SWIFT

3:00 PM – History Mysteries

More might be added to the list tomorrow morning. Remember to join the chat room to suggest questions, and report issues. We will do our best to accommodate. Scott Miller from Astronomy Cast is manning the camera and the UStream Chat (and wowing the UStream and AAS world, I might add!)

January 5, 2009December 24, 2015 by Nancy Atkinson

Triple Whammy: Milky Way More Massive, Spinning Faster and More Likely to Collide

Artist's Conception of our Milky Way Galaxy: Blue, green dots indicate distance measurements. CREDIT: Robert Hurt, IPAC; Mark Reid, CfA, NRAO/AUI/NSF

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For many of us, looking closely in the mirror and stepping on the bathroom scale just after the holidays can reveal a substantial surprise. Likewise, astronomers looking closely at the Milky Way have found our galaxy is more massive than previously thought. High-precision measurements of the Milky Way disclose our galaxy is rotating about 100,000 miles per hour faster than previously understood. That increase in speed, said Mark Reid of the Harvard-Smithsonian Center for Astrophysics, increases the Milky Way’s mass by 50 percent. The larger mass, in turn, means a greater gravitational pull that increases the likelihood of collisions with the Andromeda galaxy or smaller nearby galaxies. So even though we’re faster, we’re also heavier and more likely to be annihilated. Bummer!

The scientists are using the National Science Foundation’s Very Long Baseline Array (VLBA) radio telescope to remake the map of the Milky Way. Taking advantage of the VLBA’s unparalleled ability to make extremely detailed images, the team is conducting a long-term program to measure distances and motions in our Galaxy. At the American Astronomical Society’s meeting in Long Beach, California, Reid said they are using trigonometric parallax to make the measurements. “This is exactly what surveyors use on Earth to measure distances,” he said. “And this is gold standard of measurement in astronomy.”

Trigonometric parallax was first used in 1838 to measure the first stellar distance. However, with better technology, the accuracy is now about 10,000 times greater.

Our solar system is about 28,000 light-years from the Milky Way’s center. At that distance, the new observations indicate, we’re moving at about 600,000 miles per hour in our Galactic orbit, up from the previous estimate of 500,000 miles per hour.

The scientists observed 19 regions of prolific star formation across the Galaxy. In areas within these regions, gas molecules are strengthening naturally-occurring radio emission in the same way that lasers strengthen light beams. These areas, called cosmic masers, serve as bright landmarks for the sharp radio vision of the VLBA. By observing these regions repeatedly at times when the Earth is at opposite sides of its orbit around the Sun, the astronomers can measure the slight apparent shift of the object’s position against the background of more distant objects.

The astronomers found that their direct distance measurements differed from earlier, indirect measurements, sometimes by as much as a factor of two. The star-forming regions harboring the cosmic masers “define the spiral arms of the Galaxy,” Reid explained. Measuring the distances to these regions thus provides a yardstick for mapping the Galaxy’s spiral structure.

The star forming regions are shown in the green and blue dots on the image above. Our sun (and us!) are where the red circle is located.

The VLBA can fix positions in the sky so accurately that the actual motion of the objects can be detected as they orbit the Milky Way’s center. Adding in measurements of motion along the line of sight, determined from shifts in the frequency of the masers’ radio emission, the astronomers are able to determine the full 3-dimensional motions of the star-forming regions. Using this information, Reid reported that “most star-forming regions do not follow a circular path as they orbit the Galaxy; instead we find them moving more slowly than other regions and on elliptical, not circular, orbits.”

The researchers attribute this to what they call spiral density-wave shocks, which can take gas in a circular orbit, compress it to form stars, and cause it to go into a new, elliptical orbit. This, they explained, helps to reinforce the spiral structure.

Reid and his colleagues found other surprises, too. Measuring the distances to multiple regions in a single spiral arm allowed them to calculate the angle of the arm. “These measurements,” Reid said, “indicate that our Galaxy probably has four, not two, spiral arms of gas and dust that are forming stars.” Recent surveys by NASA’s Spitzer Space Telescope suggest that older stars reside mostly in two spiral arms, raising a question of why the older stars don’t appear in all the arms. Answering that question, the astronomers say, will require more measurements and a deeper understanding of how the Galaxy works.

So, now that we know we’re more massive, how do we compare with other galaxies in our neighborhood? “In our local group of galaxies, Andromeda was thought to be the dominant big sister,” said Reid at the conference, “but we’re basically equal in size and mass. We’re not identical twins, but more like fraternal twins. And its likely the two galaxies will collide sooner than we thought, but it depends on a measurement of the sideways motion, which hasn’t been done yet.”

The VLBA is a system of 10 radio-telescope antennas stretching from Hawaii to New England and the Caribbean. It has the best resolving power, of any astronomical tool in the world. The VLBA can routinely produce images hundreds of times more detailed than those produced by the Hubble Space Telescope. The VLBA’s tremendous resolving power, equal to being able to read a newspaper in Los Angeles from the distance of New York, is what permits the astronomers to make precise distance determinations.

Source: AAS, Harvard-Smithsonian Center for Astrophysics

January 5, 2009December 24, 2015 by Nancy Atkinson

Hubble, Spitzer Collaborate for Stunning Panorama of Galactic Center

Galactic center in unprecedented detail.Credit for Hubble image: NASA, ESA, and Q.D. Wang (University of Massachusetts, Amherst)

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Two of the biggest space telescopes have combined forces to create a HUGE panorama of the center of the Milky Way galaxy. This sweeping, composite color panorama is the sharpest infrared picture ever made of the Galactic core. Revealed in the image are a new population of massive stars and new details of complex structures in the hot gas and dust swirling around, created by solar winds and supernova explosions. The image shows an area about 300 light-years across. Click here for options in seeing this image in small, medium or super-sized extra large resolution! Click here for a stunning movie showing the location and more detail of this image in visible light. Astronomers at the American Astronomical Society meeting pointed out the actual galactic center is in the large white region near the lower right side of the image. If you need something to keep you occupied for awhile, try counting the number of stars in this image!

More about this image…

This image provides insight into how massive stars form and influence their environment in the often violent nuclear regions of other galaxies. This view combines the sharp imaging of the Hubble Space Telescope’s Near Infrared Camera and Multi-Object Spectrometer (NICMOS) with color imagery from a previous Spitzer Space Telescope survey done with its Infrared Astronomy Camera (IRAC). The Galactic core is obscured in visible light by intervening dust clouds, but infrared light penetrates the dust. The spatial resolution of NICMOS corresponds to 0.025 light-years at the distance of the galactic core of 26,000 light-years. Hubble reveals details in objects as small as 20 times the size of our own solar system. The NICMOS images were taken between February 22 and June 5, 2008.

Source: HubbleSite

January 5, 2009December 24, 2015 by Nancy Atkinson

Broken-up Asteroids Found Orbiting White Dwarfs

Artists concept of a shredded asteroid getting too close to a star. (NASA/JPL-Caltech)

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Astronomers studying white dwarfs have found the remains of “shredded” asteroids around some of these dead stars. This finding suggests that the same materials that make up Earth and our solar system’s other rocky bodies could be common in the universe. If the materials are common, then rocky planets could be, too. “If you ground up our asteroids and rocky planets, you would get the same type of dust we are seeing in these star systems,” said Michael Jura of the University of California, Los Angeles, who presented the results today at the American Astronomical Society meeting in Long Beach, Calif. “This tells us that the stars have asteroids like ours — and therefore could also have rocky planets.” But most surprising, astronomers have been able to use the rocky debris to study the evolution of planets.

Observations with NASA’s Spitzer Space Telescope reveal six dead “white dwarf” stars littered with the remains of shredded asteroids.

Asteroids and planets form out of dusty material that swirls around young stars. The dust sticks together, forming clumps and eventually full-grown planets. Asteroids are the leftover debris. When a star like our sun nears the end of its life, it puffs up into a red giant that consumes its innermost planets, while jostling the orbits of remaining asteroids and outer planets. As the star continues to die, it blows off its outer layers and shrinks down into a skeleton of its former self — a white dwarf.

Sometimes, a jostled asteroid wanders too close to a white dwarf and meets its demise — the gravity of the white dwarf shreds the asteroid to pieces. A similar thing happened to Comet Shoemaker Levy 9 when Jupiter’s gravity tore it up, before the comet ultimately smashed into the planet in 1994.

Spitzer observed shredded asteroid pieces around white dwarfs with its infrared spectrograph, an instrument that breaks light apart into a rainbow of wavelengths, revealing imprints of chemicals.

Silicates in Alien Asteroids. Credit: NASA/JPL/Caltech

“While no one yet has the ability to directly see the smashed up debris and measure its composition, we have the tools to measure the potential capacity for planets,” said Jura at today’s press conference.

Spitzer analyzed the asteroid dust around two so-called polluted white dwarfs; the new observations bring the total to eight. Jura said only 1% of white dwarfs observed have broken up asteroids in their vicinity.

“Now, we’ve got a bigger sample of these polluted white dwarfs, so we know these types of events are not extremely rare,” said Jura.

In all eight systems observed, Spitzer found that the dust contains a glassy silicate mineral similar to olivine and commonly found on Earth. “This is one clue that the rocky material around these stars has evolved very much like our own,” said Jura.

The Spitzer data also suggest there is no carbon in the rocky debris — again like the asteroids and rocky planets in our solar system, which have relatively little carbon.

A single asteroid is thought to have broken apart within the last million years or so in each of the eight white-dwarf systems. The biggest of the bunch was once about 200 kilometers (124 miles) in diameter, a bit larger than Los Angeles County.

Jura says the real power of observing these white dwarf systems is still to come. When an asteroid “bites the dust” around a dead star, it breaks into very tiny pieces. Asteroid dust around living stars, by contrast, is made of larger particles. By continuing to use spectrographs to analyze the visible light from this fine dust, astronomers will be able to see exquisite details — including information about what elements are present and in what abundance. This will reveal much more about how other star systems sort and process their planetary materials.

“It’s as if the white dwarfs separate the dust apart for us,” said Jura.

Source: Spitzer Space Telescope, AAS Press Conference