Posted on by Nancy Atkinson

Two Views of a Lopsided Galaxy

This picture of the Meathook Galaxy (NGC 2442) was taken by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at La Silla, Chile. Credit: ESO

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From an ESO press release:

The Meathook Galaxy, or NGC 2442, has a dramatically lopsided shape. One spiral arm is tightly folded in on itself and host to a recent supernova, while the other, dotted with recent star formation, extends far out from the nucleus. The MPG/ESO 2.2-metre telescope and the NASA/ESA Hubble Space Telescope have captured two contrasting views of this asymmetric spiral galaxy.

The Meathook Galaxy, or NGC 2442, in the southern constellation of Volans (The Flying Fish), is easily recognised for its asymmetric spiral arms. The galaxy’s lopsided appearance is thought to be due to gravitational interactions with another galaxy at some point in its history — though astronomers have not so far been able to positively identify the culprit.

This broad view, taken by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at La Silla, Chile, very clearly shows the double hook shape that gives the galaxy its nickname. This image also captures several other galaxies close to NGC 2442 as well as many more remote galaxies that form a rich backdrop. Although the Wide Field Imager, on the ground, cannot approach the sharpness of images from Hubble in space, it can cover a much bigger section of sky in a single exposure. The two tools often provide complementary information to astronomers.

This close-up Hubble view of the Meathook Galaxy (NGC 2442) focuses on the more compact of its two asymmetric spiral arms as well as the central regions. The spiral arm was the location of a supernova that exploded in 1999. These observations were made in 2006 in order to study the aftermath of this supernova. Ground-based data from MPG/ESO 2.2-metre telescope were used to fill out parts of the edges of this image. Credit: NASA/ESA and ESO

A close-up image from the NASA/ESA Hubble Space Telescope (eso1115b) focuses on the galaxy’s nucleus and the more compact of its two spiral arms. In 1999, a massive star at the end of its life exploded in this arm in a supernova. By comparing older ground-based observations, previous Hubble images made in 2001, and these shots taken in late 2006, astronomers have been able to study in detail what happened to the star in its dying moments. By the time of this image the supernova itself had faded and is not visible.

ESO’s observations also highlight the other end of the life cycle of stars from Hubble. Dotted across much of the galaxy, and particularly in the longer of the two spiral arms, are patches of pink and red. This colour comes from hydrogen gas in star-forming regions: as the powerful radiation of new-born stars excites the gas in the clouds they formed from, it glows a bright shade of red.

The interaction with another galaxy that gave the Meathook Galaxy its unusual asymmetric shape is also likely to have been the trigger of this recent episode of star formation. The same tidal forces that deformed the galaxy disrupted clouds of gas and triggered their gravitational collapse.

Posted on by Nancy Atkinson

Hit and Run Asteroid Caused Scheila’s Comet-like Behavior

Faint dust plumes bookend asteroid (596) Scheila, which is overexposed in this composite. Visible and ultraviolet images from Swift's UVOT (circled) are merged with a Digital Sky Survey image of the same region. The UVOT images were acquired on Dec. 15, 2010, when the asteroid was about 232 million miles from Earth. Credit: NASA/Swift/DSS/D. Bodewits (UMD)

Asteroid or comet? That was the question astronomers were asking after an asteroid named Scheila had unexpectedly brightened, and seemingly sprouted a tail and coma. But follow-up observations by the Swift satellite and the Hubble Space Telescope show that these changes likely occurred after Scheila was struck by a much smaller asteroid.

“Collisions between asteroids create rock fragments, from fine dust to huge boulders, that impact planets and their moons,” said Dennis Bodewits, an astronomer at the University of Maryland in College Park and lead author of the Swift study. “Yet this is the first time we’ve been able to catch one just weeks after the smash-up, long before the evidence fades away.”

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On Dec. 11, 2010, images from the University of Arizona’s Catalina Sky Survey, a project of NASA’s Near Earth Object Observations Program, revealed the Scheila to be twice as bright as expected and immersed in a faint comet-like glow. Looking through the survey’s archived images, astronomers inferred the outburst began between Nov. 11 and Dec. 3.

Three days after the outburst was announced, Swift’s Ultraviolet/Optical Telescope (UVOT) captured multiple images and a spectrum of the asteroid. Ultraviolet sunlight breaks up the gas molecules surrounding comets; water, for example, is transformed into hydroxyl (OH) and hydrogen (H). But none of the emissions most commonly identified in comets — such as hydroxyl or cyanogen (CN) — showed up in the UVOT spectrum. The absence of gas around Scheila led the Swift team to reject the idea that Scheila was actually a comet and that exposed ice accounted for the brightening.

Hubble observed the asteroid’s fading dust cloud on Dec. 27, 2010, and Jan. 4, 2011. Images show the asteroid was flanked in the north by a bright dust plume and in the south by a fainter one. The dual plumes formed as small dust particles excavated by the impact were pushed away from the asteroid by sunlight.

The science teams from the two space observatories found the observations were best explained by a collision with a small asteroid impacting Scheila’s surface at an angle of less than 30 degrees, leaving a crater 1,000 feet across. Laboratory experiments show a more direct strike probably wouldn’t have produced two distinct dust plumes. The researchers estimated the crash ejected more than 660,000 tons of dust–equivalent to nearly twice the mass of the Empire State Building.

The Hubble Space Telescope imaged (596) Scheila on Dec. 27, 2010, when the asteroid was about 218 million miles away. Scheila is overexposed in this image to reveal the faint dust features. The asteroid is surrounded by a C-shaped cloud of particles and displays a linear dust tail in this visible-light picture acquired by Hubble's Wide Field Camera 3. Because Hubble tracked the asteroid during the exposure, the star images are trailed. Credit: NASA/ESA/D. Jewitt (UCLA)

“The Hubble data are most simply explained by the impact, at 11,000 mph, of a previously unknown asteroid about 100 feet in diameter,” said Hubble team leader David Jewitt at the University of California in Los Angeles. Hubble did not see any discrete collision fragments, unlike its 2009 observations of P/2010 A2, the first identified asteroid collision.

Scheila is approximately 113 km (70 miles) across and orbits the sun every five years.

“The dust cloud around Scheila could be 10,000 times as massive as the one ejected from comet 9P/Tempel 1 during NASA’s UMD-led Deep Impact mission,” said co-author Michael Kelley, also at the University of Maryland. “Collisions allow us to peek inside comets and asteroids. Ejecta kicked up by Deep Impact contained lots of ice, and the absence of ice in Scheila’s interior shows that it’s entirely unlike comets.”

The studies will appear in the May 20 edition of The Astrophysical Journal Letters.

Source: NASA Goddard

Posted on by Nancy Atkinson

Hubble Captures Ancient Beauty: M5

A new Hubble image of the Messier 5 cluster. Credit: ESA/Hubble & NASA

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This is just plain pretty. You’re looking at some of the oldest stars in the Universe. This new Hubble image of the globular cluster Messier 5 shows this giant huddle of stars, which is one of the oldest clusters in the Milky Way. Astronomers say the majority of M5’s stars formed more than 12 billion years ago. But there are some new and blue stars among the mix, adding some vitality and color to this ancient bunch.

Stars in globular clusters form in the same stellar nursery and grow old together. The most massive stars age quickly, exhausting their fuel supply in less than a million years, and end their lives in spectacular supernovae explosions. This process should have left the ancient cluster Messier 5 with only old, low-mass stars, which, as they have aged and cooled, have become red giants, while the oldest stars have evolved even further into blue horizontal branch stars.

Yet astronomers have spotted many young, blue stars in this cluster, hiding among the much more luminous ancient stars. Astronomers think that these laggard youngsters, called blue stragglers, were created either by stellar collisions or by the transfer of mass between binary stars. Such events are easy to imagine in densely populated globular clusters, in which up to a few million stars are tightly packed together.

Messier 5 lies at a distance of about 25 000 light-years in the constellation of Serpens (The Snake). This image was taken with Wide Field Channel of Hubble’s Advanced Camera for Surveys.

Source: ESA’s Hubble website.

Posted on by Nancy Atkinson

Hubble Comes of Age With Dramatic New Image

In celebration of the 21st anniversary of the Hubble Space Telescope’s deployment into space, astronomers pointed Hubble at Arp 273. Credit: NASA, ESA and the Hubble Heritage Team (STScI/AURA

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Hubble has now turned 21, and unlike human young adults, we don’t have to worry about it staying up all night carousing at orbital drinking establishments. Instead the space telescope celebrates by doing what is has done best the past two decades, taking a marvelous image. This dramatic look at Arp 273 shows the very photogenic group of interacting galaxies that glow bright with intense star formation, perhaps triggered by a little carousing the two galaxies are doing with each other as they approach and interact.

Arp 273 lies in the constellation Andromeda and is roughly 300 million light-years away from Earth. The image shows a tenuous tidal bridge of material between the two galaxies that are actually separated by tens of thousands of light-years from each other. But still, the gravitational pull between the two is causing distortions: visible in the larger of the spiral galaxies, known as UGC 1810, is a distorted disc. The swathe of blue stars across the top is the combined light from clusters of intensely bright and hot young stars.

These massive stars glow fiercely in ultraviolet light. A series of uncommon spiral patterns in the large galaxy are a telltale sign of interaction, say the Hubble astronomers. The large, outer arm appears partially as a ring, a feature that is seen when interacting galaxies actually pass through one another, so astronomers believe the smaller companion actually dived deeply, but off-center, through UGC 1810.

The smaller, nearly edge-on companion below is known as UGC 1813. It also shows distinct signs of intense star formation at its nucleus.

The larger galaxy has a mass that is about five times that of the smaller galaxy. In unequal pairs such as this, the relatively rapid passage of a companion galaxy produces the lopsided or asymmetric structure in the main spiral. Also in such encounters, the starburst activity typically begins earlier in the minor galaxy than in the major galaxy. These effects could be due to the fact that the smaller galaxies have consumed less of the gas present in their nucleus, from which new stars are born.

The image was taken on December 17, 2010, with Hubble’s Wide Field Camera 3 (WFC3).

Happy Birthday Hubble! (and many more…)

See more information on this image at ESA’s Hubble website, or NASA’s HubbleSite

Posted on by Nancy Atkinson

A Twisted Sister Galaxy

Galaxy ESO 510-G13. Credit: NASA/ESA and The Hubble Heritage Team STScI/AURA

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This is an older image from Hubble but I came across it today and wanted to share it. It shows an unusual edge-on galaxy, that has been twisted by a recent collision with a nearby galaxy, and is in the process of being swallowed up. This could be a spiral sister to our own Milky Way, as the dust and arms of normal spiral galaxies appear flat when viewed edge-on. And the twisting effect could be an example of what could happen to our galaxy in about 3 billion years when it begins to collide with the Andromeda galaxy.


As the gravitational forces distort the structures of the galaxies as their stars, gas, and dust merge together, it also sparks star formation. In the outer regions of ESO 510-G13, especially on the right-hand side of the image, the twisted disk contains not only dark dust, but also bright clouds of new, blue stars.
Eventually, in millions of years, all the matter will coalesce and the activity and disturbances will die out, and ESO 510-G13 will become a normal-looking single galaxy.

This galaxy was first observed by ESO’s ground based telescopes, and Hubble’s Wide Field Planetary Camera 2 (WFPC2) observed ESO 510-G13 in April 2001.

See more about the image at the HubbleSite.

Posted on by Nancy Atkinson

Space Telescopes Observe Unprecedented Explosion

mages from Swift's Ultraviolet/Optical (white, purple) and X-ray telescopes (yellow and red) were combined in this view of GRB 110328A. The blast was detected only in X-rays, which were collected over a 3.4-hour period on March 28. Credit: NASA/Swift/Stefan Immler

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From a NASA press release:

NASA’s Swift, Hubble Space Telescope and Chandra X-ray Observatory have teamed up to study one of the most puzzling cosmic blasts yet observed. More than a week later, high-energy radiation continues to brighten and fade from its location.

Astronomers say they have never seen anything this bright, long-lasting and variable before. Usually, gamma-ray bursts mark the destruction of a massive star, but flaring emission from these events never lasts more than a few hours.

Although research is ongoing, astronomers say that the unusual blast likely arose when a star wandered too close to its galaxy’s central black hole. Intense tidal forces tore the star apart, and the infalling gas continues to stream toward the hole. According to this model, the spinning black hole formed an outflowing jet along its rotational axis. A powerful blast of X- and gamma rays is seen if this jet is pointed in our direction.

On March 28, Swift’s Burst Alert Telescope discovered the source in the constellation Draco when it erupted with the first in a series of powerful X-ray blasts. The satellite determined a position for the explosion, now cataloged as gamma-ray burst (GRB) 110328A, and informed astronomers worldwide.

This is a visible-light image of GRB 110328A's host galaxy (arrow) taken on April 4 by the Hubble Space Telescope's Wide Field Camera 3. The galaxy is 3.8 billion light-years away. Credit: NASA/ESA/A. Fruchter (STScI)

As dozens of telescopes turned to study the spot, astronomers quickly noticed that a small, distant galaxy appeared very near the Swift position. A deep image taken by Hubble on April 4 pinpoints the source of the explosion at the center of this galaxy, which lies 3.8 billion light-years away.

That same day, astronomers used NASA’s Chandra X-ray Observatory to make a four-hour-long exposure of the puzzling source. The image, which locates the object 10 times more precisely than Swift can, shows that it lies at the center of the galaxy Hubble imaged.

“We know of objects in our own galaxy that can produce repeated bursts, but they are thousands to millions of times less powerful than the bursts we are seeing now. This is truly extraordinary,” said Andrew Fruchter at the Space Telescope Science Institute in Baltimore.

NASA's Chandra X-ray Observatory completed this four-hour exposure of GRB 110328A on April 4. The center of the X-ray source corresponds to the very center of the host galaxy imaged by Hubble (red cross). Credit: NASA/CXC/ Warwick/A. Levan

“We have been eagerly awaiting the Hubble observation,” said Neil Gehrels, the lead scientist for Swift at NASA’s Goddard Space Flight Center in Greenbelt, Md. “The fact that the explosion occurred in the center of a galaxy tells us it is most likely associated with a massive black hole. This solves a key question about the mysterious event.”

Most galaxies, including our own, contain central black holes with millions of times the sun’s mass; those in the largest galaxies can be a thousand times larger. The disrupted star probably succumbed to a black hole less massive than the Milky Way’s, which has a mass four million times that of our sun

Astronomers previously have detected stars disrupted by supermassive black holes, but none have shown the X-ray brightness and variability seen in GRB 110328A. The source has repeatedly flared. Since April 3, for example, it has brightened by more than five times.

Scientists think that the X-rays may be coming from matter moving near the speed of light in a particle jet that forms as the star’s gas falls toward the black hole.

“The best explanation at the moment is that we happen to be looking down the barrel of this jet,” said Andrew Levan at the University of Warwick in the United Kingdom, who led the Chandra observations. “When we look straight down these jets, a brightness boost lets us view details we might otherwise miss.”

This brightness increase, which is called relativistic beaming, occurs when matter moving close to the speed of light is viewed nearly head on.

Astronomers plan additional Hubble observations to see if the galaxy’s core changes brightness.

For more information see this NASA press release.

Posted on by Nancy Atkinson

Contest: Win IMAX Hubble DVD

When I saw the IMAX Hubble movie last year when it was released in theaters, it’s portrayal of the immensity and gloriousness of our universe literally brought me to tears (read my review here) Now you can have a copy of your very own IMAX Hubble, as it was just released on DVD. And Universe Today has 5 copies to give away, courtesy of Warner Brothers! Just send an email to info@universetoday with “IMAX Hubble” in the subject line for your chance to win. Contest ends on Monday, April 4, 2011 at 1500 GMT.

See the original movie trailer, below.
Continue reading “Contest: Win IMAX Hubble DVD”

Posted on by Nancy Atkinson

Hubble Rules Out One Alternative to Dark Energy

NGC 5584. Credit: NASA, ESA, A. Riess (STScI/JHU), L. Macri (Texas A&M University), and Hubble Heritage Team (STScI/AURA)

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From a NASA press release:

Astronomers using NASA’s Hubble Space Telescope have ruled out an alternate theory on the nature of dark energy after recalculating the expansion rate of the universe to unprecedented accuracy.

The universe appears to be expanding at an increasing rate. Some believe that is because the universe is filled with a dark energy that works in the opposite way of gravity. One alternative to that hypothesis is that an enormous bubble of relatively empty space eight billion light-years across surrounds our galactic neighborhood. If we lived near the center of this void, observations of galaxies being pushed away from each other at accelerating speeds would be an illusion.

This hypothesis has been invalidated because astronomers have refined their understanding of the universe’s present expansion rate. Adam Riess of the Space Telescope Science Institute (STScI) and Johns Hopkins University in Baltimore, Md., led the research. The Hubble observations were conducted by the SHOES (Supernova H0 for the Equation of State) team that works to refine the accuracy of the Hubble constant to a precision that allows for a better characterization of dark energy’s behavior. The observations helped determine a figure for the universe’s current expansion rate to an uncertainty of just 3.3 percent. The new measurement reduces the error margin by 30 percent over Hubble’s previous best measurement in 2009. Riess’s results appear in the April 1 issue of The Astrophysical Journal.

“We are using the new camera on Hubble like a policeman’s radar gun to catch the universe speeding,” Riess said. “It looks more like it’s dark energy that’s pressing the gas pedal.”

Riess’ team first had to determine accurate distances to galaxies near and far from Earth. The team compared those distances with the speed at which the galaxies are apparently receding because of the expansion of space. They used those two values to calculate the Hubble constant, the number that relates the speed at which a galaxy appears to recede to its distance from the Milky Way. Because astronomers cannot physically measure the distances to galaxies, researchers had to find stars or other objects that serve as reliable cosmic yardsticks. These are objects with an intrinsic brightness, brightness that hasn’t been dimmed by distance, an atmosphere, or stellar dust, that is known. Their distances, therefore, can be inferred by comparing their true brightness with their apparent brightness as seen from Earth.

To calculate longer distances, Riess’ team chose a special class of exploding stars called Type 1a supernovae. These stellar explosions all flare with similar luminosity and are brilliant enough to be seen far across the universe. By comparing the apparent brightness of Type 1a supernovae and pulsating Cepheid stars, the astronomers could measure accurately their intrinsic brightness and therefore calculate distances to Type Ia supernovae in far-flung galaxies.

Using the sharpness of the new Wide Field Camera 3 (WFC3) to study more stars in visible and near-infrared light, scientists eliminated systematic errors introduced by comparing measurements from different telescopes.

“WFC3 is the best camera ever flown on Hubble for making these measurements, improving the precision of prior measurements in a small fraction of the time it previously took,” said Lucas Macri, a collaborator on the SHOES Team from Texas A&M in College Station.

Knowing the precise value of the universe’s expansion rate further restricts the range of dark energy’s strength and helps astronomers tighten up their estimates of other cosmic properties, including the universe’s shape and its roster of neutrinos, or ghostly particles, that filled the early universe.

“Thomas Edison once said ‘every wrong attempt discarded is a step forward,’ and this principle still governs how scientists approach the mysteries of the cosmos,” said Jon Morse, astrophysics division director at NASA Headquarters in Washington. “By falsifying the bubble hypothesis of the accelerating expansion, NASA missions like Hubble bring us closer to the ultimate goal of understanding this remarkable property of our universe.”

Science Paper by: Adam G. Riess et al. (PDF document)

Posted on by Nancy Atkinson

Hubble Captures the “V”

Hubble's latest view of the very unusual Westbrook Nebula. Credit: NASA/ESA

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Looking oddly reminiscent of the “V” depicted in the logo for the sci-fi television series “V,” this has to be one of the strangest objects in space. It’s the Westbrook Nebula — also known as PK166-06, CRL 618 and AFGL 618 — and is a protoplanetary nebula. But this highly irregular bundle of disconnected jets and clouds is the result of a burst of a dying star expelling toxic gases such as carbon monoxide and hydrogen cyanide. Well, toxic to us, anyway, but maybe not to The Visitors!

There are only a few hundred protoplanetary nebulae known in the Milky Way. The appear during a star’s rapid stellar evolution between the late asymptotic giant branch phase and the subsequent planetary nebula phase.

But these short-lived clouds of gas are faint and very hard to see. They emit strong in infrared radiation, and are cool in temperature, so they emit small amounts of visible light. So, astronomers have a few tricks up their telescopic sleeves to try and get images of protoplanetary nebula, and the results are well worth it, as this image demonstrates.

This is a composite image where the astronomers have used exposures in visible light which shows light reflected from the cloud of gas, combined with other exposures in the near-infrared part of the spectrum, showing the dim glow, invisible to human eyes, that is coming from different elements deep in the cloud itself, so this is a kind of reflection nebula.

(See the “Light Echoes” podcast by Astronomy Cast for more information on reflected light.)

Hubble has taken images of the Westbrook Nebula before, but this new one is clearly sharper and provides more detail. See more info on what techniques were used at the Hubble ESA website.

Posted on by Nancy Atkinson

Hollywood-like Galactic Encounter Results in Baby Stars

Images of the core of NGC 4150, taken in near-ultraviolet light with the sharp-eyed Wide Field Camera 3 (WFC3). Credit: NASA, ESA, R.M. Crockett (University of Oxford, U.K.), S. Kaviraj (Imperial College London and University of Oxford, U.K.), J. Silk (University of Oxford), M. Mutchler (Space Telescope Science Institute, Baltimore), R. O'Connell (University of Virginia, Charlottesville), and the WFC3 Scientific Oversight Committee

Like news ripped from a Hollywood tabloid, this saga includes an encounter between two individuals; one aging, and thought to be past its prime, the other youthful and vigorous. And for good measure, thrown in on this story are cannibalism and even zombies. The result of the meet-up? Babies. Baby stars, that is, and the individual galaxies in this tale ended up, seemingly, living together happily-ever-after. The Hubble Space Telescope’s Wide Field Camera 3 (WFC3) captured images of NGC 4150, an aging elliptical galaxy, and at the core of the galaxy was some vigorous star birth. The star-making days of this galaxy should have ended long ago, but here was active star birth taking place. This isn’t the first time astronomers have seen something like this, so they took a closer look.
Continue reading “Hollywood-like Galactic Encounter Results in Baby Stars”