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”

Posted on by Nancy Atkinson

Hubble Provides Most Detailed Dark Matter Map Yet

Cosmic Noise
This NASA Hubble Space Telescope image shows the distribution of dark matter in the center of the giant galaxy cluster Abell 1689, containing about 1,000 galaxies and trillions of stars. Credit: NASA, ESA, D. Coe (NASA Jet Propulsion Laboratory/California Institute of Technology, and Space Telescope Science Institute), N. Benitez (Institute of Astrophysics of Andalusia, Spain), T. Broadhurst (University of the Basque Country, Spain), and H. Ford (Johns Hopkins University)

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Using Hubble’s Advanced Camera for Surveys, astronomers have been able to chart invisible dark matter in a distant galaxy, which enabled them to create one of the sharpest and most detailed maps of dark matter in the universe. Looking for invisible and indeterminate matter is a difficult job, but one that astronomers have been trying to do for over a decade. This new map also might provide clues on that other mysterious stuff in the universe — dark energy – and what role it played in the universe’s early formative years.

A team led by Dan Coe at JPL used Hubble to look at Abell 1689, located 2.2 billion light-years away. The cluster’s gravity, which mostly comes from dark matter, acts like a cosmic magnifying glass, bending and amplifying the light from distant galaxies behind it. This effect, called gravitational lensing, produces multiple, warped, and greatly magnified images of those galaxies, making the galaxies look distorted and fuzzy. By studying the distorted images, astronomers estimated the amount of dark matter within the cluster. If the cluster’s gravity only came from the visible galaxies, the lensing distortions would be much weaker.

What they found suggests that galaxy clusters may have formed earlier than expected, before the push of dark energy inhibited their growth.

Dark energy pushes galaxies apart from one another by stretching the space between them, thereby suppressing the formation of giant structures called galaxy clusters. One way astronomers can probe this primeval tug-of-war is through mapping the distribution of dark matter in clusters.

“The lensed images are like a big puzzle,” Coe said. “Here we have figured out, for the first time, a way to arrange the mass of Abell 1689 such that it lenses all of these background galaxies to their observed positions.” Coe used this information to produce a higher-resolution map of the cluster’s dark matter distribution than was possible before.

Based on their higher-resolution mass map, Coe and his collaborators confirm previous results showing that the core of Abell 1689 is much denser in dark matter than expected for a cluster of its size, based on computer simulations of structure growth. Abell 1689 joins a handful of other well-studied clusters found to have similarly dense cores. The finding is surprising, because the push of dark energy early in the universe’s history would have stunted the growth of all galaxy clusters.

“Galaxy clusters, therefore, would had to have started forming billions of years earlier in order to build up to the numbers we see today,” Coe said. “At earlier times, the universe was smaller and more densely packed with dark matter. Abell 1689 appears to have been well fed at birth by the dense matter surrounding it in the early universe. The cluster has carried this bulk with it through its adult life to appear as we observe it today.”

Astronomers are planning to study more clusters to confirm the possible influence of dark energy. A major Hubble program that will analyze dark matter in gigantic galaxy clusters is the Cluster Lensing and Supernova survey with Hubble (CLASH). In this survey, the telescope will study 25 clusters for a total of one month over the next three years. The CLASH clusters were selected because of their strong X-ray emission, indicating they contain large quantities of hot gas. This abundance means the clusters are extremely massive. By observing these clusters, astronomers will map the dark matter distributions and look for more conclusive evidence of early cluster formation, and possibly early dark energy.

For more information see the HubbleSite.

Posted on by Nancy Atkinson

VLT, Hubble Smash Record for Eyeing Most Distant Galaxy

Planck Time
The Universe. So far, no duplicates found@

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Using the Hubble Space Telescope and the Very Large Telescope (VLT), astronomers have looked back to find the most distant galaxy so far. “We are observing a galaxy that existed essentially when the Universe was only about 600 million years old, and we are looking at this galaxy – and the Universe – 13.1 billion years ago,” said Dr. Matt Lehnert from the Observatoire de Paris, who is the lead author of a new paper in Nature. “Conditions were quite different back then. The basic picture in which this discovery is embedded is that this is the epoch in which the Universe went from largely neutral to basically ionized.”

Lehnert and an international team used the VLT to make follow-up observations of the galaxy — called UDFy-38135539 – which Hubble observations in 2009 had revealed. The astronomers analyzed the very faint glow of the galaxy to measure its distance — and age. This is the first confirmed observations of a galaxy whose light is emerging from the reionization of the Universe.

The reionization period is about the farthest back in time that astronomers can observe. The Big Bang, 13.7 billion years ago, created a hot, murky universe. Some 400,000 years later, temperatures cooled, electrons and protons joined to form neutral hydrogen, and the murk cleared. Some time before 1 billion years after the Big Bang, neutral hydrogen began to form stars in the first galaxies, which radiated energy and changed the hydrogen back to being ionized. Although not the thick plasma soup of the earlier period just after the Big Bang, this galaxy formation started the reionization epoch, clearing the opaque hydrogen fog that filled the cosmos at this early time.

A simulation of galaxies during the era of deionization in the early Universe. Credit: M. Alvarez, R. Kaehler, and T. Abel

“The whole history of the Universe is from the reionization,” Lehnert said during an online press briefing. “The dark matter that pervades the Universe began to drag the gas along and formed the first galaxies. When the galaxies began to form, it reionized the Universe.”

UDFy-38135539 is about 100 million light-years farther than the previous most distant object, a gamma-ray burst.

Studying these first galaxies is extremely difficult, Lehnert said, as the dim light falls mostly in the infrared part of the spectrum because its wavelength has been stretched by the expansion of the Universe — an effect known as redshift. During the time of less than a billion years after the Big Bang, the hydrogen fog that pervaded the Universe absorbed the fierce ultraviolet light from young galaxies.

The new Wide Field Camera 3 on the NASA/ESA Hubble Space Telescope discovered several candidate objects in 2009, and with 16 hours of observations using the VLT, the team was able to was used to detect the very faint glow from hydrogen at a redshift of 8.6.

The team used the SINFONI infrared spectroscopic instrument on the VLT and a very long exposure time.

“Measuring the redshift of the most distant galaxy so far is very exciting in itself,” said co-author Nicole Nesvadba (Institut d’Astrophysique Spatiale), “but the astrophysical implications of this detection are even more important. This is the first time we know for sure that we are looking at one of the galaxies that cleared out the fog which had filled the very early Universe.”

One of the surprising things about this discovery is that the glow from UDFy-38135539 seems not to be strong enough on its own to clear out the hydrogen fog. “There must be other galaxies, probably fainter and less massive nearby companions of UDFy-38135539,” said co-author Mark Swinbank from Durham University, “which also helped make the space around the galaxy transparent. Without this additional help the light from the galaxy, no matter how brilliant, would have been trapped in the surrounding hydrogen fog and we would not have been able to detect it.”

Sources: ESO, press briefing

Posted on by Nancy Atkinson

Hubble Spins the Wheel on Star Birth

Galaxies
Spiral galaxy NGC 3982. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

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Galaxies are like snowflakes, with no two looking exactly the same. The latest image released from the Hubble Space Telescope shows a striking face-on spiral galaxy named NGC 3982, which is a swirl of activity and star birth along with its winding arms. The arms are lined with pink star-forming regions of glowing hydrogen, newborn blue star clusters, and obscuring dust lanes that provide the raw material for future generations of stars. The bright nucleus is home to an older population of stars, which grow ever more densely packed toward the center.

NGC 3982 is located about 68 million light-years away in the constellation Ursa Major. The galaxy spans about 30,000 light-years, one-third of the size of our Milky Way galaxy. This color image is composed of exposures taken by three different instruments, taken over a substantial portion of the space telescope’s life, from March 2000 and August 2009: The Wide Field Planetary Camera 2 (WFPC2), the Advanced Camera for Surveys (ACS), and the Wide Field Camera 3 (WFC3). The observations were taken between The rich color range comes from the fact that the galaxy was photographed in visible and near-infrared light. Also used was a filter that isolates hydrogen emission that emanates from bright star-forming regions dotting the spiral arms.

Source: HubbleSite

Posted on by Nicholos Wethington

Hubble Sees Asteroid Collision in Slow-Motion

The collision between two asteroids in early 2009 produced a strange, X-shaped aftermath. Image Credit: NASA, ESA and D. Jewitt (UCLA)

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Alas, the image above is not marking alien pirate treasure in space – for the first time, the aftermath of a collision between two asteroids has been imaged. Last January, an international team of astronomers saw the strange X-shaped object with the Hubble Space Telescope after ground-based observatories spotted evidence of an asteroid collision in the asteroid belt. The team has now used Hubble to do follow-up observations and uncovered a few surprises about the collision.

The collision produced an X shape, followed by a long comet-like tail. The astronomers, led by David Jewitt of the University of California in Los Angeles, were surprised to find that the collision did not happen as recently as they’d thought, but had actually occurred almost a year previous to the detection. It’s likely that the two asteroids smashed together sometime in February or March of 2009.

“When I saw the Hubbble image I knew it was something special,” said ESA astronomer Jessica Agarwal in a press release.

Named P/2010 A2, the object is located in the asteroid belt between Mars and Jupiter. Asteroid collisions are thought to be a commonplace occurrence, and are responsible for kicking up dust in our Solar System and other planetary systems. Just how much dust is produced, and how frequent the collisions happen is still a hazy topic, and the recent observation of P/2010 A2 should help astronomers to better model this phenomenon.

By figuring out how much dust is produced by the process of ‘collisional grinding’, astronomers could better model the dusty debris disks of other planetary systems, as well as our own.

The team monitored the slow-motion expansion of the leftovers of the colliding asteroids with the Hubble Space Telescope between January and May of 2010. They’ve determined that P/2010 A2 is about 120 meters (393 feet) wide, and the particles of dust that make up the tail following it are between 1 millimeter (0.04 inches) to 2.5 centimeters (1 inch) in diameter.

The collision producing the object P/2010 A2, as observed over the course of a few months by Hubble. Image Credit: NASA, ESA and D. Jewitt (UCLA)

The remnants of the collision suggest that a smaller asteroid – 3 to 5 meters (10-16 feet) wide – collided into a larger one at about 18,000 km per hour (11,000 miles per hour). This vaporized the smaller asteroid, and ejected material from the larger one.

Why is the object X-shaped? That mystery has yet to be determined. It is likely, according to the team, that the filaments produced by the collision suggest asymmetries in the colliding objects. Further observations of P/2010 A2 with the Hubble in 2011 will show just how the collision continues to change, allowing for a more precise model of how it started out.

The observed tail is caused by the same mechanism that produces cometary tails – radiation pressure from the Sun pushes the dust away from the nucleus of the object.

As to why we don’t have thousands of Hubble images to produce a whole alphabet of asteroid collisions shapes – “Catching colliding asteroids on camera is difficult because large impacts are rare, while small ones, such as the one that produced P/2010 A2, are exceedingly faint,” Jewitt said. The results of their observations will be published in the October 14th issue of the journal Nature.

Source: ESA Press Release

Posted on by Nancy Atkinson

Hubble: Helium Reionization Was a Hot Time in the Ol’ Universe

A diagram of the evolution of the universe from the big bang to the present, with two epochs of reionization. Credit: NASA, ESA, and A. Feild (STScI)

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Using Hubble’s newest tool, the Cosmic Origins Spectrograph (COS), researchers have nailed down and enhanced our understanding of the reionization of helium in the early Universe, clarifying the time frame of 11.7 to 11.3 billion years ago when the universe stripped electrons off from primeval helium atoms. Hubble scientists say it was the equivalent of global warming, except that a heat wave blasted through the entire early universe at that time, inhibiting the growth of small galaxies for almost 500 million years.

The universe went through an initial heat wave over 13 billion years ago when energy from early massive stars ionized cold interstellar hydrogen from the Big Bang. This epoch is actually called reionization because the hydrogen nuclei were originally in an ionized state shortly after the Universe’s beginnings.

It took another 2 billion years before the universe produced sources of ultraviolet radiation with enough energy to reionize the helium produced in the Big Bang, which heated intergalactic gas and inhibited it from gravitationally collapsing to form new generations of stars in some small galaxies. The lowest-mass galaxies were not even able to hold onto their gas, and it escaped back into intergalactic space.

This radiation didn’t come from stars, but rather from quasars, the brilliant cores of active galaxies. In fact the epoch when the helium was being reionized corresponds to a transitory time in the universe’s history when quasars were most abundant.

his ultraviolet-light data from the Hubble Space Telescope's Cosmic Origins Spectrograph shows strong helium II absorption and transmission lines from a quasar, identifying an era 11.7 to 11.3 billion years ago when electrons were stripped from primeval helium atoms — a process called reionization. Credit: Shull et al.,

Michael Shull of the University of Colorado and his team were able to find the telltale helium spectral absorption lines in the ultraviolet light from a quasar. The quasar beacon shines light through intervening clouds of otherwise invisible gas, like a headlight shining through a fog. The beam allows for a core-sample probe of the clouds of gas interspersed between galaxies in the early universe.

It was a raucous time. Galaxies frequently collided, and this engorged supermassive black holes in the cores of galaxies with infalling gas. The black holes furiously converted some of the gravitational energy of this mass to powerful far-ultraviolet radiation that would blaze out of galaxies. This heated the intergalactic helium from 18,000 degrees Fahrenheit to nearly 40,000 degrees. After the helium was reionized in the universe, intergalactic gas again cooled down and dwarf galaxies could resume normal assembly.

“I imagine quite a few more dwarf galaxies may have formed if helium reionization had not taken place,” said Shull.

So far Shull and his team only have one sightline to measure the helium transition, but the COS science team plans to use Hubble to look in other directions to see if the helium reionization uniformly took place across the universe.

The science team’s results will be published in the October 20 issue of The Astrophysical Journal.

Source: HubbleSite