Posted on by Nancy Atkinson

Starbursts from Dwarf Galaxies Like Fireworks

These images, taken by NASA's Hubble Space Telescope, show myriad stars residing in the central regions of the three dwarf galaxies NGC 4163, NGC 4068, and IC 4662. Credit: NASA, ESA, K. McQuinn (University of Minnesota, Minneapolis), and I. Karachentsev (Special Astrophysical Observatory of the Russian Academy of Sciences, Russia)

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Fireworks in space? Astronomers are comparing “starbursts” from a galaxy that is in the throes of star formation to a Fourth of July fireworks display. And three particular galaxies are like my children’s favorite part of a fireworks display: the grand finale. These bursts occur at a fast and furious pace, lighting up a region for a short time before winking out. But that’s only part of the story. Archived data from the Hubble Space Telescope are showing that starbursts — intense regions of star formation — sweep across the whole galaxy and last 100 times longer than astronomers thought. The longer duration may affect how dwarf galaxies change over time, and therefore may shed light on galaxy evolution.

A group of astronomers studied three dwarf galaxies, NGC 4163, NGC 4068, and IC 4662. Their distances range from 8 million to 14 million light-years away. The trio is part of a survey of starbursts in 18 nearby dwarf galaxies.

“Our analysis shows that starburst activity in a dwarf galaxy happens on a global scale,” explains Kristen McQuinn of the University of Minnesota in Minneapolis and leader of the study. “There are pockets of intense star formation that propagate throughout the galaxy, like a string of firecrackers going off.” According to McQuinn, the duration of all the starburst events in a single dwarf galaxy would total 200 million to 400 million years.

These longer timescales are vastly more than the 5 million to 10 million years proposed by astronomers who have studied star formation in dwarf galaxies. “They were only looking at individual clusters and not the whole galaxy, so they assumed starbursts in galaxies lasted for a short time,” McQuinn says.

Hubble ACS image of NGC 4163. Click for larger version.
Hubble ACS image of NGC 4163. Click for larger version.

Dwarf galaxies are considered by many astronomers to be the building blocks of the large galaxies seen today, so the length of starbursts is important for understanding how galaxies evolve.

“Astronomers are really interested to find out the steps of galaxy evolution,” McQuinn says. “Exploring these smaller galaxies is important because, according to popular theory, large galaxies are created from the merger of smaller, dwarf galaxies. So understanding these smaller pieces is an important part of filling in that scenario.”

With the high resolution Hubble data, McQuinn and her team were able to pick out individual stars in the galaxies and measure their brightness and color, two important characteristics astronomers use to determine stellar ages. By determining the ages of the stars, the astronomers could reconstruct the starburst history in each galaxy.

Two of the galaxies, NGC 4068 and IC 4662, show active, brilliant starburst regions in the Hubble images. The most recent starburst in the third galaxy, NGC 4163, occurred 200 million years ago and has faded from view.

The team looked at regions of high and low densities of stars, piecing together a picture of the starbursts. The galaxies were making a few stars, when something, perhaps an encounter with another galaxy, pushed them into high star-making mode. Instead of forming eight stars every thousand years, the galaxies started making 40 stars every thousand years, which is a lot for a small galaxy, McQuinn says. The typical dwarf is 10,000 to 30,000 light-years wide. By comparison, a normal-sized galaxy such as our Milky Way is about 100,000 light-years wide.

About 300 million to 400 million years ago star formation occurred in the outer areas of the galaxies. Then it began migrating inward as explosions of massive stars triggered new star formation in adjoining regions. Starbursts are still occurring in the inner parts of NGC 4068 and IC 4662.

The total duration of starburst activity depends on many factors, including the amount of gas in a galaxy, the distribution and density of the gas, and the event that triggered the starburst. A merger or an interaction with a large galaxy, for example, could create a longer starburst event than an interaction with a smaller system.

McQuinn plans to expand her study to another larger sample of more than 20 galaxies. “Studying nearby dwarf galaxies, where we can see the stars in great detail, will help us interpret observations of galaxies in the distant universe, where starbursts were much more common because galaxies had more gas with which to make stars,” McQuinn explains.

McQuinn’s results appeared in the April 10 issue of The Astrophysical Journal.

Source: HubbleSite

Posted on by Nancy Atkinson

New Hubble Survey Supports Cold Dark Matter in Early Universe

NICMOS Image of the GOODS North field. Credit: C Conselice, A Bluck, GOODS NICMOS Team.

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A new survey is revealing how the most massive galaxies formed in the early Universe, and the findings support the theory that Cold Dark Matter played a role. A team of scientists from six countries used the NICMOS near infrared camera on the Hubble Space Telescope to carry out the deepest ever survey of its type at near infrared wavelengths. Early results show that the most massive galaxies, which have masses roughly 10 times larger than the Milky Way, were involved in significant levels of galaxy mergers and interactions when the Universe was just 2-3 billion years old.

“As almost all of these massive galaxies are invisible in the optical wavelengths, this is the first time that most of them have been observed,” said Dr. Chris Conselice, who is the Principal Investigator for the survey. “To assess the level of interaction and mergers between the massive galaxies, we searched for galaxies in pairs, close enough to each other to merge within a given time-scale. While the galaxies are very massive and at first sight may appear fully formed, the results show that they have experienced an average of two significant merging events during their life-times.”

The results show that these galaxies did not form in a simple collapse in the early universe, but that their formation is more gradual over the course of the Universe’s evolution, taking about 5 billion years.

NICMOS image of merging galaxies. Credit: C Conselice, A Bluck, GOODS NICMOS Team
NICMOS image of merging galaxies. Credit: C Conselice, A Bluck, GOODS NICMOS Team

“The findings support a basic prediction of the dominant model of the Universe, known as Cold Dark Matter,” said Conselice, “so they reveal not only how the most massive galaxies are forming, but also that the model that’s been developed to describe the Universe, based on the distribution of galaxies that we’ve observed overall, applies in its basic form to galaxy formation.”

The Cold Dark Matter theory is a refinement of the Big Bang theory, which includes the assumption that most of the matter in the Universe consists of material that cannot be observed by its electromagnetic radiation and hence is dark matter, while at the same time the particles making up this matter are slow and are thereforer cold.

The preliminary results are based on a paper led by PhD student Asa Bluck at the University of Nottingham, and were presented this week at the European Week of Astronomy and Space Science at the University of Hertfordshire.

The observations are part of the Great Observatories Origins Deep Survey (GOODS), a campaign that is using NASA’s Spitzer, Hubble and Chandra space telescopes together with ESA’s XMM Newton X-ray observatory to study the most distant Universe.

Source: RAS

Posted on by Nancy Atkinson

New Image of Jet-Driven Galactic Shock Wave is a Shocker

The image shows in red the X-ray emission produced by high-energy particles accelerated at the shock front where Centaurus A's expanding radio lobe (shown in blue) collides with the surrounding galaxy. (In the top-left corner X-ray emission from close to the central black hole, and from the X-ray jet extending in the opposite direction can also be seen.) Credit: NASA

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The Chandra X-ray observatory has taken a closer look at the galaxy Centaurus A, and new images have revealed in detail the effects of a shock wave blasting through the galaxy. Powerful jets of plasma emanating from a supermassive black hole at the galactic core are creating the shock wave, and the new observation, have enabled astronomers to revise dramatically their picture of how jets affect the galaxies in which they live.

A team led by Dr. Judith Croston from the University of Hertfordshire and Dr. Ralph Kraft, of the Harvard-Smithsonian Center for Astrophysics used very deep X-ray observations from Chandra to get a new view of the jets in Centaurus A. The jets inflate large bubbles filled with energetic particles, driving a shock wave through the stars and gas of the surrounding galaxy. By analyzing in detail the X-ray emission produced where the supersonically expanding bubble collides with the surrounding galaxy, the team were able to show for the first time that particles are being accelerated to very high energies at the shock front, causing them to produce intense X-ray and gamma-ray radiation. Very high-energy gamma-ray radiation was recently detected from Centaurus A for the first time by another team of researchers using the High Energy Stereoscopic System (HESS) telescope in Namibia.

“Although we expect that galaxies with these shock waves are common in the Universe, Centaurus A is the only one close enough to study in such detail,” said Croston. “By understanding the impact that the jet has on the galaxy, its gas and stars, we can hope to understand how important the shock waves are for the life cycles of other, more distant galaxies.”

Centaurus A (NGC 5128) is one of our closest galactic neighbors, and is located in the southern constellation of Centaurus. The supermassive black hole is the source of strong radio and X-ray emissions. Visible in the image below, (click here for a zoomable image from Chandra) a combined image from Chandra and the Atacama Pathfinder Experiment (APEX) telescope in Chile, is a dust ring encircling the giant galaxy, and the fast-moving radio jets ejected from the galaxy center.

Centaurus A. Credit: ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray)
Centaurus A. Credit: ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray)

The powerful jets are found in only a small fraction of galaxies but are most common in the largest galaxies, which are thought to have the biggest black holes. The jets are believed to be produced near to a central supermassive black hole, and travel close to the speed of light for distances of up to hundreds of thousands of light years. Recent progress in understanding how galaxies evolve suggests that these jet-driven bubbles, called radio lobes, may play an important part in the life cycle of the largest galaxies in the Universe.

Energetic particles from radio galaxies may also reach us directly as cosmic rays hitting the Earth’s atmosphere. Centaurus A is thought to produce many of the highest energy cosmic rays that arrive at the Earth. The team believes that their results are important for understanding how such high-energy particles are produced in galaxies as well as for understanding how massive galaxies evolve.

The results of this research will be published in a forthcoming issue of the Monthly Notices of the Royal Astronomical Society and were presented at the European Week of Astronomy and Space Science in the UK.

Source: RAS

Posted on by Nancy Atkinson

Oldest and Most Distant Water in the Universe Detected

The image is made from HST data and shows the four lensed images of the dusty red quasar, connected by a gravitational arc of the quasar host galaxy. The lensing galaxy is seen in the centre, between the four lensed images. Credit: John McKean/HST Archive data

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Astronomers have found the most distant signs of water in the Universe to date. The water vapor is thought to be contained in a maser, a jet ejected from a supermassive black hole at the center of a galaxy, named MG J0414+0534. The radiation from the water maser was emitted when the Universe was only about 2.5 billion years old, a fifth of its current age. “The radiation that we detected has taken 11.1 billion years to reach the Earth, said Dr. John McKean of the Netherlands Institute for Radio Astronomy (ASTRON). “However, because the Universe has expanded like an inflating balloon in that time, stretching out the distances between points, the galaxy in which the water was detected is about 19.8 billion light years away.”

The water emission is seen as a maser, where molecules in the gas amplify and emit beams of microwave radiation in much the same way as a laser emits beams of light. The faint signal is only detectable by using a technique called gravitational lensing, where the gravity of a massive galaxy in the foreground acts as a cosmic telescope, bending and magnifying light from the distant galaxy to make a clover-leaf pattern of four images of MG J0414+0534. The water maser was only detectable in the brightest two of these images.

“We have been observing the water maser every month since the detection and seen a steady signal with no apparent change in the velocity of the water vapor in the data we’ve obtained so far, McKean said. “This backs up our prediction that the water is found in the jet from the supermassive black hole, rather than the rotating disc of gas that surrounds it.”

Detection of the earliest and most distant water. CREDIT: Milde Science Communication, STScI, CFHT, J.-C. Cuillandre, Coelum.
Detection of the earliest and most distant water. CREDIT: Milde Science Communication, STScI, CFHT, J.-C. Cuillandre, Coelum.

Although since the initial discovery the team has looked at five more systems that have not had water masers, they believe that it is likely that there are many more similar systems in the early Universe. Surveys of nearby galaxies have found that only about 5% have powerful water masers associated with active galactic nuclei. In addition, studies show that very powerful water masers are extremely rare compared to their less luminous counterparts. The water maser in MG J0414+0534 is about 10,000 times the luminosity of the Sun, which means that if water masers were equally rare in the early Universe, the chances of making this discovery would be improbably slight.

“We found a signal from a really powerful water maser in the first system that we looked at using the gravitational lensing technique. From what we know about the abundance of water masers locally, we could calculate the probability of finding a water maser as powerful as the one in MG J0414+0534 to be one in a million from a single observation. This means that the abundance of powerful water masers must be much higher in the distant Universe than found locally because I’m sure we are just not that lucky!” said Dr McKean.

The discovery of the water maser was made by a team led by Dr. Violette Impellizzeri using the 100-metre Effelsberg radio telescope in Germany during July to September 2007. The discovery was confirmed by observations with the Expanded Very Large Array in the USA in September and October 2007. The team included Alan Roy, Christian Henkel and Andreas Brunthaler, from the Max Planck Institute for Radio Astronomy, Paola Castangia from Cagliari Observatory and Olaf Wucknitz from the Argelander Institute for Astronomy at Bonn University. The findings were published in Nature in December 2008.

The team is now analyzing high-resolution data to find out how close the water maser lies to the supermassive black hole, which will give them new insights into the structure at the center of active galaxies in the early Universe.

“This detection of water in the early Universe may mean that there is a higher abundance of dust and gas around the super-massive black hole at these epochs, or it may be because the black holes are more active, leading to the emission of more powerful jets that can stimulate the emission of water masers. We certainly know that the water vapour must be very hot and dense for us to observe a maser, so right now we are trying to establish what mechanism caused the gas to be so dense,” said Dr McKean.

McKean presented the team’s findings at the European Week of Astronomy and Space Science in the UK this week.

Source: RAS

Posted on by Nancy Atkinson

New Findings Challenge Galaxy Formation Ideas

The most distant submillimetre galaxy discovered by the LESS collaboration.

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An international team of astronomers have undertaken a survey with a new submillimeter camera have discovered more than a hundred dusty galaxies in the early Universe, each of which is in the throes of an intense burst of star formation. These submillimeter galaxies are associated with the early formation of some of the most massive galaxies in the present-day Universe: giant elliptical galaxies. One of these galaxies is an example of a rare class of starburst, seen just 1 billion years after the Big Bang, and may present a direct challenge to current ideas of how galaxies formed.

The team (known as the LESS collaboration) used the new Large Apex Bolometer Camera (LABOCA) camera on the Atacama Pathfinder Experiment (APEX) telescope sited in the Atacama Desert in Chile to make a map of the distant galaxies in a region of the sky called the Extended Chandra Deep Field South.

These galaxies are so far away that we see them as they appeared billions of years ago. LABOCA is sensitive to light at wavelengths just below 1mm (submillimetre radiation), and is able to find very dusty and very luminous galaxies at very early times in the history of the Universe, when giant elliptical galaxies formed

For many years it has been thought that these giant elliptical galaxies formed most of their stars at very early times in the Universe, within the first billion years after the Big Bang. However, very few examples of these very distant and very bright dusty sources have been found in submillimeter surveys, until the LESS collaboration completed their survey of a Full Moon-sized patch of sky in the southern hemisphere constellation of Fornax. Their survey is the largest and deepest of its kind in submillimeter radiation and reveals over a hundred galaxies that are forming stars at a prodigious rate.

Working with their new map, the team identified one of the submillimeter sources as being associated with a star forming galaxy which is seen just 1 billion years after the Big Bang. This remarkable galaxy shows the signatures of both intense star formation and obscured black hole growth when the Universe was only 10 percent of its current age. Dr. Kristin Coppin of Durham University and the LESS team suggest that there could be far more submillimeter galaxies lurking at these early times than had previously been thought. “The discovery of a larger number of such active galaxies at such an early time would be at odds with current galaxy formation models,” said Coppin.

Coppin presented the team’s findings at the European Week of Astronomy and Space Science conference.

Source: RAS

Posted on by Nancy Atkinson

Do We Need a New Theory of Gravitation?

Draco satellite dwarf galaxy. Credit: Mischa Schirmer, University of Bonn

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A group of physicists say that the distribution of satellite galaxies that orbit the Milky Way, as well as the apparent dark matter within them, presents a direct challenge to Newton’s theory of gravitation, as the galaxies are not where they should be. “There is something odd about their distribution,” said Professor Pavel Kroupa from the University of Bonn in Germany. “They should be uniformly arranged around the Milky Way, but this is not what we found.” Standard cosmological models predict the presence of hundreds of these companions around most of the larger galaxies, but up to now only 30 have been observed around the Milky Way. The physicists say that Newton’s theory of gravitation should be modified.

The astronomers from Germany, Austria and Australia looked at the small dwarf galaxies that orbit the Milky Way and discovered that the eleven brightest of the dwarf galaxies lie more or less in the same plane – in a kind of disk shape – and that they revolve in the same direction around the Milky Way (in the same way as planets in the Solar System revolve around the Sun). Some of these contain only a few thousand stars and so are relatively faint and difficult to find.

Professor Kroupa and the other physicists believe that this can only be explained if today’s satellite galaxies were created by ancient collisions between young galaxies. Team member Dr. Manuel Metz said, “Fragments from early collisions can form the revolving dwarf galaxies we see today, but this introduces a paradox. Calculations suggest that the dwarf satellites cannot contain any dark matter if they were created in this way. But this directly contradicts other evidence. Unless the dark matter is present, the stars in the galaxies are moving around much faster than predicted by Newton’s standard theory of gravitation.”

Metz added, “The only solution is to reject Newton’s theory. If we live in a Universe where a modified law of gravitation applies, then our observations would be explainable without dark matter.”

With this evidence, the team share the convictions of a number of groups around the world who believe that some of the fundamental principles of physics have been incorrectly understood. If their ideas are correct, it will not be the first time that Newton’s theory of gravitation has been modified. In the 20th century it happened when Einstein introduced his Special and General Theories of Relativity and again when quantum mechanics was developed to explain physics on sub-atomic scales. The anomalies detected by Dr. Metz and Professor Kroupa and their collaborators imply that where weak accelerations predominate, a ‘modified Newtonian dynamic’ may have to be used. If the scientists are right then this has far-reaching consequences for our understanding of the Universe we live in.

The two studies will appear in papers in Monthly Notices of the Royal Astronomical Society and the Astrophysical Journal.

Source: RAS

Posted on by Anne Minard

Hubble Immortalizes Itself With New Image: “Fountain of Youth”


To commemorate the Hubble Space Telescope’s 19 years in space, the ESA and NASA have released an image of a celestial celebration. 

Two members in this trio of galaxies are apparently engaged in a gravitational tug-o-war, giving rise to a bright streamer of newborn blue stars that stretches 100,000 light years across.

 

fountain-region
Constellation region near ARP 194. Credit: NASA, ESA Z. Levay and A. Fujii

Resembling a pair of owl’s eyes, the two nuclei of the colliding galaxies can be seen in the process of merging at the upper left. The bizarre blue bridge of material extending out from the northern component looks as if it connects to a third galaxy but in reality this galaxy is in the background, and not connected at all.

Hubble’s sharp view allows astronomers to try and sort out visually which are the foreground and background objects when galaxies, superficially, appear to overlap.

The blue “fountain” is the most striking feature of this galaxy troupe and it contains complexes of super star clusters that may have as many as dozens of individual young star clusters in them. It formed as a result of the interactions among the galaxies in the northern component of Arp 194. The gravitational forces involved in a galaxy interaction can enhance the star formation rate and give rise to brilliant bursts of star formation in merging systems.

The stream of material lies in front of the southern component of Arp 194, as shown by the dust that is silhouetted around the star cluster complexes.

The details of the interactions among the multiple galaxies that make up Arp 194 are complex. The system was most likely disrupted by a previous collision or close encounter. The shapes of all the galaxies involved have been distorted by their gravitational interactions with one another.

Arp 194, located in the constellation of Cepheus, resides approximately 600 million light-years away from Earth. Arp 194 is one of thousands of interacting and merging galaxies known in our nearby Universe.

The observations were taken in January 2009 with the Wide Field Planetary Camera 2. Blue, green and red filters were composited together to form the galaxy interaction image.

This picture was issued to celebrate the 19th anniversary of the launch of the Hubble Space Telescope aboard the space shuttle Discovery in 1990. In the past 19 years, Hubble has made more than 880,000 observations and snapped over 570,000 images of 29,000 celestial objects.

Image credit: NASA, ESA and the Hubble Heritage Team (STScI/AURA)

Source: HubbleSite

Posted on by Anne Minard

Researchers Describe ‘Most Spectacular and Most Disturbed’ Galaxy Cluster

Composite image of MACSJ0717. Credit: X-ray (NASA/CXC/IfA/C. Ma et al.); Optical (NASA/STScI/IfA/C. Ma et al.)

Composite image of MACSJ0717. Credit: X-ray (NASA/CXC/IfA/C. Ma et al.); Optical (NASA/STScI/IfA/C. Ma et al.)

It’s hot. It’s crowded. And it’s one of the most raucuous space parties astronomers have ever seen.

A research team using a combination of three powerful telescopes is spilling the beans on the galaxy cluster MACSJ0717.5+3745 (MACSJ0717 for short), located about 5.4 billion light years from Earth. The wild system contains four separate galaxy clusters undergoing a triple merger — the first time such a phenomenon has been documented — and that’s just the beginning. 

Galaxy clusters are the largest objects bound by gravity in the Universe. Using data from NASA’s Chandra X-ray Observatory, Hubble Space Telescope and the Keck Observatory on Mauna Kea, Hawaii, astronomers were able to determine the three-dimensional geometry and motion in MACSJ0717.

Its 13-million-light-year-long stream of galaxies, gas and dark matter — known as a filament — is pouring into a region already full of galaxies. Like a freeway of cars emptying into a full parking lot, this flow of galaxies has caused one collision after another.

“In addition to this enormous pileup, MACSJ0717 is also remarkable because of its temperature,” said lead author Cheng-Jiun Ma, of the University of Hawaii. “Since each of these collisions releases energy in the form of heat, MACS0717 has one of the highest temperatures ever seen in such a system.”

While the filament leading into MACJ0717 had been previously discovered, these results show for the first time that it was the source of this galactic pummeling. The evidence is two-fold. First, by comparing the position of the gas and clusters of galaxies, the researchers tracked the direction of clusters’ motions, which matched the orientation of the filament in most cases. Secondly, the largest hot region in MACSJ0717 is where the filament intersects the cluster, suggesting ongoing impacts.

“MACSJ0717 shows how giant galaxy clusters interact with their environment on scales of many millions of light years,” said team member Harald Ebeling, also from the University of Hawaii. “This is a wonderful system for studying how clusters grow as material falls into them along filaments.”

Computer simulations show that the most massive galaxy clusters should grow in regions where large-scale filaments of intergalactic gas, galaxies, and dark matter intersect, and material falls inward along the filaments.

“It’s exciting that the data we get from MACSJ0717 appear to beautifully match the scenario depicted in the simulations,” said Ma.

In the future, Ma and his team hope to use even deeper X-ray data to measure the temperature of gas over the full 13-million-light-year extent of the filament. Much remains to be learned about the properties of hot gas in filaments and whether infall along these structures can significantly heat the gas in clusters over large scales.

“This is the most spectacular and most disturbed cluster I have ever seen,” says Ma, “and we think that we can learn a whole lot more from it about how structure in our Universe grows and evolves.”

The paper describing these results appeared in the March 10 issue of Astrophysical Journal Letters. 

Source: Harvard University’s Chandra site. More information can be found at NASA’s Chandra site, and the paper is available here.

Posted on by Nancy Atkinson

Incredible Light Show: Gas Jet Flaring From M87’s Black Hole

Hubble image of a gas jet blasing from the core of M87. Credit: NASA, ESA, and J. Madrid (McMaster University)

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Sometimes reality is stranger than fiction. The Hubble Space Telescope has been keeping an eye on the very active galaxy M87 for years, and has now captured a flare-up in a jet of matter blasting from the galaxy’s monster black hole. This 5,000-light-year-long, narrow beam of radiation and plasma is as bright as a Star Wars light saber and as destructive as the Death Star. This extragalactic jet is being fueled and ejected from the vicinity of a monster black hole that is 3 billion times the mass of our Sun. “I did not expect the jet in M87 or any other jet powered by accretion onto a black hole to increase in brightness in the way that this jet does,” says astronomer Juan Madrid of McMaster University in Hamilton, Ontario. “It grew 90 times brighter than normal. But the question is, does this happen to every single jet or active nucleus, or are we seeing some odd behavior from M87?”


The outburst is coming from a blob of matter, called HST-1, embedded in the jet, a powerful narrow beam of hot gas produced by the supermassive black hole residing in the core of this giant elliptical galaxy. HST-1 is so bright that it is outshining even M87’s brilliant core, whose monster black hole is one of the most massive yet discovered.

The glowing gas clump has taken astronomers on a rollercoaster ride of suspense. Astronomers watched HST-1 brighten steadily for several years, then fade, and then brighten again. They say it’s hard to predict what will happen next.

Hubble has been following the surprising activity for seven years, providing the most detailed ultraviolet-light view of the event. Other telescopes have been monitoring HST-1 in other wavelengths, including radio and X-rays. The Chandra X-ray Observatory was the first to report the brightening in 2000. HST-1 was first discovered and named by Hubble astronomers in 1999. The gas knot is 214 light-years from the galaxy’s core.

The flare-up may provide insights into the variability of black hole jets in distant galaxies, which are difficult to study because they are too far away. M87 is located 54 million light-years away in the Virgo Cluster, a region of the nearby universe with the highest density of galaxies.
Hubble gives astronomers a unique near-ultraviolet view of the flare that cannot be accomplished with ground-based telescopes. “Hubble’s sharp vision allows it to resolve HST-1 and separate it from the black hole,” Madrid explains.

Despite the many observations by Hubble and other telescopes, astronomers are not sure what is causing the brightening. One of the simplest explanations is that the jet is hitting a dust lane or gas cloud and then glows due to the collision. Another possibility is that the jet’s magnetic field lines are squeezed together, unleashing a large amount of energy. This phenomenon is similar to how solar flares develop on the Sun and is even a mechanism for creating Earth’s auroras.

The disk around a rapidly spinning black hole has magnetic field lines that entrap ionized gas falling toward the black hole. These particles, along with radiation, flow rapidly away from the black hole along the magnetic field lines. The rotational energy of the spinning accretion disk adds momentum to the outflowing jet.

Gas jet from M87. Credit: NASA, ESA, and J. Madrid (McMaster University)
Gas jet from M87. Credit: NASA, ESA, and J. Madrid (McMaster University)

Madrid assembled seven years’ worth of Hubble archival images of the jet to capture changes in the HST-1’s behavior over time. Some of the images came from observing programs that studied the galaxy, but not the jet.

He found data from the Space Telescope Imaging Spectrograph (STIS) that showed a noticeable brightening between 1999 and 2001. In images from 2002 to 2005, HST-1 continued to rise steadily in brightness. In 2003 the jet knot was more brilliant than M87’s luminous core. In May 2005 HST-1 became 90 times brighter than it was in 1999. After May 2005 the flare began to fade, but it intensified again in November 2006. This second outburst was fainter than the first one.

“By watching the outburst over several years, I was able to follow the brightness and see the evolution of the flare over time,” Madrid says. “We are lucky to have telescopes like Hubble and Chandra, because without them we would see the increase in brightness in the core of M87, but we would not know where it was coming from.”

Madrid hopes that future observations of HST-1 will reveal the cause of the mysterious activity. “We hope the observations will yield some theories that will give us some good explanations as to the mechanism that is causing the flaring,” Madrid says. “Astronomers would like to know if this is an intrinsic instability of the jet when it plows its way out of the galaxy, or if it is something else.”

The study’s results are published in the April 2009 issue of the Astronomical Journal.

Source: HubbleSite

Posted on by Anne Minard

Balloon Experiment Solves Mystery of Far Infrared Background

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Scientists have found a way to look past Earth’s atmosphere — and ancient cosmic dust — to glimpse galaxies that were formed in the first 5 billion years of the Universe.

A new study, released today in the journal Nature, reveals first-ever news from star-forming regions both near and far — including some from the edges of the Universe, which are racing away from us the fastest because of the Universe’s expansion.

The findings also clear up the sources of the Far Infrared Background, long shrouded in mystery.

The discoveries hail from the Balloon-borne Large Aperture Submillimetre Telescope (BLAST), which floated 120,000 feet (36,576 meters) above Antarctica in 2006.

The BLAST team chose to map a particular region of the sky called the Great Observatories Origins Deep Survey–South (GOODS-South), which was studied at other wavelengths by NASA’s three “great observatories” — the Hubble, Spitzer, and Chandra space telescopes. In one epic 11-day balloon flight, BLAST found more than 10 times the total number of submillimeter starburst galaxies detected in a decade of ground-based observations.

“We measured everything, from thousands of small clouds in our own galaxy undergoing star formation to galaxies in the Universe when it was only a quarter of its present age,” said lead author Mark Devlin, from the University of Pennsylvania.

In the 1980s and 1990s, certain galaxies called Ultraluminous InfraRed Galaxies were found to be birthing hundreds of times more stars than our own local galaxies. These “starburst” galaxies, 7-10 billion light years away, were thought to make up the Far Infrared Background discovered by the COBE satellite. Since the initial measurement of this background radiation, higher-resolution experiments have tried to detect the individual galaxies that comprise it.

The BLAST study combines telescope survey measurements at wavelengths below 1 millimeter with data at much shorter infrared wavelengths from the Spitzer Space Telescope. The results confirm that all the Far Infrared Background comes from individual distant galaxies, essentially solving a decade-old question of the radiation’s origin.

Star formation takes place in clouds composed of hydrogen gas and a small amount of dust. The dust absorbs the starlight from young, hot stars, heating the clouds to roughly 30 degrees above absolute zero (or 30 Kelvin). The light is re-emitted at much longer infrared and submillimeter wavelengths.

Thus, as much as 50 percent of the Universe’s light energy is infrared light from young, forming galaxies. In fact, there is as much energy in the Far Infrared Background as there is in the total optical light emitted by stars and galaxies in the Universe. Familiar optical images of the night sky are missing half of the picture describing the cosmic history of star formation, the authors say.

“BLAST has given us a new view of the Universe,” said Barth Netterfield of the University of Toronto, the Canadian principal investigator for BLAST, “enabling the BLAST team to make discoveries in topics ranging from the formation of stars to the evolution of distant Galaxies.”

In an accompanying News & Views piece, author Ian Smail, a computational cosmologist from Durham University in the UK, wrote that “the implication of these observations is that the active growth phase of most galaxies that are seen today is well behind them — they are declining into their equivalent of middle age.”

He also pointed out that studies of these extreme star-forming events in the early Universe will be aided by three major advances due over the next year or so: the submillimeter camera on the ESA/NASA Herschel Space Observatory; the development of large-format detectors working at submillimeter wavelengths, including one mounted on the James Clerk Maxwell Telescope; and the first phase of the Atacama Large Millimeter Array (ALMA).

“Such observations will allow astronomers to study the distribution of gas and star formation within these early galaxies,” Smail wrote, “which in turn will help to identify the physical process that triggers these ultraluminous bursts of star formation and their role in the formation of the galaxies we see in the Universe today.”

LEAD IMAGE CAPTION: The BLAST telescope just before launch in Antarctica. BLAST is in the foreground, next the 28 million cubic foot balloon, in the background is the volcano Mount Erebus. Credit: Mark Halpern

Source: Nature and a University of Pennsylvania press release (not yet online).  Images, photographs, sky maps and the complete study are available at the BLAST Web site.