‘Lopsided’ Ghostly Galactic Halo Has Some Starry Surprises

Centaurus A — that popular target for astrophotographers in the southern hemisphere — has a much wider halo than expected, astronomers revealed. Turns out the galaxy’s ghostly glow is about eight times the apparent width of the full moon in the sky. Examining this halo in more detail could reveal much about how galaxies come together, astronomers said.

It’s relatively easy for scientists to spot the halo around the Milky Way since we are a part of it, but it’s much harder to observe them in other galaxies because they are so faint. Looking at Centaurus A (10 million to 16 million light-years away) required the power of two Hubble Space Telescope instruments: the Advanced Camera for Surveys and the Wide Field Camera 3.

“Tracing this much of a galaxy’s halo gives us surprising insights into a galaxy’s formation, evolution, and composition,” stated lead author Marina Rejkuba of the European Southern Observatory in Germany. “We found more stars scattered in one direction than the other, giving the halo a lopsided shape — which we hadn’t expected.”

The Centaurus A Extreme Deep Field. (Image Courtesy of Astrophotography byRolf Oslen. Used with Permision).
The Centaurus A Extreme Deep Field. (Image Courtesy of Astrophotography byRolf Oslen. Used with Permision).

The astronomers examined a region that is about 295,000 light-years across — more than double the diameter of the Milky Way’s 120,000 light years. The stars inside the glow appeared to have abundant heavier elements, even in the fringes of the galaxy — a contrast to the much lighter hydrogen and helium that are found in the fringes of the Milky Way and nearby spiral galaxies.

It’s possible the heavier stars arose because Centaurus A merged with a spiral galaxy long ago, removing stars from the intruder and sticking in Centaurus A, the astronomers said.

“Even at these extreme distances, we still haven’t reached the edge of Centaurus A’s halo, nor have we detected the very oldest generation of stars,” stated co-author Laura Greggio of Italy’s INAF (Istituto Nzaionale de Astrofisica, or National Institute for Astrophysics).

“This aged generation is very important. The larger stars from it are responsible for manufacturing the heavy elements now found in the bulk of the galaxy’s stars. And even though the large stars are long dead, the smaller stars of the generation still live on and could tell us a great deal.”

The results are available in Astrophysical Journal Letters and in preprint version on Arxiv.

Source: Hubble European Space Agency Information Centre

An Amazing Deep-Field View of Centaurus A

Sometimes, you just have to say “Wow!”

The view you’re looking at above is of Centaurus A (NGC 5128), a galaxy about 10-16 million light years distant in the southern hemisphere sky. It’s a favorite of astrophotographers and professional observatories alike.

But what makes this image so special is that it was taken by an amateur astrophotographer.

To construct this amazing image, New Zealand-based astrophotographer Rolf Wahl Olsen exposed the field of view for 120 hours over 43 nights spanning February to May of this year.

Rolf recently shared his motivation to construct this image;

“Over the past few months I have been on a mission to achieve a long time dream of mine: taking a deep sky image with more than 100 hours of exposure.”

Rolf also noted that the stars in the frame are visible down to magnitude +25.45, which “appears to go deeper than the recent ESO release” and believes that it may well be “the deepest view ever obtained of Centaurus A,” As well as “the deepest image ever taken with amateur equipment.”

Not only is the beauty and splendor of the galaxy revealed in this stunning mosaic, but you can see the variations in the populations of stars in the massive regions undergoing an outburst of star formation.

One can also see the numerous globular clusters flocking around the galaxy, as well as the optical counterparts to the radio lobes and the faint trace of the relativistic jets. The extended halo of the outer shell of stars is also visible, along with numerous foreground stars visible in the star rich region of Centaurus.

Finally, we see the dusty lane bisecting the core of this massive galaxy as seen from our Earthly vantage point.

To our knowledge, many of these features have never been captured visually by backyard observers before, much less imaged. Congrats to Rolf Wahl Olsen on a spectacular capture and sharing his view of the universe with us!

Read more on the Centaurus A deep field on Google+.

-Check out the comparison images of the Centaurus A deep field showing the relativistic jet (!) background galaxies and clusters.

-Explore more of Rolf’s outstanding work at his website.

New Image Shows Beautiful Violence in Centaurus A

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The mysterious galaxy Centaurus A is a great place to study the extreme processes that occur near super-massive black holes, scientists say, and this beautiful new image from the combined forces of the Herschel Space Observatory and the XMM-Newton x-ray satellite reveals energetic processes going on deep in the galaxy’s core. This beautiful image tells a tale of past violence that occurred here.

The twisted disc of dust near the galaxy’s heart shows strong evidence that Centaurus A underwent a cosmic collision with another galaxy in the distant past. The colliding galaxy was ripped apart to form the warped disc, and the formation of young stars heats the dust to cause the infrared glow.

This multi-wavelength view of Centaurus A shows two massive jets of material streaming from a immense black hole in the center. When observed by radio telescopes, the jets stretch for up to a million light years, though the Herschel and XMM-Newton results focus on the inner regions.

At a distance of around 12 million light years from Earth, Centaurus A is the closest large elliptical galaxy to our own Milky Way.

“Centaurus A is the closest example of a galaxy to us with massive jets from its central black hole,” said Christine Wilson of McMaster University, Canada, who is leading the study of Centaurus A with Herschel. “Observations with Herschel, XMM-Newton and telescopes at many other wavelengths allow us to study their effects on the galaxy and its surroundings.”

Find more information on this image at ESA’s website.

Hubble’s Stunning New View of Centaurus A

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From a HubbleSite press release:

Resembling looming rain clouds on a stormy day, dark lanes of dust crisscross the giant elliptical galaxy Centaurus A. Hubble’s panchromatic vision, stretching from ultraviolet through near-infrared wavelengths, reveals the vibrant glow of young, blue star clusters and a glimpse into regions normally obscured by the dust.

The warped shape of Centaurus A’s disk of gas and dust is evidence for a past collision and merger with another galaxy. The resulting shockwaves cause hydrogen gas clouds to compress, triggering a firestorm of new star formation. These are visible in the red patches in this Hubble close-up.

At a distance of just over 11 million light-years, Centaurus A contains the closest active galactic nucleus to Earth. The center is home for a supermassive black hole that ejects jets of high-speed gas into space, but neither the supermassive or the jets are visible in this image.

This image was taken in July 2010 with Hubble’s Wide Field Camera 3.

Ring of Stars in Centaurus A Uncovered

Centaurus A (NGC 5128) is one of the most studied objects in the Southern sky, because it is the giant elliptical galaxy with the closest proximity to our own Milky Way. It lies 11 million light years away from the Milky Way, and is believe to have merged with another gaseous galaxy about 200 to 700 million years ago. The result of this galactic mashup: the birth of hundreds of thousands of stars in a kiloparsec-spanning ring near the core.

This is the first time that the inner structure of the galaxy has been resolved in such detail. Using the SOFI large field Infra-Red (1-2.5 micron) spectro-imager at the ESO New Technology Telescope, a research team led by Jouni Kainulainen of the University of Helsinki and Max Planck Institute for Astronomy was able to image a large ring of stars that have formed – and are still continuing to form – near the center of the galaxy. The brightest sources in the ring are red supergiants, or low-mass star clusters.

“It is important to note that it is not decisively the instrument (the telescope or the instrument attached to it) that enables us to see through dust, but the data analysis technique that is used to analyze the images taken with it. Of course, the instrument plays a big role in a sense that adequately high-quality images are needed to perform the analysis,” Dr. Kainulainen said in an email interview.

“There is a fundamental difference between the images we use in our paper and the Spitzer images: the wavelength that the images cover. In the images we used in our work, the dust lane of Centaurus A shows itself as “a shadow”, or more precisely, as an absorption feature (the wavelength is 1-2 micrometers). The Spitzer images represent somewhat longer wavelengths, and show the radiation emitted by the dust itself. As a concrete example, the most famous Spitzer image of Centaurus A … shows a parallelogram-like structure, but the image describes radiation mainly from dust, not from stars,” he said.

There is a large, S- or bar-shaped dust lane straight through the center of Centaurus A that obscures observations in the visible light spectrum. As shown in the image below, the ring structure of star formation is obscured by dust, but visible in the near-infrared.A comparison of Centaurus A in the visible and near-infrared spectra. Image Credit:ESO

Centaurus A is believe to house a supermassive black hole that has the mass of 200 million Suns at its core, evidenced by the radio emissions streaming out from the galaxy. Previous images of the galaxy from the Spitzer Space Telescope, the ESA’s Infrared Space Observatory and the Hubble Space Telescope revealed some aspects of the structure of the galaxy. The infrared eyes of Spitzer peered partway through the dust to show a warped parallelogram, the cause of which is the gravitational disturbance caused by the merger of Centaurus A with a smaller spiral galaxy.

The presence of rings such as the one seen in Centaurus A is probably not common among other elliptical galaxies, but other such galaxies are known to exist. It’s possible that they are present during only certain periods of an elliptical galaxy’s formation after it merges with another galaxy.

Dr. Kainulainen commented on this possiblity: “One should consider that seeing so bright ring structure is probably quite time-critical. The rings are believed to be induced by “a violent event” of merging galaxies, and they may evolve rather quickly to something that no longer looks like a clear, bright ring. Therefore, they might actually be quite common for merging galaxies, but they “last” only such a short time that we don’t see them in so many galaxies.”

The analysis technique used by the team could be applied to other galaxies to resolve formation structures previously hidden by dust, and provide more information about how violent events alter the formation of elliptical galaxies.

“Potentially, the technique can be applied to any relatively nearby galaxy showing prominent dust features. Such targets could be M31, M83, M51, Fornax A, or any similarly large, bright, dust containing galaxy. Due to geometrical reasons, Centaurus A was a very suitable target for applying the method. It will be more challenging in the case of, for example, normal Spiral galaxies. However, we have already experimented with such galaxies and feel positive about the possibilities they give,” said Dr. Kainulainen.

The striking image of Centaurus A’s ring of star formation was a somewhat surprising result of the imaging that the astronomers took of the galaxy, though there were hints from images taken by other telescopes that stellar formation was present in the obscured, dusty core.

Dr. Kainulainen said, “It was very surprising that the structure contained so much stars and star-forming activity, and that we could reveal it in such great detail. However, it was expected that a structure of this kind exists there, and contains at least some star formation. This was evident, for example, from the earlier Spitzer images. But when I first saw our result, “The Naked Picture of Centaurus A”, on my computer screen, it really was a big WOW-feeling!”

Further observations of Centaurus A are definitely in order to further explore the structure of the stellar ring, and the gravitational dynamics that allowed for its formation.

“Our plans include observations with the Very Large Telescope (European Southern Observatory) and the Hubble Space Telescope. In that work, the information we got about the dust lane in our published Letter will play a significant role. The planned observations aim particularly at determining how long, and in what magnitude, the structure has been forming stars in the past. Such information will help to understand galaxy-merging process, which is not an uncommon event in the Universe.

Dr. Kainulainen and his team published their results in a letter to Astronomy & Astrophysics, published online July 2nd, 2009. The full text of the letter is available here.

Source: ESO, Astronomy and Astrophysics, email interview with Jouni Kainulainen