galaxies Archives

June 21, 2011December 24, 2015 by Tammy Plotner

The ATLAS3D Project: Calling A Different Tune

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In 1926, astronomer Edwin Hubble gave us our first basic galaxy classification scenario – the Hubble Sequence. Using photographic plates, Hubble derived a simplistic system based on three visually known structures: elipitical, spiral and lenticular. This sequence, when plotted out, gave the appearance of a common object and eventually became known as the “Hubble Tuning Fork” (as seen above). For many decades, this served as a standard. Now the ATLAS3D Project is calling a different tune…

Just who is the pied piper in this merry band? The ATLAS3D project is a multiwavelength survey combined with a theoretical modelling effort. The observations it takes spans from the radio to the millimetre and optical. It provides multicolor imaging, as well as two-dimensional kinematics of the atomic, molecular and ionized gases, together with the kinematics and population of the stars, Where does it dance? Only around a carefully selected, volume-limited sample of 260 early-type galaxies.

Heading up the project is a team of 25 astronomers from Europe and Northern America, including ASTRON astronomers Morganti, Oosterloo, and Serra – and all with a mission – to update and revise our understanding of galactic evolution. Employing the SAURON spectrograph on the 4.2-meter William Herschel Telescope on La Palma, the team was able to distinguish stellar movement in the pre-determined galactic candidates. These new assessments show that spheroid galaxies belong to the spiral galaxy classification. How did they come to that conclusion? The largest portion of spheroids – or early types – are basically the same family as spirals and evolve along a similar line. But with ATLAS3D findings, we’re looking at new concepts.

We’re seeing beyond the optical (photographic plates) which founded Hubble’s original diagram – where once galaxies were separated by their distinct characteristics such as rapid rotators rich in stars and gas – or as slowly moving, gas-poor models. Up until now, it was also next to impossible to distinguish sparse “face-on” structure from edge-on spheroids. With the aid of kinematic data astronomers can “see” rotation – allowing observation of all galaxy types from any angle.

“Slow and fast rotators tend to be classified as ellipticals and lenticulars, respectively, but the contamination is strong enough to affect results solely based on such a scheme: 20 per cent of all fast rotators are classified as ellipticals, and more importantly 66 per cent of all ellipticals in the ATLAS3D sample are fast rotators.” says the team. “Our complete sample of 260 ETGs leads to a new criterion to disentangle fast and slow rotators which now includes a dependency on the apparent ellipticity. It separates the two classes significantly better than the previous prescription.”

While it will take many years and many more observations to sort out all the new data, it would seem that our current understanding of galactic evolution just might need a “tune up”.

Oringinal Story Source: ASTRON.

June 16, 2011December 24, 2015 by Nancy Atkinson

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.

June 13, 2011December 24, 2015 by Tammy Plotner

Carbon Monoxide Reveals Distant Milky Way Arm

The Milky Way's basic structure is believed to involve two main spiral arms emanating from opposite ends of an elongated central bar. But only parts of the arms can be seen - gray segments indicate portions not yet detected. Other known spiral arm segments--including the Sun's own spur--are omitted for clarity. Credit: T. Dame

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Our Milky Way Galaxy’s elemental form is hypothesized to be a barred structure – made up of two major spiral arms originating at both poles of the central bar. But from our vantage point, we can only see portions of those arms. Because of huge amounts of dust literally blocking our view, we can’t be as confident of our structure as other galaxies we can study as a whole. However, by “sniffing our galaxy’s tailpipe”, we’re able to judge our structure just a little bit better.

We’re all aware of theoretical models of the Milky Way… a sprawling, pinwheel-like structure with sweeping, grandiose arms loaded with stars, gases and dust. We’re also aware our Solar System is lodged in a spur of those arms, slowly orbiting and located about 25,000 light-years from the center. But hard and fast details of our Galaxy haven’t been possible until now. Thanks to the use of radio waves, we’re able to cut through the murk and see wavelengths that give us clues. These architectural hints are coming to us in the forms of molecules like carbon monoxide – a great tracer of our galactic format.

Using a small 1.2-meter radio telescope on the roof of their science building in Cambridge, CfA astronomers Tom Dame and Pat Thaddeus used carbon monoxide emissions to ferret out proof there is more spiral structure located in the most distant parts of our galactic home. What they uncovered was a previously reported new spiral arm at the far end of the Scutum-Centaurus Arm – but how they did it was by verifying vast, dense concentrations of this molecular gas.

Where does it come from? Try the “exhaust” of carbon stars. These late-type stars have an atmosphere which is higher in carbon than oxygen. When the two combine in the upper layers of the star they create carbon monoxide. It also happens in “normal” stars like our Sun, too. It’s richer in oxygen than carbon, but still cool enough to form carbon monoxide. “After preliminary Galactic surveys in the mid-1970’s revealed the vast extent of CO emission on the sky,” says Dame, “It became clear that even with the relatively large beams of the 1.2 meter telescopes a sensitive, well-sampled survey of the entire Galaxy would require many years.”

And its time has come…

Original Story Source: Smithsonian Astrophysical Observatory.

June 12, 2011December 24, 2015 by Steve Nerlich

Astronomy Without A Telescope – Oh-My-God Particles

Centaurus A - the closest galaxy with an active galactic nucleus - a mere 10-16 million light years away. Now I wonder where all those ultra high energy cosmic rays are coming from. Hmmm...

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Cosmic rays are really sub-atomic particles, being mainly protons (hydrogen nuclei) and occasionally helium or heavier atomic nuclei and very occasionally electrons. Cosmic ray particles are very energetic as a result of them having a substantial velocity and hence a substantial momentum.

The Oh-My-God particle detected over Utah in 1991 was probably a proton traveling at 0.999 (and add another 20 x 9s after that) of the speed of light and it allegedly carried the same kinetic energy as a baseball traveling at 90 kilometers an hour.

Its kinetic energy was estimated at 3 x 10²⁰ electron volts (eV) and it would have had the collision energy of 7.5 x 10¹⁴ eV when it hit an atmospheric particle – since it can’t give up all its kinetic energy in the collision. Fast moving debris carries some of it away and there’s some heat loss too. In any case, this is still about 50 times the collision energy we expect the Large Hadron Collider (LHC) will be able to generate at full power. So, this gives you a sound basis to scoff at doomsayers who are still convinced that the LHC will destroy the Earth.

Now, most cosmic ray particles are low energy, up to 10¹⁰ eV – and arise locally from solar flares. Another more energetic class, up to 10¹⁵ eV, are thought originate from elsewhere in the galaxy. It’s difficult to determine their exact source as the magnetic fields of the galaxy and the solar system alter their trajectories so that they end up having a uniform distribution in the sky – as though they come from everywhere.

But in reality, these galactic cosmic rays probably come from supernovae – quite possibly in a delayed release process as particles bounce back and forth in the persisting magnetic field of a supernova remnant, before being catapulted out into the wider galaxy.

And then there are extragalactic cosmic rays, which are of the Oh-My-God variety, with energy levels exceeding 10¹⁵ eV, even rarely exceeding 10²⁰ eV – which are more formally titled ultra-high-energy cosmic rays. These particles travel very close to the speed of light and must have had a heck of kick to attain such speeds.

**Left image:** The energy spectrum of cosmic rays approaching Earth. Cosmic rays with low energies come in large numbers from solar flares (yellow range). Less common, but higher energy cosmic rays originating from elsewhere in the galaxy are in the blue range. The least common but most energetic extragalactic cosmic rays are in the purple range. **Right image:** The output of the active galactic nucleus of Centaurus A dominates the sky in radio light - this is its apparent size relative to the full Moon. It is likely that nearly all extragalactic cosmic rays that reach Earth originate from Centaurus A.

However, a perhaps over-exaggerated aura of mystery has traditionally surrounded the origin of extragalactic cosmic rays – as exemplified in the Oh-My-God title.

In reality, there are limits to just how far away an ultra-high-energy particle can originate from – since, if they don’t collide with anything else, they will eventually come up against the Greisen–Zatsepin–Kuzmin (GZK) limit. This represents the likelihood of a fast moving particle eventually colliding with a cosmic microwave background photon, losing momentum energy and velocity in the process. It works out that extragalactic cosmic rays retaining energies of over 10¹⁹ eV cannot have originated from a source further than 163 million light years from Earth – a distance known as the GZK horizon.

Recent observations by the Pierre Auger Observatory have found a strong correlation between extragalactic cosmic rays patterns and the distribution of nearby galaxies with active galactic nuclei. Biermann and Souza have now come up with an evidence-based model for the origin of galactic and extragalactic cosmic rays – which has a number of testable predictions.

They propose that extragalactic cosmic rays are spun up in supermassive black hole accretion disks, which are the basis of active galactic nuclei. Furthermore, they estimate that nearly all extragalactic cosmic rays that reach Earth come from Centaurus A. So, no huge mystery – indeed a rich area for further research. Particles from an active supermassive black hole accretion disk in another galaxy are being delivered to our doorstep.

Further reading: Biermann and Souza On a common origin of galactic and extragalactic cosmic rays.

June 3, 2011December 24, 2015 by VirtualAstro

Supernova Discovered in M51 The Whirlpool Galaxy

A new supernova (exploding star) has been discovered in the famous Whirlpool Galaxy, M51.

M51, The Whirlpool galaxy is a galaxy found in the constellation of Canes Venatici, very near the star Alkaid in the handle of the saucepan asterism of the big dipper. Easily found with binoculars or a small telescope.

The discovery was made on June 2nd by French astronomers and the supernova is reported to be around magnitude 14. More information (In French) can be found here or translated version here.

Image by BBC Sky at Night Presenter Pete Lawrence

The supernova will be quite tricky to spot visually and you may need a good sized dobsonian or similar telescope to spot it, but it will be a easy target for those interested in astro imaging.

The whirlpool galaxy was the first galaxy discovered with a spiral structure and is one of the most recognisable and famous objects in the sky.

May 29, 2011December 24, 2015 by Jon Voisey

Testing the Spiral Density Wave Theory

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Spiral galaxies are one of the most captivating structures in astronomy, yet their nature is still not fully understood. Astronomers currently have two categories of theories that can explain this structure, depending on the environment of the galaxy, but a new study, accepted for publication in the Astrophysical Journal, suggests that one of these theories may be largely wrong.

For galaxies with nearby companions, astronomers have suggested that tidal forces may draw out spiral structure. However, for isolated galaxies, another mechanism is required in which galaxies form these structures without intervention from a neighbor. A possible solution to this was first worked out in 1964 by Lin & Shu in which they suggested that the winding structure is merely an illusion. Instead, these arms weren’t moving structures, but areas of greater density which remained stationary as stars entered and exited them similar to how a traffic jam remains in position although the component cars travel in and out. This theory has been dubbed the Lin-Shu density wave theory and has been largely successful. Previous papers have reported a progression from cold, HI regions and dust on the inner portion of the spiral arms, that crash into this higher density region and trigger star formation, making hot O & B class stars that die before exiting the structure, leaving the lower mass stars to populate the remainder of the disk.

One of the main questions on this theory has been the longevity of the overdense region. According to Lin & Shu as well as many other astronomers, these structures are generally stable over long time periods. Others suggest that the density wave comes and goes in relatively short-lived, recurrent patterns. This would be similar to the turn signal on your car and the one in front of you at times seeming to synch up before getting out of phase again, only to line up again in a few minutes. In galaxies, the pattern would be composed of the individual orbits of the stars, which would periodically line up to create the spiral arms. Teasing out which of these was the case has been a challenge.

To do so, the new research, led by Kelly Foyle from McMaster University in Ontario, examined the progression of star formation as gas and dust entered the shock region produced by the Lin-Shu density wave. If the theory was correct, they should expect to find a progression in which they would first find cold HI gas and carbon monoxide, and then offsets of warm molecular hydrogen and 24 μm emission from stars forming in clouds, and finally, another offset of the UV emission of fully formed and unobscured stars.

The team examined 12 nearby spiral galaxies, including M 51, M 63, M 66, M 74, M 81, and M 95. These galaxies represented several variations of spiral galaxies such as grand design spirals, barred spirals, flocculent spirals and an interacting spiral.

When using a computer algorithm to examine each for offsets that would support the Lin-Shu theory, the team reported that they could not find a difference in location between the three different phases of star formation. This contradicts the previous studies (which were done “by eye” and thus subject to potential bias) and casts doubt on long lived spiral structure as predicted by the Lin-Shu theory. Instead, this finding is in agreement with the possibility of transient spiral arms that break apart and reform periodically.

Another option, one that salvages the density wave theory is that there are multiple “pattern speeds” producing more complex density waves and thus blurs the expected offsets. This possibility is supported by a 2009 study which mapped these speeds and found that several spiral galaxies are likely to exhibit such behavior. Lastly, the team notes that the technique itself may be flawed and underestimating the emission from each zone of star formation. To settle the question, astronomers will need to produce more refined models and explore the regions in greater detail and in more galaxies.

May 25, 2011December 24, 2015 by Jason Major

Hubble Finds “Oddball” Stars in Milky Way Hub

Astronomers using the Hubble Space Telescope to peer deep into the central bulge of our galaxy have found a population of rare and unusual stars. Dubbed “blue stragglers”, these stars seem to defy the aging process, appearing to be much younger than they should be considering where they are located. Previously known to exist within ancient globular clusters, blue stragglers have never been seen inside our galaxy’s core – until now.

The stars were discovered following a seven-day survey in 2006 called SWEEPS – the Sagittarius Window Eclipsing Extrasolar Planet Search – that used Hubble to search a section of the central portion of our Milky Way galaxy, looking for the presence of Jupiter-sized planets transiting their host stars. During the search, which examined 180,000 stars, Hubble spotted 42 blue stragglers.

Of the 42 it’s estimated that 18 to 37 of them are genuine.

What makes blue stragglers such an unusual find? For one thing, stars in the galactic hub should appear much older and cooler… aging Sun-like stars and old red dwarfs. Scientists believe that the central bulge of the Milky Way stopped making new stars billions of years ago. So what’s with these hot, blue, youthful-looking “oddballs”? The answer may lie in their formation.

Artist's concept of a blue straggler pair. NASA, ESA, and G. Bacon (STScI)

A blue straggler may start out as a smaller member of a binary pair of stars. Over time the larger star ages and gets even bigger, feeding material onto the smaller one. This fuels fusion in the smaller star which then grows hotter, making it shine brighter and bluer – thus appearing similar to a young star.

However they were formed, just finding the blue stragglers was no simple task. The stars’ orbits around the galactic core had to be determined through a confusing mix of foreground stars within a very small observation area. The region of the sky Hubble studied was no larger than the width of a fingernail held at arm’s length! Still, within that small area Hubble could see over 250,000 stars. Incredible.

“Only the superb image quality and stability of Hubble allowed us to make this measurement in such a crowded field.”

– Lead author Will Clarkson, Indiana University in Bloomington and the University of California in Los Angeles

The discovery of these rare stars will help astronomers better understand star formation in the Milky Way’s hub and thus the evolution of our galaxy as a whole.

Hubble Hunts Down Star Formation in Canes Venatici

Hubble's view of NGC 4214, Canes Venatici (The Hunting Dogs). Credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration

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Lots of activity taking place inside NGC 4214, and Hubble has peered inside this dwarf galaxy to see stars in all stages of their evolution, as well as gas clouds with huge cavities blown out by stellar winds. Wow! Also visible are bright stellar clusters and complex patterns of glowing hydrogen, some forming a candy-cane-like structure in the upper right of this optical and near-infrared image. NGC 4214 is located in the constellation of Canes Venatici (The Hunting Dogs), about 10 million light-years away. Hubble scientists say this galaxy is an ideal laboratory to research the triggers of star formation and evolution.

Observations of this dwarf galaxy have also revealed clusters of much older red supergiant stars. Additional older stars can be seen dotted all across the galaxy. The variety of stars at different stages in their evolution indicates that the recent and ongoing starburst periods are not the first, and the galaxy’s abundant supply of hydrogen means that star formation will continue into the future.

This color image was taken using the Wide Field Camera 3 in December 2009. See the HubbleSite for a larger view of this colorful galaxy.

May 11, 2011December 24, 2015 by Jon Voisey

Energizing the Filaments of NGC 1275

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When examining clusters of galaxies, astronomers often find massive elliptical galaxies lurking at the centers. In some of these, long filaments of gas and dust extend outwards from the core. One of the best examples of this is the relatively nearby galaxy NGC 1275 which lies in the constellation of Perseus. In this galaxy these tendrils are exceptionally narrow, only about 200 light years across, but as long as 20,000 light years in length. While many groups have studied them, their nature is a topic of much debate. The structures tend to be far removed from star forming regions which can cause the gas to glow. So what energy source powers these gaseous ribbons?

Answering this question is the goal of a recent paper by a team of astronomers led by Andrew Fabian at Cambridge University. Previous studies have explored the spectra of these filaments. Although the filaments have strong Hα emission, created by warm hydrogen gas, the spectra of these tendrils are unlike any nebulae within our own galaxy. The closest resemblance to galactic objects was the Crab Nebula, the remnant of a supernova that was witnessed in 1054 AD. Additionally, the spectra also reveal the presence of molecules such as carbon monoxide and H₂.

Another, previous challenge astronomers faced with these tendrils was explaining their formation. Since molecules were present, it meant the gas was cooler than the surrounding gas. In this case, the clouds should collapse due to their self gravity to form more stars than are actually present. But surrounding these tendrils is ionized plasma which should interact with the cold gas, heating it and causing it to disperse. While these two forces would counteract one another, it is impossible to consider that they would balance each other perfectly in one case, let alone for the numerous tendrils in numerous central galaxies.

This problem was apparently solved in 2008, when Fabian published a paper in Nature suggesting that these filaments were being columnated by extremely weak magnetic fields (only 0.01% the strength of Earth’s). These field lines could prevent the warmer plasma from directly entering the cold filaments since, upon interaction with the magnetic field, they would be redirected. But could this property help to explain the lesser degree of heating that still causes the emission spectra? Fabian’s team thinks so.

In the new paper, they suggests that some of the particles of the surrounding plasma do eventually penetrate the cold tendrils which explains some of the heating. However, this flow of charged particles also affects the field lines themselves inducing turbulence which also heats the gas. These effects make up the main bulk of the observed spectra. But the tendrils also exhibit an anomalous amount of X-ray flux. The team proposes that some of this is due to charge exchange in which the ionized gas entering the filaments steals electrons from the cold gas. Unfortunately, the interactions are expected to be too infrequent to explain all of the observed X-rays leaving this portion of the spectrum not fully explained by the new model.

In this article I’ve used the words “magnetic field”, “charge”, and “plasma” throughout, so of course the Electric Universe crowd is going to come flocking, declaring this validates everything they’ve ever said, just as they did when magnetic fields were first implicated in 2008. So before closing completely, I want to take a bit to consider how this new study conforms to their predictions. In general, the study agrees with their claims. However, that doesn’t mean their claims are correct. Rather, it implies they’re worthlessly vague and can be made to fit any circumstance that even briefly mentions such words as I listed above.

The EU supporters consistently refuse to provide any quantitative models which could provide true discriminating tests for their propositions. Instead, they leave the claims suspiciously vague and insist that complex physics is completely understandable with no more understanding than high school level E&M. As a result, the mere scale of their claims is horrifically inconsistent wherein they propose things like the paltry field in this article, or the slight charge on lunar craters are indicative of overwhelming currents powering stars and entire galaxies.

So while articles like this one do reinforce the EU position that electromagnetics does play a role in astronomy, it does not support the grandiose claims on entirely different scales. In the meantime, astronomers don’t argue that electromagnetic effects don’t exist (like EU supporters frequently claim). Rather, we analyze them and appreciate them for what they are: Generally weak effects that are important here and there, but they’re not some all powerful energy field pervading the universe.

May 4, 2011December 24, 2015 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.