Posted on by Ray Sanders

Hubble Spots Mysterious Dark Matter ‘Core’

This composite image shows the distribution of dark matter, galaxies, and hot gas in the core of the merging galaxy cluster Abell 520, formed from a violent collision of massive galaxy clusters. Image Credit: NASA, ESA, CFHT, CXO, M.J. Jee (University of California, Davis), and A. Mahdavi (San Francisco State University)

[/caption]Astronomers are left scratching their heads over a new observation of a “clump” of dark matter apparently left behind after a massive merger between galaxy clusters. What is so puzzling about the discovery is that the dark matter collected into a “dark core” which held far fewer galaxies than expected. The implications of this discovery present challenges to current understandings of how dark matter influences galaxies and galaxy clusters.

Initially, the observations made in 2007 were dismissed as bad data. New data obtained by the Hubble Space Telescope in 2008 confirmed the previous observations of dark matter and galaxies parting ways. The new evidence is based on observations of a distant merging galaxy cluster named Abell 520. At this point, astronomers have a challenge ahead of them in order to explain why dark matter isn’t behaving as expected.

“This result is a puzzle,” said astronomer James Jee (University of California, Davis). “Dark matter is not behaving as predicted, and it’s not obviously clear what is going on. Theories of galaxy formation and dark matter must explain what we are seeing.”

Current theories on dark matter state that it may be a kind of gravitational “glue” that holds galaxies together. One of the other interesting properties of dark matter is that by all accounts, it’s not made of same stuff as people and planets, yet interacts “gravitationally” with normal matter. Current methods to study dark matter are to analyze galactic mergers, since galaxies will interact differently than their dark matter halos. The current theories are supported by visual observations of galaxy mergers in the Bullet Cluster, and have become a classic example of our current understanding of dark matter.

Studies of Abell 520 are causing astronomers to think twice about our current understanding of dark matter. Initial observations found dark matter and hot gas, but lacked luminous galaxies – which are normally detected in the same regions as dark matter concentrations. Attempting to make sense of the observations, the astronomers used Hubble’s Wide Field Planetary Camera 2 to map dark matter in the cluster using a gravitational lensing technique.

“Observations like those of Abell 520 are humbling in the sense that in spite of all the leaps and bounds in our understanding, every now and then, we are stopped cold,” said Arif Babul (University of Victoria, British Columbia).

Jee added, “We know of maybe six examples of high-speed galaxy cluster collisions where the dark matter has been mapped, but the Bullet Cluster and Abell 520 are the two that show the clearest evidence of recent mergers, and they are inconsistent with each other. No single theory explains the different behavior of dark matter in those two collisions. We need more examples.”

The team has worked on numerous possibilities for their findings, each with their own set of unanswered questions. One such possibility is that Abell 520 was a more complicated merger than the Bullet Cluster encounter. There may have been several galaxies merging in Abell 520 instead of the two responsible for the Bullet Cluster. Another possibility is that like well-cooked rice, dark matter may be sticky. When particles of ordinary matter collide, they lose energy and, as a result, slow down. It may be possible for some dark matter to interact with itself and remain behind after a collision between two galaxies.

Another possibility may be that there were more galaxies in the core, but were too dim for Hubble to detect. Being dimmer, the galaxies would have formed far fewer stars than other types of galaxies. The team plans to use their Hubble data to create computer simulations of the collision, in the hopes of obtaining vital clues in the efforts to better understand the unusual behavior of dark matter.

If you’d like to learn more about the Hubble Space Telescope, visit: http://www.nasa.gov/hubble

Posted on by Nancy Atkinson

More Details from Hubble Reveal Strange Exoplanet is a Steamy Waterworld

GJ1214b, shown in this artist’s view, is a super-Earth orbiting a red dwarf star 40 light-years from Earth. Credit: NASA, ESA, and D. Aguilar (Harvard-Smithsonian Center for Astrophysics)

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Would Kevin Costner’s character in the movie “Waterworld” be at home on this exoplanet? The planet GJ 1214b was discovered in 2009 and was one of the first planets where an atmosphere was detected. In 2010, scientists were able to measure the atmosphere, finding it likely was composed mainly of water. Now, with infrared spectra taken during transit observations by the Hubble Space Telescope, scientists say this world is even more unique, and that it represents a new class of planet: a waterworld underneath a thick, steamy atmosphere.

“GJ 1214b is like no planet we know of,” said Zachary Berta of the Harvard-Smithsonian Center for Astrophysics (CfA). “A huge fraction of its mass is made up of water.”

GJ 1214b is a super-Earth — smaller than Uranus but larger than Earth — and is about 2.7 times Earth’s diameter. That gives it a volume 20 times as great as Earth yet it has less than seven times as much mass, so it’s actually kind of a lightweight. This world is also hot: it orbits a red-dwarf star every 38 hours at a distance of 2 million kilometers, giving it an estimated temperature of 230 degrees Celsius.

Berta and a team of international astronomers used Hubble’s Wide Field Camera 3 (WFC3) to study GJ 1214b when it crossed in front of its host star. During such a transit, the star’s light is filtered through the planet’s atmosphere, giving clues to the mix of gases.

“We’re using Hubble to measure the infrared color of sunset on this world,” Berta said.

Hazes are more transparent to infrared light than to visible light, so the Hubble observations help to tell the difference between a steamy and a hazy atmosphere. They found the spectrum of GJ 1214b to be featureless over a wide range of wavelengths, or colors. The atmospheric model most consistent with the Hubble data is a dense atmosphere of water vapor.

Since the planet’s mass and size are known, astronomers can calculate the density, of only about 2 grams per cubic centimetre. Water has a density of 1 gram per cubic centimetre, while Earth’s average density is 5.5 grams per cubic centimetre. This suggests that GJ 1214b has much more water than Earth does, and much less rock.

As a result, the internal structure of GJ 1214b would be extraordinarily different from that of our world.

“The high temperatures and high pressures would form exotic materials like ‘hot ice’ or ‘superfluid water’, substances that are completely alien to our everyday experience,” Berta said.

Theorists expect that GJ 1214b formed further out from its star, where water ice was plentiful; later the planet migrated inward towards the star. In the process, it would have passed through the star’s habitable zone, where surface temperatures would be similar to Earth’s. How long it lingered there is unknown.

GJ 1214b is located in the constellation of Ophiuchus (The Serpent Bearer), and just 40 light-years from Earth. Scientists say it will be a prime candidate for study by the NASA/ESA/CSA James Webb Space Telescope, planned for launch later this decade.

This article was updated on Feb. 23

Read the team’s paper (pdf).

Source: ESA Hubble

Posted on by Tammy Plotner

Light Echoes: The Re-Run Of The Eta Carinae “Great Eruption”

The color image at left shows the Carina Nebula, a star-forming region located 7,500 light-years from Earth. The massive double-star system Eta Carinae resides near the top of the image. The star system, about 120 times more massive than the Sun, produced a spectacular outburst that was seen on Earth from 1837 to 1858. The three black-and-white images at right show light from the eruption illuminating dust clouds near the doomed star system as it moves through them. The effect is like shining a flashlight on different regions of a vast cavern. The images were taken over an eight-year span by the U.S. National Optical Astronomy Observatory's Blanco 4-meter telescope at the CTIO. Credit: NASA, NOAO, and A. Rest (Space Telescope Science Institute, Baltimore, Md.)

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In this modern age, we’re used to catching a favorite program at a later time. We use our DVR equipment and, not so long ago, a VCR to record now and watch later. Once upon a great time ago we relied upon a quaint customer called the “re-run” – the same program broadcast at a later date. However, a re-run can’t occur when it comes to astronomy event… Or can it? Oh, you’re gonna’ love this!

Way back in 1837, Eta Carinae had an event they called the “Great Eruption”. It was an outburst so powerful that it was observable in the southern night sky for 21 years. While it could be seen, sketched and recorded for astronomy posterity, one thing didn’t happen – and that was study with modern scientific instruments. But this great double star was about to do an even greater double-take as the light from the eruption continued away from Earth and on towards some dust clouds. Now, 170 years later, the “Great Eruption” has returned to us again in an effect known as a light echo. Because of its longer path, this re-run only took 17 decades to play again!

“When the eruption was seen on Earth 170 years ago, there were no cameras capable of recording the event,” explained the study’s leader, Armin Rest of the Space Telescope Science Institute in Baltimore, Maryland. “Everything astronomers have known to date about Eta Carinae’s outburst is from eyewitness accounts. Modern observations with science instruments were made years after the eruption actually happened. It’s as if nature has left behind a surveillance tape of the event, which we are now just beginning to watch. We can trace it year by year to see how the outburst changed.”

As one of the largest and brightest systems in the Milky Way, Eta Carinae is at home some 7,500 light years from Earth. During the outburst, it shed around one solar mass for every 20 years it was active and it became the second brightest star in the sky. During that time, its signature twin lobes formed. Being able to study an event like this would help us greatly understand the lives of powerful, massive stars on the eve of destruction. Because it is so close, Eta has also been prime candidate for spectroscopic studies, giving us insight on its behavior, including the temperature and speed of the ejected material.

But there’s more…

Eta Carinae could possibly be considered more famous for its “misbehavior”. Unlike stars of its class, Eta is more of a Luminous Blue Variable – an uber bright star known for periodic outbursts. The temperature of the outflow from Eta Carinae’s central region, for example, is about 8,500 degrees Fahrenheit (5,000 Kelvin), which is much cooler than that of other erupting stars. “This star really seems to be an oddball,” Rest said. “Now we have to go back to the models and see what has to change to actually produce what we are measuring.”

Through the eyes of the U.S. National Optical Astronomy Observatory’s Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile, Rest and the team first spotted the light echo in 2010 and then again in 2011 while comparing visible light observations. From there he quickly compared it with another set of CTIO observations taken in 2003 by astronomer Nathan Smith of the University of Arizona in Tucson and pieced together the 20 year old puzzle. What he saw was nothing short of amazing…

“I was jumping up and down when I saw the light echo,” said Rest, who has studied light echoes from powerful supernova blasts. “I didn’t expect to see Eta Carinae’s light echo because the eruption was so much fainter than a supernova explosion. We knew it probably wasn’t material moving through space. To see something this close move across space would take decades of observations. We, however, saw the movement over a year’s time. That’s why we thought it was probably a light echo.”

While the images would appear to move with time, this is only an “optical illusion” as each parcel of light information arrives at a different time. Follow up observations include more spectroscopy pinpointing the outflow’s speed and temperature – where ejected material was clocked at speed of roughly 445,000 miles an hour (more than 700,000 kilometers an hour) – a speed which matched computer modeling predictions. Rest’s group also cataloged changes in the light echo intensity using the Las Cumbres Observatory Global Telescope Network’s Faulkes Telescope South in Siding Spring, Australia. Their results were then compared the historic measurements during the actual event and the peak brightness findings matched!

You can bet the team is continuing to monitor this re-run very closely. “We should see brightening again in six months from another increase in light that was seen in 1844,” Rest said. “We hope to capture light from the outburst coming from different directions so that we can get a complete picture of the eruption.”

Original Story Source: HubbleSite News Release. For Further Reading: Nature Science Paper by A. Rest et al.

Posted on by Tammy Plotner

Young Star Cluster In Disintegrated Galaxy Reveals First-Ever Intermediate Mass Black Hole

This spectacular edge-on galaxy, called ESO 243-49, is home to an intermediate-mass black hole that may have been stripped off of a cannibalized dwarf galaxy. Credit: NASA, ESA, and S. Farrell (Sydney Institute for Astronomy, University of Sydney)

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Score another first for NASA’s Hubble Space Telescope! Along with observations taken with the Swift X-ray telescope, a team of astronomers have identified a young stellar cluster of stars pointing the way towards the first verified intermediate mass black hole. This grouping of stars provides significant indication that black holes of this type may have been at the center of a now shredded dwarf galaxy – a finding which increases our knowledge of galaxy evolution.

“For the first time, we have evidence on the environment, and thus the origin, of this middle-weight black hole,” said Mathieu Servillat, a member of the Harvard-Smithsonian Center for Astrophysics research team.

Designated as ESO 243-49 HLX-1, this incredible intermediate mass black hole was discovered in 2009 by Sean Farrell, of the Sydney Institute for Astronomy in Australia, using the European Space Agency’s XMM-Newton X-ray space telescope. Hyper-Luminous X-ray Source 1 is a 20,000 solar mass beauty which resides at the edge of galaxy ESO 243-49 some 290 million light years away. However, the Newton’s findings weren’t the only contribution – HLX-1 was also verified with NASA’s Swift observatory in X-ray and Hubble in near-infrared, optical, and ultraviolet wavelengths. What stands out is the presence of a cluster of young stars encircling the black hole and stretching out across about 250 light years of space. While the stars themselves are too far away to be resolved, their magnitude and spectra match with other young clusters seen in similar galaxies.

Just what clued the team to the presence of a star cluster? In this case their instruments revealed the blue spectrum of hot gases being emitted from the accretion disk located at the periphery of the black hole… and there was more. They also noted the presence of red light spawned by cooler gases which may indicate the presences of stars. Time to match up the findings against computer modeling.

“What we can definitely say with our Hubble data is that we require both emission from an accretion disk and emission from a stellar population to explain the colors we see.” said Farrell.

Why is the presence of a young star cluster unusual? According to what we know so far, they just don’t occur outside a flattened disk such as HLX-1. This finding may indicate the intermediate mass black hole may have once been at the heart of a dwarf galaxy engaged in a merger event. The dwarf galaxy’s stars were stripped away, but not its capabilities to form new. During the interaction, the gas around the black hole was compressed and star formation began again… but how long ago?

“The age of the population cannot be uniquely constrained, with both very young and very old stellar populations allowed. However, the very old solution requires excessively high levels of disc reprocessing and an extremely small disc, leading us to favour the young solution with an age of ~13 Myr.” says the team. “In addition, the presence of dust lanes and the lack of any nuclear activity from X-ray observations of the host galaxy lead us to propose that a gas-rich minor merger may have taken place less than ~200 Myr ago. Such a merger event would explain the presence of the intermediate mass black hole and support a young stellar population.”

Discoveries such as HLX-1 will help astronomers further understand how supermassive black holes are formed. Current conjecture is that intermediate mass black holes may migrate together to form their larger counterparts. Studying the trajectory of this new find may provide valuable information… even if it is unknown at this point. HLX-1 may be drawn into a merger event and it may just end up orbiting ESO 243-49. Regardless of what happens, chances are it will fade away in X-ray as it exhausts its gas supply.

“This black hole is unique in that it’s the only intermediate-mass black hole we’ve found so far. Its rarity suggests that these black holes are only visible for a short time,” said Servillat.

Original Story Source: Harvard Center for Astrophysics News Release. For Further Reading: A Young Massive Stellar Population Around the Intermediate Mass Black Hole ESO 243-49 HLX-1.

Posted on by Nancy Atkinson

Hubble Captures a Classic Barred Spiral Galaxy

The barred spiral galaxy NGC 1073, which is found in the constellation of Cetus (The Sea Monster). Credit: NASA & ESA

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Is this what we look like? Astronomers don’t know for sure exactly what the Milky Way looks like, but searching out other barred spiral galaxies like this one is helping scientists to learn more about our home. Galaxy NGC 1073 is located in the constellation of Cetus (The Sea Monster).Most of the known spiral galaxies have a bar structure in their center, and this new image offer a stunning, if not clear view of one of these types of galaxies.

One piece of information that might be available from a central bar is the galaxy’s age. Some astronomers have suggested that the formation of a this structure might signal a spiral galaxy’s passage from intense star-formation into adulthood. Two-thirds of nearby, younger galaxies have the bar, while only a fifth of older, more distant spirals have one.

While Hubble’s image of NGC 1073 is in some respects an archetypal portrait of a barred spiral, the Hubble team have pointed out a couple of quirks.

One, ironically, is almost — but not quite — invisible to optical telescopes like Hubble. In the upper left part of the image, a rough ring-like structure of recent star formation hides a bright source of X-rays. Called IXO 5, this X-ray source is likely to be a binary system featuring a black hole and a star orbiting each other. Comparing X-ray observations from the Chandra spacecraft with this Hubble image, astronomers have narrowed the position of IXO 5 down to one of two faint stars visible here. However, X-ray observations with current instruments are not precise enough to conclusively determine which of the two it is.

Hubble’s image does not only tell us about a galaxy in our own cosmic neighborhood, however. We can also discern glimpses of objects much further away, whose light tells us about earlier eras in cosmic history.

Right across Hubble’s field of view, more distant galaxies are peering through NGC 1073, with several reddish examples appearing clearly in the top left part of the frame.

More intriguing still, three of the bright points of light in this image are neither foreground stars from the Milky Way, nor even distant stars in NGC 1073. In fact they are not stars at all. They are quasars, incredibly bright sources of light caused by matter heating up and falling into supermassive black holes in galaxies literally billions of light-years from us. The chance alignment through NGC 1073, and their incredible brightness, might make them look like they are part of the galaxy, but they are in fact some of the most distant objects observable in the Universe.

Source: ESA Hubble

Posted on by Tammy Plotner

Hubble Captures Giant Lensed Galaxy Arc

Thanks to the presence of a natural "zoom lens" in space, this is a close-up look at the brightest distant "magnified" galaxy in the universe known to date. Credit: NASA, ESA, J. Rigby (NASA Goddard Space Flight Center), K. Sharon (Kavli Institute for Cosmological Physics, University of Chicago), and M. Gladders and E. Wuyts (University of Chicago)

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Less than a year ago, the Hubble Space Telescope’s Wide Field Camera 3 captured an amazing image – a giant lensed galaxy arc. Gravitational lensing produces a natural “zoom” to observations and this is a look at one of the brightest distant galaxies so far known. Located some 10 billion light years away, the galaxy has been magnified as a nearly 90-degree arc of light against the galaxy cluster RCS2 032727-132623 – which is only half the distance. In this unusual case, the background galaxy is over three times brighter than typically lensed galaxies… and a unique look back in time as to what a powerful star-forming galaxy looked like when the Universe was only about one third its present age.

A team of astronomers led by Jane Rigby of NASA’s Goddard Space Flight Center in Greenbelt, Maryland are the parties responsible for this incredible look back into time. It is one of the most detailed looks at an incredibly distant object to date and their results have been accepted for publication in The Astrophysical Journal, in a paper led by Keren Sharon of the Kavli Institute for Cosmological Physics at the University of Chicago. Professor Michael Gladders and graduate student Eva Wuyts of the University of Chicago were also key team members.

“The presence of the lens helps show how galaxies evolved from 10 billion years ago to today. While nearby galaxies are fully mature and are at the tail end of their star-formation histories, distant galaxies tell us about the universe’s formative years. The light from those early events is just now arriving at Earth.” says the team. “Very distant galaxies are not only faint but also appear small on the sky. Astronomers would like to see how star formation progressed deep within these galaxies. Such details would be beyond the reach of Hubble’s vision were it not for the magnification made possible by gravity in the intervening lens region.”

This graphic shows a reconstruction (at lower left) of the brightest galaxy whose image has been distorted by the gravity of a distant galaxy cluster. The small rectangle in the center shows the location of the background galaxy on the sky if the intervening galaxy cluster were not there. The rounded outlines show distinct, distorted images of the background galaxy resulting from lensing by the mass in the cluster. The image at lower left is a reconstruction of what the lensed galaxy would look like in the absence of the cluster, based on a model of the cluster's mass distribution derived from studying the distorted galaxy images. Illustration Credit: NASA, ESA, and Z. Levay (STScI) Science Credit: NASA, ESA, J. Rigby (NASA Goddard Space Flight Center), K. Sharon (Kavli Institute for Cosmological Physics, University of Chicago), and M. Gladders and E. Wuyts (University of Chicago)

But the Hubble isn’t the only eye on the sky examining this phenomenon. A little over 10 years ago a team of astronomers using the Very Large Telescope in Chile also measured and examined the arc and reported the distant galaxy seems to be more than three times brighter than those previously discovered. However, there’s more to the picture than meets the eye. Original images show the magnified galaxy as hugely distorted and it shows itself more than once in the foreground lensing cluster. The challenge was to create a image that was “true to life” and thanks to Hubble’s resolution capabilities, the team was able to remove the distortions from the equation. In this image they found several incredibly bright star-forming regions and through the use of spectroscopy, they hope to better understand them.

Original Story Source: Hubble News Release.

Posted on by Paul Scott Anderson

New Research Suggests Fomalhaut b May Not Be a Planet After All

The Fomalhaut b photograph. Credit: NASA, ESA, and P. Kalas (University of California, Berkeley, USA)

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When the Hubble Space Telescope photographed the apparent exoplanet Fomalhaut b in 2008, it was regarded as the first visible light image obtained of a planet orbiting another star. The breakthrough was announced by a research team led by Paul Kalas of the University of California, Berkeley. The planet was estimated to be approximately the size of Saturn, but no more than three times Jupiter’s mass, or perhaps smaller than Saturn according to some other studies, and might even have rings. It resides within a debris ring which encircles the star Fomalhaut, about 25 light-years away.

Another team at Princeton, however, has just announced that they believe the original findings are in error, and that the planet is actually a dust cloud, based on new observations by the Spitzer Space Telescope. Their paper has just been accepted by the Astrophysical Journal.

According to the abstract:

The nearby A4-type star Fomalhaut hosts a debris belt in the form of an eccentric ring, which is thought to be caused by dynamical influence from a giant planet companion. In 2008, a detection of a point-source inside the inner edge of the ring was reported and was interpreted as a direct image of the planet, named Fomalhaut b. The detection was made at ~600–800 nm, but no corresponding signatures were found in the near-infrared range, where the bulk emission of such a planet should be expected. Here we present deep observations of Fomalhaut with Spitzer/IRAC at 4.5 µm, using a novel PSF subtraction technique based on ADI and LOCI, in order to substantially improve the Spitzer contrast at small separations. The results provide more than an order of magnitude improvement in the upper flux limit of Fomalhaut b and exclude the possibility that any flux from a giant planet surface contributes to the observed flux at visible wavelengths. This renders any direct connection between the observed light source and the dynamically inferred giant planet highly unlikely. We discuss several possible interpretations of the total body of observations of the Fomalhaut system, and find that the interpretation that best matches the available data for the observed source is scattered light from transient or semi-transient dust cloud.

Kalas has responded to the new study, saying that they considered the dust cloud possibility but ruled it out for various reasons. For one thing, Spitzer lacks the light sensitivity to detect a Saturn-sized planet, and bright rings could also explain the optical characteristics observed. He says, “We welcome the new Spitzer data, but we don’t really agree with this interpretation.”

The Princeton team, interestingly, thinks that there may be a real planet orbiting Fomalhaut, but still hiding from detection. From the paper:

In particular, we find that there is almost certainly no direct flux from a planet contributing to the visible-light signature. This, in combination with the existing body of data for the Fomalhaut system, strongly implies that the dynamically inferred giant planet companion and the visible-light point source are physically unrelated. This in turn implies that the ‘real’ Fomalhaut b still hides in the system. Although we do find a tentative point source in our images that could in principle correspond to this object, its significance is too low to distinguish whether it is real or not at this point.

A resolution to the debate may come from the James Webb Space Telescope, scheduled to launch in 2018.

Of course it will be disappointing if Fomalhaut b does turn out to not be a planet after all, but let’s not forget that thousands of other ones are being discovered and confirmed. There may occasionally be hits-and-misses, but so far the planetary hunt overall has been nothing short of a home run…

The paper is available here.

Posted on by VirtualAstro

Why Does Sirius Twinkle?

Orion and Sirius Credit Adrian West

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At this time of year, after dark we in the northern hemisphere are able to see the mighty constellation of Orion rise high in the sky with a very bright companion in a nearby constellation: Sirius – The Dog Star.

Sirius is the brightest star in the sky and can easily be found in the faint constellation of Canis Major to the left and below Orion. Its name comes from ancient Greek meaning “glowing” or “scorcher.”

Sirius (α CMa) is the alpha star in this trusty hound and is roughly 8.5 light years away from Earth, making it one of the closest stars to us. It has a tiny companion star making it a binary system composed of “Sirius A” the main component (which is a white main sequence star) and “Sirius B,” a white dwarf star. As seen with the naked eye, Sirius can be seen to twinkle many different colours low in the winter evening sky.

Sirius A
Sirius. Image credit: Hubble

So why does Sirius twinkle?

It’s not just Sirius that twinkles; all stars twinkle. Light travels many light years from stars and right at the end of its journey, it hits Earth’s atmosphere, which consists of nitrogen, oxygen and other gasses.

Earth’s atmosphere is constantly swirling around, and wind and air currents etc distort light travelling through it. This causes the light to slightly bend or shimmer and the light from distant stars twinkle. An extreme, more down-to-Earth example of this would be heat rising off of a road or a desert causing objects behind it to distort, shimmer and change colour.

Sirius appears to twinkle or shimmer more than other stars for some very simple reasons. It is very bright, which can amplify atmospheric effects and it is also very low down in the atmosphere for those in the northern hemisphere. We are actually looking at it through a very dense part of the atmosphere which can be turbulent and contain many different particles and dust. The lower towards the horizon an observer is looking, the thicker the atmosphere. The higher an observer is looking, the thinner the atmosphere. This is also the cause of colourful sunrise and sunsets.

(Addition due to the questions in the comment section: planets don’t usually twinkle because they are closer and therefore bigger — they are disks of light instead of faraway points of light. The larger disks of light usually aren’t distorted; however if you are looking through especially turbulent areas of our atmosphere, and even sometimes when looking at planets that are low in the thicker parts of the atmosphere, they will twinkle. Phil Plait, the Bad Astronomer explains it very well on his website.)

This optical illusion is a big pain for astronomers and some very large telescopes such as those in Chile and Hawaii use special equipment and techniques to reduce the effects of the atmosphere.

One of most famous telescope of them all, the Hubble Space Telescope doesn’t get affected at all by our atmosphere as it is in space, making the light from stars crystal clear.

Twinkle, twinkle little star, now we know what you are (and why you are twinkling!)

Posted on by Tammy Plotner

Supernova Primo – Out To Far Frontiers

The top image shows part of the Hubble Ultra Deep Field, the region where astronomers were looking for a supernova blast. The white box pinpoints the area where the supernova is later seen. The image combines observations taken in visible and near-infrared light with the Advanced Camera for Surveys and the Wide Field Camera 3. The image at bottom left, taken by the Wide Field Camera 3, is a close-up of the field without the supernova. A new bright object, identified as the supernova, appears in the Wide Field Camera 3 image at bottom right. Credit: NASA, ESA, A. Riess (Space Telescope Science Institute and The Johns Hopkins University), and S. Rodney (The Johns Hopkins University)

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Its nickname is SN Primo and it’s the farthest Type Ia supernova to have its distance spectroscopically confirmed. When the progenitor star exploded some 9 billion years ago, Primo sent its brilliant beacon of light across time and space to be captured by the Hubble Space Telescope. It’s all part and parcel of a three-year project dealing specifically with Type Ia supernovae. By splitting its light into constituent colors, researchers can verify its distance by redshift and help astronomers better understand not only the expanding Universe, but the constraints of dark energy.

“For decades, astronomers have harnessed the power of Hubble to unravel the mysteries of the Universe,” said John Grunsfeld, associate administrator for NASA’s Science Mission Directorate in Washington. “This new observation builds upon the revolutionary research using Hubble that won astronomers the 2011 Nobel Prize in Physics, while bringing us a step closer to understanding the nature of dark energy which drives the cosmic acceleration.”

Type Ia supernovae are theorized to have originated from white dwarf stars which have collected an excess of material from their companions and exploded. Because of their remote nature, they have been used to measure great distances with acceptable accuracy. Enter the CANDELS+CLASH Supernova Project… a type of census which utilizes the sharpness and versatility of Hubble’s Wide Field Camera 3 (WFC3) to aid astronomers in the search for supernovae in near- infrared light and verify their distance with spectroscopy. CANDELS is the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey and CLASH is the Cluster Lensing and Supernova Survey with Hubble.

“In our search for supernovae, we had gone as far as we could go in optical light,” said Adam Riess, the project’s lead investigator, at the Space Telescope Science Institute and The Johns Hopkins University in Baltimore, Md. “But it’s only the beginning of what we can do in infrared light. This discovery demonstrates that we can use the Wide Field Camera 3 to search for supernovae in the distant Universe.”

However, discovering a supernova like Primo just doesn’t happen overnight. It took the research team several months of work and a huge amount of near-infrared images to locate the faint signature. After capturing the elusive target in October 2010, it was time to employ the WFC3’s spectrometer to validate SN Primo’s distance and analyze the spectra for confirmation of a Type Ia supernova event. Once verified, the team continued to image SN Primo for the next eight months – collecting data as it faded away. By engaging the Hubble in this type of census, astronomers hope to further their understanding of how such events are created. If they should discover that Type Ia supernova don’t always appear the same, it may lead to a way of categorizing those changes and aid in measuring dark energy. Riess and two other astronomers shared the 2011 Nobel Prize in Physics for discovering dark energy 13 years ago, using Type Ia supernova to plot the Universe’s expansion rate.

“If we look into the early Universe and measure a drop in the number of supernovae, then it could be that it takes a long time to make a Type Ia supernova,” said team member Steve Rodney of The Johns Hopkins University. “Like corn kernels in a pan waiting for the oil to heat up, the stars haven’t had enough time at that epoch to evolve to the point of explosion. However, if supernovae form very quickly, like microwave popcorn, then they will be immediately visible, and we’ll find many of them, even when the Universe was very young. Each supernova is unique, so it’s possible that there are multiple ways to make a supernova.”

Original Story Source: Hubble Site News Release.

Posted on by Nancy Atkinson

Hubble Provides Evidence for ‘Double Degenerate Progenitor’ Supernova

Supernova remnant SNR 0509-67.5. Supernovae provided the heavier elements in the Sun. Image credit: NASA/ESA/CXC
Supernova remnant SNR 0509-67.5. Supernovae provided the heavier elements in the Sun. Image credit: NASA/ESA/CXC

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What happened 400 years ago to create this stunningly beautiful supernova remnant – and were there two culprits or just one? This Hubble Space Telescope view of a Type Ia-created remnant has helped astronomers solve a longstanding mystery on the type of stars that cause some supernovae, known as a progenitor.

“Up until this point we haven’t really known where this type of supernova came from, despite studying them for decades,” said Ashley Pagnotta of Louisiana State University, speaking at a press briefing at the American Astronomical Society meeting on Wednesday. “But we now can say we have the first definitive identification of a Type 1a progenitor, and we know this one must have had a double degenerate progenitor – it is the only option.”

This supernova remnant that has a telephone number-like name of SNR 0509-67.5, lies 170,000 light-years away in the Large Magellanic Cloud galaxy.

Astronomers have long suspected that two stars were responsible for the explosion – as is the case with most type 1a supernovae — but weren’t sure what triggered the explosion. One explanation could be that it was caused by mass transfer from a companion star where a nearby star spills material onto a white dwarf companion, setting off a chain reaction that causes one of the most powerful explosions in the universe. This is known as the ‘single-degenerate’ path – which seems to be the most plausible, common and most preferred explanation for many Type 1a supernovae.

The other option is the collision of two white dwarfs, which is known as ‘double-degenerate, which seems to be the less common and not as widely accepted explanation for supernovae. To many astrophysicists, the merger scenario seemed to be less likely because too few double-white-dwarf systems appear to exist; indeed, there appear to be just handful that have been discovered so far.

The problem with SNR 0509-67.5 was that astronomers could not find any remnant of the companion star. That’s why the double degenerate scenario was considered, as in that case, there won’t be anything left as both white dwarfs are consumed in the explosion. In the case of a single progenitor, the non-white dwarf star will still be near the explosion site and will still look very much as it did before the explosion.

Therefore, a possible way to distinguish between the various progenitor models has been to look deep in the center of an old supernova remnant to search for the ex-companion star.

“We know Hubble has the sensitivity necessary to detect the faintest white dwarf remnants that could have caused such explosions,” said lead investigator Bradley Schaefer from LSU. “The logic here is the same as the famous quote from Sherlock Holmes: ‘when you have eliminated the impossible, whatever remains, however improbable, must be the truth.'”

In 2010, Schaefer and Pagnotta were preparing a proposal to look for any faint ex-companion stars in the center of four supernova remnants in the Large Magellanic Cloud when they saw an Astronomy Picture of the Day photo showing an image the Hubble Space Telescope had already had taken of one of their target remnants, SNR 0509-67.5.

(Note: the January 12, 2012 APOD image is of SNR 0509-67.5!)

Because the remnant appears as a nice symmetric shell or bubble, the geometric center can be determined accurately. In analyzing in more detail the central region, they found it to be completely empty of stars down to the limit of the faintest objects Hubble can detect in the photos. The young age also means that any surviving stars have not moved far from the site of the explosion. They were able to cross off the list all the possible single degenerate scenarios, and were left with the double degenerate model in which two white dwarfs collide.

“Since we can exclude all the possible single degenerates, we know it must be a double degenerate,” Pagnotta said. “The cause of SNR 0509-67.5 can be explained best by two tightly orbiting white dwarf stars spiraling closer and closer until they collided and exploded.”

Pagnotta also noted that this supernova is actually not a normal Type 1a supernova, but a subclass called 1991t, which is an extra bright supernova.

A paper in 2010 by Marat Gilfanov of the Max Planck Institute for Astrophysics indicated that perhaps many Type 1a supernova were caused by two white dwarf stars colliding, which was a surprise to many astronomers. Additionally, a review of the recent supernova SN 2011fe, which exploded in August of 2011, explores the possibility of the double degenerate progenitor. An open question remains whether these white dwarf mergers are the primary catalyst for Type Ia supernovae in spiral galaxies. Further studies are required to know if supernovae in spiral galaxies are caused by mergers or a mixture of the two processes.

Schaefer and Pagnotta plan to look at other supernova remnants in the Large Magellenic Cloud to further test their observations.

Pagnotta confirmed that anyone with an internet connection could have made this discovery, as all the Hubble images used were available publicly, and the use of the Hubble data was sparked by APOD.

Sources: Science Paper by Bradley E. Schaefer and Ashley Pagnotta (PDF document), HubbleSite, AAS press briefing