Posted on by Tammy Plotner

Exploring Geomagnetic Substorms

Schematic view of Cluster C3 and C1 satellite trajectories Copyright: ESA

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Every now and again, a sudden pulse of energy in Earth’s magnetosphere just cuts loose. As a result, we have a bright polar auroral display. While we’re beginning to understand more about magnetism and the Sun/Earth connection, there’s still a few rogues left in the gallery. Just what is a geomagnetic substorm and what does it do?

Although we’ve known about them for years, the exact process behind a geomagnetic substorm has been a mystery… one that’s being solved with data from missions like ESA’s Cluster spacecraft. Earth is continually being bathed in incoming sheets of electrons and protons – the product of an active Sun. These highly energized particles are simply a part of solar winds flowing from coronal holes and even powerful blasts from events like coronal mass ejections. For the most part, we’re shielded by the magnetosphere – but sometimes a wee bit escapes and collects in the magnetotail – stored like a battery charge. At a point, it’s released… and when it does, it re-arranges our magnetic field lines. The energy then conducts itself along these lines like a filament in a light bulb. When the watts hit the fan? Wow… We have polar aurora!

It’s not a new concept, but there’s never been a clear understanding of where these geomagnetic storms originate. Do they come from a sudden disruption of electric current about 64 000 km from the planet? Or are the created by a process called magnetic reconnection which occurs much further down the magnetotail, at a distance of around 125 000 – 200 000 km? If you remember our recent study of Alfven waves, then you know current consensus points towards the reconnection theory. But there’s only one problem. Alfven waves are slow movers, traveling at a reconnection speed of about 250 seconds. What we’re seeing is an event that occurs about 60 seconds after reconnection… and the birth of a new movement. The kinetic Alfven wave (KAW).

“We ran a very simple system, and simulated how the reconnection event released energy in the plasma sheet of charged particles,” said Shay. “We were looking for a faster mechanism for propagating the signal from the explosion than the Alfven waves that were already widely recognized.”

Unlike its predecessor which motivates both ions and electrons, the KAW only excites the electron, moving them through the plasma at twice the speed. Through simulations, it’s been proved the kinetic Alfven wave could be spawned by reconnection, move away from the explosion and activate aurora. The data was returned by the Fluxgate Magnetometer (FGM) and the Electric Fields and Waves (EFW) instrument and found by Jonathan Eastwood, a Research Fellow at The Blackett Laboratory, Imperial College London.

“I found 18 events which occurred at the time the four spacecraft were flying through the tail region,” said Dr. Eastwood. “The fast signal predicted by Michael Shay showed up in the Cluster data, supporting the theory that kinetic Alfven waves generated by reconnection were rapidly energizing the auroras.”

“It’s rather like what happens in a thunderstorm,” he added. “The fast-moving lightning flash arrives first, followed some time later by the slower sound waves of the thunderclap.”

Fancy that… Coming from a substorm!

Original Story Source: ESA Science and Technology News. For Further Reading: Super-Alfvenic Propagation of Substorm Reconnection Signatures and Poynting Flux.

Posted on by Tammy Plotner

Milky Way Harbors “Ticking Time Bombs”

New research shows that some old stars known as white dwarfs might be held up by their rapid spins, and when they slow down, they explode as Type Ia supernovae. Thousands of these "time bombs" could be scattered throughout our Galaxy. In this artist's conception, a supernova explosion is about to obliterate an orbiting Saturn-like planet. Credit: David A. Aguilar (CfA)

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According to new research, the only thing that may be keeping elderly stars from exploding is their rapid spin. In a galaxy filled with old stars, this means we could literally be sitting on a nearby “time bomb”. Or is this just another scare tactic?

“We haven’t found one of these ‘time bomb’ stars yet in the Milky Way, but this research suggests that we’ve been looking for the wrong signs. Our work points to a new way of searching for supernova precursors,” said astrophysicist Rosanne Di Stefano of the Harvard-Smithsonian Center for Astrophysics (CfA).

In light of the two recently discovered supernova events in Messier 51 and Messier 101, it isn’t hard to imagine the Milky Way having more than one candidate for a Type Ia supernova. This is precisely the type of stellar explosion Di Stefano and her colleagues are looking for… and it happens when a white dwarf star goes critical. It has reached Chandrasekhar mass. Add any more weight and it blows itself apart. How does this occur? Some astronomers believe Type Ia supernova are sparked by accretion from a binary companion – or a collision of two similar dwarf stars. However, there hasn’t been much – if any – evidence to support either theory. This has left scientists to look for new answers to old questions. Di Stefano and her colleagues suggest that white dwarf spin might just be what we’re looking for.

“A spin-up/spin-down process would introduce a long delay between the time of accretion and the explosion. As a white dwarf gains mass, it also gains angular momentum, which speeds up its spin. If the white dwarf rotates fast enough, its spin can help support it, allowing it to cross the 1.4-solar-mass barrier and become a super-Chandrasekhar-mass star. Once accretion stops, the white dwarf will gradually slow down. Eventually, the spin isn’t enough to counteract gravity, leading to a Type Ia supernova.” explains Di Stefano. “Our work is new because we show that spin-up and spin-down of the white dwarf have important consequences. Astronomers therefore must take angular momentum of accreting white dwarfs seriously, even though it’s very difficult science.”

Sure. It might take a billion years for the spin down process to happen – but what’s a billion years in cosmic time? In this scenario, it’s enough to allow accretion to have completely stopped and a companion star to age to a white dwarf. In the Milky Way there’s an estimated three Type Ia supernovae every thousand years. If figures are right, a typical super-Chandrasekhar-mass white dwarf takes millions of years to spin down and explode. This means there could be dozens of these “time bomb” systems within a few thousand light-years of Earth. While we’re not able to ascertain their locations now, upcoming wide-field surveys taken with instruments like Pan-STARRS and the Large Synoptic Survey Telescope might give us a clue to their location.

“We don’t know of any super-Chandrasekhar-mass white dwarfs in the Milky Way yet, but we’re looking forward to hunting them out,” said co-author Rasmus Voss of Radboud University Nijmegen, The Netherlands.

And the rest of us hope you don’t find them…

Original Story Source: Harvard Smithsonian Center for Astrophysics News. For Further Reading: Spin-Up/Spin-Down models for Type Ia Supernovae.

Posted on by Tammy Plotner

Astrophoto: “The Center Of Our Galaxy Is A Busy Place” by Mike Romine

Not only is the center of our galaxy a busy place for seeing deep space objects – but near ones as well! In this photo taken by Mike Romine, you’ll see many Messier and NGC objects, but one feature really stands out – the ISS. Before you move on, stop and take a closer look. You’ll also find the signatures of an airplane and a tumbling satellite in the frame as well! (Hint: These show up as perfectly spaced series of dots.)

This image was taken on September 4 with a Canon EOS 50D, 135mm lens, F/5.6, ISO 1600, 90 seconds, mounted on a Celestron SCT on a CG5-GT mount at approximately 9:00 pm EST.

Want to get your astrophoto featured on Universe Today? Join our Flickr group, post in our Forum or send us your images by email (this means you’re giving us permission to post them). Please explain what’s in the picture, when you took it, the equipment you used, etc.

Posted on by Tammy Plotner

Astrophoto: “Hanging On To A Comet” by Mike Romine

For those of us who had the opportunity to chase Comet Garradd this weekend, half the joy was catching it crossing the “Coathanger” cluster! In this great shot by Mike Romine, the comet appears along the curve of the upside down 2 of the asterism. Mike took this shot without a telescope, using a Canon EOS 50D, 135mm lens, F/5.6, ISO 1600, 90 seconds, mounted on a Celestron SCT on a CG5-GT mount at 12:45 AM. Nice catch!

Want to get your astrophoto featured on Universe Today? Join our Flickr group, post in our Forum or send us your images by email (this means you’re giving us permission to post them). Please explain what’s in the picture, when you took it, the equipment you used, etc.

Posted on by Tammy Plotner

NASA – Eyes On The Solar System

Are you ready for a fascinating virtual experience? Then check out “Eyes on the Solar System”! This clever compilation of visualizations and real images takes you on a journey that’s sure to keep you entertained for hours!

If you’ve had the chance to use high dollar astronomy software, you’ll appreciate this free program. Inside is a 3-D environment full of real NASA mission data which lets you explore the cosmos from the comfort of your computer. You can choose exploring an asteroid, scouring around a planet or taking a look at Earth from above. Fly with NASA’s Voyager 2 spacecraft or join Cassini. You can even see the entire solar system moving in real time! Just check out a very small part of the features in this introductory video…

There’s so much more there, too. Imagine the possibilities of Kepler, Lunar Reconnaissance Orbiter and the Spitzer Space Telescope! Move forward and backward in time… You’re in command of this space journey! According to the developers, the awesome modeling team is currently working on a number of spacecraft models. In the near future, expect to see finished models of Phoenix (cruise), Mars Exploration Rovers (cruise), Mars Science Laboratory (cruise), Mars Odyssey, and Mars Express. There are many spacecraft in the pipeline, so be patient!

While NASA’s “Eyes on the Solar System” is compatible with Windows and Mac OS X, the partially Java-scripted format has a certain dependence on what browser is used. Firefox is recommended for smoothest operation, but it also works with IE and Safari. (I personally use Opera and encountered no problems – but avoid Chrome.) Other than that? Grab and comfy seat and take flight!

Posted on by Tammy Plotner

Mars Express Delivers Views Of Martian Lake

Holden crater is 140 km across, filling the left side of the image, while to the right is the remaining part of Eberswalde crater, with a diameter of about 65 km. They are located in the southern highlands of Mars. North is to the right of the image. The image was acquired by Mars Express at approximately 25°S / 326°E during orbit 7208 on 15 August 2009. The images have a ground resolution of about 22 m per pixel. Credits: ESA/DLR/FU Berlin (G. Neukum)

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In the southern highlands of Mars, Eberswalde crater to be exact, ESA’s Mars Express exploration has pinpointed an area which once held a lake. Although it may have been some 4 billion years ago, the geologic remains – called a delta – are still evident in the new images. This region of dark sediments are a shadowed reminder that Mars once had water.

Formed by an asteroid strike, Eberswalde crater has nearly eroded away with time. After it formed, it was partially obliterated by another impact which shaped 140 km diameter crater Holden. Although this second strike buried Eberswalde with ejecta, 115 square kilometers of delta area and feeder channels survived. These channels once were the arteries that pumped water along the surface to pool in the crater’s interior, forming a lake. As they carried water, they also carried sediments and – just as on Earth – left their mark. With time, the water dried up and even more sediments were carried along by the wind, exposing the area in vivid relief.

NASA’s Mars Global Surveyor spacecraft spied the delta in earlier missions, giving even further solidification that Mars was once a wet world. While Eberswalde crater and Holden crater were once a part of a list of possible landing sites for the Mars Science Laboratory, Gale crater was selected as the Curiosity’s landing site, given its high mineral and structural diversity related to water. But don’t count this wonderful, wet confession of a lake out forever. Thanks to high mineral diversity and suggestive structure, we’re sure to visit the delta of Eberswalde and Holden again, from orbit or with another landing mission.

Original Story Source: ESA News.

Posted on by Tammy Plotner

HARPS Tunes In On Habitable Planet

Artist Concept of Extra-Solar Planet Courtesy of NASA

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Using the High Accuracy Radial velocity Planet Searcher (HARPS), a team of scientists at University of Geneva, Switzerland, led by the Swiss astronomer Stephane Udry made a sound discovery… an Earth-like planet orbiting star HD 85512. Located about 36 light years away in the constellation of Vela, this extrasolar planet is one of the smallest to be documented in the “habitable zone” and could very well be a potential home to living organisms.

Circling its parent star every 54 days at about the quarter of the distance which Earth orbits the Sun, the newly discovered planet shows every sign of a temperate climate and a possibility of water. However, the rocky little world would need to exhibit some very cloudy skies to make the grade.

“We model rocky planets with H2O/CO2/N2 atmospheres, representative of geological active planets like Earth, to calculate the maximum Bond albedo as a function of irradiation and atmosphere composition and the edges of the HZ for HD 85512 b. These models represent rocky geological active planets and produce a dense CO2 atmosphere at the outer edge, an Earth-like atmosphere in the middle, and a dense H2O atmospheres at the inner edge of the HZ.” says the team. “The inner limit for the 50% cloud case corresponds to the “Venus water loss limit”, a limit that was empirically derived from Venus position in our Solar System (0.72 AU).”

But there’s always from one extreme to another when it comes to a planet being in just the right place. “The inner edge of the (Habitable zone) denotes the location where the entire water reservoir can be vaporized by runaway greenhouse conditions, followed by the photo-dissociation of water vapor and subsequent escape of free hydrogen into space. The outer boundary denotes the distance from the star where the maximum greenhouse effect fails to keep CO2 from condensing permanently, leading to runaway glaciation,” says the Kaltenegger/Udry/Pepe study.

While the whole scenario might not be exciting to some, the study is helping to lay a very solid foundation for evaluating current and future planet candidates for life supporting conditions. “A larger sample will improve our understanding of this field and promises to explore a very interesting parameter space that indicates the potential coexistence of extended H/He and H2O dominated atmospheres as well as rocky planet atmospheres in the same mass and temperature range.” says Kaltenegger. “HD 85512 b is, with Gl 581 d, the best candidate for exploring habitability to date, a planet on the edge of habitability.”

And one step closer to better understanding what’s out there…

For further reading: A Habitable Planet around HD 85512?.

Posted on by Tammy Plotner

Weekend Observing Alert: Moon Occults Delta Scorpii

Occultation Path For Delta Scorpii - September 3, 2011 Courtesy of IOTA

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Are you ready for a weekend observing treat? Then get out your binoculars, telescopes, or just your eyes as the Moon passes over a bright star. Who, what, when and where? Come on inside and find out…

On September 3, 2001 the dark limb of the Moon will encounter 2.3 magnitude Delta Scorpii. The event can be seen from the eastern and southern United States to northern Venezuela. But don’t be discouraged if you aren’t right in that “zone”. For observers from roughly New York City through central Texas to Baja California, you’ll have an event called a “graze” – where the star will appear to slide along the edge – or just be mighty close.

When do you need to observe? Thankfully the event takes place in the early evening, starting around 10:30 p.m. Eastern Daylight Savings time. But don’t wait until that moment to begin your observations! Get your equipment set up in advance and consult with this IOTA page for precise times and locations.

What do you need to observe an occultation? In this circumstance, the Moon isn’t quite half lit, so the glare won’t be so bad that you can’t observe with your eyes alone. However, a pair of binoculars or a small telescope will make the event far more interesting! For even more fun, take along an accurate watch and time it yourself. If you are in the occultation path, watch to see if Delta disappears and reappears behind a crater rim. Then watch as the whole scene shifts west and the star emerges again!

It’s all great fun and we wish you clear skies!

Posted on by Tammy Plotner

Galaxy Bets On A Pair Of Black Holes

How X-rays Work
This main image is a composite of X-rays from Chandra (blue) and optical data from the Hubble Space Telescope (gold) of the spiral galaxy NGC 3393. Meanwhile, the inset box shows the central region of NGC 3993 as observed just by Chandra.

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About 160 million light years away in the constellation of Hydra, spiral galaxy NGC 3393 has been keeping a billion year old secret. It might have a poker face, but it has a pair of black holes up its sleeve…

Using information obtained through NASA’s Chandra X-ray Observatory combined with Hubble Space Telescope imaging, scientists have uncovered first time evidence that NGC 3393 is harboring twin supermassive black holes. Residing only 490 light years apart, the duo may have been the product of a “minor merger” – where a small and large galaxy met. Although the hypothesis of two black holes within one galaxy isn’t new, it has been difficult to prove because the results of two galaxies combining material would result in a rather ordinary looking spiral.

“The current picture of galaxy evolution advocates co-evolution of galaxies and their nuclear massive black holes, through accretion and galactic merging.” says G. Fabbiano, lead author of a recent Nature paper. “Pairs of quasars, each with a massive black hole at the centre of its galaxy, have separations of 6,000 to 300,000 light years and exemplify the first stages of this gravitational interaction.”

If scientific calculations are correct, a smaller galaxy should have contained a smaller mass black hole. This leaves us with an odd situation. If both of these newly discovered black holes have similar mass, shouldn’t the merging pair also be of similar mass? If so, how could a minor merger be the answer?

“The final stages of the black-hole merging process, through binary black holes and final collapse into a single black hole with gravitational wave emission, are consistent with the sub-light-year separation inferred from the optical spectra and light-variability of two such quasars. The double active nuclei of a few nearby galaxies with disrupted morphology and intense star formation demonstrate the importance of major mergers of equal-mass spiral galaxies in this evolution.” says Fabbiano. “Minor mergers of a spiral galaxy with a smaller companion should be a more common occurrence, evolving into spiral galaxies with active massive black-hole pairs, but have hitherto not been seen. The regular spiral morphology and predominantly old circum-nuclear stellar population of this galaxy, and the closeness of the black holes embedded in the bulge, provide a hitherto missing observational point to the study of galaxy/black hole evolution.”

Lay down your bets, gentlemen… It seems the game changes each time it is played!

Original Story Source: Chandra News. For Further Reading: A close nuclear black-hole pair in the spiral galaxy NGC 3393.

Posted on by Tammy Plotner

The Genesis of Galaxy Eris…

This image of the Eris simulation shows the stars in the galaxy as observers would see it. Blue colors are regions of recent star formation, while redder regions are associated with older stars. The spiral arms are typically star-forming, and the central bulge is basically "red and dead." Credit: J. Guedes and P. Madau.

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In as much time as it takes to give birth to human life, a supercomputer and a team of researchers at the University of California, Santa Cruz, and the Institute for Theoretical Physics in Zurich have given rise to the first simulation of the physics involved in galaxy formation that produced the Milky Way. They named their child Eris…

“Previous efforts to form a massive disk galaxy like the Milky Way had failed, because the simulated galaxies ended up with huge central bulges compared to the size of the disk,” said Javiera Guedes, who recently earned her Ph.D. in astronomy and astrophysics at UC Santa Cruz and is first author of a paper which has been accepted for publication in the Astrophysical Journal.

This comparison shows the Eris simulation (top) and the Milky Way (bottom). Credit: S. Callegari, J. Guedes, and the 2MASS collaboration.
Like the Milky Way, Eris is a lovely barred spiral galaxy – her figure and star content as identical as modeling can make it. By studying our own galaxy and others like it, this simulation fits the mold from every angle. “We dissected the galaxy in many different ways to confirm that it fits with observations,” Guedes said.

And “seven sisters” were involved in the project, too. NASA’s state-of-the-art Pleiades supercomputer took on the task of 1.4 million processor-hours. But the calculations didn’t stop there. Simulations on supercomputers at UCSC and the Swiss National Supercomputing Center were involved, too. “We took some risk spending a huge amount of supercomputer time to simulate a single galaxy with extra-high resolution,” Madau said.

For over two decades, attempts at creating the evolution of a Milky Way type galaxy have been just outside the grasp of researchers. They just weren’t able to produce the proper shape, size and population to fit known properties. Thanks to this new breakthrough, support for the “cold dark matter” theory has predominated and the Big Bang theory supported. What gave Eris the edge? Try our now better understanding star formation.

“Star formation in real galaxies occurs in a clustered fashion, and to reproduce that out of a cosmological simulation is hard,” Madau said. “This is the first simulation that is able to resolve the high-density clouds of gas where star formation occurs, and the result is a Milky Way type of galaxy with a small bulge and a big disk. It shows that the cold dark matter scenario, where dark matter provides the scaffolding for galaxy formation, is able to generate realistic disk-dominated galaxies.”

Giving birth to Eris wasn’t an easy task. Through low-resolution simulations, researchers began assembling clumps of dark matter – shaping them into galactic halos. From there they selected information on a halo with similar mass and merger history to our own and “rewound the tape” to its infancy. By focusing on a small area, they were able to add additional particle information and step up the resolution.

“The simulation follows the interactions of more than 60 million particles of dark matter and gas. A lot of physics goes into the code–gravity and hydrodynamics, star formation and supernova explosions–and this is the highest resolution cosmological simulation ever done this way,” said Guedes, who is currently a postdoctoral researcher at the Swiss Federal Institute of Technology in Zurich (ETH Zurich).

What sets Eris apart from its predecessors is the ability to “see” in high resolution / high density. This allows for a more pragmatic approach to star formation and placement. It’s an important consideration, because supernova occur in high density regions and high resolution allows them to be taken into account.

“Supernovae produce outflows of gas from the inner part of the galaxy where it would otherwise form more stars and make a large bulge,” Madau said. “Clustered star formation and energy injection from supernovae are making the difference in this simulation.”

Arise, Eris… Your time has come!

Original Story Source: University of Santa Cruz News. For Further Reading: Forming Realistic Late-Type Spirals in a LCDM Universe: The Eris Simulation.