28 Aug 2014

September 2014 | Comets Unveiled

Comets are colourful fuzz-balls in space that have a small rocky nucleus, a shimmering hallo of dust known as the coma, and a long dusty tail stretching thousands of miles in length. They have been seen by sky watchers for centuries, and were once believed to be omens to bad fortune.

Over the last decade, a number of spacecraft have visited comets, and have helped to reveal their secrets, in this month's program we look at some of their findings to help better understand the discoveries that await us from Rosetta over the next year.

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Scientists spot white dwarf reigniting and exploding

1409185370430_wps_2_Astronomers_studying_SN20It is a blaze of glory rarely seen in the universe.

Astronomers have proved for the first time that dead stars known as white dwarfs can reignite and explode as supernovae.

These incredible images were created to show the stages of the spectacular death,The finding came after the unique signature of gamma rays from the radioactive elements created in one of these explosions was captured for the first time.

Astronomers using ESA's Integral gamma-ray observatory now say they have demonstrated beyond doubt that dead stars known as white dwarfs can reignite and explode as supernovae. 

The 'smoking gun' in this case was evidence for radioactive nuclei being created by fusion during the thermonuclear explosion of the white dwarf star, the European Space agency said.

'Integral has all the capabilities to detect the signature of this fusion, but we had to wait for more than ten years for a once-in-a-lifetime opportunity to catch a nearby supernova,' says Eugene Churazov, from the Space Research Institute (IKI) in Moscow, Russia and the Max Planck Institute for Astrophysics,in Garching, Germany.

Although Type IA supernovae are expected to occur frequently across the Universe they are rare occurrences in any one galaxy, with typical rates of one every few hundred years.

Integral's chance came on 21 January 2014, when students at the University College London's teaching observatory at Mill Hill, UK detected a type IA supernova, later named SN2014J, in the nearby galaxy M82.

According to the theory of such explosions, the carbon and oxygen found in a white dwarf should be fused into radioactive nickel during the explosion.

This nickel should then quickly decay into radioactive cobalt, which would itself subsequently decay, on a somewhat longer timescale, into stable iron. Because of its proximity – at a distance of about 11.5 million light-years from Earth, SN2014J is the closest of its type to be detected in decades – Integral stood a good chance of seeing the gamma rays produced by the decay.

Within one week of the initial discovery, an observing plan to use Integral had been drawn-up and approved.

Using Integral to study the aftermath of the supernova explosion, scientists looked for the signature of cobalt decay – and they found it, in exactly the quantities that the models predicted.

'The consistency of the spectra, obtained by Integral 50 days after the explosion, with that expected from cobalt decay in the expanding debris of the white dwarf was excellent,' says Churazov, who is lead author of a paper describing this study and reported in the journal Nature.

With that confirmation in hand, other astronomers could begin to look into the details of the process. In particular, how the white dwarf is detonated in the first place.

24 Aug 2014

Spectacular Landscape of Star Formation

NGC 3603 is an open cluster of stars situated in the Carina spiral arm of the Milky Way around 20,000 light-years away from the Solar System.

Constellation: Carina
Magnitude +9.1
Right ascension 11h 15m 09.1s
Declination −61° 16′ 17″

NGC 3603 has been subject to intense study as a starburst region for more than a century because it represents a unique combination of proximity, low visual extinction, brightness and compactness. It was observed by John Herschel on the 14th of March 1834 during his visit to South Africa, who remarked that it was "a very remarkable object...perhaps a globular cluster". Herschel catalogued it as nebula 3334 in his Results of Astronomical Observations made at the Cape of Good Hope, published in 1847. In 1864 the Royal Society published his General Catalogue of Nebulae and Clusters, where he listed it as number 2354. It was subsequently incorporated into the New General Catalogue as by J. L. E. Dreyer as NGC 3603.

This video/ image, captured by the Wide Field Imager at ESO’s La Silla Observatory in Chile, shows two dramatic star formation regions in the southern Milky Way. The first is of these, on the left, is dominated by the star cluster NGC 3603, located 20 000 light-years away, in the Carina–Sagittarius spiral arm of the Milky Way galaxy. The second object, on the right, is a collection of glowing gas clouds known as NGC 3576 that lies only about half as far from Earth.1024px-NGC_3603b
        NGC 3603 is a very bright star cluster and is famed for having the highest concentration of massive stars that have been discovered in our galaxy so far. At the centre lies a Wolf–Rayet multiple star system, known as HD 97950. Wolf–Rayet stars are at an advanced stage of stellar evolution, and start off with around 20 times the mass of the Sun. But, despite this large mass, Wolf–Rayet stars shed a considerable amount of their matter due to intense stellar winds, which blast the star’s surface material off into space at several million kilometres per hour, a crash diet of cosmic proportions.
        NGC 3603 is in an area of very active star formation. Stars are born in dark and dusty regions of space, largely hidden from view. But as the very young stars gradually start to shine and clear away their surrounding cocoons of material they become visible and create glowing clouds in the surrounding material, known as HII regions. HII regions shine because of the interaction of ultraviolet radiation given off by the brilliant hot young stars with the hydrogen gas clouds. HII regions can measure several hundred light-years in diameter, and the one surrounding      NGC 3603 has the distinction of being the most massive in our galaxy.
        The cluster was first observed by John Herschel on 14 March 1834 during his three-year expedition to systematically survey the southern skies from near Cape Town. He described it as a remarkable object and thought that it might be a globular star cluster. Future studies showed that it is not an old globular, but a young open cluster, one of the richest known.
        NGC 3576, on the right of the image, also lies in the Carina–Sagittarius spiral arm of the Milky Way. But it is located only about 9000 light-years from Earth — much closer than NGC 3603, but appearing next to it in the sky.
NGC 3576 is notable for two huge curved objects resembling the curled horns of a ram. These odd filaments are the result of stellar winds from the hot, young stars within the central regions of the nebula, which have blown the dust and gas outwards across a hundred light-years. Two dark silhouetted areas known as Bok globules are also visible in this vast complex of nebulae. These black clouds near the top of the nebula also offer potential sites for the future formation of new stars.
        NGC 3576 was also discovered by John Herschel in 1834, making it a particularly productive and visually rewarding year for the English astronomer.

18 Aug 2014

NASA's RXTE Satellite Decodes the Rhythm of Unusual Black Hole

The signals have helped astronomers identify an unusual midsize black hole called M82 X-1, which is the brightest X-ray source in a galaxy known as Messier 82. Most black holes formed by dying stars are modestly-sized, measuring up to around 25 times the mass of our sun. And most large galaxies harbor monster, or supermassive, black holes that contain tens of thousands of times more mass.

“Between the two extremes of stellar and supermassive black holes, it's a real desert, with only about half a dozen objects whose inferred masses place them in the middle ground," said Tod Strohmayer, an astrophysicist at NASA's Goddard Space Flight Centre in Greenbelt, Maryland.

Astronomers from Goddard and the University of Maryland, College Park (UMCP) have suspected M82 X-1 of being midsize for at least a decade, but compelling evidence excluding it from being a stellar black hole proved elusive.

"For reasons that are very hard to understand, these objects have resisted standard measurement techniques," said Richard Mushotzky, a professor of astronomy at UMCP.

By going over past RXTE observations, the astronomers found specific changes in brightness that helped them determine M82 X-1 measures around 400 solar masses.

17 Aug 2014

The Demise of Comet ISON

Before comet ISON raced past the Sun, it stopped producing dust and gas, as data from the SUMER spectrograph on SOHO show.

On November 28th of last year, thousands of people worldwide watched comet ISON’s fiery ride past the Sun. Researchers at the Max Planck Institute for Solar System Research (MPS) have now reconstructed the comet’s activity during its final hours. Their conclusion: already hours before its perihelion passage, ISON stopped emitting dust and gas into space. The new analysis is based on data from the spectrograph SUMER on board the solar observatory SOHO, a joint space mission of ESA and NASA. SUMER was the only instrument that was able to obtain data of the comet during the minutes of its closest approach to the Sun.

Ison spectroImages of the comet ISON taken by the spectrograph SUMER on board the solar observatory Soho on 28 November 2013 at 6.01 pm (Central European Time) reveal the tail & shape. The red dots mark the predicted positions of the comet & nucleus in intervals of one minute, the red cross depicts the last position at the time of the picture recording. The white arrow indicates the direction to the sun. Brightness contours and centreline of the tail clarify its appearance.
 
When comet ISON was discovered in the autumn of 2012, scientists and amateur astronomers alike hoped for a “comet of the century”. On November 28th, 2013, only 1.8 million kilometres would separate ISON from the Sun. Due to its brightness, the comet promised to be a unique research object – and, should it survive its flyby of the Sun, a stunning celestial phenomenon in the weeks preceding Christmas. But the story took a different course: already during the final phase of the approach to perihelion, the comet’s tail grew fainter and fainter. It soon became clear, that ISON’s activity had ceased or that the nucleus most likely had completely been disintegrated.

However, what exactly happened on November 28th, 2013 1.8 million kilometres away from the Sun is still not entirely clear. Did the comet break apart before it reached the point closest to the Sun? Or did it withstand the indescribable heat a while longer? Did the dust tail that could be discerned after the flyby maybe even block the view of a remaining solid nucleus? “Our measurements and calculations indicate that ISON ran out of steam before perihelion”, says Dr. Werner Curdt from the MPS, first author of the new publication. Apparently, 8.5 hours before the comet should pass by the Sun, a short and violent outburst occurred that set free a great amount of dust. After that, the dust production completely stopped within a few hours.

Key to the new insights were images of the dust tail which the MPS researchers obtained on November 28th between 17.56 and 18.01 UTC near closest approach with the instrument SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on board SOHO (Solar and Heliospheric Observatory). Hours earlier, stunning shots taken by SOHO’s coronagraph LASCO (Large Angle and ison sunSpectrometric Coronagraph) had shown the long stretched tail of the onrushing comet. In order to make structures in the vicinity of our star visible, the instrument occults the solar disk – as in an artificial solar eclipse. However, ISONs trajectory took the comet so close to the Sun that the final phase was obscured by the occulter.

"The only instrument that could obtain serviceable data at this time was SUMER", says Curdt, who has been head of the SUMER team since 2002. "For everyone involved, this was a huge challenge," he adds. The detection of a comparatively faint comet is not what the instrument was designed for, namely to investigate plasma flows, temperatures, and density in the Sun’s hot outer atmosphere.

By operating the instrument in camera mode the researchers were able to record images of the comet’s tail in ultraviolet light with a wavelength of 121.6 nanometres. This light is emitted from the solar disk and reflected by the dust particles into space.

The SUMER images show a slightly curved, pointed tail with a length of at least 240000 kilometres. No signs of a particularly bright area were found at the predicted position of the comet, indicative of an active nucleus. To understand what processes generated this tail shape, the researchers compared the images with computer simulations: they calculated what the tail would look like under certain assumptions regarding the size of the dust particles, their speed, and the time of their emission.

"We were not able to reconstruct anything resembling our images, assuming that ISON was still active during the SUMER observations," says comet researcher and co-author Dr. Hermann Böhnhardt from the MPS, who is the Lead Scientist of Rosetta’s landing mission. The model is most consistent with a scenario where ISON has stopped producing dust and gas hours before. Whether the nucleus had been completely disintegrated cannot be settled without doubt, Böhnhardt explains. Several signs indicate this – for example the distinct increase in dust production approximately 8.5 hours earlier. The scientists’ calculations show that the comet must have emitted around 11500 tons of dust at this time equivalent to a sphere with a diameter of 280 meters.

It is most likely, that the final break-up of the nucleus triggered this dusty firework. Gas and dust trapped inside the nucleus would have been abruptly released in such an event.

11 Aug 2014

August 2014 | What’s on view this month

 

1/08/2014 | The Summer Sky from Richard Pearson on Vimeo.

During August evenings the Milky Way is a fine sight. It begins from the constellations of Perseus in the NW, then passes up through the 'W' of Cassiopeia, Cygnus (The swan) high over head, and then passes down through Scorpio and into Sagittarius close to the southern horizon. There are also a large number of globular clusters on show, as well as some splendid deep sky objects. In this month's program we have some magnificent images taken by several of the very best astronomical photographers.

CREDITS: I am most grateful to Jeff Johnson, Vincent K.H. Cheng, Zlatko Orbanic, Oliver Czernetz, Terry Hancock, Noodle Van, Roberto Colombari, Robert Gendler and Alex Cherney for allowing me to use their splendid deep-sky images. The image of M57 was a corroboration between Trever Hancock & Fred Herrmann.

Out Now Free on line space magazine

Ashampoo_Snap_2014.08.10_17h07m56s_004_The new August issue of Amateur Astro Photography Ezine has now been published. It is full of amazing space images, and brimming with advice for budding space photographers click on the link | http://astrophotomag.com/issue07/

5 Aug 2014

August 17th 2014 | Conjunction of Venus & Jupiter

There will be a nice photo opportunity on the morning of August 17 when the brilliant planet Venus, magnitude -3.9 will be a short distance away from Jupiter ( -1.8) low in the east just before sunrise. The pair will make a lovely pair several mornings before and after this date. It would be nice to see some of your nice photographs of this event during the next month.