night reflections

night reflections, upload feito originalmente por davedehetre.

Startrails

Startrails [54min Exposure], upload feito originalmente por g_e_r_r_y.

Bow Shock

A bow shock is created in space when two streams of gas collide. The young star LL Ori Emits a solar wind, a stream of charged particles moving rapidly outward from the star. The material in the wind collides with the gas evaporating away from the center of the Orion Nebula, creating the crescent-shaped collision area in the image.
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stellar bomb

Astronomers have been puzzling over the engine behind the historical 1843 outburst of Eta Carinae since it happened, but new observations with the Gemini South and the Blanco telescopes in Chile add a startling new clue. The new observations reveal faint but extremely fast material indicative of a powerful shock wave produced by the 1843 event, suggesting that its driving mechanism was an explosion rather than a steady wind. The research, led by Nathan Smith of the University of California, Berkeley, shows that the famous nebulosity around the star Eta Carinae contains extremely fast-moving filaments of material that had not been seen before, and are not explained by current theories. The result is featured in the September 11, 2008 issue of the journal Nature.

The Gemini spectroscopy, obtained with the Gemini Near-Infrared Spectrometer (GNIRS) helped confirm the high speed and geometry of this material and shows that the 1843 outburst released even more energy than previously estimated. In particular, the high speeds require that the 1843 event generated a shock wave analogous to a supernova-type event, but with less energy. The observations revealed far-flung material moving at more than three times faster than the fastest material seen previously (up to 3,500-6,000 kilometers/second). This work has implications for similar events observed in other galaxies where the resulting outbursts have not quite matched the energy of a supernova, and currently lack any theoretical explanation.

sorce: gemini observatory

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the missing link

Observations from NASA’s Rossi X-ray Timing Explorer (RXTE) have revealed that the youngest known pulsing neutron star has thrown a temper tantrum. The collapsed star occasionally unleashes powerful bursts of X-rays, which are forcing astronomers to rethink the life cycle of neutron stars. "We are watching one type of neutron star literally change into another right before our very eyes. This is a long-sought missing link between different types of pulsars," says Fotis Gavriil of NASA’s Goddard Space Flight Center in Greenbelt, Md., and the University of Maryland, Baltimore. Gavriil is lead author of a paper in the February 21 issue of Sciencexpress.

A neutron star forms when a massive star explodes as a supernova, leaving behind an ultradense core. Most known neutron stars emit regular pulsations that are powered by rapid spins. Astronomers have found nearly 1,800 of these so-called pulsars in our galaxy. Pulsars have incredibly strong magnetic fields by Earthly standards, but a dozen of them — slow rotators known as magnetars — actually derive their energy from incredibly powerful magnetic fields, the strongest known in the universe. These fields can stress the neutron star’s solid crust past the breaking point, triggering starquakes that snap magnetic-field lines, producing violent and sporadic X-ray bursts. But what is the evolutionary relationship between pulsars and magnetars? Astronomers would like to know if magnetars represent a rare class of pulsars, or if some or all pulsars go through a magnetar phase during their life cycles. Gavriil and his colleagues have found an important clue by examining archival RXTE data of a young neutron star, known as PSR J1846-0258 for its sky coordinates in the constellation Aquila.

Previously, astronomers had classified PSR J1846 as a normal pulsar because of its fast spin (3.1 times per second) and pulsar-like spectrum. But RXTE caught four magnetar-like X-ray bursts on May 31, 2006, and another on July 27, 2006. Although none of these events lasted longer than 0.14 second, they all packed the wallop of at least 75,000 Suns. "Never before has a regular pulsar been observed to produce magnetar bursts," says Gavriil. "Young, fast-spinning pulsars were not thought to have enough magnetic energy to generate such powerful bursts," says coauthor Marjorie Gonzalez, who worked on this paper at McGill University in Montreal, Canada, but who is now based at the University of British Columbia in Vancouver. "Here’s a normal pulsar that’s acting like a magnetar."

Observations from NASA’s Chandra X-ray Observatory also provided key information. Chandra observed the neutron star in October 2000 and again in June 2006, around the time of the bursts. Chandra showed the object had brightened in X-rays, confirming that the bursts were from the pulsar, and that its spectrum had changed to become more magnetar-like. Astronomers know that PSR J1846 is very young for several reasons. First, it resides inside a supernova remnant known as Kes 75, an indicator that it hasn’t had time to wander from its birthplace. Second, based on the rapidity that its spin rate is slowing down, astronomers calculate that it can be no older than 884 years — an infant on the cosmic timescale. Magnetars are thought to be about 10,000 years old, whereas most pulsars are thought to be considerably older.

The fact that PSR J1846’s spin rate is slowing down relatively fast also means that it has a strong magnetic field that is braking the rotation. The implied magnetic field is trillions of times stronger than Earth’s field, but it’s 10 to 100 times weaker than typical magnetar field strengths. Coauthor Victoria Kaspi of McGill University notes, "PSR J1846’s actual magnetic field could be much stronger than the measured amount, suggesting that many young neutron stars classified as pulsars might actually be magnetars in disguise, and that the true strength of their magnetic field only reveals itself over thousands of years as they ramp up in activity."

Robert Naeye
Goddard Space Flight Center (+)

eta carinae

Eta Carinae (η Carinae or η Car) is a highly luminous hypergiant double star. Estimates of its mass range from 100–150 times the mass of the Sun, and its luminosity is about four million times that of the Sun.

Very large stars like Eta Carinae use up their fuel very quickly because of their disproportionately high luminosities. Eta Carinae is expected to explode as a supernova or hypernova some time within the next million or so years. As its current age and evolutionary path are uncertain, it could explode within the next several millennia or even in the next few years. LBVs such as Eta Carinae may be a stage in the evolution of the most massive stars; the prevailing theory now holds that they will exhibit extreme mass loss and become Wolf-Rayet Stars before they go supernova, if they are unable to hold their mass to explode as a hypernova.

More recently another possible Eta Carinae analogue was observed; namely SN 2006jc some 77 million light years away in UGC 4904, in the constellation of Lynx. It brightened on 20 October 2004 and was reported by amateur astronomer Koichi Itagaki as supernova. However, it survived and finally exploded two years later as a Mag 13.8 type Ib supernova on 9 October 2006. Its earlier brightening was a supernova impostor event; the initial explosion hurled 0.01 solar masses (~20 Jupiters) of material into space.

Due to the similarity of Eta Carinae and SN 2006jc, Stefan Immler of NASA's Goddard Space Flight Center suggests that Eta Carinae could explode in our lifetime or even in the next few years. However, Stanford Woosley of the University of California in Santa Cruz disagrees with Immler’s suggestion, and he says it is likely that Eta Carinae is at an earlier stage of evolution and that it has several kinds of material left for nuclear fusion.

scared sun

click on the image for better detail

The Sun on June 1 2005 in white light. TOA-130 refractor, Baader helioscope, STL-11000M CCD Camera. Credit: Thierry Legault's Astrophotography

photo session: nebulas

cone nebula

triangulum nebula

rotten egg nebula

ant nebula

gomez's hambuerger

orion rising

Orion always comes up sideways ... and was caught in the act earlier this month by astronomer Jimmy Westlake, stargazing eastward over the Rocky Mountains north of Leadville, Colorado, USA. To make this gorgeous image, Westlake placed his camera on a tripod for two exposures. The first lasted for 18 minutes allowing the stars to trail as they rose above the mountain range. After a minute long pause, the second exposure began and lasted only 25 seconds decorating the end of each trail with a celestial point of light. The three bright stars in Orion's belt stand in a nearly vertical line above the mountain peak right of center. Hanging from his belt, the stars and nebulae of the Hunter's sword follow the slope down and to the right. A festive yellow-orange Betelgeuse is the brightest star above the peak just left of center, but brighter still, planet Saturn shines near the upper left corner. In the foreground on planet Earth, a frozen lake and snowy mountains are lit by a four day old crescent Moon.

Credit & Copyright: Jimmy Westlake (Colorado Mountain College)

largest known star

VY Canis Majoris (VY CMa) is a red hypergiant located in the constellation of Canis Major. This is the largest known star and one of the most luminous stars known.

Roberta M. Humphreys (2006) estimates the radius of VY CMa is between 1800 and 2100 solar radii. If our sun were replaced with such a star, its surface could extend to the orbit of Saturn. If we take its radius to be that higher figure of 2100 solar radii, it would take more than 8 hours for light to travel around its circumference. If it were possible for a human to walk on the surface of Canis Majoris, at 3 miles an hour for 8 hours a day, it would take him or her 650,000 years to walk the entire circumference (compared with 2 years 11 months to complete the same task on the Earth).

Object Name:
VY Canis Majoris
Object Description:
Variable Star with Circumstellar Nebula
Position (J2000):
R.A. 07h 22m 58s.33Dec. -25° 46' 3".2
Constellation:
Canis Major
Distance:
Approximately 5,000 light-years (1.5 kiloparsecs)
Dimensions:
These images are roughly 35 arcseconds (0.85 light-years or 0.25 parsecs) across.

VY Canis Majoris Credit: NASA, ESA, and R. Humphreys (University of Minnesota)