Astronomy Picture Discover the cosmos!

Discover the cosmos! photograph of our fascinating universe is featured, along with a brief explanation



Hoag's Object: A Strange Ring Galaxy

Is this one galaxy or two? This question came to light in 1950 when astronomer Art Hoag chanced upon this unusual extragalactic object. On the outside is a ring dominated by bright blue stars, while near the center lies a ball of much redder stars that are likely much older. Between the two is a gap that appears almost completely dark. How Hoag'sObject formed remains unknown, although similar objects have now been identified and collectively labeled as a form of ring galaxy. Genesis hypotheses include a galaxy collision billions of years ago and perturbative gravitational interactions involving an unusually shaped core. The above photo taken by the Hubble Space Telescope in July 2001 reveals unprecedented details of Hoag's Object and may yield a better understanding. Hoag's Object spans about 100,000 light years and lies about 600 million light years away toward the constellation of Serpens. Coincidentally, visible in the gap (at about one o'clock) is yet another ring galaxy that likely lies far in the distance.



Venus Beyond the Storm

A thunderstorm, lightning, a bright star and a bright planet all graced an evening sky for a short while near Bismarck, North Dakota, USA two weeks ago. Thick thunderclouds from a passing storm are the origin of a strong cloud to ground lightning strike. Small areas of rain darken portions of the orange sunset, visible at the horizon above the vast prairie. The planet Venus peeks below the clouds on the lower left of the image. Blue sky shines high above the distant storm, streaked with high white cirrus clouds. The bright star Arcturus glitters near the image top, just left of center. Just a few minutes later, only a memory and this picture remained




Pluto & Charon Eclipse a Triple Star

Explanation

Occasionally, a planet in our Solar System will pass in front of a bright star. Since stars and planets take up so little space on the sky, such events are quite rare. Two months ago, however, Pluto and its large moon Charon passed in front of a comparativelybright triple star system known as P126. By noting how P126 A dimmed, the event was useful for studying Pluto's relatively unknown atmosphere. A Very Large Telescope in Chile using a deformable mirror to counter the blurring effect of Earth's atmosphere captured the above image.



X-Rays From Tycho's Supernova Remnant


In 1572, Danish astronomer Tycho Brahe recorded the sudden appearance of a bright new star in the constellation Cassiopeia. The new star faded from view over a period of months and is believed to have been a supernova, one of the last stellar explosions seen in our Milky Way galaxy. Now known as Tycho's Supernova Remnant, the expanding debris cloud is shown in this detailed false-color x-ray image from the orbiting Chandra Observatory. Represented in blue, the highest energy x-rays come from shocked regions along the outer edges of the supernova remnant, corresponding to gas at temperatures of 20 million degrees Celsius. X-rays from cooler gas (only 10 million degrees or so!) dominate the remnant's interior. Unlike some other supernova remnants, no hot central point source can be found, supporting the theory that the origin of this stellar explosion was a runaway nuclear detonation that ultimately destroyed a white dwarf star. At a distance of about 7,500 light-years, Tycho's Supernova Remnant appears to be nearly 20 light-years across. This x-ray picture's field of view slightly cuts off the bottom of the generally spherical cloud



Aristarchus Plateau

Explanation
Anchored in the vast lava flows of the Moon's Oceanus Procellarum lies the Aristarchus Plateau. Recorded from a backyard observatory on planet Earth, this sharp, amazingly colorful view nicely captures the geologically diverse area, including the brownish plateau, Aristarchus and Herodotus craters, and the meandering Vallis Schroteri. Thebright impact crater at the corner of the plateau is Aristarchus, a young crater 42 kilometers wide and 3 kilometers deep, surrounded by a radial system of light-colored rays. Only slightly smaller, lava flooded Herodotus crater is above and to the left. A valley or rille feature likely carved by rapidly flowing lava or a collapsed lava tunnel, Vallis Schroteri begins just to the right of Herodotus and winds across the plateau for about 160 kilometers, eventually turning toward the top of the picture and the shadow of the lunar terminator. Aristarchus Plateau itself is like a rectangular island about 200 kilometers across, raised up to 2 kilometers or so above the smooth surface of the lunar Ocean of Storms

The cosmos is green

For the first time, researchers have observed a singular cosmic act of rebirth: the transformation of an ordinary, slow-rotating pulsar into a superfast millisecond pulsar with an almost infinitely extended lifespan.

The discovery was made during a large radio sky survey by an international team of astrophysicists at McGill University, the University of British Columbia (UBC), West Virginia University, the U.S. National Radio Astronomy Observatory (NRAO) and several other institutions in the United States, the Netherlands and Australia.

The sky survey used the Robert C. Byrd radio telescope at Green Bank, West Virginia to observe nearly a third of the celestial sphere. The team's results will be published online by the journal Science on May 21.

The discovery was made by astrophysics PhD candidate Anne Archibald and her supervisor, Prof. Victoria Kaspi of the McGill Pulsar Group. "This survey has found many new pulsars, but this one is truly special -- it is a very freshly 'recycled' pulsar that is emerging straight from the recycling plant." said Archibald. The McGill researchers worked with Asst. Prof. Ingrid Stairs of UBC and Scott Ransom of NRAO as well as others from the collaboration to carry out more observations of this unusual pulsar.

Pulsars are rapidly rotating, highly magnetized neutron stars, the remnants left after massive stars have exploded as supernovae. Pulsars emit lighthouse-like beams of radio waves that sweep around as the star rotates. Most rotate relatively slowly, ten times a second or less, and their magnetic fields ordinarily slow them down even further over the course of millennia. Millisecond pulsars, however, rotate hundreds of times a second.

"We know normal pulsars typically pulsate in the radio spectrum for one million to ten million years, but eventually they slow down enough to die out," explained Kaspi. "But a few of these old pulsars get 'recycled' into millisecond pulsars. They end up spinning extremely fast, and then they can pulsate forever. How does nature manage to be so green?"

It has long been theorized that millisecond pulsars are created in double-star systems when matter from the companion star falls into the pulsar's gravity well and increases the rotation speed, but until now the process has never been observed directly.

"Imagine a ping-pong ball in the bathtub, and then you take the plug out of the drain," explained Archibald. "All the water swirling around the ping-pong ball suddenly makes it spin a lot faster than when it was just bobbing on the surface.

"We've seen systems that are undergoing spin-up, because when the matter is falling in, the stars get really bright in X-rays and they're easy to see," she added. "But we've never seen radio pulsations from these stars during the process of spin-up. At last we've found a true radio pulsar that shows direct evidence for having just been recycled."

The pulsar found by the survey team was fortuitously observed by an independent, optical research group to have had swirling matter surrounding it roughly a decade ago -- the blink of an eye in astronomical time. That group recorded the observation as puzzling, never dreaming that a full-fledged radio pulsar would emerge.

"In other words, for the first time, we have caught a glimpse at an actual cosmic recycling factory in action," said Ingrid Stairs of UBC, who has been visiting the Australia Telescope National Facility and Swinburne University of Technology this year. "This system gives us an unparalleled cosmic laboratory for studying how millisecond pulsars evolve and get reborn."