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(Astronomy) Hubble Telescope: Xena's Mysterious Sparkle

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PostPosted: Sat Apr 15, 2006 8:35 am    Post subject: (Astronomy) Hubble Telescope: Xena's Mysterious Sparkle Reply with quote

Xena's Mysterious Sparkle
19 April 2006
Emily Sohn

In addition to the nine planets that everyone learns about, there's a 10th object in the solar system that's tentatively being called a planet. Its name is Xena. It's three times farther from the sun than Pluto is. And it's surprisingly shiny.

New images from the Hubble Space Telescope show that the unofficial planet measures 2,384 kilometers (1,490 miles) across. This makes it a little larger than Pluto, which is 1,422 miles wide.

Earlier observations from telescopes on the ground had suggested that Xena was considerably larger than this. It turns out, however, that Xena is much brighter than astronomers had estimated.

A distant object can look bright to an observer because it's dim but has a large size (surface area) and so reflects a lot of light. Or, it can look bright because it's small but has an especially shiny surface that reflects a lot of light. Xena belongs in the second category.

In fact, Xena reflects more light that any object in the solar system other than Saturn's moon Enceladus. It reflects 86 percent of the sunlight that hits it. Pluto reflects only 60 percent of the sunlight that hits it.

Scientists aren't sure why Xena reflects so much light, but they have two theories. One idea is that the planet spews out methane gas, which freezes and keeps the surface covered with a blanket of fresh snow. For this theory to be true, something would have to be heating up the planet. So far, there's no obvious source of heat.

The other idea is that Xena's atmosphere is full of methane. This atmosphere forms when the planet is closest to the sun during its 560-year-long orbit. As the planet gets farther away from the sun, the methane freezes. But scientists aren't sure whether the resulting frost would be bright enough to fully account for Xena's special sparkle.—E. Sohn



Questions to explore further this topic:

An intro to the solar system;id=1080

What is Kuiper Belt Object 2003 UB313 (Xena)?

Is Xena the tenth planet of the solar system?

The Discovery of Xena;id=3401

Does Xena have its own moon?;id=3536

Latest news about the tenth planet

How does Xena's size compare to other Kuiper Belt objects?

Experience the Hubble

How are Hubble images made?

The best Hubble images

Videos of Hubble

Videos from Hubble

Kid's drawings of the Hubble

Who is Hubble?

Discover the Hubble

A Long Time Ago in a Galaxy far, far away……

Big Things, Big Numbers

Discovering Star Life Cycles in Galactic Fireworks

Orion Star Nursery

Planet Birth

Saturn Reflecting the Spectrum

Seasons on Saturn

How Did the Galaxy Get a Black Eye

Hit and Run: a Cosmic Collision

Growing Faster than the Speed of Light

What are We Looking at

What is a space observatory?

Powerpoint presentations for space observatory

Hubble: 15 Years Educational Material

Discoveries of the Hubble

The Fits Liberator Program (processing Hubble images)

Other software tools

Online Explorations

Watch Tonight's Sky

Astronomy exercises from the European Space Agency


Last edited by adedios on Sat Jan 27, 2007 5:04 pm; edited 2 times in total
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PostPosted: Fri Aug 18, 2006 7:37 am    Post subject: Hubble images some of galaxy's dimmest stars Reply with quote

Rice University
17 August 2006

Hubble images some of galaxy's dimmest stars

Survey of nearby globular cluster pushes limits of orbiting observatory
Houston, Aug. 17, 2006 -- Using the Hubble Space Telescope, astronomers have imaged some of the galaxy's oldest and dimmest stars, offering a rare experimental glimpse of two mysterious star types – tiny, slow burners less than one-tenth the size of our sun and once giant stars that still glow more than 10 billion years after their deaths.

The research appears in this week's issue of the journal Science.

"This project pushed the limits of what even Hubble can do," said study co-author Jay Anderson, a research scientist at Rice University. "These stars can't be reliably detected in a single image. You have to combine a large number of images to find them."

In total, the research team trained Hubble's cameras on the same patch of sky for more than 75 hours, gathering 378 overlapping images. The target was a region of space containing about 1 percent of the globular cluster NGC 6397 – a collection of stars that formed early in our galaxy's history.

"When we look at random stars in the sky they have a variety of ages," Anderson said. "Globular clusters offer unique opportunities for astronomers to study a population of stars that are all the same age. All the stars we see in clusters are ancient, because they were created when the galaxy was forming. They're fossils from the galaxy's earliest days."

There are about 150 globular clusters in our galaxy, and most contain between 100,000 and 1 million stars. While most of the galaxy's stars – including our own sun – orbit the galactic center in the plane of the galaxy, globular clusters predate the flattening of the Milky Way, so they're scattered in a more spherical distribution.

NGC 6397 is one of the nearest clusters to Earth, located just 8,500 light years away. But even at this relatively close astronomical distance, the light from NGC 6397's faintest stars is easily lost in the glare from its brightest stars.

To survey the dimmest objects, Anderson and colleagues relied on computers. Anderson, whose specialty is writing programs to sift through astronomical data, spent months writing and refining software that could examine each Hubble image, pixel by pixel, and find the faintest stars.

The two types of object imaged represent the heavy end and the light end of the stellar mass spectrum.

A star's destiny is determined by its mass. There's a minimum mass that a star must have in order to burn hydrogen, and objects below that threshold cool rapidly and fade away. From the NGC 6397 survey, Anderson and his colleagues identified the smallest visible stars yet seen in a globular cluster, stars less than one-tenth the mass of Earth's sun. This is very near the predicted theoretical threshold, and Anderson said data from the survey will be helpful for verifying and refining theories about the structure and evolution of low-mass stars.

On the other end of the stellar mass spectrum are stars that are significantly larger than the sun. Stars about eight times the mass of the sun burn quickly and die in spectacular planetary nebulae, explosions that spew much of the star's material into space. Upon their final collapse, these stars become white dwarfs, extremely dense objects that radiate heat for billions of years as they slowly fade into darkness. Anderson said that while the brightest – and therefore youngest – white dwarfs have been seen in many clusters, the new survey yielded the first images of the faintest and oldest white dwarfs in an ancient cluster. The brightness of the white dwarfs at this end of the scale can help astronomers find out how long the stars have been cooling. From that, they can better determine the age of the cluster, which in turn can be used to narrow estimates of the lower limit of the age of the universe.

Co-authors on the study include principal investigator Harvey Richer, James Brewer, Saul Davis and Peter Stetson, all of the University of British Columbia; Gregory Fahlman of the Herzberg Institute of Astrophysics in Victoria, British Columbia; Brad Hansen, David Reitzel and Michael Rich, all of the University of California Los Angeles; Jarrod Hurley of Australia's Monash University; Jasonjot Kalirai of the University of California Santa Cruz; Ivan King of the University of Washington; and Michael Shara of the American Museum of Natural History.

The research was funded by the Natural Sciences and Engineering Research Council of Canada, the University British Columbia, NASA and the Space Telescope Science Institute.
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PostPosted: Sat Feb 03, 2007 8:53 am    Post subject: Space Camera Glitch Reply with quote

Space Camera Glitch
Emily Sohn

Feb. 7, 2007

NASA has announced some bad news about the Hubble Space Telescope. The spacecraft has been orbiting Earth and collecting information about space since 1990. Now, Hubble's sharpest camera has died, and there's no way to bring it back to its full power.
Until it broke down, the Advanced Camera for Surveys (ACS) was the most popular instrument on board, accounting for two-thirds of the observations made by the orbiting telescope. It also captured the deepest picture ever taken of the universe, which reveals disks of gas and dust turning into planets around other stars. The ACS was installed in March 2002.

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