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Entries in Estrelas (5)

Tuesday
Feb262013

White Dwarf Stars Offer Best Potential to Identify Twin Earths

"In the quest for extraterrestrial biological signatures, the first stars we study should be white dwarfs," said Avi Loeb, theorist at the Harvard-Smithsonian Center for Astrophysics (CfA) and director of the Institute for Theory and Computation. Even dying stars could host planets with life - and if such life exists, we might be able to detect it within the next decade. This encouraging result comes from a new theoretical study of Earth-like planets orbiting white dwarf stars. Researchers found that we could detect oxygen in the atmosphere of a white dwarf's planet much more easily than for an Earth-like planet orbiting a Sun-like star.

When a star like the Sun dies, it puffs off its outer layers, leaving behind a hot core called a white dwarf. A typical white dwarf is about the size of Earth. It slowly cools and fades over time, but it can retain heat long enough to warm a nearby world for billions of years. Since a white dwarf is much smaller and fainter than the Sun, a planet would have to be much closer in to be habitable with liquid water on its surface. A habitable planet would circle the white dwarf once every 10 hours at a distance of about a million miles.* Before a star becomes a white dwarf it swells into a red giant, engulfing and destroying any nearby planets. Therefore, a planet would have to arrive in the habitable zone after the star evolved into a white dwarf. A planet could form from leftover dust and gas (making it a second-generation world), or migrate inward from a larger distance.

If planets exist in the habitable zones of white dwarfs, we would need to find them before we could study them. The abundance of heavy elements on the surface of white dwarfs suggests that a significant fraction of them have rocky planets. Loeb and his colleague Dan Maoz (Tel Aviv University) estimate that a survey of the 500 closest white dwarfs could spot one or more habitable Earths.

The best method for finding such planets is a transit search - looking for a star that dims as an orbiting planet crosses in front of it. Since a white dwarf is about the same size as Earth, an Earth-sized planet would block a large fraction of its light and create an obvious signal.

More importantly, we can only study the atmospheres of transiting planets. When the white dwarf's light shines through the ring of air that surrounds the planet's silhouetted disk, the atmosphere absorbs some starlight. This leaves chemical fingerprints showing whether that air contains water vapor, or even signatures of life, such as oxygen.

Astronomers are particularly interested in finding oxygen because the oxygen in the Earth's atmosphere is continuously replenished, through photosynthesis, by plant life. Were all life to cease on Earth, our atmosphere would quickly become devoid of oxygen, which would dissolve in the oceans and oxidize the surface. Thus, the presence of large quantities of oxygen in the atmosphere of a distant planet would signal the likely presence of life there.

NASA's James Webb Space Telescope (JWST), scheduled for launch by the end of this decade, promises to sniff out the gases of these alien worlds. Loeb and Maoz created a synthetic spectrum, replicating what JWST would see if it examined a habitable planet orbiting a white dwarf. They found that both oxygen and water vapor would be detectable with only a few hours of total observation time.

"JWST offers the best hope of finding an inhabited planet in the near future," said Maoz.* Recent research by CfA astronomers Courtney Dressing and David Charbonneau showed that the closest habitable planet is likely to orbit a red dwarf star (a cool, low-mass star undergoing nuclear fusion). Since a red dwarf, although smaller and fainter than the Sun, is much larger and brighter than a white dwarf, its glare would overwhelm the faint signal from an orbiting planet's atmosphere. JWST would have to observe hundreds of hours of transits to have any hope of analyzing the atmosphere's composition.

"Although the closest habitable planet might orbit a red dwarf star, the closest one we can easily prove to be life-bearing might orbit a white dwarf," said Loeb. *Their paper has been accepted for publication in the Monthly Notices of the Royal Astronomical Society and is available online.

Source:

http://www.dailygalaxy.com/my_weblog/2013/02/-white-dwarf-stars-offer-best-potential-to-identify-habitable-planets.html

Tuesday
Feb262013

Future Evidence for Extraterrestrial Life Might Come from Dying Stars

A new study finds that we could detect oxygen in the atmosphere of a habitable planet orbiting a white dwarf (as shown in this artist's illustration) much more easily than for an Earth-like planet orbiting a Sun-like star. Here the ghostly blue ring is a planetary nebula -- hydrogen gas the star ejected as it evolved from a red giant to a white dwarf. (Credit: David A. Aguilar (CfA))

Even dying stars could host planets with life -- and if such life exists, we might be able to detect it within the next decade. This encouraging result comes from a new theoretical study of Earth-like planets orbiting white dwarf stars. Researchers found that we could detect oxygen in the atmosphere of a white dwarf's planet much more easily than for an Earth-like planet orbiting a Sun-like star.

"In the quest for extraterrestrial biological signatures, the first stars we study should be white dwarfs," said Avi Loeb, theorist at the Harvard-Smithsonian Center for Astrophysics (CfA) and director of the Institute for Theory and Computation.

When a star like the Sun dies, it puffs off its outer layers, leaving behind a hot core called a white dwarf. A typical white dwarf is about the size of Earth. It slowly cools and fades over time, but it can retain heat long enough to warm a nearby world for billions of years.

Since a white dwarf is much smaller and fainter than the Sun, a planet would have to be much closer in to be habitable with liquid water on its surface. A habitable planet would circle the white dwarf once every 10 hours at a distance of about a million miles.

Before a star becomes a white dwarf it swells into a red giant, engulfing and destroying any nearby planets. Therefore, a planet would have to arrive in the habitable zone after the star evolved into a white dwarf. A planet could form from leftover dust and gas (making it a second-generation world), or migrate inward from a larger distance.

If planets exist in the habitable zones of white dwarfs, we would need to find them before we could study them. The abundance of heavy elements on the surface of white dwarfs suggests that a significant fraction of them have rocky planets. Loeb and his colleague Dan Maoz (Tel Aviv University) estimate that a survey of the 500 closest white dwarfs could spot one or more habitable Earths.

The best method for finding such planets is a transit search -- looking for a star that dims as an orbiting planet crosses in front of it. Since a white dwarf is about the same size as Earth, an Earth-sized planet would block a large fraction of its light and create an obvious signal.

More importantly, we can only study the atmospheres of transiting planets. When the white dwarf's light shines through the ring of air that surrounds the planet's silhouetted disk, the atmosphere absorbs some starlight. This leaves chemical fingerprints showing whether that air contains water vapor, or even signatures of life, such as oxygen.

Astronomers are particularly interested in finding oxygen because the oxygen in Earth's atmosphere is continuously replenished, through photosynthesis, by plant life. Were all life to cease on Earth, our atmosphere would quickly become devoid of oxygen, which would dissolve in the oceans and oxidize the surface. Thus, the presence of large quantities of oxygen in the atmosphere of a distant planet would signal the likely presence of life there.

NASA's James Webb Space Telescope (JWST), scheduled for launch by the end of this decade, promises to sniff out the gases of these alien worlds. Loeb and Maoz created a synthetic spectrum, replicating what JWST would see if it examined a habitable planet orbiting a white dwarf. They found that both oxygen and water vapor would be detectable with only a few hours of total observation time.

"JWST offers the best hope of finding an inhabited planet in the near future," said Maoz.

Recent research by CfA astronomers Courtney Dressing and David Charbonneau showed that the closest habitable planet is likely to orbit a red dwarf star (a cool, low-mass star undergoing nuclear fusion). Since a red dwarf, although smaller and fainter than the Sun, is much larger and brighter than a white dwarf, its glare would overwhelm the faint signal from an orbiting planet's atmosphere. JWST would have to observe hundreds of hours of transits to have any hope of analyzing the atmosphere's composition.

"Although the closest habitable planet might orbit a red dwarf star, the closest one we can easily prove to be life-bearing might orbit a white dwarf," said Loeb.

Their paper has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Source:

http://www.sciencedaily.com/releases/2013/02/130225131618.htm

Sunday
Jan062013

Galactic Geysers Fueled by Star Stuff

Galactic Geysers. A view of the 'galactic geysers' that have been mapped. Click for largest resolution. (Credit: ESA Planck Collaboration (Microwave) NASA DOE Fermi LAT, Dobler et al. Su et al. (Gamma Rays).)

Enormous outflows of charged particles from the centre of our Galaxy, stretching more than halfway across the sky and moving at supersonic speeds, have been detected and mapped with CSIRO's 64-m Parkes radio telescope.

Corresponding to the "Fermi Bubbles" found in 2010, the recent observations of the phenomenon were made by a team of astronomers from Australia, the USA, Italy and The Netherlands, with the findings reported in the January 2 issue ofNature.

"There is an incredible amount of energy in the outflows," said co-author Professor Lister-Staveley-Smith from The University of Western Australia node of the International Centre for Radio Astronomy Research in Perth and Deputy Director of the ARC Centre of Excellence for All-sky Astrophysics (CAASTRO).

"The source of the energy has been somewhat of a mystery, but we know there is a lot there, about a million times as much energy as a supernova explosion (a dying star)."

From top to bottom the outflows extend 50,000 light-years [five hundred thousand million million kilometres] out of the Galactic Plane. That's equal to half the diameter of our Galaxy (which is 100,000 light-years -- a million million million kilometres -- across).

"Our Solar System is located approximately 30,000 light-years from the centre of the Milky Way Galaxy, but we're perfectly safe as the jets are moving in a different direction to us," said Professor Staveley-Smith.

Seen from Earth, but invisible to the human eye, the outflows stretch about two-thirds across the sky from horizon to horizon.

They match previously identified regions of gamma-ray emission detected with NASA's Fermi Space Telescope (then-called "Fermi Bubbles") and the "haze" of microwave emission spotted by the Wilkinson Microwave Anisotropy Probe (WMAP) and Planck Space Telescope.

"Adding observations by the ground-based Parkes radio telescope to those made in the past by space telescopes finally allows us to understand how these enormous outflows are powered," said Professor Staveley-Smith.

Previously it was unclear whether it was quasar-like activity of our Galaxy's central super-massive black hole or star formation that kept injecting energy into the outflows.

The recent findings, reported in Nature, show that the phenomenon is driven by many generations of stars forming and exploding in the Galactic Centre over the last hundred million years.

"We were able to analyse the magnetic energy content of the outflows and conclude that star formation must have happened in several bouts," said CAASTRO Director Professor Bryan Gaensler.

Further analyses of the polarisation properties and magnetic fields of the outflows can also help us to answer one of astronomy's big questions about our Galaxy.

"We found that the outflows' radiation is not homogenous but that it actually reveals a high degree of structure -- which we suspect is key to how the Galaxy's overall magnetic field is generated and maintained," said Professor Gaensler.

Source: http://www.sciencedaily.com/releases/2013/01/130102140156.htm

Tuesday
Oct162012

Uma Nebulosa Espiral Ao Redor da Estrela R Sculpitoris É Observada Pelo ALMA

O que está acontecendo ao redor dessa estrela? Uma estrutura espiral pouco comum foi descoberta ao redor de uma estrela da Via Láctea, a R Sculpitoris, uma estrela gigante vermelha localizada a aproximadamente 1500 anos-luz de distância da Terra na direção da constelação do Sculptor. A estrela foi observada com o novo Atacama Large Millimeter/submillimeter Array, ou ALMA, o mais poderoso conjunto de telescópios que observa o universo nos comprimentos de ondas milimétricos, que é a parte do espectro situada bem além da luz vermelha e entre as micro-ondas e as ondas de rádio. Os dados das observações feitas com o ALMA foram usados para criar uma visualização 3D do gás e da poeira imediatamente ao redor da estrela. Uma fatia digital feita através desse dado mostra uma inesperada estrutura espiral. Embora pouco comum, um padrão espiral similar a esse já havia sido descoberto recentemente ao redor da estrela LL Pegasi. Uma vez analisando os dados, uma hipótese foi desenvolvida indicando que a estrela gigante vermelha em R Sculptoris poderia estar bombeando gás em direção a uma estrela companheira invisível. A dinâmica do sistema pode ser particularmente importante pois ela pode nos dar pistas sobre como as estrelas gigantes se desenvolvem em direção ao fim de suas vidas, além de poder estar lançando alguns elementos de volta ao meio interestelar de modo que novas estrelas podem ser formadas.

Fonte:

http://apod.nasa.gov/apod/ap121016.html


Monday
Oct152012

Um Belo Panorama da Nebulosa da Carina e Um Comunicado Importante

A espetacular imagem panorâmica acima combina uma imagem mais recente do campo ao redor da estrela Wolf-Rayet WR 22 na Nebulosa da Carina (direita) com uma imagem mais antiga da região ao redor da única estrela Eta Carinae localizada no coração da nebulosa (esquerda). A imagem foi criada a partir de outras imagens obtidas com o instrumento chamado de Wide Field Imager montado no telescópio MPG/ESO de 2.2 metros do ESO no Observatório de La Silla no Chile.

Comunicado: Olá leitores dos meus canais na internet, o blog CIENCTEC e o site CIENCTEC estarão passando por uma manutenção até quarta-feira 17 de Outubro de 2012 e não estarão sendo atualizados. Vou soltar nas redes sociais alguns dos posts mais lidos do blog que poderão continuar sendo acessados normalmente como todo o conteúdo lá publicado. O blog está passando por uma grande mudança e em breve todos vocês poderão ver essas mudanças e comentar também se gostaram ou não, eu, sinceramente espero que gostem. Essa semana ainda pretendo lançar outro vídeo no canal do CIENCTEC no youtube e no próprio blog, que mesmo não finalizado deve voltar a ativa na quarta-feira. Enquanto isso, utilizarei esse meu outro canal aqui no SQUARESPACE para publicar o conteúdo e as notícias de astronomia que não podem parar. Obrigado a todos pela compreensão e pelo apoio. Bons céus a todos!!

Fonte:

http://www.wired.com/wiredscience/2012/02/space-photo-of-the-day/?pid=5090