Sunday, September 23, 2012

Planet Destroyed By Red Giant Expansion

An international team of astronomers has found evidence that a planet was destroyed by its ageing star. Led by Pennsylvania State University (Penn State) in the United States, the team showed that the missing planet was 'consumed' as the star expanded into a 'red giant', what experts refer to as the advanced age of stars.

An artist's impression of a red supergiant engulfing a Jupiter-like planet as it expands. 
An artist's impression of a red supergiant engulfing a Jupiter-like planet as it expands.
Credit: NASA

Presented in the Astrophysical Journal Letters, the study was funded in part by the PLANES ('Unfolding the evolution of planetary systems') project, which has received a Marie Curie Action Reintegration grant worth EUR 100 000 under the EU's Seventh Framework Programme (FP7).

'A similar fate may await the inner planets in our solar system, when the Sun becomes a red giant and expands all the way out to Earth's orbit some 5 billion years from now,' said co-author Alexander Wolszczan, Evan Pugh Professor of Astronomy and Astrophysics at Penn State University in the United States.

The researchers from Poland, Spain and the United States made their discovery after using the Hobby-Eberly Telescope to examine the ageing star and to investigate planets around it. Their results showed the strange chemical composition of the star, and a huge planet in an elliptical orbit around the same red giant star, called BD+48 740. Its radius is around 11 times bigger than the Sun. 

The first evidence of a planet's destruction by its aging star indicates that the missing planet was devoured as the star began expanding into a "red giant" — the stellar equivalent of advanced age. "A similar fate may await the inner planets in our solar system, when the Sun becomes a red giant and expands all the way out to Earth's orbit some five-billion years from now," said Alexander Wolszczan, Evan Pugh Professor of Astronomy and Astrophysics at Penn State and the discoverer of the first planet ever found outside our solar system. 
The Hobby-Eberly Telescope at night. Credit: Marty Harris/McDonald Obs./UT-Austin
Credit: Marty Harris/McDonald Obs./UT-Austin

'Our detailed spectroscopic analysis reveals that this red-giant star, BD+48 740, contains an abnormally high amount of lithium, a rare element created primarily during the Big Bang 14 billion years ago,' said lead author Dr Monika Adamow of Nicolaus Copernicus University in Poland. 

Studies of oscillation frequencies of many stars with very high precision gives insights into stellar evolution by knowing how the cores of stars change (starting in the bottom left corner in the sequence above) from hydrogen fusion-burning cores to helium fusion-burning cores, with intermediate stages where hydrogen fusion-burning shells expand into red giant sizes. A Hydrogen shell fusion star and a Helium core fusion star are indistinguishable when looking only at their surface properties. On the inside, they are radically different.

Image credit: Thomas Kallinger, University of British Columbia and University of Vienna

Astronomers say lithium is easily destroyed in stars, making the researchers wonder why there was such a high quantity of lithium in the older star. 'Theorists have identified only a few, very specific circumstances, other than the Big Bang, under which lithium can be created in stars,' Dr Wolszczan pointed out. 'In the case of BD+48 740, it is probable that the lithium production was triggered by a mass the size of a planet that spiralled into the star and heated it up while the star was digesting it.'

With respect to the highly elliptical orbit of the star's newly discovered planet, the astronomers said the planet revolves around the star in an orbit that is just wider than that of Mars at its narrowest point. 'But it is much more extended at its farthest point,' said Dr Andrzej Niedzielski of Nicolaus Copernicus University. 'Such orbits are uncommon in planetary systems around evolved stars and, in fact, the BD+48 740 planet's orbit is the most elliptical one detected so far.'

According to the team, gravitational interactions between planets generate the unusual orbits. So the 'dive of the missing planet toward the star before it became a giant could have given the surviving massive planet a burst of energy, throwing it into an eccentric orbit like a boomerang', they explained.

'Catching a planet in the act of being devoured by a star is an almost improbable feat to accomplish because of the comparative swiftness of the process, but the occurrence of such a collision can be deduced from the way it affects the stellar chemistry,' said Eva Villaver of the Universidad Autonoma de Madrid in Spain. 'The highly elongated orbit of the massive planet we discovered around this lithium-polluted red-giant star is exactly the kind of evidence that would point to the star's recent destruction of its now-missing planet.'

Kepler, the paparazzi of the celestial stars, takes snapshots of oscillations that can can be used to tell the size and age of the star. As a star "burns" hydrogen in fusion reactions, helium builds up in the star's core. Helium is more dense than hydrogen, and since waves travel more quickly through denser material, waves travel faster through the core as helium builds up there. Waves that go straight through the center (white) line and waves that bounce around outside the core (colored lines) produce oscillations in surface brightness.

Image credit: Travis Metcalfe, National Center for Atmospheric Research

Red Giant Blow A Bubble

To give you a better idea of what the end of a star looks like here is a photo captured by the Hubble Space Telescope as a red giant blows a bubble as it nears the end of its life.

Camelopardalis, or U Cam for short, is a star nearing the end of its life. As stars run low on fuel, they become unstable. Every few thousand years, U Cam coughs out a nearly spherical shell of gas as a layer of helium around its core begins to fuse. The gas ejected in the star’s latest eruption is clearly visible in this picture as a faint bubble of gas surrounding the star.
Image Credit: ESA/NASA

U Cam is an example of a carbon star, a rare type of star with an atmosphere that contains more carbon than oxygen. Due to its low surface gravity, typically as much as half of the total mass of a carbon star may be lost by way of powerful stellar winds. Located in the constellation of Camelopardalis (The Giraffe), near the North Celestial Pole, U Cam itself is much smaller than it appears in this Hubble image. In fact, the star would easily fit within a single pixel at the center of the image. Its brightness, however, is enough to saturate the camera's receptors, making the star look much larger than it is.

The shell of gas, which is both much larger and much fainter than its parent star, is visible in intricate detail in Hubble’s portrait. This phenomenon is often quite irregular and unstable, but the shell of gas expelled from U Cam is almost perfectly spherical.

Orion's Big Head Revealed in Infrared And A Look At Super Giant Red Star Betelgeuse 

The bright blue star in the lower left corner of the image is the star Betelgeuse, which represents one shoulder of the hunter Orion. The name Betelgeuse is actually a corruption of the original Arabic phrase "Yad al-Jauza'," meaning "hand of the giant one." Betelgeuse is well known for being a red supergiant star, yet in WISE's infrared view it appears blue, as do most stars in WISE images. This is because most stars, including Betelgeuse, put out more light in the shortest infrared wavelengths of light captured by WISE, and those shorter wavelengths are presented in WISE images as blue and cyan. 
Orion's Big Head Revealed in Infrared
In Greek mythology, Orion was a hunter whose vanity was so great that he angered the goddess Artemis. As his punishment, Artemis banished the hunter to the sky where he can be seen as the famous constellation Orion. In the constellation, Orion's head is represented by the star Lamdba Orionis (fuzzy red dot in middle). When viewed in infrared light, NASA's Wide-field Infrared Survey Explorer, or WISE, shows a giant nebula around Lambda Orionis, inflating Orion's head to huge proportions.

Lambda Orionis is a hot, massive star that is surrounded by several other hot, massive stars, all of which are creating radiation that excites a ring of dust, creating the "Lambda Orionis molecular ring." Also known as SH 2-264, the Lambda Orionis molecular ring is sometimes called the Meissa ring. In Arabic, the star Lambda Orionis is known as "Meissa" or "Al-Maisan," meaning "the shining one." The Meissa Ring is of interest to astronomers because it contains clusters of young stars and proto-stars, or forming stars, embedded within the clouds. With a diameter of approximately 130 light-years, the Lambda Orionis molecular ring is notable for being one of the largest star-forming regions WISE has seen. This is also the largest single image featured by WISE so far, with an area of the sky approximately 10 by 10 degrees in size, equivalent to a grid of 20 by 20 full moons. Nevertheless, at less than one percent of the whole sky's area, it is just a taste of WISE data.

In visible light, Orion's other shoulder is clearly marked by the variable star Bellatrix. In infrared light, however, Bellatrix is a somewhat unremarkable cyan-colored star in the right side of the image. In Latin, Bellatrix means "female warrior," which is perhaps why the name was chosen for a female witch character in the popular Harry Potter books.

Also seen in this image are two dark nebulae, Barnard 30 and Barnard 35, which are parts of the Meissa ring that are so dense they block out visible light. Barnard 30 is the bright knob of gas and dust in the top center part of the image. Barnard 35 appears as a hook extending towards the center of the ring just above and to the right of the star Betelgeuse. The bright reddish object seen to in the middle right part of the image is the star HR 1763, which is surrounded by another star-forming region, LBN 867.

Color in this image represents specific wavelengths of infrared light. Blue and cyan represent 3.4- and 4.6-microns, primarily light emitted by hot stars. Green and red represent 12- and 22-micron light, which is mainly radiation from warm dust.

Contacts and sources:
Penn State

For more information, please visit:
The Astrophysical Journal Letters

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