Star Destroys Planet As It Expands Into Red Giant, It’s The Fate That Awaits Earth

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.

‘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.

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.’

Image credit: Travis Metcalfe, National Center for Atmospheric Research 

Red Giant Blows A Bubble

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.  
 
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.