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Unprecedented Images Show Betelgeuse Has Sunspots


Caption:The surface of Betelgeuse in near infrared at 1.64 micron in wavelength, obtained with the IOTA interferometer (Arizona). The image has been re-constructed with two different algorithms, which yield the same details, of 9 milliarcseconds (mas). The star diameter is about 45 milliarcseconds. Credit: Copyright 2010 Haubois / Perrin (LESIA, Observatoire de Paris)

An international team of astronomers has obtained an unprecedented image of the surface of the red supergiant Betelgeuse, in the constellation Orion. The image reveals the presence of two giant bright spots, which cover a large fraction of the surface. Their size is equivalent to the Earth-Sun distance. This observation provides the first strong and direct indication of the presence of the convection phenomenon, transport of heat by moving matter, in a star other than the Sun. This result provides a better understanding of the structure and evolution of supergiants.

Betelgeuse is a red supergiant located in the constellation of Orion, and is quite different from our Sun. First, it is a huge star. If it were the center of our Solar System it would extend to the orbit of Jupiter. At 600 times larger than our Sun, it radiates approximately 100,000 times more energy. Additionally, with an age of only a few million years, the Betelgeuse star is already nearing the end of its life and is soon doomed to explode as a supernova. When it does, the supernova should be seen easily from Earth, even in broad daylight.

But we now know Betelgeuse has some similarities to the Sun, as it also has sunspots. The surface has bright and dark spots, which are actually regions that are hot and cold spots on the star. The spots appear due to convection, i.e., the transport of heat by matter currents. This phenomenon is observed every day in boiling water. On the surface of the Sun, these spots are rather well-known and visible. However, it is not at all the case for other stars and in particular supergiants. The size, physical characteristics, and lifetime of these dynamical structures remain unknown.

Betelgeuse is a good target for interferometry because its size and brightness make it easier to observe. Using simultaneously the three telescopes of the Infrared Optical Telescope Array (IOTA) interferometer on Mount Hopkins in Arizona (since removed), and the Paris Observatory (LESIA) the astronomers were able to obtain a numerous high-precision measurements. These made it possible to reconstruct an image of the star surface thanks to two algorithms and computer programs.

Two different algorithms gave the same image. One was created by Eric Thiebaut from the Astronomical Research Center of Lyon (CRAL) and the other was developed by Laurent Mugnier and Serge Meimon from ONERA. The final image reveals the star surface with unprecedented, never-before-seen details. Two bright spots clearly show up next to the center of the star.

The analysis of the brightness of the spots shows a variation of 500 degrees compared to the average temperature of the star (3,600 Kelvin). The largest of the two structures has a dimension equivalent
to the quarter of the star diameter (or one and a half the Earth-Sun distance). This marks a clear difference with the Sun where the convection cells are much finer and reach hardly 1/20th of the solar radius (a few Earth radii). These characteristics are compatible with the idea of luminous spots produced by convection. These results constitute a first strong and direct indication of the presence of convection on the surface of a star other than the Sun.

Convection could play an important role in the explanation of the mass-loss phenomenon and in the gigantic plume of gas that is expelled from Betelgeuse. The latter has been discovered by a team led by Pierre Kervella from Paris Observatory (read our article about this discovery). Convection cells are potentially at the origin of the hot gas ejections.

The astronomers say this new discovery provides new insights into supergiant stars, opening up a new field of research.

Sources: Abstract: arXiv, Paper: “Imaging the spotty surface of Betelgeuse in the H band,” 2009, A&A, 508, 923″. Paris Observatory

About 

Nancy Atkinson is Universe Today's Senior Editor. She also works with Astronomy Cast, and is a NASA/JPL Solar System Ambassador.

Comments on this entry are closed.

  • Lawrence B. Crowell January 15, 2010, 4:56 AM

    We might ponder how it is that the sizes of stars were known before we ever imaged them. There is a quantum mechanical process called the Hanbury Brown-Twiss (HBT) effect, sometimes called photon bunching. If two photons from two different points on a source reach a homodyne detector they may enter into a quantum entanglement with some interference pattern. This means a photon which leaves the limb of Betelgeuse and the center are placed into a quantum entanglement throughout the path of the two photons. The detection of the two photons acts as a superselection of state entanglements into the past. This has a relationship to the Wheeler Delay Experiment (WDE), where the choice of detection observables “now” selects the quantum configuration into the past. This is an odd development, and one of those strange results of quantum mechanics. The detection of these photons are used to calculate the size of stars, and used long before we had any ability to image them.

    There are Wikipedia sites on HBT and WDE, so I leave it up to the reader to look deeper into these topics. This is relies upon quantum physics which requires considerable background discussion or study to understand fully.

    The detection of photons from the limb of a sphere and the leading center is changed little if the sphere is replaced by a disk. In either case the photons are de-correlated from each other, so the small time delay has no consequence. If the two photons enter into an HBT entanglement then they are correlated, but the WDE quantum logic also renders the time delay inconsequential. So long as the object you are detecting is sufficiently constant in its configuration over the small time difference between photons leaving the limb and the center of the star this small time delay difference is of no consequence.

    LC

  • IVAN3MAN January 15, 2010, 8:45 AM

    @ Lawrence B. Crowell,

    Thanks for that information, I’ll look them up in Wikipedia…

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