June 4th, 2013 by James Ayre
A rare stellar alignment that will occur twice within the next couple of years is creating a ‘perfect’ opportunity for the search for exoplanets around one of our closest neighbors — the red dwarf Proxima Centauri. NASA’s Hubble Space Telescope will be perfectly situated to take advantage of the events and possibly discover Earth-sized exoplanets around the star.
The rare stellar alignment in question — when Proxima Centauri will pass right in front of two other stars, as seen from the Earth — will occur in October 2014 and February 2016. Researchers have plotted the exact path that Proxima Centauri will make in the sky, and can thus predict the two perfect opportunities by using data from Hubble.
“Proxima Centauri’s trajectory offers a most interesting opportunity because of its extremely close passage to the two stars,” said Kailash Sahu, an astronomer with the Space Science Telescope Institute in Baltimore, Md. Sahu leads a team of scientists whose work he presented Monday at the 222nd meeting of American Astronomical Society in Indianapolis.
Of all the different types of stars in the Milky Way, Red dwarfs are present in the largest quantity, not stars like our Sun. Estimates state that for every Sun-like star, that there are at least 10 red dwarfs. Such stars are less-massive than our Sun, and as a result tend to be one of the best places to look for Earth-sized exoplanets.
Researchers have previously looked for planets around Proxima Centauri, but as of now haven’t seen any. But these upcoming, rare stellar alignments may change that — by allowing researchers to utilize the microlensing effects created during them.
Microlensing occurs when a foreground star passes close to our line of sight to a more distant background star. These images of the background star may be distorted, brightened and multiplied depending on the alignment between the foreground lens and the background source. These microlensing events, ranging from a few hours to a few days in duration, will enable astronomers to measure precisely the mass of this isolated red dwarf. Getting a precise determination of mass is critical to understanding a star’s temperature, diameter, intrinsic brightness, and longevity.
Astronomers will measure the mass by examining images of each of the background stars to see how far the stars are offset from their real positions in the sky. The offsets are the result of Proxima Centauri’s gravitational field warping space. The degree of offset can be used to measure Proxima Centauri’s mass. The greater the offset, the greater the mass of Proxima Centauri. If the red dwarf has any planets, their gravitational fields will produce a second small position shift.
Because Proxima Centauri is so close to Earth, the area of sky warped by its gravitation field is larger than for more distant stars. This makes it easier to look for shifts in apparent stellar position caused by this effect. However, the position shifts will be too small to be perceived by any but the most sensitive telescopes in space and on the ground. The European Space Agency’s Gaia space telescope and the European Southern Observatory’s Very Large Telescope on Mt. Cerro Paranal in Chile may be able to make measurements comparable to Hubble’s.
In order to become aware of stellar alignment events such as these, the researchers looked through a catalog of over 5,000 stars known to have a high rate of angular motion across the sky. During the search, Proxima Centauri was singled out because of its relative closeness to us. “It crosses a section of sky with the apparent width of the full moon as observed from Earth every 600 years.”
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