Saturday, October 31, 2009

The Gould Belt Shaped by Dark Matter

Within our Milky Way Galaxy, our sun is part of an area of space known as the Gould Belt, containing a swirl of stars. This partial ring is about 3,000 light-years across and is tilted toward the galactic plane by about 16 to 20 degrees. The Gould Belt is named after American astronomer Benjamin Apthorp Gould (1824-896), who first identified it in 1879. The Gould Belt contains many relatively young stars--perhaps 2 million of them are less than 60 million years old. While our sun is part of the Gould Belt, it is much older--with an estimated age of 4.6 billion years.

In 1997, astronomer Wolfgang G. L. Pöppel of Argentine Institute of Radio Astronomy noted that using the common explanations, astronomers could not explain where all of the Gould Belt’s young stars came from. Pöppel thought that, since these young stars surround our own sun, it might be nice for us to know how they came to be.

In a study published earlier this year, astrophysicist Kenji Bekki of the University of New South Wales, Australia, suggests that within the last 60 million years, this area of our galaxy was struck by a huge, invisible wrecking ball made of a clump of dark matter--mysterious particles created in the aftermath of the Big Bank. The clump proposed to have affected this area would have the mass of 10 million suns. The impact resulted in the Gould Belt and its young stars.

So far, astronomers have only detected dark matter by its gravitational pull on galaxies. Because it does not emit or reflect light, dark matter is impossible to see with optical telescopes. This leads astronomers to believe that the bulk of dark matter is so-called “weakly-interacting massive particles” (WIMPS). These WIMPS are exotic particles much like neutrinos that only rarely interact electromagnetically with normal atoms. Despite its invisibility, the observed gravitational pull of dark matter suggests that there is about five times more of it than what we consider to be normal matter--the stuff that makes up planets, stars and us.

Bekki’s study proposes that the Gould Belt was one of the stellar substructures that were formed from high-speed, off-center collisions between giant clouds of gas and dust and clumps of dark matter, both of which are orbiting the Galaxy. Bekki’s computer modeling shows that the Gould Belt could have been created within 45 million years.

Bekki’s study also suggests that, because of the gravitation effects of the dark matter at the time of the collision, the dark matter may be responsible for perturbing the orbits of the objects in the Kuiper belt, causing them to fall toward the sun and creating a wave of comets in the inner solar system over the last several million years.

Bekki admits that these are speculations. However, he notes that if the Milky Way has 20 dark matter clumps surrounding it, Bekki reasons that a Gould Belt-like ring of stars would be likely to form from dark matter collisions every billions years or so, and that about one tenth of one percent of the stars in our galaxy may have been started in this way.

To learn about Bekki’s study and about dark matter, check out these links:

“Dark Impact and Galactic Star Formation: Origin of the Gould Belt.” Submitted June 28, 2009. Kenji Bekki. arXiv.org, Cornell University Library.
http://arxiv.org/abs/0906.5117

University of New South Wales, Australia
http://www.unsw.edu.au/

Argentine Institute of Radio Astronomy (Instituto Argentino de Radioastronomía)
http://www.iar.unlp.edu.ar/

Dark Matter. NASA’s Imagine the Universe Web Site.
http://imagine.gsfc.nasa.gov/docs/science/know_l1/dark_matter.html

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