The disc of the Milky Way is bigger than we thought

Spiral galaxies such as the Milky Way have discs which are really thin, in which the major fraction of their stars are found. These discs are limited in size, so that beyond certain radius there are very few stars left.

In our galaxy we were not aware that there are stars in the disc at distances from the centre more than twice that of the Sun. This means that our own star was apparently orbiting at about half the galactic radius. However now we know that there are stars quite a bit further out, at more than three times this distance, and it is probable that some stars are at more than four times the distance of the Sun from the galactic centre.

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Credit: Instituto de Astrofisica de Canarias (IAC)

A team of researchers at the Instituto de Astrofísica de Canarias (IAC) and at the National Astronomical Observatories of Beijing (NAOC) have published a paper which suggests that if we could travel at the speed of light it would take us 200,000 years to cross the disc of our galaxy.

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Two ringlike structures of stars wrapping around the Milky Way's outer disk now appear to belong to the disk itself.

The results, detailed in the March 10 edition of the Astrophysical Journal., show that the disk is about 60% larger than previously thought.

Not only do the results extend the size of the Milky Way, they also reveal a rippling pattern, which raises intriguing questions about what sent wavelike fluctuations rippling through the disk.

The researchers said the likely culprit was a dwarf galaxy. It might have plunged through the Milky Way's center long ago, sparking the rippling patterns astronomers have now detected for the first time.