Astronomers discover galaxies spin like clockwork

Astronomers discover galaxies spin like clockwork
This Hubble image reveals the gigantic Pinwheel galaxy, one
of the best known examples of “grand design spirals”, and
its supergiant star-forming regions in unprecedented
detail. The image is the largest and most detailed photo of
a spiral galaxy ever released from Hubble. Credit: ESA/NASA

Astronomers have discovered that all galaxies rotate once
every billion years, no matter how big they are.

The Earth spinning around on its axis once gives us the length
of a day, and a complete orbit of the Earth around the Sun
gives us a year.

“It’s not Swiss watch precision,” said Professor Gerhardt
Meurer from the UWA node of the International Centre for Radio
Astronomy Research (ICRAR).

“But regardless of whether a galaxy is very big or very small,
if you could sit on the extreme of its disk as it spins, it would take you
about a billion years to go all the way round.”

Professor Meurer said that by using simple maths, you can show
all of the same size have the same average
interior density.

“Discovering such regularity in galaxies really helps us to
better understand the mechanics that make them tick-you won’t
find a dense galaxy rotating quickly, while another with the
same size but lower density is rotating more slowly,” he said.

Professor Meurer and his team also found evidence of older
stars existing out to the edge of galaxies.

“Based on existing models, we expected to find a thin
population of young stars at the very edge of the galactic
disks we studied,” he said.

Astronomers have discovered that all galaxies rotate once
every billion years, no matter how big they are. Credit:

“But instead of finding just gas and newly formed stars at the
edges of their disks, we also found a significant population of
older stars along with the thin smattering of young and .”

“This is an important result because knowing where a galaxy
ends means we astronomers can limit our observations and not
waste time, effort and computer processing power on studying
data from beyond that point,” said Professor Meurer.

“So because of this work, we now know that galaxies rotate once
every billion years, with a sharp edge that’s populated with a
mixture of interstellar gas, with both old and .”

Professor Meurer said that the next generation of radio
telescopes, like the soon-to-be-built Square Kilometre Array
(SKA), will generate enormous amounts of data, and knowing
where the edge of a galaxy lies will reduce the needed to search through the

“When the SKA comes online in the next decade, we’ll need as
much help as we can get to characterise the billions of
galaxies these telescopes will soon make available to us.”

Explore further:
of distant galaxies challenges the understanding of how stars

More information:Cosmic
clocks: A Tight Radius – Velocity Relationship for HI-Selected
‘, Monthly Notices of the Royal Astronomical
March 14th, 2018.