A newly discovered form of circle dancing is
perplexing astronomers; not due to its complex choreography, but because
it's unclear why the dancers – dwarf galaxies – are dancing in a ring
around the much larger Andromeda Galaxy. The
finding presents a challenge to our ideas of how all galaxies form and
evolve. The surprising research result reveals that around half of
Andromeda's 30-odd known dwarf galaxy satellites are orbiting the larger
Andromeda Galaxy – the closest giant cosmic neighbor to our Milky Way.
The international group of astronomers who discovered the curious cosmic choreography, including Professor Geraint Lewis
from the University of Sydney's School of Physics, and Australian
astronomers Anthony Conn, a PhD student at Macquarie University, and Dr
Dougal Mackey from the Australian National University, were surprised at the circle around Andromeda that the small orbiting galaxies have formed.
"Astronomers have been observing Andromeda since Persian astronomers
first noted it over a thousand years ago, but it is only in the past
decade that we have truly studied it in exquisite detail with the Pan-Andromeda Archaeological Survey,"
said Lewis. "The Pan-Andromeda Archaeological Survey – cutely called
PAndAS – is a large project that ran between 2008 and 2011, using the Canada-France-Hawaii Telescope situated on the Mauna Kea volcano on the Big Island of Hawaii.
Now that we're examining the data it collected, it is providing our
first panoramic view of our closest large companion in the cosmos,"
explained Lewis.
"When we looked at the dwarf galaxies surrounding Andromeda, we
expected to find them buzzing around randomly, like angry bees around a
hive. "Instead, we've found that half of Andromeda's satellites are
orbiting together in an immense plane, which is more than a million
light years in diameter but only 30 000 light years thick. These dwarf
galaxies have formed a ring around Andromeda." "This was completely
unexpected – the chance of this happening randomly is next to nothing.
It really is just weird," Lewis said.
Large galaxies, like Andromeda and our own Milky Way, have long been
known to be orbited by an entourage of smaller galaxies. These small
galaxies, which are individually anywhere from ten to at least hundreds
of thousands of times fainter than their bright hosts, were thought to
trace a path around the big galaxy that was independent of every other
dwarf galaxy. For several decades, astronomers have used computer models
to predict how dwarf galaxies should orbit large galaxies, and every
time they found that dwarfs should be scattered randomly over the sky.
Never, in these synthetic universes, did they see dwarfs arranged in a
plane like that observed around Andromeda.
"Now that we've found that the majority of these dwarf galaxies orbit
in a disc around the giant galaxy Andromeda, it looks like there must
be something about how these galaxies formed or subsequently evolved
that has led them to trace out this peculiar coherent structure," said
Professor Lewis. "Dwarf galaxies are the most numerous galaxy type in
the universe, so understanding why and how they form this disc around
the giant galaxy is expected to shed new light on the formation of
galaxies of all masses."
here have been similar claims of an extensive plane of dwarf
galaxies about our own Milky Way Galaxy, with some claiming that the
existence of such strange structures points to a failing in our
understanding of the fundamental nature of the Universe. "We don't yet
know where this is pointing us, but it surely is very exciting," said Dr
Rodrigo Ibata, from the Observatoire astronomique de Strasbourg, in
France, and lead author on the report.
The top left hand image below is a truecolour photograph (taken with
the Canada-France-Hawaii Telescope) of the Andromeda galaxy, the closest
giant galaxy to our own, and in many ways our Milky Way’s twin sister.
Also visible in this photograph are two of its satellites (these are
much smaller galaxies, containing up to about a billion stars). Our
study has measured the distances and velocities of 27 other such dwarf
galaxies : their three-dimensional positions are shown with red spheres
in the other panels. The top right hand panel depicts how these appear
to us as viewed from Earth, while the bottom left panel shows the
positions of the satellites as they would be seen from the side. This
immense grouping is more than a million light years across and rotates
in the sense shown by the arrows.
Journal reference: Nature
Source: The Daily Galaxy via University of Sydney
No hay comentarios:
Publicar un comentario