Was our galaxy formed by a 'Council of Giants'?
Giant galaxies arranged in a ring around the Milky Way might have shaped its very formation, reveals a new study.
This is a diagram showing the brightest galaxies within 20 million light years of the Milky Way, as seen from above. The largest galaxies, here shown in yellow at different points around the dotted line, make up the "Council of Giants."
Marshall McCall / York University
Our mysterious neighbors in space have finally revealed themselves.
It turns out that our Local Group – a cluster of 54 galaxies dominated by the Andromeda galaxy and our own Milky Way galaxy – is encircled by twelve large galaxies.
This cosmic assembly's discoverer has given it an appropriately grand name. The galaxies are "arranged in a ring about 24-million light years across – this ‘Council of Giants’ stands in gravitational judgment of the Local Group by restricting its range of influence," says Marshall McCall, professor at York University who published the findings of the study in the journal of Monthly Notices of the Royal Astronomical Society.
"That is why I called it a 'council,'" says Dr. McCall.
The Local Group of galaxies along with the giant galaxies "are organized in a ‘Local Sheet’ 34-million light years across and only 1.5-million light years thick,” McCall added.
There are two huge elliptical galaxies in the sheet that are sitting at the opposite sides of the Council, McCall told the Monitor.
Winds expelled by these elliptical galaxies in their early phases of formation might have driven gases inward toward the Local Group helping in the formation of discs around the Milky Way and Andromeda that we see today.
“Thinking of a galaxy as a screw in a piece of wood, the direction of spin can be described as the direction the screw would move (in or out) if it were turned the same way as the galaxy rotates. Unexpectedly, the spin directions of Council giants are arranged around a small circle on the sky. This unusual alignment might have been set up by gravitational torques imposed by the Milky Way and Andromeda when the universe was smaller," he said in a press release.
The study also sheds light on how the Milky Way was formed.
It is known that the Milky Way and the Andromeda Galaxy are in a binary system where they revolve around each other. It's possible that these elliptical galaxies, which were laid down first, had a role to play in having us end up in such a binary system, McCall says,
Also, the "gravitational tug of war," between the Council and the Local Group might have restricted the availability of matter for our Milky Way galaxy, in a way restricting its growth, he added.
To examine the galaxies, McCall selected those galaxies that were intrinsically brighter than a certain limit or magnitude (galaxies brighter than four percent the Milky Way). Those categorized as "giants" were twice of that limit in their brightness.