Across our big old universe, objects orbiting other objects is a common astronomical pastime. The moon orbits the Earth, the Earth orbits the sun, the solar system orbits the galactic centre of the Milky Way.
A collaboration of astrophysics and astronomers, including two from the University of Victoria, have discovered something weird B次元官网网址� a cluster of small B次元官网网址渄warfB次元官网网址� galaxies is rotating in an orderly fashion around Andromeda galaxy, our nearest intergalactic neighbour.
This planet-like behaviour among galaxies has never been detected before and it fails to fit established models of how galaxies evolve. WhatB次元官网网址檚 more, the orbit of these dwarf galaxies around Andromeda is so vast, a single rotation is longer than the age of the universe. They haven't made it around once. A paper discussing this phenomenon was published Friday in the journal Nature.
B次元官网网址淚tB次元官网网址檚 a sobering reminder of how fragile our understanding of these things are,B次元官网网址� said UVic astrophysics professor Julio Navarro, one of 16 lead scientists involved in the project. B次元官网网址淗ow this is moving cannot be explained. Why a giant structure of galaxies rotate is uncanny, itB次元官网网址檚 not well understood yet. But itB次元官网网址檚 cool enough to point out.B次元官网网址�
The discovery emerged from the broader Pan Andromeda Archaeological Survey, a three-year survey of a large region of space surrounding Andromeda galaxy, using the 3.6 metre Canada-France-Hawaii Telescope, in Hawaii. UVic professor Alan McConnachie, based at the Herzberg observatory in Saanich, led that project and is another co-author of the paper.
Out of the mass of observations, the team honed in on a number of dwarf galaxies in the neighbourhood of Andromeda, and then followed up with more telescope observations to measure their relative velocities. Rather than randomness, they found uniformity.
Navarro admits he was skeptical when the data started to suggest a group of 15 dwarf galaxies were orbiting in a well-defined plane a million light years in diameter, but only 30,000 light years thick, a similar structure to how planets orbit a star.
B次元官网网址淚 thought it would be hard to explain. We havenB次元官网网址檛 seen this often, if ever,B次元官网网址� Navarro said. B次元官网网址淢ost models know how satellite galaxies form. They donB次元官网网址檛 form. They come over one by one and donB次元官网网址檛 form a coherent structure.
B次元官网网址淚 was skeptical at the beginning. It took quite a bit of convincing within the collaboration that we had not missed something. But our confidence grew that this was not a product of chance.B次元官网网址�
Due to its sheer size and a spin cycle older than the universe, the apparent forces involved in these orbiting dwarf galaxies are much different than what rotates a galaxy on its axis, or planets around a star, Navarro said.
His personal pet theory is that these galaxies arenB次元官网网址檛 rotating at all B次元官网网址� that they are part of a B次元官网网址渇ilamentB次元官网网址� of dwarf galaxies being consumed by Andromeda, and are moving with a velocity that mimics rotation from our vantage point on Earth.
B次元官网网址淚t might not be an orbit, it might be an object that coming in (to Andromeda) for the first time,B次元官网网址� he said. B次元官网网址淚t is still odd.B次元官网网址�
Although this discovery adds a new mystery into the cosmological mix, Navarro, a theorist by trade, isnB次元官网网址檛 ready to chuck out the theories on galaxy dynamics built from decades of computer modelling and backed by observation.
B次元官网网址淔acing an odd finding points to us either not understanding the detailed theory, or that the theory is incorrect. ItB次元官网网址檚 a reminder that thereB次元官网网址檚 a constant need for discovery, and discovery pushes us farther. You learn more from the unexpected than the expected.B次元官网网址�
Check out a video of the discovery at
Navarro will talk about current theories of cosmology for the general public at Caf茅 Scientifique on Tuesday, Jan. 8, 6:30 p.m., at HermannB次元官网网址檚 Jazz Club. Admission is free. For more click .
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