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The Atacama Large Millimeter/submillimeter Array (ALMA) by night Credit: ALMA (ESO/NAOJ/NRAO)/B. Tafreshi (twanight.org) |
One of the most distant known galaxies, observed in the very earliest years of the Universe, appears to be rotating at less than a quarter of the speed of the Milky Way today, according to a new study involving University of Cambridge researchers.
For the study, published in The Astrophysical Journal Letters, an international team of researchers analyzed data from a galaxy known as MACS1149-JD1 (JD1), obtained from observations by the Atacama Large Millimeter/submillimeter Array (ALMA), an assembly of radio telescopes in Chile.
The galaxy is so far away that its light comes to us from a time when the Universe was only 550 million years old – 4% of its present age.
The researchers, led by Tsuyoshi Tokuoka of Waseda University, found subtle variations in the wavelengths of the light indicating that parts of the galaxy were moving away from us while other parts were moving towards us. From these variations, they concluded that the galaxy was disc-shaped and rotating at a speed of 50 kilometers a second. By contrast, the Milky Way, at the Sun’s position, rotates with a speed of 220 kilometers per second today.
From the size of the galaxy and the speed of its rotation, the researchers were able to infer its mass, which in turn enabled them to confirm that it was likely 300 million years old and therefore formed about 250 million years after the Big Bang.
“This is by far the furthest back in time we have been able to detect a galaxy’s spin,” said co-author Professor Richard Ellis from University College London (UCL). “It allows us to chart the development of rotating galaxies over 96% of cosmic history – rotations that started slowly initially, but became more rapid as the Universe aged.