Phew, galactic accident helps boffins explain dark matter riddle

Texan-led team find ancient oddity that's full of the stuff

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An accidental discovery by a team of astronomers has helped answer one of the burning questions about dark matter and where it came from.

Previous studies found that galaxies created over ten billion years ago contained low levels of dark matter. This posed the annoying question of where it all came from since then, as dark matter is so plentiful in younger galaxies.

But a team of astrophysicists has accidentally stumbled across an anomaly galaxy that may help resolve the issue. Patrick Drew, a graduate student at the University of Texas at Austin and a team from Manhattan College, the Space Telescope Science Institute and John Hopkins University have published a paper in The Astrophysical Journal about DSFG850.95, a galaxy created about 9.6 billion years ago.

The team were studying a slightly different branch of astroboffinry, looking for so-called “dusty star-forming galaxies” that pump out more suns than usual. But data from the the Keck Telescope in Hawaii showed one galaxy that stood out as unusual.

DSFG850.95 is a massive disk galaxy and is viewed from Earth at an angle that allowed the team to measure the speed of its rotation across different radii. This rotation curve is used to determine how much dark matter a galaxy contains and in this case the team found similar amounts of dark matter compared to younger galaxies like our own.

Professor Caitlin Casey from UT Austin said that previous research showed ancient galaxies containing little dark matter so and had decreasing rotation curves as they rotated slower on the outside. They were “fundamentally different to galaxies in the present-day universe.”

“The galaxy we found is a clear counter-example of that, where it seems to have dark matter behaving in the normal way, as it does in the present-day universe.”

The findings mean that dark matter should have had pretty much the same effect on galaxies since the Big Bang to present time. That helps current theories on how galaxies are formed, since scientists have yet to answer why dark matter levels would have increased over time.

“This galaxy does what’s expected of galaxies like it and it is the first solid confirmation that what happens in these galaxies in the current-day universe is the same as what happened in the early universe,” said Drew. ®


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