There's half as much dark matter in the Milky Way as we thought, new research suggests
FIONA MACDONALD
FRIDAY, 10 OCTOBER 2014
Scientists have long known that everything we see only makes up a tiny part of the Universe - the majority of it is hidden to us.
"Stars, dust, you and me, all the things that we see, only make up about 4 percent of the entire Universe," said lead researcher Prajwal Kafle from the University of Western Australia node of the International Center for Radio Astronomy Research (ICRAR) in a press release.
"About 25 percent is dark matter and the rest is dark energy," he explained.
But because dark matter is impossible to see, it's also hard to measure. Now using a technique developed almost 100 years ago in 1915 by British astronomer James Jeans, Kafle has managed to more accurately calculate how much dark matter is in our galaxy, and it's helped solve a decades-old astronomical mystery.
According to his calculations, the weight of dark matter in the Milky Way is 800,000,000,000 (or 8 x 1011) times the mass of the Sun. Although that sounds large, it's actually half the amount astronomers had previously predicted.
This also helps to explain why there aren't as many galaxies around the Milky Way as astronomers had previously expected.
"The current idea of galaxy formation and evolution, called the Lambda Cold Dark Matter theory, predicts that there should be a handful of big satellite galaxies around the Milky Way that are visible with the naked eye, but we don't see that," said Kafle in the press release.
"When you use our measurement of the mass of the dark matter the theory predicts that there should only be three satellite galaxies out there, which is exactly what we see; the Large Magellanic Cloud, the Small Magellanic Cloud and the Sagittarius Dwarf Galaxy."
According to Geraint Lewis, an astrophysicist from the University of Sydney who was also involved in the work, this mystery had been a "thorn in the cosmological side for almost 15 years".
We still have a long way to go before we fully understand how much dark matter is in our universe and the role it plays in galaxy formation, but this is an important step forward.
Source: ICRAR
Article and resources:
http://www.sciencealert.com.au/news/20141010-26316.html
http://physicsworld.com/cws/article/...p-giant-mirror
http://www.scienceclarified.com/Co-Di/Dark-Matter.html
