Dark matter – Cosmic Log

America’s particle physics plan gets a status update

RALEIGH, N.C. — Particle physicist Hitoshi Murayama admits that he used to worry about being known as the “most hated man” in his field of science. But the good news is that now he can joke about it.

Last year, the Berkeley professor chaired the Particle Physics Project Prioritization Panel, or P5, which drew up a list of multimillion-dollar physics experiments that should move ahead over the next 10 years. The list focused on phenomena ranging from subatomic smash-ups to cosmic inflation. At the same time, the panel also had to decide which projects would have to be left behind for budgetary reasons, which could have turned Murayama into the Dr. No of physics.

Although Murayama has some regrets about the projects that were put off, he’s satisfied with how the process turned out. Now he’s just hoping that the federal government will follow through on the P5’s top priorities.

This galaxy is made of 99.99% dark matter

Image: Dragonfly 44 — The dark galaxy Dragonfly 44 appears to have about as much mass as our own Milky Way galaxy, but only 0.01 percent of that mass is in the form of stars and normal matter. The rest is dark matter, scientists say. (Credit: Pieter van Dokkum and Roberto Abraham / Gemini Observatory / AURA)

About 85 percent of the mass of the universe consists of mysterious stuff known as dark matter, but a galaxy called Dragonfly 44 appears to be even darker: 99.99 percent dark, according to newly published findings.

Dragonfly 44, which lies about 300 million light-years away in the Coma galaxy cluster, is the subject of a study published in the Astrophysical Journal Letters.

“It has so few stars that it would quickly be ripped apart unless something was holding it together,” Yale astronomer Pieter van Dokkum, the study’s lead author, said in a news release.

Van Dokkum and his colleagues tracked the motions of the stars in the galaxy using the Keck Observatory and the Gemini North telescope in Hawaii. The stars’ motions told the astronomers about the gravitational field surrounding Dragonfly 44.

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