This episode is presented by eBay.

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Then when you're buying, you can discover loads of hidden gems. There's so many items where you think I would have never found that anywhere else. Then when you're selling, it's so simple and most

importantly, free. It's free, Rob. When it's this easy to sell for free and there's great deals

on things you love. You can't help but say when it's eBay. It excludes vehicles and business

sellers.

Welcome to Science Talk, the podcast of Scientific American for the seven days starting September 6th. I'm Steve Murski. This week on the podcast, we're going to talk about one of the most

mysterious objects in the universe. No, not the teenage brain. That was last week. This week,

the mysterious dark matter with MIT astrophysicist

Paul Schechter. Journalist Karen Hopkins will tell us a little about this program's new companion,

the Daily Scientific American 60 Second Science podcast. We'll test your knowledge about some recent

science in the news, and Scientific American magazine contributing editor Sarah Simpson shares some thoughts

about the late Steve Irwin.

First up, astrophysicist Paul Schechter.

There was quite a buzz a couple of weeks ago when a NASA Harvard University study announced

striking new evidence for dark matter.

I wanted Schechter's perspective on the new findings.

I got through to him last week while he was doing his own dark matter research at the Serra Las Campanis Observatory in Chile.

Professor Schechter, thanks for talking to us today.

It's my pleasure to be with you. Can you give us the brief introduction to dark matter?

Astronomers measure the masses of things by measuring the motions of things. And so we measure the masses of stars by watching the orbit around each other. We measure the masses of galaxies by watching the stars orbit in the galaxies. And by watching the motions of massive bodies around other massive bodies, we can infer masses. In the 1930s, Fritz Wickey, an astronomer at Caltech, measured the mass of the

coma cluster of galaxies. A cluster of galaxies is what it sounds like. It's a cluster of Milky Ways,

...