"I have failed to find dark matter, but I got a very pleasant consolation prize"
nytimes.com
nytimes.com
The source of the bubbles is a mystery. One possibility is that they are fueled by a wave of star births and deaths at the center of the galaxy. Another option is a gigantic belch from the black hole known to reside, like Jabba the Hutt, at the center of the Milky Way. What it is apparently not is dark matter, the mysterious something that astronomers say makes up a quarter of the universe and holds galaxies together.
> ...known to reside, like Jabba the Hutt, at the center of the Milky Way.
A lesson to all the mainstream writers out there: don't drop references if you can't get them right. :P
Perhaps it comes down to the aggregator's audience. Some will be more willing to pay to get past paywalls, for articles recommended to them by that aggregator, or have a higher tendency to already be paying customers. Hence P(article recommendation will be appreciated) will tend higher there, because P(article will be viewable) is higher.